Aging in selected anthropometric dimensions in a rural Zapotec-speaking community in the Valley of Oaxaca, Mexico

So~, St i & M e d Vol 16. pp 217 to 222, 1982 Printed in Great Britain All righls reserved

0277-9536 82 020217-06503 00 t) Copyright rL~ 1982 Pergamon Pro,, Lid

A G I N G IN SELECTED A N T H R O P O M E T R I C D I M E N S I O N S IN A RURAL ZAPOTEC-SPEAKING C O M M U N I T Y IN THE VALLEY OF OAXACA, MEXICO ROBERT M. MALINA, PETER H. BUSCHANG, WENDY L. ARONSON and HENRY A. SELBY Department of Anthropology, University of Texas, Austin, U.S.A. Abstract--Stature, weight, arm circumference, triceps skinfold and grip strength were measured in a cross-sectional sample of 116 men and 113 women, 20-82 years of age, from a rural Zapotec-speaking community in the Valley of Oaxaca in southern Mexico. Mortality statistics, growth, and maturity status of children in the village are indicative of chronic mild-to-moderate under-nutrition. Adult Zapotecs are smaller, lighter and leaner than reference data for better-off populations. Sex differences are clearly evident for stature, fatness and grip strength. Body weight shows little sex difference after 40 years of age. Estimated mid-arm muscle circumference, however, is larger in males at all ages except over 60 years. Weight, arm circumference, the triceps skinfold and estimated muscle circumference are generally lowest in women 20-39 years, most likely reflecting the depletion of energy stores due to successive pregnancies and lactation. When stature is adjusted for the estimated loss associated with aging, there is suggestion of a secu~,r increase in males but not in females. Sa]npling ~ariation, small numbers at the older ages, and perhaps selective out migration must be considered in evaluating possible secular effects. Although absolute grip strength of adult Zapotecs is less than that of better-off samples of adults, grip strength per unit body weight is similar.

INTRODUCTION Physical+ physiological and psychological alterations with aging are reasonably well documented in populations from developed countries [e.g. 1-7], The time course of changes after full growth is attained is most often observed through cross-sectional data, although the need for longitudinal observations is increasingly evident [e.g. 3, 8+ 9]. Data for aging in developing or less developed areas of the world are not so extensive [e+g. 10-13] as to allow one to inquire on the extent of changes with age in various bodily functions and dimensions. To this end, selected anthropometric dimensions were examined in a cross-sectional sample of adults from a rural Zapotec-speaking community in the Valley of Oaxaca in southern Mexico. More specifically, this paper considers age and sex differences in the selected dimensions during adulthood+ and the effects of age and secular factors on the adult stature of Zapotecs in the Valley of Oaxaca. METHODS As a part of our continuing study in the Valley of Oaxaca, we did an anthropometric survey of 229 adults from a rural Zapotec-speaking community in the Fall of 1978. The community is located in the Etla wing of the Valley of Oaxaca, northwest of the city of Oaxaca de Juarez [14, 15]. It is a subsistence agricultural communit,~ of about 1700 inhabitants in 1978. Life style in the village is typical of traditional Middle-American communities: socially, they are based on kinship and are largely endogamous (96°o of first marriages are between people living in the community/, and economically, they are characterized by' small-scale farmers working tiny' plots of individuallyowned land. There is no doctor in the village. although a public health nurse now visits the community once a week and a mid-wife with some public 217

health experience lives in the village. The nearest medical clinic is about 5 km away, while the major medical facilities are in the city of Oaxaca. The public health nurse works mostly with children and young mothers. As is typical of Meso-American communities, there are traditional healers in this community but their activities are limited largely to psychosomatic illnesses (e.g. susto). Nutritional status of the community is at best marginal. Estimated caloric and protein intakes [163 are considerably lower than recommendations for Mexico [17]. These observations are based upon 24-hour recall, generally from the wife of the head of the household. The dietary intake of 31 families was obtained for a single day, while the intake of 7 families was followed over 30 consecutive days. Of the latter, a random sample of 5 days was selected for evaluation. The reported foodstuffs were analyzed by the use of published tables of food composition for Mexico and then estimated intakes were compared to the dietary intake recommendations provided by the Instituto Nacional de Nutricion [173. which are designed for individuals consuming a Mexican diet. Estimated intakes for adults in the community approximate about 60-65°,; and 65-75'!o of the values recommended for calories and protein respectively. and intakes are generally better for males than females. The marginal nutritional status of the community is also reflected in the heights and weights of schoolchildren, which are small felative to reference data for Mexico [143. and delayed maturation [1819]. This pattern is apparently representative of the relatively poor nutritional status that characterizes the population in the rural south of Mexico. which includes the state of Oaxaca [_.20, 21]. The rural arcas of Oaxaca are also characterized by high infant and preschool mortality rates [22-24] Our mortalit 5 data for the community under study are not extensixe, but

ROBERT M. MALINA et al.

218

Table 1. Sample size per age group, and means and standard deviations for age of Zapotec adults Males

Females

Age group

N

M

SD

N

M

SD

20-29 30-39 40--49 50--59 60+ Total

59 17 21 10 9 116

24.0 33.5 44.2 54.9 68.1 35.2

2.7 3.2 3.1 3.2 3.9 14.3

70 12 11 12 8 113

23.0 34.7 43.4 51.4 69.3 32.5

2.5 3.4. 2.5 1.8 7.3 14.6

the estimated crude death rate for the 1960's was about 24/1000 population. This value is similar to that for another Zapotec community in the Valley of Oaxaca, for which we have more extensive mortality data (26/1000 population). Infant and preschool mortality are high, accounting for about 50~o of the reported deaths. Stature, weight, arm circumference, the triceps skinfold and grip strength were measured on 229 adults. There were 116 males, 20-75 years, and 113 females, 20-82 years, of age (Table 1). About 56~o of the younger women (20-39 years) were lactating and several were in the early stages of pregnancy. This should not be a significant factor in looking at age differences in body weight or fatness. The usual pattern of weight gain or fat accumulation during pregnancy is one of minimal change during the first trimester. Data for rural women from East Java, living under similar conditions to those in the present study, show no significant difference in mean weight and arm circumference among non-pregnant/non-lactating, non-pregnant/lactating, and pregnant/first trimester women 1-25]. Since weight increases linearly after the first trimester, several women in the middle and later stages of pregnancy were deleted from the analysis. Mean body weight of pregnant Mexican women from a semi-rural area in Tlaxcala (N = 57) is about 53.0 kg at 24 weeks of gestation 1-26]. This figure is 3.2 kg greater than the body weight of women 20-29 years of age in the present study (49.8 kg). Our sample comprises about 68 and 62~o of the total number of males and females respectively in the census count of the 20-29 year age group. The older age groups are less representative of the census distribution, ranging from 18 to 30~o of the age groups for males above 30 years of age, and 17 to 25~o of those for females, Measurements were taken at the household during a demographic survey of the community. Stature was measured to the nearest millimeter with an anthropometer. Weight was measured to the nearest one-half pound and converted to kilograms. The adults wore ordinary costumes, with personal ornaments, accessories and shoes (if they wore any) removed. In the majority of cases, the clothing was generally light weight, suitable for the moderate temperature that characterizes the region from June to October (mean monthly temperatures range from 21.3 to 19.7°C) [27]. N o correction for this clothing was made, although samples varied between 0.5 and 1.0 kg. However, for a small number of older women (45 + years, about 10), who wore the traditional Zapotec apparel

of a full skirt, huipil and soyate, a woven wicker belt 1-28] an appropriate correction factor (2 kg) was used. The correction was based on the weight of the skirt. huipil and woven wicker belt compared to that of the light Western dresses worn by most women. We chose to report body weight including ordinary clothing since comparative data for adults are often reported in this manner and in earlier surveys of Oaxaca no correction for clothing was made. Left arm circumference was measured with a flexible steel tape to the nearest millimeter at the level midway between the acromial and olecranon processes, with the arm hanging freely relaxed. The triceps skinfold was measured to the nearest 0.5 mm with a Lange skinfold caliper and at the same level as arm circumference. Grip strength was recorded for . the right and left hands using an adjustable Smedley dynamometer. The better of two trials for each hand was used. Arm circumference was corrected for the thickness of the triceps skinfold to provide an estimate of mid-arm muscle circumference 1,29]. All measurements were made by a single observer (PHB). Intra-and inter-examiner technical errors of measurement for stature, weight, arm circumference and the triceps skinfold were small, and lower than those for the U.S. Health Examination Survey [30, 31]. Age differences were evaluated with analysis of variance procedures, and then with a multiple range test if the F-value was statistically significant. A 0.01 level of significance was accepted.

RESULTS Age changes and sex differences in the selected anthropometric dimensions are shown in Figs 1-4. Stature is, on the average, greatest in the young adults (20-29 years), and gradually decreases with age in both sexes. Weight, arm circumference, and estimated mid-arm muscle circumference show slight change with age from 20-59 years in males, and then decrease considerably in the oldest age. group. A m o n g females, on the other hand, the younger women (20-39 years) are lighter and leaner than the older women t40-59 years). Mean values for weight, arm circumference and the triceps skinfold do not change in the 20-29 and the 30-39 year age groups, and then increase in the 40-49 year age group. The three measurements then generally decline with age, the decrease being least for estimated mid-arm muscle circumference. The older group of women (60 + years) are similar in weight and fatness to the younger women (20-39 years), but larger in arm and estimated mid-arm muscle circumferences. Absolute strength of grip and strength per unit body weight are greatest in the younger men and women, and then decrease with age. Differences between the right and left hands are generally small. Sex differences are most apparent for stature, fatness, strength, and estimated mid-arm muscle circumference (except for the 60 + age group in arm musculature). Males are, on the average, taller, leaner and stronger in grip strength, while females are fatter. Weight and arm circumference show a different ageassociated pattern of sex differences. Prior to 40 years

Aging in a Zapotec-speaking Community STATURE

cm 160

cm 29

219

ARM CIRC.

27

,e.. l! I

155

26

150

24

145

e.

140

t

20~29

O F

. . . . . .

i

I

I

30-39

40-49

50-59

/

21

.o..

•

eF eM

,,i

•

60 +

Age, years k~ 60

I

/

22 •

~,~

/

20-29

30-39

40-49 50-59 Age, years

60 +

Fig 3 Arm circumference and estimated mid-arm muscle circumference in adults from a Zapotcc-speaking com-

WEIGHT

munity in Oaxaca. Mexico 0

45

I

20-29

I

30-39

I

I

4 0 - 4 9 50-59 Age, years

60+

Fig. 1. Stature and weight in adults from a Zapotec-speaking community in Oaxaca, Mexico. of age. males are heavier and have larger arm circumferences: but after 40 years of age, males are only slightly heavier while females have. on the average, larger arm circumferences. ARM CIRC.

cm

28 2? 26

O

•

/

~e--

25

•

,/

/

24 23

o ~ . 0

F

--__.~/

I 20-29

I 30-39

i 40-49

50-59

The statistical significance of age differences in the selected anthropometric dimensions are summarized in Table 2. Only statute and grip strength show significant differences among the age groups of males, while arm circumference, the triceps skinfoid, estimated mid-arm muscle circumference, and grip strength show significant differences among the age groups of females. Tests of the independence among mean stature and grip strength for specific age groups of males generally show that the differences between the youngest and oldest age groups are statistically significant (P < 0.01), while the remaining age groups (30-39, 40--49, 50-59) do not differ significantly from each other. Among females, tests of independence among means for specific age groups are not as consistent. For example, mean arm circumference of the 40-49 year age group is significantly larger (P < 0.01) than the 20-29 and 30-39 year age groups, but not significantly different from the 50-59 and 60 + age groups; however, the 20-29, 30-39, 50-59 and 60 + age groups do not differ statistically from each other in arm circumference. For the triceps skinfold, only the 40-49 and 60 + age groups differ significantly (P < 0.01); for estimated mid-arm muscle circumference, only the 40-49 and 20-29 year age groups differ significantly ( P < 0.01); and in grip

60+ kg

mm 17

TRICEPS SKINFOLD

15

/ z |

MALES

/" x

//

13

GRIP STRENGTH

40 I ' | .

/

% "-x

•

%

II

~o F

9

5

20- 29

30°39

I

I

J

40-49

50-59

60+

Age, years

Fig. 2. Arm circumference and the triceps skinfold in adults from a Zapotec-speaking community in Oaxaca, Mexico.

20-ZS 30-39 4o-4s 5o-s9

so+

Age, yea~

Fig. 4. Right and left grip strength in adults from a Zapotee-speaking community in Oaxaca, Mexico.

220

ROBERT M. MALINA et

Table 2. Summar', of analyses of ',ariance of age differences in anthropometric dimensions of Zapotec adults

Dimension

Males [dr= 4, 111)

Females (df= 4, 108)

F

P

F

P

NS <0.01 NS NS

2.00 2.22 5.34 3.73

NS NS <0.0l <0.01

NS <0.01 <0.01

5.61 l 1.82 8.42

<0.01 <0.01 <0.01

Weight 2.05 Stature 3.53 Arm circumference 2.15 Triceps Skinfold 0.72 E~timated muscle circumference 1,62 Right grip 20,78 Left grip 20.06

strength, only the youngest and oldest groups differ significantly (P < 0.01). The effect of age and secular factors on stature were evaluated by the linear regression of stature and stature adjusted for estimated effects of aging after 30 years of age [32] with year of birth (Table 3). The regression coefficient (b) gives the average change in stature per year due to secular and age factors com: bined and secular factors alone. The combined secular and age change in stature is approximately 0.14cm and 0.09cm per year in males and females respect. ively, or 1.4 cm and 0.9 cm per decade. The change is significant (P < 0.01) in both sexes. However, adjusting for estimated change in stature due to aging reduces the amount of stature increase attributable to secular factors. 0.09 cm per year in males and 0.05 cm per year in females. The change is significant in males (P = 0.01), but not in females. If it may be assumed that Zapotec adults lose stature with age at the same rate as adults in developed countries, then the estimated secular change of 0.9 cm per decade in males is similar to the l cm per decade reported by Tanner [33] and greater than the 0.6 cm per decade reported by Meredith [32]. On the other hand. the estimated secular change of 0.5 cm per decade in females is less than that suggested by Tanner [33], but similar to that suggested by Meredith [34]. DISCUSSION The pattern of change in stature and grip strength with aging in adults from a rural community in the Valley of Oaxaca is generally similar to that reported for cross-sectional studies of adults in developed countries [1, 3, 7, 8]. Adult Zapotecs, however, are smaller, lighter and leaner, and weaker in absolute grip strength than these better-off samples of adults. Adult Zapotecs are also among the shortest Indian

aL

groups in Mexico. There is a gradient in the distribution of adult stature in Mexico. On the average. statures are greatest in the north and decrease southward, with the Oaxaca region characterized as a center of low stature [35]. The age-associated differences in stature in crosssectional studies, however, are greater than those reported in longitudinal studies [8. 9, 36]. Changes in cross-sectional surveys reflect both aging and secular factors. Correcting for estimated stature loss with age after 30 years in our sample of adult Zapotecs reduced the apparent secular effect. However, the estimated secular effect in our sample of males (0.9 cm per decade) is greater than that reported by Himes and Malina [32] (0.3 cm per decade) for a sample of Zapotec males from two communities in the Valley of Oaxaca surveyed in 1971 and 1972. Sampling variation, measurement variability, and perhaps smaller numbers at the older ages in the latter study may underlie the differences in estimated secular effects. The role of selective migration is an additional factor that requires consideration. Out-migration from rural communities in Mexico has accelerated in the past decade. Although some evidence from Europe indicates that migrants are generally taller than sedents [37], Lasker [38, 39] reported little difference in the anthropometric characteristics of Mexican males who never migrated compared to those who migrated after 27 years of age. The evidence thus suggests little effect of physical selection of migrants. We do not have migration data on adults in our survey. However, in our 1978 survey we attempted to follow-up a cohort of school children measured in 1968, at which time they were 6-14 years of age. We were able to locate about two-thirds of the initial cohort in 1978, at which time they ranged from 16-24 years of age. With the exception of several deaths and the inability to locate a few individuals, the remaining one-third of the initial 1968 cohort were reported to be working in Mexico City. Comparison of the 1968 growth status of those who remained in the community and those who are currently in Mexico City showed no differences. In contrast to stature and strength, weight, arm circumference, estimated mid-arm muscle circumference and the triceps skinfold show a different pattern of change with aging in Zapotec adults compared to populations in developed countries. The pattern of aging in the latter is one of increasing weight and fatness with age until about 60 years in women and to about 40-45 years in men. followed by a decrease [40-44]. Among Zapotec males, weight, arm circumference, mid-arm muscle circumference and the triceps skinfold change little between the 20-29 and the

Table 3. Regression of stature (S) and adjusted stature (ASt with year of Birth for adults from a Zapotec community in the Valley of Oaxaca. Mexico Regression coefficient Sex (Nt Males (116) Females 11131

r S AS S AS

0.35 0.23 0.27 0.14

(b) _+ SEb 0. t40 0.091 0,093 0.046

___0.036 (cm/yr) + 0.036 (cm/yr) +_ 0.031 tcm/yr) + 0.031 [cm yr)

t

P

3.93 2.55 2.95 1.45

<0.01 <0.05 = 0.01 <0.01 NS

Aging in a Zapotec-speaking Community 50-59 year age groups, and then decrease after 60 years of age. Among Zapotec women, the four measurements are generally low in the younger women (20-39 years), increase into the 40-49 age group, and then decrease. This pattern probably reflects the depletion of energy stores in younger women due to successive pregnancies and lactation. Among healthy pregnant women, the triceps skinfold ordinarily shows little change during pregnancy, decreasing in fact during the last 8-10 weeks of gestation. In contrast, skinfolds on the trunk and thigh, the more centrally located fatfolds generally increase during pregnancy [45]. However, undernourished women do not necessarily follow the pattern of fat accumulation during pregnancy observed in healthy women [26, 46]. Many lose fat centrally and peripherally. Estimates of calorie and protein intakes of lactating women in the Zapotec community approximate only 45~o of adequate levels [16]. Such intakes would suggest a continuous drainage of maternal stores and thus influence weight, circumference and skinfold measurements. However, in the 4 0 ~ 9 year age group, when many women are no longer lactating and nearing the end of their reproductive years, weight, arm circumference, mid-arm muscle circumference and the triceps skinfold increase considerably compared to the younger ages. Since strength is related to body size [47], the absolutely lower values of grip strength in adult Zapotecs compared to better nourished Western samples [1, 7] perhaps reflect this size difference. This is in fact the case when grip strength is expressed per unit body weight. In the 20-29 year age group of Zapotec males, for example, mean strength of the stronger hand per unit body weight is 0.70 kg/kg, and in the 30-39 year age group it is 0.62 kg/kg. Corresponding values for well nourished males in the same age range, estimated from means for grip strength and weight are 0.71 kg/ kg [48] and 0.62 kg/kg [49]. In Zapotec women 20-29 years of age. mean strength of the stronger hand per unit weight is 0.52 kg/kg. An estimated value for college age women, using a different dynamometer, is 0.60 kg/kg [50]. These observations on adults are also evident in the grip strength and motor performance of school children in the community. The children are smaller than reference data and perform below levels attained by better nourished children. However. when height and weight differences are controlled, the rural Zapotec children show greater grip strength and throwing distance per unit height and weight, and perform commensurately with their smaller body size in the 35-yard dash and standing long jump [51]. Similar observations have been reported for physical working capacity in Bantu [52], East African [53] and Ethiopian E54] children and youth, and in Guatemalan adults [55]. However. in severely undernourished adults, there is a significant reduction in maximal working capacity [56]. These results suggest a complex relationship between nutritional state, and performance capacity. Grip strength of the right and left hands are highly related Ir = 0.87 in males and 0.85 in females). It is perhaps of interest to note that the differences between mean strength of the right and left grip of Zapotec men and women are smaller than noted in

221

U.S. adults [1, 57]. The grip strength data of Gomez Robleda et al. 1-58] for Oaxaca Zapotecs and that reported by Comas [59] for other Indian groups in Mexico show a pattern of right-left differences similar to that noted in our sample. It is also of interest that mean strength of the left grip is consistently greater than the right grip in Zapotec males, while the opposite and generally observed pattern of right grip greater than the left is apparent in females. This trend may be related to occupational activities. Acknowledgement--This research was supported in part by NSF Grant Number BNS 78-10642. REFERENCES

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