Determinants of Breast-Feeding and Weaning in Alberta, Canada

DETERMINANTS OF BREAST-FEEDING AND WEANING IN ALBERTA, CANADA QiuyingYang, MD, PhD,I,2 Shi Wu Wen, MB, PhD,2 Lise Dubois, PhD,IYue Chen, MD, PhD,3 Mark C.Walker, MD, MSc, FRCSC,2 Daniel Krewski, PhD 1,3 I Mclaughlin Centre for Population Health Risk Assessment, Institute of Population Health, University of Ottawa, Ottawa ON 20MNI Research Group, Department of Obstetrics and Gynecology, University of Ottawa, Ottawa ON 3Department of Epidemiology and Community Medicine, University of Ottawa, Ottawa ON

Abstract Objective: To assess the determinants of breast-feeding initiation and duration at the population level in Alberta, Canada. Methods: Determinants of breast-feeding were assessed based on data from a sample of I I I 3 women, who represented 150 898 fertile women in Alberta, in the second cycle of the National Population Health Survey conducted 1996-97. Logistic regression analysis was used to estimate the independent effects of various determinants of breast-feeding initiation and duration dichotomized at 4 weeks, 8 weeks, 12 weeks, and 6 months postpartum. All analyses used analytic weights to take both the average design effect and population weights for the complex survey design into account. Results: The proportion of breast-feeding initiation was 85.6%. It was observed that 71.3% of mothers continued breast-feeding for at least 3 months, and 37.2% of mothers breast-fed their infants for more than 6 months. Determinants of breast-feeding initiation were marital status, education, maternal smoking behaviour, and annual family income. White women and women who were older than 35 years of age were more likely to continue breast-feeding for longer periods, whereas those who smoked during pregnancy were less likely to breast-feed their infants for extended periods. The primary reasons for weaning were breast problems at less than I week, insufficient milk production during weeks I to 12, and infants who weaned themselves after 3 months. Conclusions: Smoking cessation during pregnancy, adequate treatment of early breast problems, and breast-feeding promotion campaigns targeting socioeconomically disadvantaged populations could serve to increase breast-feeding in Canada. Resume Objectif : Evaluer les determinants de I'amorce et de la duree de

KeyWords Breast feeding, statistics & numerical data; prenatal care, socioeconomic factors; health knowledge, attitudes, practice; weaning

I'allaitement maternel au niveau de la population en Alberta, au Canada. Methodes: Les determinants de I'allaitement maternel ont ete evalues en fonction des donnees tirees d'un echantillon de I I 13 femmes, lequel representait 150 898 femmes fertiles en Alberta, du second cycle de I'Enquete nationale sur la sante de la population menee en 1996-97. Une analyse de regression logistique a ete utilisee pour estimer les effets independants de divers determinants de I'amorce et de la duree de I'allaitement maternel dichotomises it 4 semaines, it 8 semaines, it 12 semaines et it 6 mois post-partum. Toutes les analyses ont fait appel it des coefficients de ponderation anaIytiques en vue de tenir compte des ponderations moyennes (tant de la population que de I'effet de la conception) propres it la complexe conception de I'enquete en question. Resultats : La proportion de I'amorce de I'allaitement maternel etait de 85,6 %. On a constate que 71,3 % des meres ont poursuivi I'allaitement pendant au moins trois mois et que 37,2 % des meres allaitaient leur enfant pendant plus de six mois. Les determinants de I'amorce de I'allaitement maternel etaient I'etat matrimonial, I'education, les habitudes maternelles quant au tabagisme et Ie revenu familial annuel. Les femmes blanches et les femmes de plus de 35 ans presentaient une tendance accrue it poursuivre I'allaitement pendant des periodes prolongees, alors que les femmes qui avaient fume au cours de leur grossesse presentaient plutot une tendance moindre it en faire autant. Les principales raisons motivant Ie sevrage etaient les problemes mammaires (it moins d'une semaine), la production de lait insuffisante (entre la Ire et la 12e semaine) et les enfants qui se sevraient eux-memes (apres 3 mois). Conclusions : L'abandon du tabac au cours de la grossesse, Ie traitement adequat des problemes mammaires precoces et la mise en ceuvre de campagnes de promotion de I'allaitement maternel visant les populations defavorisees sur Ie plan socioeconomique pourraient entrainer une hausse de I'allaitement maternel au Canada.

J Obstet

Gynaecol Can 2004;26( I 1):975-81.

INTRODUCTION

Competing interests: None declared.

Human breast milk has many beneficial health effects. Several studies have identified breast-feeding as a key factor in the

Received on March 12. 2004 Revised and accepted on May 6. 2004 JOGe

NOVEMBER 2004

prevention of sudden infant death syndrome 1 and increased cognitive function. 2,3 A study in Norway suggested that longterm breast-feeding might reduce the risk of lower respiratory tract infection. 4 Breast-feeding appeared to be protective against the development of asthma5 and decreased severity of bronchial asthma. 6 In a study conducted in Ontario, Canada, Moxley et at. determined that exclusive breast-feeding of infants for 4 months could save at least $862 000 per year through reduced need for treatment of otitis media, and $450 000 for the treatment of 150 bottle-fed babies hospitalized annually for gastroenteritis. 2 The US Department of Health and Human Services has set a goal of 50% for the breast-feeding continuation rate at 5 to 6 months in its Healthy People 2010 recommedations? Many factors have been identified as possibly influencing the initiation and duration of breast-feeding. Amir and Nonath conducted a systematic review of the literature and concluded that the association between maternal smoking and lack of breastfeeding was consistent across different study designs in several countries. 8 Smoking has been demonstrated to exert a strong dose-dependent negative influence on breast-feeding duration. 9-12 Older married women more frequently reported breast-feeding than younger non-married women. 11,13 Education and socioeconomic status were positively related to continued breast-feeding. 14,15 Although a number of studies have examined the determinants of breast-feeding in Canada,16-19 these studies were subject to limitations. Few have examined the association between smoking and breast-feeding,17 and few have involved data at the population leveI.2° The objective of the present study was to identifY the factors influencing the initiation and duration of breast-feeding at the population level. METHODS

This study was based on data collected from the second cycle of the National Population Health Survey (NPHS), a representative sample of the Canadian population conducted by Statistics Canada, 1996-97. When the province of Alberta commissioned Statistics Canada to conduct the 1996-97 Health Promotion Survey (HPS), in order to reduce data collection costs, the HPS questions were integrated into the NPHS. The HPS included detailed questions on breast-feeding, and smoking and drinking during pregnancy. Questions regarding general health (Part 2 of the NPHS) were posed only to non-proxy women (those women who answered the questions themselves) between 15 and 49 years of age. Respondents who answered the following question affirmatively were considered as study subjects: "Have you given birth in the past 5 years?" Those who responded "yes" were further asked to respond to the question: "[For your last baby], did you breast-feed or try to breast-feed your child, even if only for a short time?" Those who answered "yes" were further asked to IOGC

respond to the question: '~e you still breast-feeding [your last child]?" Those who answered "no" were asked the additional questions: "How long did you breast-feed [your last child]?" and "What is the main reason that you stopped?" Questions regarding smoking and drinking during pregnancy were: "Did you smoke during your last pregnancy?" and "Did you drink any alcohol during your last pregnancy?" Our selection of potentially important determinants of breast-feeding behaviour was based on a review of the literature. We searched the literature at PubMed using keywords of "breast-feeding," "determinants," "risk factors," "smoking," "Canadian," and "weaning reasons." Maternal age, race, marital status, education, total household income, self-perceived well-being, exercise, and smoking and drinking during pregnancy were included in the final list of important determinants for analysis. Following Statistics Canadas data publication guides,21 data were weighted up to the population level in all analyses. The NPHS 1996-97 data were based on a complex survey design incorporating stratification, multiple stages of selection, and unequal probabilities of respondent selection. As a consequence, standard statistical methods may not be appropriate for the analysis of these data. The NPHS 1996-97 public release data file provides population weights that represent the effect of the complex survey design on variance estimates through the design effect. The design effect is the ratio of the variance based on the complex survey design to that based on a simple random sample of the population. 22 We used an approximate method for incorporating the design effect into the analysis,23 since exact methods24 require detailed information on the survey design, which were not available in the public use data files for the NPHS 1996-97. Since this analytic weight incorporates the population weight from the survey, missing responses and population stratification were also taken into account. 22 Multivariate-weighted logistic regression was used to model the independent factors associated with breast-feeding initiation among mothers who had given birth in the past 5 years. Breast-feeding duration was dichotomized at 4 weeks, 8 weeks, 12 weeks, and 6 months among the mothers who had initiated breast-feeding after giving birth, and who had stopped breastfeeding at the time of the interview. In the calculation of initiation proportion of breast-feeding, the adjusted variances were used to calculate 95% confidence intervals for initiation proportion ofbreast-feeding. 23 The analysis was conducted using SAS software (version 8.2). RESULTS The 1113 women included in this study, who had reported having given birth in the past 5 years in Alberta in the NPHS 1996-97, represented an effective population of 150 898 women when weighted up to the population level. Of these NOVEMBER 2004

1113 women, only 1 woman (representing a population of 197 women after weighting) did not answer the breast-feeding question. The overall proportion of initiation of breast-feeding was 85.6%. Table 1 presents data on the number of women who initiated breast-feeding among different subgroups. The breast-feeding initiation proportion was low among those mothers who were single, young (especially teenagers, data not shown), not white, and inactive, as well as among mothers with low education, low f.unily income, or poor health. Maternal smoking and not drinking during pregnancy were also associated with lower proportion of breast-feeding initiation. Duration of breast-feeding is illustrated in the Figure. There were an estimated 20 089 women (based on an unweighted sample of n = 145 women) who still breast-fed their last child at the time of the interview, among a total of 128 945 (n = 949) women who nursed their babies after they gave birth. Among 108856 (n = 804) women who initiated breast-feeding after giving birth and who had stopped breast-feeding at the time of the interview, the proportion of breast-feeding was stable between initiation (85.6%) and 4 weeks (84.0%), decreased to 71.3% at 12 weeks, and dropped sharply to 37.2% at 6 months. The adjusted odds ratios for breast-feeding initiation and breast-feeding duration at 4 weeks, 8 weeks, 12 weeks, and 6 months of breast-feeding are presented in Table 2. The proportion of breast-feeding initiation was lower in mothers who were single, with lower education, and who smoked during pregnancy, whereas the proportion was higher in mothers who drank during pregnancy. Annual family income demonstrated a positive association with breast-feeding initiation among women in families with an annual income of $30 000 to $49999, as compared with those in families earning more than $50 000. White women and women who were older than 35 years of age were more likely to breast-feed their infants for more than 6 months after giving birth, whereas women who smoked during pregnancy were less likely to breast-feed their infants for an extended period. The reasons for weaning at different durations of breastfeeding are summarized in Table 3. The principal reasons for weaning was "other" at less than 1 week of breast-feeding, "insufficient milk production" from 1 to 12 weeks, "child weaned him/herself" or that the mother "returned to work/school" from 3 to 6 months, and "child weaned him/herself" after 6 months.

child development in Quebec, 1998-2002 (72%).20 This estimat; was similar to that in an earlier survey in Red Deer, Alberta in 1995 (85%),25 but much higher than the previous studies il Edmonton, Alberta, in 1984 (76.5%),26 and in Calgary, Alber ta, in 1982 (63%).27 These differences could be due to tim Table 1. Estimated Number of Women Who Breast-Fed or Tried to Breast-Feed, Among Subgroups of Alberta Women (National Population Health Survey, 1996-1997) Characteristic

Number of Women

%

95% CI*

143 284 307 215

80.04 84.23 87.24 87.99

78.90-81.18 83.84-84.62 86.93-87.55 87.66-88.32

859 85

85.86 83.60

85.66-86.06 82.99-84.21

790 79 79

87.48 67.96 81.67

87.28-87.68 66.94-68.98 80.81-82.53

328 464 155

80.97 86.29 93.38

80.60-81.34 86.02-86.56 93.07-93.69

77 148 265 303 156

80.51 83.43 91.16 86.51 79.47

79.67-81.35 83.70-84.96 90.87-91.45 86.20-86.82 78.92-80.02

312 365 221 51

87.08 88.05 82.02 75.67

86.77-87.39 87.78-88.32 81.59-82.45 74.61-76.73

192 236 519

88.93 87.11 83.63

88.56-89.30 86.74-87.48 83.36-83.90

206 314 429

76.11 88.58 88.08

75.58-76.64 88.29-88.89 87.83-88.33

116 756 77

91.41 84.10 90.38

90.98-91.84 83.86-84.34 89.87-90.89

Age 15-24 years 25-29 years 30-34 years ~35 years

Race White Other Marital Status Married!common-Iaw partner Single Widowed/separated/divorced Education Levelt Low Middle High Income <$15000 $15000-$29999 $30 000-$49 999 ~$50 000 Not stated

Sense Of Well-Being Excellent Very good Good Fair or poor Exercise Active Moderate Inactive Smoking During Pregnancy Yes No Missing Alcohol Drinking During Pregnancy

DISCUSSION

The proportion of women who initiated breast-feeding in Alberta (85.6%) was slightly higher than the proportion of women in Ontario (82.8%, data available upon request) in the National Population Health Survey 1996--97, and higher than the Quebec provincial proportion in the longitudinal study of lOGC

Yes No Missing

*CJ: confidence interval. tEducation level: Low; no schooling, elementary school, some secondary school, or secondary school graduation; Middle: some trade or college education; diploma or certification from a college, trade school, or CEGEPi or some university education; High:

bachelor's degree, master's degree, PhD, or degree in medicine.

NOVEMBER 2004

effect and/or regional differences and/or differences in sampling procedures or research design. Previous studies have found that early cessation of breastfeeding was common in Canada. In the 1970s, Canadian women usually ended breast-feeding within 3 months of childbirth,28 and fewer than half of all Canadian women who initiated breast-feeding continued to 4 months postpartum in the early 1990s.1 8,29,30 However, 63% of mothers continued for at least 3 months in a recent study in Ontario,17 slightly lower than the figure of71.3% in our study. These data demonstrate that the proportion of breast-feeding initiation and breast-feeding duration in Alberta have improved substantially over the past decade. We speculate that this increase is most likely due to extensive breast-feeding promotion campaigns. Our results are encouraging, as breast-feeding in the first 3 to 4 months oflife, a period when gastrointestinal development is at a critical stage, is important. 31 However, these findings still fall short of the Canadian Paediatric Society recommendation that infants should be breast-fed for the first 9 to 12 months oflife,32 and the recent World Health Organization (WHO) recommendation that on a population basis, exclusive breast-feeding for 6 months is the optimal way of feeding infants. 33 Our findings indicate that single, smoking, and low-education mothers had a reduced breast-feeding initiation rate. Annual family income had positive association with breast-feeding initiation for women in families earning between $30 000 and $49 999 annually, as compared with those in families earning more than $50 000. The results of this study are not entire-

ly in accordance with those of other studies, which have indicated a strong positive influence of income on breast-feeding. 16,19,26 However, the results are consistent with findings from a recent Quebec study that indicated when maternal age and education level are equal, the probability of being breast-fed decreased with a family income of $40 000 or more as compared to a family income ofless than $20 000. 20 Our observation that maternal drinking during pregnancy was positively associated with the initiation of breast-feeding, a finding not reported in other studies, warrants further investigation. Maternal age was not associated with the initiation rate of breast-feeding in our study; possibly the mothers' decision to try breast-feeding their babies was influenced by extensive breast-feeding promotion campaigns in Canada. Our study confirmed the positive association between maternal age, race, and the duration of breast-feeding. 18,20,34,35 Like other studies,8-12 we found that maternal smoking during pregnancy was an important determinant of breast-feeding initiation and breast-feeding duration. Maternal smoking undermines breast-feeding through increased risk of early weaning, reduced milk supply, reduced prolactin concentration, and low fat concentrations in milk from smoking mothers. 10 Lack of support from clinician, family, and friends has been associated with breast-feeding discontinuation. 15,36,37 The WHO/UNICEp38 recommends the establishment of support groups, breast-feeding on demand, better information for women on the benefits and management of breast-feeding, and the establishment of breast-feeding policies, as effective meth-

120 ,----------------------------------------------------------------,

100

80 III

0()

.:3c:

III

u

60

~

0-

40

20

o <1 week 1-2 weeks 3-4 weeks 5-8 weeks

9-12 weeks

3-6 months

7-9

10-12

>12

months

months

months

Duration of breast-feeding among women in Alberta. National Population Health Survey. 1996-97. 21

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ods for promoting breast~feeding. Because the principal reasons for weaning were the occurrence of breast problems and insuf~ ficient milk production at early breast~feeding (Table 3), it is reasonable to assume that mothers who maintain adequate nutrition and are of healthy physical and mental status, with adequate support from their clinician and family, will produce

sufficient milk to maintain breast-feeding. There are some limitations in the data used in the present analysis. First, the survey retrospectively determined self~report­ ed breast-feeding and information on potentially important determinants, such as smoking, which is prone to a certain degree of recall bias. Second, the events of interest (breast~feed-

Table 2. Adjusted Odds Ratio and 95% Confidence Intervals for Breast-Feeding at Birth, and at 4, 8,12 Weeks, and 6 Months Postpartum, Among Alberta Women (National Population Health Survey, 1996-1997) OR (95% CI) Characteristic Age 15-24 years 25-29 years 30-34 years ~35 years

Initiation of Breast-Feeding

Breast-Feeding at 4 Weeks

Breast-Feeding at 8 Weeks

Breast-Feeding at 12 Weeks

Breast-Feeding at 6 Months

0.95 (0.50-1.85) 0.79 (0.46-1.37) 1.02 (0.59-1.74) 1.00

0.44 (O.21....(). 91) 0.72 (0.38-1.35) 1.07 (0.58-1.96) 1.00

0.30 (O.16....().57) 0.64 (0.37-1.08) 0.92 (0.55-1.53) 1.00

0.36 (O.19....().66) 0.56 (0.33-0.92) 0.82 (0.51-1.31) 1.00

0.28 (0.14-0.54) 0.42 (O.26....().66) 0.54 (O.36....().81) 1.00

0.86 (0.48-1.63) 1.00

0.68 (0.34-1.43) 1.00

0.75 (0.40-1.44) 1.00

0.76 (0.42-1.40) 1.00

0.48 (0.26-0.89) 1.00

0.33 (O.17....().63) 0.66 (0.32-1.46) 1.00

1.07 (0.47-2.61) 0.99 (0.43-2.52) 1.00

1.07 (0.51-2.35) 1.11 (0.52-2.52) 1.00

0.95 (1.46-2.00) 1.02 (0.50-2.1 7) 1.00

0.78 (0.34-1.70) 0.63 (0.29-1.29) 1.00

0.42 (0.20-0.81) 0.55 (0.27-1.04) 1.00

0.59 (0.24--1.34) 0.57 (0.25-1.20) 1.00

0.59 (0.29-1.15) 0.67 (0.35-1.23) 1.00

0.71 (0.38-1.30) 0.79 (0.44-1 .3 7) 1.00

0.66 (0.39-1.12) 0.79 (0.50-1.25) 1.00

1.75 1.46 2.39 1.00 0.94

(0.55-1.63)

0.77 (0.32-1. 92) 1 .07 (0.53-2.19) 1.09 (0.60--1.98) 1.00 1.91 (0.89--4.37)

0.97 1.26 1.01 1.00 1.41

(0.76-2.67)

1.04 (0.48-2.30) 1.19 (0.67-2.14) 0.95 (0.59-1.52) 1.00 1.63 (0.91-2.99)

1.80 0.99 0.95 1.00 0.87

0.56 (0.26-1.26) 0.94 (0.56-1.60) 1.17 (0.72-1.89) 1.00

0.78 (0.32-2.04) 0.82 (0.45-1 .48) 1.44 (0.82-2.52) 1.00

0.78 (0.35-1.80) 0.99 (0.59-1.67) 1.30 (0.82-2.07) 1.00

0.42 (O.19....().92) 0.83 (0.50-1.35) 1.29 (0.83-2.00) 1.00

0.57 (0.23-1.33) 0.76 (0.47-1.23) 0.94 (0.64-1.39) 1.00

1.08 (0.58-2.04) 1.00 0.71 (0.43-1.14)

0.79 (0.42-1.48) 1.00 1.01 (0.58-1.73)

0.59 (0.34-1 .02) 1.00 0.72 (0.44-1.14)

0.57 (O.34....().97) 1.00 0.77 (0.49-1.19)

1.42 (0.86-2.33) 1.00 1.51 (1.00-2.29)

0.42 (O.25....().69) 1.00 0.78 (0.47-1.28)

0.69 (0.39-1.23) 1.00 1.35 (0.79-2.32)

0.59 (O.36....().96) 1.00 1.28 (0.81-2.01)

0.61 (O.38....().98) 1.00 1.39 (0.91-2.13)

0.59 (0.35-0.97) 1.00 1.37 (0.93-2.01)

2.68 (1.36-5.85) 1.00 1.83 (0.85--4.40)

0.96 (0.51-1.89) 1.00 0.93 (0.40-2.40)

0.69 (0.41-1.20) 1.00 1.08 (0.52-2.43)

0.83 (0.49-1.42) 1.00 0.89 (0.45-1.82)

1.05 (0.63-1.74) 1.00 0.85 (0.45-1.57)

Race Other White Marital Status Single Widowed/separated/divorced Married/common-law partner Education Level* Low Middle High Income <$15000 $15000-$29999 $30 000--$49 999 ~$50 000 Not stated

(0.78--4.01) (0.79-2.76) (1.35--4.32)

(0.43-2.21) (0.69-2.37) (0.61-1.66)

(0.81--4.00) (0.57-1.72) (0.61-1.47) (0.52-1.47)

Sense of Well-Being Fair or poor Good Very good Excellent Exercise Active Moderate Inactive Smoking During Pregnancy Yes No Missing Alcohol Drinking During Pregnancy Yes No Missing

'Education level: Low: no schooling, elementary school, some secondary school, or secondary school graduation; Middle: some trade or college education; diploma or certification from a college, trade, CEGEP; or some university education; High: bachelor's degree, master's degrees, PhD, or degree in medicine.

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ing status) could have occurred as long ago as 5 years prior to the survey, whereas the sociodemographic profiles were contemporaneous. These discrepancies in the time of outcomes measurement and determinants may introduce some degree of bias into the results. Third, some important determinants of breast-feeding such as parity, previous feeding, and support from health-care providers and family members 15 ,16,39-42 were not collected in the 1996-97 NPHS. Despite these limitations, the robustness of the associations observed in our study is evidenced by the ability to repeatedly produce similar results in different populations. Although our study was restricted to Alberta, it is reasonable to extrapolate the study findings to Canadian women from other provinces, as our findings are consistent with those relating to Ontario women in the same survey.

Our findings suggest that although rates of breast-feeding have been improved substantially, smoking cessation, adequate treatment of breast problems, specific attention to the issue of proper technique, and community support to maintain proper technique, especially in the first 3 months, and breast-feeding campaigns targeting the socioeconomically disadvantaged population, could further improve the rate of breast-feeding in Canada. Other measures, such as extending maternal leave and providing support for women who are breast-feeding in the workplace, may also be helpful. ACKNOWLEDGEMENTS

Shi Wu Wen and Yue Chen are recipients of Career InvestigaTable 3. Main Reasons for Stopping Breast-Feeding Among Alberta Women, by Duration of Breast-feeding (National Population Health Survey, 1996-97)

Insufficient milk production Inconvenienced/fatigue Difficulty with the techniques Sore nipples, mastitis, etc. Illness Planned to stop at this time Child weaned him/herself Advice of doctor Mother returned to work/school Other

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CONCLUSIONS

Main Reason for Stopping Breast-Feeding

tor awards from the Canadian Institutes of Health Research. Lise Dubois is a Canada Research Chair in Nutrition and Population Health. Mark Walker is a Career Scientist of the Ontario Ministry of Health and Long-Term Care. Daniel Krewski is the NSERC/SSHRC/McLaughlin Chair in Population Health Risk Assessment at the University of Ottawa.

Duration of Breast-Feeding* <1

1-12

3-6

~7

Week

Weeks

Months

Months

18.46

29.39

17.29

2.15

5.40 16.38

11.18 6.48

7.48 0.23

1.56 0.00

17.53

7.34

3.00

1.32

3.92 1.65

1.96 6.55

2.95 14.46

1.40 24.36

1.68 2.79 0.00

5.72 0.96 3.13

20.94 1.34 20.16

44.74 0.40 10.28

32.19

27.29

12.15

13.79

*Shown as % of women indicating that reason for termination of breast-feeding.

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4. Nafstad P, Jaakkola lJ. Hagen JA. Botten G. Kongerud J. Breastfeeding. maternal smoking and lower respiratory tract infections. Eur Respir J 1996;9:2624-9. 5. Dell S.ToT. Breastfeeding and asthma in young children: finding from a population-based study. Arch Pediatr Adolesc 200 1; 155: 1261-5. 6. Wafula EM. Limbe MS.Onyango FE. Nduati R. Effects of passive smoking and breastfeeding on childhood bronchial asthma. East Afr Med J 1999;76:606-9. 7. US Department of Health and Human Services. Developing objectives for healthy people 201 O.Washington (DC): US Department of Health and Human Services. Office of Disease Prevention and Health Promotion; 1997. 8. Amir LH. Nonath SM. Does maternal smoking have a negative physiological effect on breastfeeding! The epidemiological evidence. Birth 2002;29:112-23. 9. Knudsen A. Pedersen H. Klebe JG.lmpact of smoking on the duration of breastfeeding in mothers with insulin-dependent diabetes mellitus. Acta Paediatr 200 I;90:926-30. 10. Horta BL. Kramer MS. Platt RVY. Maternal smoking and the risk of early weaning: a meta-analysis. Am J Public Health 200 1;91 :304-7.

II. Haug K.lrgens LM. Baste V. MarkestadT. Skjaerven R. Schreuder P. Secular trends in breastfeeding and parental smoking. Acta Paediatr 1998;87:1023-7. 12. Letson Gw, Rosenberg KD. Wu L. Association between smoking during pregnancy and breastfeeding at about 2 weeks of age.J Hum Lact 2002; 18:368-72. 13. Hill PD. Aldag Jc. Smoking and breastfeeding status. Res Nurs Health 1996; 19: 125-32. 14. Najdawi F, Faouri M. Maternal smoking and breastfeeding. East Mediterr Health J 1999;5:450-6. 15. Taveras EM. Capra AM. Braveman PA.Jensvold NC. Escobar GJ. Lieu TA. Clinical support and psychosocial risk factors associated with breastfeeding discontinuation. Pediatrics 2003; I 12: I08-15. NOVEMBER 2004

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3 I. Lebenthal E, Lee PC, Heitlinger LA. Impact of development of the gastrointestinal tract on infant feeding.J Pediatr 1984; 102: 1-9.

18. Nolan L, Goel V. Sociodemographic factors related to breastfeeding in Ontario: results from the Ontario Health Survey. Can J Public Health 1995;86:309-12.

32. Canadian Paediatric Society, Nutrition Committee. Meeting the iron needs of infants and young children: an update. CMAJ 1991;144:1451-4.

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