- Email: [email protected]
Do health behaviors mediate the association between social capital and health?
Preventive Medicine 43 (2006) 488 – 493 www.elsevier.com/locate/ypmed
Do health behaviors mediate the association between social capital and health? Wouter Poortinga ⁎ Welsh School of Architecture, Cardiff University, Bute Building, King Edward VII Avenue, Cardiff, Wales, CF10 3NB, UK Available online 24 July 2006
Abstract Introduction. There is increasing evidence that social capital is important for people's health. However, there is still considerable disagreement about the specific pathways that links social capital to health. This study investigates the hypothesis that the association between social capital and health is mediated by people's health behaviors. Method. Data from the 2002 Health Survey for England (n = 7394) were used and analyzed from a multilevel perspective. The association between social capital and self-rated health were examined before and after controlling for smoking, alcohol intake, and fruit/vegetable consumption. Results. Social capital was found to be associated with self-rated health, as well as with the different health behaviors. In addition, the health behaviors were significantly related to self-rated health. However, controlling for smoking, alcohol intake, and fruit/vegetable consumption did not substantially affect the association between social capital and self-rated health. Conclusions. The results demonstrate that social capital and support are important determinants of self-rated health and health behaviors. But only limited support was found for the hypothesis that health behaviors mediate the association between social capital and health. © 2006 Elsevier Inc. All rights reserved. Keywords: Social capital; Social support; Health behaviors; Self-rated health
Introduction There is a growing body of evidence that the social environment plays an important role in shaping people's health. Research efforts in this area have mainly focused on the concepts of social support and social capital. Social capital is generally defined as the features of social organization – such as civic participation, norms of reciprocity, and trust in others – that help facilitate cooperation for mutual benefit (see e.g., Putnam, 2000). As such, social capital can be considered a collective resource that benefits communities and can be distinguished from the individual health effects of social networks and support (see e.g., Lochner et al., 1999). Social capital has been linked to various health outcomes, among which self-rated health (Kawachi et al., 1999; Hyyppä and Mäki, 2001; Subramanian et al., 2002; Helliwell, 2003; Poortinga, 2006a, 2006b), cardiovascular and cancer mortality rates (Kawachi et al., ⁎ Fax: +44 29 2087 4623. E-mail address: [email protected]. 0091-7435/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ypmed.2006.06.004
1997), suicide rates (Helliwell, 2003), and child mental health (Caughy et al., 2003). With the recognition that social capital is important for people's health comes the need to identify the specific mechanisms that link social capital to health. It has been hypothesized that social capital provides a buffer against the adverse effects of stress (Wilkinson, 1996); that social capital helps to disseminate health information and knowledge more quickly across communities (Kawachi and Berkman, 2000); that socially cohesive communities have better access to local services and amenities because they are more likely to be successful at fighting potential cuts in services (Sampson et al., 1997; Kawachi et al., 1999); and that communities with high levels of social capital are more effective at exercising social control over different health behaviors (Kawachi and Berkman, 2000; Subramanian et al., 2002). There is some empirical support for the latter hypothesis. Social capital has been found to be associated with various health behaviors, such as physical activity (e.g., Lindström et al., 2001; Stahl et al., 2001; Addy et al., 2004), fruit and vegetable consumption (Lindström et al., 2001), smoking (Lindström, 2003), and alcohol consumption
W. Poortinga / Preventive Medicine 43 (2006) 488–493
(Weitzman and Chen, 2005). Mohan et al. (2005) provide further support for the idea that health behaviors form part of a possible mediating pathway between social capital and health. They found that the mortality effects of social capital were attenuated when controlling for differences in health-related behaviors. The aim of this study is to investigate if health behaviors mediate the association between social capital and health. More specifically, the study examines (1) whether social capital is associated with health, (2) whether social capital is associated with a number of health-related behaviors (i.e., smoking, alcohol intake, and fruit and vegetable consumption), and (3) whether controlling for the health-related behaviors attenuates the association between social capital and health. Methods Study population Data from the 2002 Health Survey for England were used. The Health Survey for England (HSE) is a series of annual studies covering the English adult population aged 16 and over living in private households. The data were collected from January 2002 to March 2003. In total, 7394 individual interviews were conducted within 4332 households that were selected from 720 postcode sectors.1 The household response rate was 74%. Table 1 summarizes the variables from the data set that are considered for the analyses in this paper.
Measures Health outcomes Self-rated health and five health behaviors were the health outcome variables of this study (see Table 1). First, respondents were asked to rate their own general health on a five-point scale ranging from very good to very bad. The original scale was dichotomized, with 1 representing fair, bad, and very bad health and 0 representing a good or very good health. Second, people's current smoking status, daily alcohol intake, and daily fruit/vegetable consumption was assessed. People who smoke were compared to people who do not smoke. Daily alcohol intake was derived from people's self-reported consumption and divided into three groups. A distinction was made between those drinking more and those drinking less than 2 U of alcohol per day.2 People not drinking at all were considered a separate group. Fruit and vegetable consumption was calculated by adding up all portions of pulses, salad, vegetables, and fresh, dried, and canned fruit that were eaten ‘yesterday’. The recommended consumption of 5 portions of fruit and vegetables a day was used as a cut-off point (Department of Health, 2001). As only few respondents managed to eat 5 portions per day (see Table 1), an additional distinction was made between those eating fewer than two portions per day, and those eating between two and five portions per day. Sociodemographics The sociodemographic variables of gender, age, individual economic status, household social class, and household tenure were included in the analyses (see Table 1). Three dummy variables represented the four age categories of 16–24 years, 25–44 years, 45–64 years, and 65 years and over. Individual economic status compared economically inactive (long-term unemployed and
1
National Centre for Social Research and University College London (2004). Department of Epidemiology and Public Health, Health Survey for England, 2002 [computer file]. Colchester, Essex: UK Data Archive [distributor], May 2004. SN: 4912. Available from: http://www.data-archive.ac.uk/. More information about the methodology of 2002 Health Survey for England can be found at http://www.archive2.official-documents.co.uk/document/deps/doh/ survey02/hse02.htm. 2 In this study, the lower end of the recommended daily alcohol consumption of 2 to 3 units for women was used as the cut-off point (Department of Health, 1995).
489
other economically inactive) with working individuals. Household social class was measured using the Registrar General's occupation-based classification: I and II (professionals and intermediates), III NM (skilled non-manual), III M (skilled manual), and IV and V (partly and unskilled manual). Household tenure compared household ownership (with or without mortgage) with renting, living rent-free, and squatting. Social capital and support Responses to seven statements were added to construct a social support scale (1: “not true”, 2: “partly true”, and 3: “certainly true”). People were subdivided into three groups with ‘no lack’ (score 21), ‘some lack’ (scores 18–20), and a ‘severe lack’ (scores 7–17) of social support (cf. Cox et al., 1987). Social trust was measured with the question “generally speaking, would you say that: most people can be trusted (coded 1) or you can't be too careful in dealing with people (coded 0)”. Civic participation was measured by asking respondents to indicate whether they regularly join in activities of fourteen types of clubs or associations. Because many were involved in none or only one organization, respondents were subdivided into three groups: low (not involved in any club or organization), medium (one club or organization), or high (two or more clubs or organizations) civic participation. The proportion of respondents in each
Table 1 Characteristics of the 2002 Health Survey for England dataset (n = 7394)
Health outcome Self-rated health
Health behaviors Smoking Units of alcohol per day
Base
Contrast
Good/very good (74.2%)
Fair/poor/very poor (25.8%)
Smoker (26.3%) More than 2 (29.0%)
Non-smoker (73.2%) 0 (11.7%) Fewer than 2, excluding 0 (58.2%) 2–5 (48.7%) 5 or more (23.9%)
Fruit/vegetable portions per day
Fewer than 2 (27.4%)
Individual-level predictors Gender Age
Female (55.1%) 16–24 (13.0%)
Individual economic status Social support
Other (76.2%) No lack (56.0%)
Trust Civic participation
Low trust (54.9%) Low (35.3%)
Household-level predictors Social class Classes I and II (38.4%) Household tenure
Other (26.3%)
Male (44.9%) 25–44 (35.8%) 45–64 (30.7%) 65+(20.6%) Inactive (23.5%) Some lack (25.0%) Severe lack (12.1%) High trust (31.9%) Medium (28.2%) High (27.2%)
Class III NM (15.3%) Class III M (24.3%) Classes IV and V (18.9%) House owner (73.0%)
Community-level predictors Social capital3 Mean = 67.7%; SD = 21.74 Note. (1) Inactive = long-term unemployed and other economically inactive, other = in employment and retired; (2) house owner = own accommodation outright and buying accommodation with the help of a mortgage or loan, other = rent accommodation, live rent-free, and squatting; (3) social capital = proportion of respondents in each sample point agreeing or strongly agreeing with the statement “this area is a place where neighbors look after each other”; the percentages in the table may not always add up to 100% due to missing values.
490
W. Poortinga / Preventive Medicine 43 (2006) 488–493
sampling point that agreed or strongly agreed with the statement “this area is a place where neighbors look after each other” was used as an indicator for social capital at the community level (Poortinga, 2006b).
Table 2 Odds ratios (OR) and 95% confidence intervals (CI) of predictors of self-rated poor health, without (Model 1) and with (Model 2) five health behavior measures as covariates (Health Survey for England 2002)
Data analysis
Self-rated health (poor health)
The mediation analysis in this study broadly follows the approach outlined by Baron and Kenny (1986). As the HSE studies are clustered on the sampling point and household level, the data set was analyzed from a multilevel perspective (see, e.g., Bryk and Raudenbush, 1992; Snijders and Bosker, 1999; Goldstein, 2003). Krull and MacKinnon (2001) demonstrate that even with small intraclass correlations single-level analysis would underestimate the standard errors of mediating effects. MLwiN software (Rasbash et al., 2002) was used to construct simple 3-level logistic regression models with individuals at level 1, households at level 2, and sampling points at level 3. First, a model was constructed in which self-reported health is regressed on all sociodemographic, social support, and social capital variables (Model 1). Second, the same set of variables was used to predict the five indicators of people's smoking, alcohol intake, and fruit/vegetable consumption. Third, the five health behavior indicators were added to the self-rated health model (Model 2). Comparing the self-rated health models with (Model 2) and without (Model 1) the five health behaviors as covariates should reveal whether the health behaviors mediate the association between social capital and health.
Model 1
Results Table 2 shows that self-rated health can be predicted from a wide range of individual, household, and community variables. Older age groups and economically inactive individuals were more likely to report poor health. A social class gradient was found for self-rated health, with ‘skilled manual’ and ‘partly and unskilled manual’ households being more likely to report poor health than ‘professional and intermediate’ households. In addition, house ownership substantially reduced the risk of reporting poor health. All social support and social capital indicators were associated with people's subjective health. People who do not experience a lack of social support, who have a high level of trust, and those with a medium or high level of civic participation were less likely to report poor health. At the community level, social capital additionally lowered the risk of reporting poor health. Table 3 shows that older age groups and homeowners were more likely, and that ‘skilled manual’ and ‘partly and unskilled manual’ households were less likely, to be a non-smoker. All social support and social capital were associated with people's smoking behavior. People who do not experience a lack of social support have a high level of trust, and those with a medium or high level of civic participation were more likely to be a non-smoker. At the same time, people living in communities with higher levels of social capital were more likely to be a non-smoker. Alcohol consumption was related to a number of sociodemographic variables, but less so to the social support and social capital variables. Men were less likely to drink between 0 and 2 U of alcohol per day. But older age groups, people living in ‘skilled non-manual’ and ‘partly and unskilled manual’ households, and homeowners were more likely to drink between 0 and 2 U of alcohol per day. Of the social support and capital variables, only high levels of civic participation and community social capital increased the likelihood of drinking 0–2 U of alcohol/day.
Model 2
Level 1 (individual) Male 1.04 0.89–1.21 n.s. 1.05 0.89–1.24 Aged 25–44 2.00 1.44–2.77 *** 1.83 1.35–2.48 Aged 45–64 6.01 4.35–8.31 *** 5.85 4.29–7.97 Aged 65+ 14.61 10.35–20.64 ** 14.14 9.84–20.32 Inactive 2.44 2.01–2.96 *** 2.28 1.86–2.78 Some lack of support 1.32 1.10–1.59 ** 1.26 1.04–1.53 Severe lack of support 2.17 1.72–2.73 *** 2.04 1.61–2.59 Trust 0.69 0.58–0.82 *** 0.72 0.61–0.85 Medium participation 0.76 0.63–0.92 ** 0.84 0.70–1.01 High participation 0.62 0.51–0.76 *** 0.71 0.58–0.85
n.s. *** *** *** *** ⁎ *** *** n.s. ***
Level 2 (household) Class III NM Class III M Classes IV and V House owner
1.21 1.52 1.83 0.48
0.93–1.56 1.22–1.90 1.44–2.32 0.39–0.58
n.s. *** *** ***
1.19 1.42 1.63 0.55
0.92–1.54 1.13–1.77 1.28–2.07 0.45–0.66
n.s. ** *** ***
Level 3 (community) Social capital
0.52
0.33–0.83
**
0.59 0.38–0.91
***
– –
– – – –
0.61 1.77 1.04 0.78
0.50–0.74 1.33–2.36 0.85–1.26 0.65–0.93
*** *** n.s. ⁎⁎
–
–
0.62 0.49–0.79
⁎⁎⁎
Health behaviors Non-smoker Alcohol: 0 U/day Alcohol: 0–2 U/day Fruit/vegetables: 2–5 portions/day Fruit/vegetables: 5+portions/day
–
Note. ⁎p < 0.05,⁎⁎p < 0.01, ⁎⁎⁎p < 0.001. n.s. = non-significant.
Whereas men and homeowners were less likely to consume no alcohol, older age groups and economically inactives were more likely to do so. Interestingly, people experiencing a severe lack of social support were more likely to consume no alcohol. In addition, people with a medium or a high level of civic participation were less likely to consume no alcohol. Social capital on the community level was not associated with this indicator. The sociodemographic variables were hardly associated with eating two to five portions of fruit/vegetables per day. Whereas people aged 65 and over were more likely to eat two to five portions of fruit/vegetables per day, economically inactive people were less likely to fall into this category. People experiencing some lack of social support were more likely to consume two to five portions of fruit/vegetables per day, as were those with a medium level of civic participation. In addition, social capital on the community level was positively associated with this fruit/vegetable consumption category. Table 3 shows that older age groups and homeowners were more likely, but that ‘skilled manual’ and ‘partly and unskilled manual’ households were less likely to eat the recommended five portions of fruit and vegetables per day. The results also suggest that social support and social capital are important for people's fruit/vegetable consumption. People who report some
W. Poortinga / Preventive Medicine 43 (2006) 488–493
491
Table 3 Odds ratios (OR) and 95% confidence intervals (CI) of predictors of five health-related behaviors (Health Survey for England 2002) Smoking
Alcohol consumption
Non-smoker
0–2 U/day
Fruit/vegetable consumption 0 U/day
2–5 portions/day
5+ portions/day
Level 1 (individual) Male Aged 25–44 Aged 45–64 Aged 65+ Inactive Some lack of support Severe lack of support Trust Medium participation High participation
0.94 0.98 1.66 7.04 0.87 0.66 0.70 1.38 2.12 2.39
0.79–1.12 0.74–1.29 1.27–2.18 4.78–10.35 0.70–1.09 0.53–0.81 0.53–0.93 1.13–1.67 1.70–2.65 1.88–3.05
n.s. n.s. *** *** n.s. *** ⁎ ** *** ***
0.29 1.99 1.86 2.77 0.98 1.02 0.81 0.97 1.06 1.25
0.25–0.34 1.57–2.53 1.45–2.39 2.09–3.68 0.81–1.19 0.86–1.22 0.65–1.02 0.83–1.12 0.88–1.28 1.05–1.50
⁎⁎⁎ *** *** *** n.s. n.s. n.s. n.s. n.s. *
0.53 1.13 1.56 4.74 2.56 1.00 1.51 0.87 0.63 0.61
0.38–0.74 0.76–1.68 1.04–2.35 2.84–7.91 1.84–3.56 0.75–1.34 1.06–1.95 0.68–1.11 0.45–0.86 0.43–0.86
*** n.s. * *** *** n.s. * n.s. ** **
1.07 1.16 1.10 1.34 0.82 1.19 1.11 1.08 1.17 1.00
0.90–1.27 0.94–1.43 0.88–1.38 1.06–1.70 0.70–0.96 1.03–1.38 0.91–1.35 0.95–1.23 1.00–1.36 0.85–1.16
n.s. n.s. n.s. * * * n.s. n.s. * n.s.
0.79 1.41 2.73 1.69 1.08 0.62 0.63 1.21 1.39 2.30
0.67–0.93 1.06–1.88 2.08–3.58 1.20–2.37 0.85–1.37 0.50–0.76 0.47–0.86 1.01–1.45 1.13–1.72 1.85–2.85
⁎⁎ ** *** *** n.s. *** ** * ** ***
Level 2 (household) Class III NM Class III M Classes IV and V House owner
0.79 0.62 0.48 3.10
0.58–1.06 0.47–0.83 0.35–0.64 2.43–3.96
n.s. ** *** ***
1.28 1.21 1.28 1.35
1.02–1.61 0.99–1.48 1.02–1.60 1.12–1.62
* n.s. * **
0.93 1.02 1.22 0.51
0.62–1.38 0.67–1.54 0.82–1.83 0.35–0.73
n.s. n.s. n.s. ***
1.14 0.91 0.96 1.13
0.94–1.38 0.77–1.08 0.79–1.15 0.98–1.31
n.s. n.s. n.s. n.s.
0.74 0.56 0.39 1.60
0.55–1.01 0.43–0.73 0.28–0.53 1.24–2.07
n.s. *** *** ***
Level 3 (community) Social capital
2.37
1.39–4.05
**
1.52
1.07–2.14
**
0.49
0.20–1.20
n.s.
1.43
1.02–2.00
*
0.62
0.42–1.03
n.s.
Note. ⁎p < 0.05,⁎⁎p < 0.01, ⁎⁎⁎p < 0.001. n.s. = non-significant.
or a severe lack of social support were less likely to eat the required five portions a day. At the same time, trusting individuals as well as people with a medium and a high level of civic participations were more likely to eat at least five portions per day. However, social capital at the community level was not associated with the consumption of the recommended 5 portions of fruit and vegetables per day. It becomes clear from Table 2 that adding the health behavior measures to the self-rated health model has only a limited effect on the associations between sociodemographic, social support, and social capital on the one hand and self-rated health on the other. Although the health behaviors seem to slightly attenuate the associations with self-rated health, only the relationship between medium participation and self-rated health was rendered non-significant. Most importantly, only limited support was found for the hypothesis that health behaviors mediate the relationship between social capital and health. Even if social capital was found to be associated with self-rated health and the different health behaviors, and the health behaviors with selfrated health, adding the health behaviors to the self-rated health model did not substantially affect the association between the community social capital variable and self-rated health. Discussion The main aim of the current study was to investigate whether health behaviors mediate the association between social capital and health. A series of multilevel analyses shows that the social capital and support variables are significantly associated with self-rated health. This confirms earlier findings that these concepts play an important role in shaping people's health (see, e.g., Subramanian et al., 2002; Kawachi et al., 2004; Poortinga, 2006b). Some interesting associations with different health
behaviors were found. As expected, social capital and support seem to discourage deviant health behaviors. Social support, trust, and civic participation appeared to be negatively associated with smoking, confirming the findings of Lindström (2003). Over and above these individual-level effects, social capital was associated with lower levels of smoking at the community level. The results suggest that social capital and support encourage moderate levels of alcohol consumption. Whereas a lack of support was associated with not drinking, people with medium and high levels of civic participation were less likely to abstain from drinking. At the same time, civic participation at the individual level and social capital at the community level were found to be associated with moderate drinking (i.e., between 0 and 2 U of alcohol per day). This suggests that alcohol consumption is a social activity, i.e., social interaction seems to stimulate a moderate intake of alcohol. With regard to fruit and vegetable consumption, individual social support, trust, and civic participation were particularly associated with eating the recommended daily intake. Social capital on the community level only increased the likelihood of consuming between 2 and 5 portions per day, but not the consumption of the recommended 5 portions of fruit and vegetables per day. These results suggest that social capital only promotes moderate levels of fruit/vegetable consumption. As might be expected, the different health behaviors were significantly associated with people's self-rated health. People who do not smoke and have moderate or high levels of fruit and vegetable consumption are less likely to report poor health. In contrast to what might be expected (e.g., Østbye et al., 2002), this study found that people who do not drink alcohol are more likely to report poor health. As shown before, social support and civic participation are linked to (moderate levels of) alcohol consumption. It might well be that the social component of
492
W. Poortinga / Preventive Medicine 43 (2006) 488–493
alcohol consumption is beneficial for people's general wellbeing. However, it is also possible that poor health leads to alcohol abstention. Only limited support was found for the hypothesis that health behaviors mediate the relationship between social capital and health. All conditions for mediation were fulfilled (i.e., social capital was associated with self-rated health; social capital was associated with the different health behaviors; and the health behaviors were associated with self-rated health) and were the strongest for smoking. According to the Cohen and Cohen (1983) joint significance test (cited in MacKinnon et al., 2002), this would mean that mediation is supported. However, adding the health behaviors to the self-rated health model did not substantially alter the association with the social capital/support variables. So, according to the Baron and Kenny (1986) method, not all conditions have been fulfilled to establish mediation. The current study has a number of limitations. The crosssectional nature of the study may be considered a weakness, as no causal inferences can be drawn from the results. For example, it may well be that poor health leads to lower civic participation instead of the other way around. Longitudinal studies could provide more definite information on the possible causal pathways from social capital, health behaviors, and people's overall health. Another limitation is the use of postcode sectors as a proxy for neighborhoods. Postcode sectors may not match the respondents' perception of their local community. Here it has to be kept in mind that the misspecification of the level of the relevant geographical area may affect the outcome of the study (Diez-Roux, 2001). As information on physical activity was only available for a limited subset of respondents, the current study did not take physical activity into account. Physical activity has been shown to be strongly associated with social capital and support (e.g., Lindström et al., 2001; Stahl et al., 2001; Addy et al., 2004). That this study was unable to replicate the findings of Mohan et al. (2005) could partly be due to the absence of this important health behavior. Moreover, the mediating and dependent variables were dichotomized in this study. It is possible that these crude measures were inadequate for determining whether health behaviors mediate the association between social capital and health. MacCallum et al. (2002) have shown that dichotomization may result in the loss of reliable information, as well as loss in effect size and power. In addition, MacKinnon et al. (2002) suggest that the Baron and Kenny (1986) method lacks statistical power to test the significance of mediating effects. Future research should address these shortcomings in order to come to firmer conclusions. Despite these caveats, the results have clear implications for prevention policies. The study links individual-level social capital and support variables to positive behaviors with regard to smoking and fruit/vegetable consumption. In addition, social capital at the community level is linked to lower levels of smoking and to moderate levels of alcohol intake and fruit/ vegetable consumption. This suggests that community-based policies aimed at smoking, combating excesses in alcohol consumption, and promoting fruit and vegetable consumption might prove successful. However, the study has also shown that
more comprehensive analyses are needed to further investigate the mechanisms linking social capital to health. References Addy, C.L., Wilson, D.K., Kirtland, K.A., Ainsworth, B.E., Sharpe, P., Kimsey, D., 2004. Associations of perceived social and physical environmental support with physical activity and walking behaviour. Am. J. Public Health 94 (3), 440–443. Baron, R.M., Kenny, D.A., 1986. The moderator-mediator variable distinction in social psychological research: conceptual, strategic and statistical considerations. J. Pers. Soc. Psychol. 51, 1173–1182. Bryk, A.S., Raudenbush, S.W., 1992. Hierarchical Linear Models: Applications and Data Analysis Methods. Sage, Newbury Park. Caughy, M.O., O'Campo, P.J., Muntaner, C., 2003. When being alone might be better: neighbourhood poverty, social capital, and child mental health. Soc. Sci. Med. 57 (2), 227–237. Cohen, J., Cohen, P., 1983. Applied Multiple Regression/Correlation Analysis for the Behavioural Sciences. Erlbaum, Hillsdale, NJ. Cox, B.D., Blaxter, M., Buckle, A.L.J., et al., 1987. The Health and Lifestyle Survey. Health Promotion Research Trust, London. Department of Health, 1995. The Sensible Drinking Report. The Results of an Interdepartmental Working Group. The Stationery Office, London. Department of Health, 2001. Five-a-Day Update. The Stationery Office, London. Diez-Roux, A., 2001. Investigating neighbourhood and area effects on health. Am. J. Public Health 91, 1783–1789. Goldstein, H., 2003. Multilevel Statistical Models, third ed. Hodder Arnold, London. Helliwell, J.F., 2003. Well-being and social capital: does suicide pose a puzzle? Presented at the Conference on Well-Being and Social Capital, Harvard 7–9 November 2003. Available from: http://www.wcfia.harvard.edu/conferences/ socialcapital/happiness%20Readings/helliwell_2003.pdf Hyyppä, M.T., Mäki, J., 2001. Individual-level relationships between social capital and self-rated health in a bilingual community. Prev. Med. 32 (2), 148–155. Kawachi, I., Berkman, L., 2000. Social cohesion, social capital and health. In: Berkman, L., Kawachi, I. (Eds.), Social Epidemiology. OUP, Oxford. Kawachi, I., Kennedy, B.P., Glass, R., 1999. Social capital and self-rated health: a contextual analysis. Am. J. Public Health 89 (8), 1187–1193. Kawachi, I., Kennedy, B.P., Lochner, K., Prothrow-Stith, D., 1997. Social capital, social inequality, and mortality. Am. J. Public Health 87 (9), 1491–1498. Kawachi, I., Kim, D., Coutts, A., Subramanian, S.V., 2004. Commentary: reconciling the three accounts of social capital. Int. J. Epidemiol. 33 (4), 682–690. Krull, J.L., MacKinnon, D.P., 2001. Multilevel modeling of individual and group level mediating effects. Multivar. Behav. Res. 36 (2), 249–277. Lindström, M., 2003. Social capital and the miniaturization of community among daily and intermittent smokers: a population-based study. Prev. Med. 36 (2), 177–184. Lindström, M., Hanson, B.S., Östergren, P.O., 2001. Socioeconomic differences in leisure time physical activity: the role of shaping participation and social capital in shaping health related behaviour. Soc. Sci. Med. 52 (3), 441–451. Lochner, K., Kawachi, I., Kennedy, B.P., 1999. Social capital: a guide to its measurement. Health Place 5 (4), 259–270. MacCallum, R.C., Zhang, S., Preacher, K.J., Rucker, D.D., 2002. On the practice of dichotomization of quantitative variables. Psychol. Methods 7 (1), 19–40. MacKinnon, D.P., Lockwood, C.M., Hoffman, J.M., West, S.G., Sheets, V., 2002. Comparison of methods to test mediated and other intervening variable effects. Psychol. Methods 7 (1), 83–104. Mohan, J., Twigg, L., Barnard, S., Jones, K., 2005. Social capital, geography and health: a small area analysis for England. Soc. Sci. Med. 60 (6), 1267–1283. Østbye, T., Taylor, D.H., Jung, S.-H., 2002. A longitudinal study of the effects of tobacco smoking and other modifiable risk factors on ill health in middleaged and old americans: results from the health and retirement study and
W. Poortinga / Preventive Medicine 43 (2006) 488–493 asset and health dynamics among the oldest old survey. Prev. Med. 34 (3), 334–345. Poortinga, W., 2006a. Social capital: an individual or collective resource for health? Soc. Sci. Med. 62 (2), 292–302. Poortinga, W., 2006b. Social relations or social capital? Individual and community health effects of bonding social capital. Soc. Sci. Med. 63 (1), 255–270. Putnam, R.D., 2000. Bowling Alone. The Collapse and Revival of American Community. Simon and Schuster, London. Rasbash, J., Browne, W., Goldstein, H., Yang, M., Plewis, I., Healy, M., Woodhouse, G., Draper, D., Langford, I., Lewis, T., 2002. A User's Guide to MLwiN (Version 2.1d for use with MLwiN 1.10). Institute of Education, University of London, London. Sampson, R., Raudenbush, S., Earls, F., 1997. Neighborhoods and violent crime: a multilevel study of collective efficacy. Science 277, 918–924.
493
Snijders, T.A.B., Bosker, R.J., 1999. Multilevel Analysis: An Introduction to Basic and Advanced Multilevel Modelling. Sage, London. Stahl, T., Rutten, A., Nutbeam, D., Bauman, A., Kannas, L., Abel, T., Luschen, G., Rodriquez, D.J., Vinck, J., van der Zee, J., 2001. The importance of the social environment for physically active lifestyle-results from an international study. Soc. Sci. Med. 52 (1), 1–10. Subramanian, S.V., Kim, D.J., Kawachi, I., 2002. Social trust and self-rated health in US communities: a multilevel analysis. J. Urban Health 79 (4), S21–S34. Weitzman, E.R., Chen, Y.Y., 2005. Risk modifying effect of social capital on measures of heavy alcohol consumption, alcohol abuse, harms, and secondhand effects: national survey findings. J. Epidemiol. Community Health 59 (4), 303–309. Wilkinson, R., 1996. Unhealthy Societies: The Afflictions of Inequality. Routledge, London.
Do health behaviors mediate the association between social capital and health? Wouter Poortinga ⁎ Welsh School of Architecture, Cardiff University, Bute Building, King Edward VII Avenue, Cardiff, Wales, CF10 3NB, UK Available online 24 July 2006
Abstract Introduction. There is increasing evidence that social capital is important for people's health. However, there is still considerable disagreement about the specific pathways that links social capital to health. This study investigates the hypothesis that the association between social capital and health is mediated by people's health behaviors. Method. Data from the 2002 Health Survey for England (n = 7394) were used and analyzed from a multilevel perspective. The association between social capital and self-rated health were examined before and after controlling for smoking, alcohol intake, and fruit/vegetable consumption. Results. Social capital was found to be associated with self-rated health, as well as with the different health behaviors. In addition, the health behaviors were significantly related to self-rated health. However, controlling for smoking, alcohol intake, and fruit/vegetable consumption did not substantially affect the association between social capital and self-rated health. Conclusions. The results demonstrate that social capital and support are important determinants of self-rated health and health behaviors. But only limited support was found for the hypothesis that health behaviors mediate the association between social capital and health. © 2006 Elsevier Inc. All rights reserved. Keywords: Social capital; Social support; Health behaviors; Self-rated health
Introduction There is a growing body of evidence that the social environment plays an important role in shaping people's health. Research efforts in this area have mainly focused on the concepts of social support and social capital. Social capital is generally defined as the features of social organization – such as civic participation, norms of reciprocity, and trust in others – that help facilitate cooperation for mutual benefit (see e.g., Putnam, 2000). As such, social capital can be considered a collective resource that benefits communities and can be distinguished from the individual health effects of social networks and support (see e.g., Lochner et al., 1999). Social capital has been linked to various health outcomes, among which self-rated health (Kawachi et al., 1999; Hyyppä and Mäki, 2001; Subramanian et al., 2002; Helliwell, 2003; Poortinga, 2006a, 2006b), cardiovascular and cancer mortality rates (Kawachi et al., ⁎ Fax: +44 29 2087 4623. E-mail address: [email protected]. 0091-7435/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ypmed.2006.06.004
1997), suicide rates (Helliwell, 2003), and child mental health (Caughy et al., 2003). With the recognition that social capital is important for people's health comes the need to identify the specific mechanisms that link social capital to health. It has been hypothesized that social capital provides a buffer against the adverse effects of stress (Wilkinson, 1996); that social capital helps to disseminate health information and knowledge more quickly across communities (Kawachi and Berkman, 2000); that socially cohesive communities have better access to local services and amenities because they are more likely to be successful at fighting potential cuts in services (Sampson et al., 1997; Kawachi et al., 1999); and that communities with high levels of social capital are more effective at exercising social control over different health behaviors (Kawachi and Berkman, 2000; Subramanian et al., 2002). There is some empirical support for the latter hypothesis. Social capital has been found to be associated with various health behaviors, such as physical activity (e.g., Lindström et al., 2001; Stahl et al., 2001; Addy et al., 2004), fruit and vegetable consumption (Lindström et al., 2001), smoking (Lindström, 2003), and alcohol consumption
W. Poortinga / Preventive Medicine 43 (2006) 488–493
(Weitzman and Chen, 2005). Mohan et al. (2005) provide further support for the idea that health behaviors form part of a possible mediating pathway between social capital and health. They found that the mortality effects of social capital were attenuated when controlling for differences in health-related behaviors. The aim of this study is to investigate if health behaviors mediate the association between social capital and health. More specifically, the study examines (1) whether social capital is associated with health, (2) whether social capital is associated with a number of health-related behaviors (i.e., smoking, alcohol intake, and fruit and vegetable consumption), and (3) whether controlling for the health-related behaviors attenuates the association between social capital and health. Methods Study population Data from the 2002 Health Survey for England were used. The Health Survey for England (HSE) is a series of annual studies covering the English adult population aged 16 and over living in private households. The data were collected from January 2002 to March 2003. In total, 7394 individual interviews were conducted within 4332 households that were selected from 720 postcode sectors.1 The household response rate was 74%. Table 1 summarizes the variables from the data set that are considered for the analyses in this paper.
Measures Health outcomes Self-rated health and five health behaviors were the health outcome variables of this study (see Table 1). First, respondents were asked to rate their own general health on a five-point scale ranging from very good to very bad. The original scale was dichotomized, with 1 representing fair, bad, and very bad health and 0 representing a good or very good health. Second, people's current smoking status, daily alcohol intake, and daily fruit/vegetable consumption was assessed. People who smoke were compared to people who do not smoke. Daily alcohol intake was derived from people's self-reported consumption and divided into three groups. A distinction was made between those drinking more and those drinking less than 2 U of alcohol per day.2 People not drinking at all were considered a separate group. Fruit and vegetable consumption was calculated by adding up all portions of pulses, salad, vegetables, and fresh, dried, and canned fruit that were eaten ‘yesterday’. The recommended consumption of 5 portions of fruit and vegetables a day was used as a cut-off point (Department of Health, 2001). As only few respondents managed to eat 5 portions per day (see Table 1), an additional distinction was made between those eating fewer than two portions per day, and those eating between two and five portions per day. Sociodemographics The sociodemographic variables of gender, age, individual economic status, household social class, and household tenure were included in the analyses (see Table 1). Three dummy variables represented the four age categories of 16–24 years, 25–44 years, 45–64 years, and 65 years and over. Individual economic status compared economically inactive (long-term unemployed and
1
National Centre for Social Research and University College London (2004). Department of Epidemiology and Public Health, Health Survey for England, 2002 [computer file]. Colchester, Essex: UK Data Archive [distributor], May 2004. SN: 4912. Available from: http://www.data-archive.ac.uk/. More information about the methodology of 2002 Health Survey for England can be found at http://www.archive2.official-documents.co.uk/document/deps/doh/ survey02/hse02.htm. 2 In this study, the lower end of the recommended daily alcohol consumption of 2 to 3 units for women was used as the cut-off point (Department of Health, 1995).
489
other economically inactive) with working individuals. Household social class was measured using the Registrar General's occupation-based classification: I and II (professionals and intermediates), III NM (skilled non-manual), III M (skilled manual), and IV and V (partly and unskilled manual). Household tenure compared household ownership (with or without mortgage) with renting, living rent-free, and squatting. Social capital and support Responses to seven statements were added to construct a social support scale (1: “not true”, 2: “partly true”, and 3: “certainly true”). People were subdivided into three groups with ‘no lack’ (score 21), ‘some lack’ (scores 18–20), and a ‘severe lack’ (scores 7–17) of social support (cf. Cox et al., 1987). Social trust was measured with the question “generally speaking, would you say that: most people can be trusted (coded 1) or you can't be too careful in dealing with people (coded 0)”. Civic participation was measured by asking respondents to indicate whether they regularly join in activities of fourteen types of clubs or associations. Because many were involved in none or only one organization, respondents were subdivided into three groups: low (not involved in any club or organization), medium (one club or organization), or high (two or more clubs or organizations) civic participation. The proportion of respondents in each
Table 1 Characteristics of the 2002 Health Survey for England dataset (n = 7394)
Health outcome Self-rated health
Health behaviors Smoking Units of alcohol per day
Base
Contrast
Good/very good (74.2%)
Fair/poor/very poor (25.8%)
Smoker (26.3%) More than 2 (29.0%)
Non-smoker (73.2%) 0 (11.7%) Fewer than 2, excluding 0 (58.2%) 2–5 (48.7%) 5 or more (23.9%)
Fruit/vegetable portions per day
Fewer than 2 (27.4%)
Individual-level predictors Gender Age
Female (55.1%) 16–24 (13.0%)
Individual economic status Social support
Other (76.2%) No lack (56.0%)
Trust Civic participation
Low trust (54.9%) Low (35.3%)
Household-level predictors Social class Classes I and II (38.4%) Household tenure
Other (26.3%)
Male (44.9%) 25–44 (35.8%) 45–64 (30.7%) 65+(20.6%) Inactive (23.5%) Some lack (25.0%) Severe lack (12.1%) High trust (31.9%) Medium (28.2%) High (27.2%)
Class III NM (15.3%) Class III M (24.3%) Classes IV and V (18.9%) House owner (73.0%)
Community-level predictors Social capital3 Mean = 67.7%; SD = 21.74 Note. (1) Inactive = long-term unemployed and other economically inactive, other = in employment and retired; (2) house owner = own accommodation outright and buying accommodation with the help of a mortgage or loan, other = rent accommodation, live rent-free, and squatting; (3) social capital = proportion of respondents in each sample point agreeing or strongly agreeing with the statement “this area is a place where neighbors look after each other”; the percentages in the table may not always add up to 100% due to missing values.
490
W. Poortinga / Preventive Medicine 43 (2006) 488–493
sampling point that agreed or strongly agreed with the statement “this area is a place where neighbors look after each other” was used as an indicator for social capital at the community level (Poortinga, 2006b).
Table 2 Odds ratios (OR) and 95% confidence intervals (CI) of predictors of self-rated poor health, without (Model 1) and with (Model 2) five health behavior measures as covariates (Health Survey for England 2002)
Data analysis
Self-rated health (poor health)
The mediation analysis in this study broadly follows the approach outlined by Baron and Kenny (1986). As the HSE studies are clustered on the sampling point and household level, the data set was analyzed from a multilevel perspective (see, e.g., Bryk and Raudenbush, 1992; Snijders and Bosker, 1999; Goldstein, 2003). Krull and MacKinnon (2001) demonstrate that even with small intraclass correlations single-level analysis would underestimate the standard errors of mediating effects. MLwiN software (Rasbash et al., 2002) was used to construct simple 3-level logistic regression models with individuals at level 1, households at level 2, and sampling points at level 3. First, a model was constructed in which self-reported health is regressed on all sociodemographic, social support, and social capital variables (Model 1). Second, the same set of variables was used to predict the five indicators of people's smoking, alcohol intake, and fruit/vegetable consumption. Third, the five health behavior indicators were added to the self-rated health model (Model 2). Comparing the self-rated health models with (Model 2) and without (Model 1) the five health behaviors as covariates should reveal whether the health behaviors mediate the association between social capital and health.
Model 1
Results Table 2 shows that self-rated health can be predicted from a wide range of individual, household, and community variables. Older age groups and economically inactive individuals were more likely to report poor health. A social class gradient was found for self-rated health, with ‘skilled manual’ and ‘partly and unskilled manual’ households being more likely to report poor health than ‘professional and intermediate’ households. In addition, house ownership substantially reduced the risk of reporting poor health. All social support and social capital indicators were associated with people's subjective health. People who do not experience a lack of social support, who have a high level of trust, and those with a medium or high level of civic participation were less likely to report poor health. At the community level, social capital additionally lowered the risk of reporting poor health. Table 3 shows that older age groups and homeowners were more likely, and that ‘skilled manual’ and ‘partly and unskilled manual’ households were less likely, to be a non-smoker. All social support and social capital were associated with people's smoking behavior. People who do not experience a lack of social support have a high level of trust, and those with a medium or high level of civic participation were more likely to be a non-smoker. At the same time, people living in communities with higher levels of social capital were more likely to be a non-smoker. Alcohol consumption was related to a number of sociodemographic variables, but less so to the social support and social capital variables. Men were less likely to drink between 0 and 2 U of alcohol per day. But older age groups, people living in ‘skilled non-manual’ and ‘partly and unskilled manual’ households, and homeowners were more likely to drink between 0 and 2 U of alcohol per day. Of the social support and capital variables, only high levels of civic participation and community social capital increased the likelihood of drinking 0–2 U of alcohol/day.
Model 2
Level 1 (individual) Male 1.04 0.89–1.21 n.s. 1.05 0.89–1.24 Aged 25–44 2.00 1.44–2.77 *** 1.83 1.35–2.48 Aged 45–64 6.01 4.35–8.31 *** 5.85 4.29–7.97 Aged 65+ 14.61 10.35–20.64 ** 14.14 9.84–20.32 Inactive 2.44 2.01–2.96 *** 2.28 1.86–2.78 Some lack of support 1.32 1.10–1.59 ** 1.26 1.04–1.53 Severe lack of support 2.17 1.72–2.73 *** 2.04 1.61–2.59 Trust 0.69 0.58–0.82 *** 0.72 0.61–0.85 Medium participation 0.76 0.63–0.92 ** 0.84 0.70–1.01 High participation 0.62 0.51–0.76 *** 0.71 0.58–0.85
n.s. *** *** *** *** ⁎ *** *** n.s. ***
Level 2 (household) Class III NM Class III M Classes IV and V House owner
1.21 1.52 1.83 0.48
0.93–1.56 1.22–1.90 1.44–2.32 0.39–0.58
n.s. *** *** ***
1.19 1.42 1.63 0.55
0.92–1.54 1.13–1.77 1.28–2.07 0.45–0.66
n.s. ** *** ***
Level 3 (community) Social capital
0.52
0.33–0.83
**
0.59 0.38–0.91
***
– –
– – – –
0.61 1.77 1.04 0.78
0.50–0.74 1.33–2.36 0.85–1.26 0.65–0.93
*** *** n.s. ⁎⁎
–
–
0.62 0.49–0.79
⁎⁎⁎
Health behaviors Non-smoker Alcohol: 0 U/day Alcohol: 0–2 U/day Fruit/vegetables: 2–5 portions/day Fruit/vegetables: 5+portions/day
–
Note. ⁎p < 0.05,⁎⁎p < 0.01, ⁎⁎⁎p < 0.001. n.s. = non-significant.
Whereas men and homeowners were less likely to consume no alcohol, older age groups and economically inactives were more likely to do so. Interestingly, people experiencing a severe lack of social support were more likely to consume no alcohol. In addition, people with a medium or a high level of civic participation were less likely to consume no alcohol. Social capital on the community level was not associated with this indicator. The sociodemographic variables were hardly associated with eating two to five portions of fruit/vegetables per day. Whereas people aged 65 and over were more likely to eat two to five portions of fruit/vegetables per day, economically inactive people were less likely to fall into this category. People experiencing some lack of social support were more likely to consume two to five portions of fruit/vegetables per day, as were those with a medium level of civic participation. In addition, social capital on the community level was positively associated with this fruit/vegetable consumption category. Table 3 shows that older age groups and homeowners were more likely, but that ‘skilled manual’ and ‘partly and unskilled manual’ households were less likely to eat the recommended five portions of fruit and vegetables per day. The results also suggest that social support and social capital are important for people's fruit/vegetable consumption. People who report some
W. Poortinga / Preventive Medicine 43 (2006) 488–493
491
Table 3 Odds ratios (OR) and 95% confidence intervals (CI) of predictors of five health-related behaviors (Health Survey for England 2002) Smoking
Alcohol consumption
Non-smoker
0–2 U/day
Fruit/vegetable consumption 0 U/day
2–5 portions/day
5+ portions/day
Level 1 (individual) Male Aged 25–44 Aged 45–64 Aged 65+ Inactive Some lack of support Severe lack of support Trust Medium participation High participation
0.94 0.98 1.66 7.04 0.87 0.66 0.70 1.38 2.12 2.39
0.79–1.12 0.74–1.29 1.27–2.18 4.78–10.35 0.70–1.09 0.53–0.81 0.53–0.93 1.13–1.67 1.70–2.65 1.88–3.05
n.s. n.s. *** *** n.s. *** ⁎ ** *** ***
0.29 1.99 1.86 2.77 0.98 1.02 0.81 0.97 1.06 1.25
0.25–0.34 1.57–2.53 1.45–2.39 2.09–3.68 0.81–1.19 0.86–1.22 0.65–1.02 0.83–1.12 0.88–1.28 1.05–1.50
⁎⁎⁎ *** *** *** n.s. n.s. n.s. n.s. n.s. *
0.53 1.13 1.56 4.74 2.56 1.00 1.51 0.87 0.63 0.61
0.38–0.74 0.76–1.68 1.04–2.35 2.84–7.91 1.84–3.56 0.75–1.34 1.06–1.95 0.68–1.11 0.45–0.86 0.43–0.86
*** n.s. * *** *** n.s. * n.s. ** **
1.07 1.16 1.10 1.34 0.82 1.19 1.11 1.08 1.17 1.00
0.90–1.27 0.94–1.43 0.88–1.38 1.06–1.70 0.70–0.96 1.03–1.38 0.91–1.35 0.95–1.23 1.00–1.36 0.85–1.16
n.s. n.s. n.s. * * * n.s. n.s. * n.s.
0.79 1.41 2.73 1.69 1.08 0.62 0.63 1.21 1.39 2.30
0.67–0.93 1.06–1.88 2.08–3.58 1.20–2.37 0.85–1.37 0.50–0.76 0.47–0.86 1.01–1.45 1.13–1.72 1.85–2.85
⁎⁎ ** *** *** n.s. *** ** * ** ***
Level 2 (household) Class III NM Class III M Classes IV and V House owner
0.79 0.62 0.48 3.10
0.58–1.06 0.47–0.83 0.35–0.64 2.43–3.96
n.s. ** *** ***
1.28 1.21 1.28 1.35
1.02–1.61 0.99–1.48 1.02–1.60 1.12–1.62
* n.s. * **
0.93 1.02 1.22 0.51
0.62–1.38 0.67–1.54 0.82–1.83 0.35–0.73
n.s. n.s. n.s. ***
1.14 0.91 0.96 1.13
0.94–1.38 0.77–1.08 0.79–1.15 0.98–1.31
n.s. n.s. n.s. n.s.
0.74 0.56 0.39 1.60
0.55–1.01 0.43–0.73 0.28–0.53 1.24–2.07
n.s. *** *** ***
Level 3 (community) Social capital
2.37
1.39–4.05
**
1.52
1.07–2.14
**
0.49
0.20–1.20
n.s.
1.43
1.02–2.00
*
0.62
0.42–1.03
n.s.
Note. ⁎p < 0.05,⁎⁎p < 0.01, ⁎⁎⁎p < 0.001. n.s. = non-significant.
or a severe lack of social support were less likely to eat the required five portions a day. At the same time, trusting individuals as well as people with a medium and a high level of civic participations were more likely to eat at least five portions per day. However, social capital at the community level was not associated with the consumption of the recommended 5 portions of fruit and vegetables per day. It becomes clear from Table 2 that adding the health behavior measures to the self-rated health model has only a limited effect on the associations between sociodemographic, social support, and social capital on the one hand and self-rated health on the other. Although the health behaviors seem to slightly attenuate the associations with self-rated health, only the relationship between medium participation and self-rated health was rendered non-significant. Most importantly, only limited support was found for the hypothesis that health behaviors mediate the relationship between social capital and health. Even if social capital was found to be associated with self-rated health and the different health behaviors, and the health behaviors with selfrated health, adding the health behaviors to the self-rated health model did not substantially affect the association between the community social capital variable and self-rated health. Discussion The main aim of the current study was to investigate whether health behaviors mediate the association between social capital and health. A series of multilevel analyses shows that the social capital and support variables are significantly associated with self-rated health. This confirms earlier findings that these concepts play an important role in shaping people's health (see, e.g., Subramanian et al., 2002; Kawachi et al., 2004; Poortinga, 2006b). Some interesting associations with different health
behaviors were found. As expected, social capital and support seem to discourage deviant health behaviors. Social support, trust, and civic participation appeared to be negatively associated with smoking, confirming the findings of Lindström (2003). Over and above these individual-level effects, social capital was associated with lower levels of smoking at the community level. The results suggest that social capital and support encourage moderate levels of alcohol consumption. Whereas a lack of support was associated with not drinking, people with medium and high levels of civic participation were less likely to abstain from drinking. At the same time, civic participation at the individual level and social capital at the community level were found to be associated with moderate drinking (i.e., between 0 and 2 U of alcohol per day). This suggests that alcohol consumption is a social activity, i.e., social interaction seems to stimulate a moderate intake of alcohol. With regard to fruit and vegetable consumption, individual social support, trust, and civic participation were particularly associated with eating the recommended daily intake. Social capital on the community level only increased the likelihood of consuming between 2 and 5 portions per day, but not the consumption of the recommended 5 portions of fruit and vegetables per day. These results suggest that social capital only promotes moderate levels of fruit/vegetable consumption. As might be expected, the different health behaviors were significantly associated with people's self-rated health. People who do not smoke and have moderate or high levels of fruit and vegetable consumption are less likely to report poor health. In contrast to what might be expected (e.g., Østbye et al., 2002), this study found that people who do not drink alcohol are more likely to report poor health. As shown before, social support and civic participation are linked to (moderate levels of) alcohol consumption. It might well be that the social component of
492
W. Poortinga / Preventive Medicine 43 (2006) 488–493
alcohol consumption is beneficial for people's general wellbeing. However, it is also possible that poor health leads to alcohol abstention. Only limited support was found for the hypothesis that health behaviors mediate the relationship between social capital and health. All conditions for mediation were fulfilled (i.e., social capital was associated with self-rated health; social capital was associated with the different health behaviors; and the health behaviors were associated with self-rated health) and were the strongest for smoking. According to the Cohen and Cohen (1983) joint significance test (cited in MacKinnon et al., 2002), this would mean that mediation is supported. However, adding the health behaviors to the self-rated health model did not substantially alter the association with the social capital/support variables. So, according to the Baron and Kenny (1986) method, not all conditions have been fulfilled to establish mediation. The current study has a number of limitations. The crosssectional nature of the study may be considered a weakness, as no causal inferences can be drawn from the results. For example, it may well be that poor health leads to lower civic participation instead of the other way around. Longitudinal studies could provide more definite information on the possible causal pathways from social capital, health behaviors, and people's overall health. Another limitation is the use of postcode sectors as a proxy for neighborhoods. Postcode sectors may not match the respondents' perception of their local community. Here it has to be kept in mind that the misspecification of the level of the relevant geographical area may affect the outcome of the study (Diez-Roux, 2001). As information on physical activity was only available for a limited subset of respondents, the current study did not take physical activity into account. Physical activity has been shown to be strongly associated with social capital and support (e.g., Lindström et al., 2001; Stahl et al., 2001; Addy et al., 2004). That this study was unable to replicate the findings of Mohan et al. (2005) could partly be due to the absence of this important health behavior. Moreover, the mediating and dependent variables were dichotomized in this study. It is possible that these crude measures were inadequate for determining whether health behaviors mediate the association between social capital and health. MacCallum et al. (2002) have shown that dichotomization may result in the loss of reliable information, as well as loss in effect size and power. In addition, MacKinnon et al. (2002) suggest that the Baron and Kenny (1986) method lacks statistical power to test the significance of mediating effects. Future research should address these shortcomings in order to come to firmer conclusions. Despite these caveats, the results have clear implications for prevention policies. The study links individual-level social capital and support variables to positive behaviors with regard to smoking and fruit/vegetable consumption. In addition, social capital at the community level is linked to lower levels of smoking and to moderate levels of alcohol intake and fruit/ vegetable consumption. This suggests that community-based policies aimed at smoking, combating excesses in alcohol consumption, and promoting fruit and vegetable consumption might prove successful. However, the study has also shown that
more comprehensive analyses are needed to further investigate the mechanisms linking social capital to health. References Addy, C.L., Wilson, D.K., Kirtland, K.A., Ainsworth, B.E., Sharpe, P., Kimsey, D., 2004. Associations of perceived social and physical environmental support with physical activity and walking behaviour. Am. J. Public Health 94 (3), 440–443. Baron, R.M., Kenny, D.A., 1986. The moderator-mediator variable distinction in social psychological research: conceptual, strategic and statistical considerations. J. Pers. Soc. Psychol. 51, 1173–1182. Bryk, A.S., Raudenbush, S.W., 1992. Hierarchical Linear Models: Applications and Data Analysis Methods. Sage, Newbury Park. Caughy, M.O., O'Campo, P.J., Muntaner, C., 2003. When being alone might be better: neighbourhood poverty, social capital, and child mental health. Soc. Sci. Med. 57 (2), 227–237. Cohen, J., Cohen, P., 1983. Applied Multiple Regression/Correlation Analysis for the Behavioural Sciences. Erlbaum, Hillsdale, NJ. Cox, B.D., Blaxter, M., Buckle, A.L.J., et al., 1987. The Health and Lifestyle Survey. Health Promotion Research Trust, London. Department of Health, 1995. The Sensible Drinking Report. The Results of an Interdepartmental Working Group. The Stationery Office, London. Department of Health, 2001. Five-a-Day Update. The Stationery Office, London. Diez-Roux, A., 2001. Investigating neighbourhood and area effects on health. Am. J. Public Health 91, 1783–1789. Goldstein, H., 2003. Multilevel Statistical Models, third ed. Hodder Arnold, London. Helliwell, J.F., 2003. Well-being and social capital: does suicide pose a puzzle? Presented at the Conference on Well-Being and Social Capital, Harvard 7–9 November 2003. Available from: http://www.wcfia.harvard.edu/conferences/ socialcapital/happiness%20Readings/helliwell_2003.pdf Hyyppä, M.T., Mäki, J., 2001. Individual-level relationships between social capital and self-rated health in a bilingual community. Prev. Med. 32 (2), 148–155. Kawachi, I., Berkman, L., 2000. Social cohesion, social capital and health. In: Berkman, L., Kawachi, I. (Eds.), Social Epidemiology. OUP, Oxford. Kawachi, I., Kennedy, B.P., Glass, R., 1999. Social capital and self-rated health: a contextual analysis. Am. J. Public Health 89 (8), 1187–1193. Kawachi, I., Kennedy, B.P., Lochner, K., Prothrow-Stith, D., 1997. Social capital, social inequality, and mortality. Am. J. Public Health 87 (9), 1491–1498. Kawachi, I., Kim, D., Coutts, A., Subramanian, S.V., 2004. Commentary: reconciling the three accounts of social capital. Int. J. Epidemiol. 33 (4), 682–690. Krull, J.L., MacKinnon, D.P., 2001. Multilevel modeling of individual and group level mediating effects. Multivar. Behav. Res. 36 (2), 249–277. Lindström, M., 2003. Social capital and the miniaturization of community among daily and intermittent smokers: a population-based study. Prev. Med. 36 (2), 177–184. Lindström, M., Hanson, B.S., Östergren, P.O., 2001. Socioeconomic differences in leisure time physical activity: the role of shaping participation and social capital in shaping health related behaviour. Soc. Sci. Med. 52 (3), 441–451. Lochner, K., Kawachi, I., Kennedy, B.P., 1999. Social capital: a guide to its measurement. Health Place 5 (4), 259–270. MacCallum, R.C., Zhang, S., Preacher, K.J., Rucker, D.D., 2002. On the practice of dichotomization of quantitative variables. Psychol. Methods 7 (1), 19–40. MacKinnon, D.P., Lockwood, C.M., Hoffman, J.M., West, S.G., Sheets, V., 2002. Comparison of methods to test mediated and other intervening variable effects. Psychol. Methods 7 (1), 83–104. Mohan, J., Twigg, L., Barnard, S., Jones, K., 2005. Social capital, geography and health: a small area analysis for England. Soc. Sci. Med. 60 (6), 1267–1283. Østbye, T., Taylor, D.H., Jung, S.-H., 2002. A longitudinal study of the effects of tobacco smoking and other modifiable risk factors on ill health in middleaged and old americans: results from the health and retirement study and
W. Poortinga / Preventive Medicine 43 (2006) 488–493 asset and health dynamics among the oldest old survey. Prev. Med. 34 (3), 334–345. Poortinga, W., 2006a. Social capital: an individual or collective resource for health? Soc. Sci. Med. 62 (2), 292–302. Poortinga, W., 2006b. Social relations or social capital? Individual and community health effects of bonding social capital. Soc. Sci. Med. 63 (1), 255–270. Putnam, R.D., 2000. Bowling Alone. The Collapse and Revival of American Community. Simon and Schuster, London. Rasbash, J., Browne, W., Goldstein, H., Yang, M., Plewis, I., Healy, M., Woodhouse, G., Draper, D., Langford, I., Lewis, T., 2002. A User's Guide to MLwiN (Version 2.1d for use with MLwiN 1.10). Institute of Education, University of London, London. Sampson, R., Raudenbush, S., Earls, F., 1997. Neighborhoods and violent crime: a multilevel study of collective efficacy. Science 277, 918–924.
493
Snijders, T.A.B., Bosker, R.J., 1999. Multilevel Analysis: An Introduction to Basic and Advanced Multilevel Modelling. Sage, London. Stahl, T., Rutten, A., Nutbeam, D., Bauman, A., Kannas, L., Abel, T., Luschen, G., Rodriquez, D.J., Vinck, J., van der Zee, J., 2001. The importance of the social environment for physically active lifestyle-results from an international study. Soc. Sci. Med. 52 (1), 1–10. Subramanian, S.V., Kim, D.J., Kawachi, I., 2002. Social trust and self-rated health in US communities: a multilevel analysis. J. Urban Health 79 (4), S21–S34. Weitzman, E.R., Chen, Y.Y., 2005. Risk modifying effect of social capital on measures of heavy alcohol consumption, alcohol abuse, harms, and secondhand effects: national survey findings. J. Epidemiol. Community Health 59 (4), 303–309. Wilkinson, R., 1996. Unhealthy Societies: The Afflictions of Inequality. Routledge, London.