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TABLE 5. Mean adult body mass indexes (BMI) by sex and by age, and prevalence of chronic energy deficiency (BMI) below 18.5)

a. Paired t tests.
b. McNemar test.

*p<.10 *p<.05. ***p< 01

The BMIs of both men and women declined significantly at harvest, more significantly in women (table 5). The decrease represented a mean loss of 1.4+3.1 kg of body weight. This is comparable to losses observed in women from Benin [6] and Zaire [27] but is much less pronounced than that observed in Sahelian women [27]. The seasonal decline in BMI was significant (p < .05) only for adults under 60 years of age. The rate of chronic energy deficiency (BMI < 18.5) tended to be higher in women than in men at both seasons, and to increase in both men and women at harvest.

We would have expected higher BMI values at harvest since energy intake tended to be higher. Several reasons may explain why this did not occur. We may have underestimated energy expenditure and therefore requirements at that time of year. Indeed, harvesting dune millet might demand more energy than harvesting wadi grains or produce, as dune fields are usually farther from the village and much larger than wadi plots. Furthermore, it is possible that the lower BMI observed at harvest is a carry-over effect from the lean season prior to harvest, although household food supply was not assessed at that time. The fact that the seasonal decline in BMI was significant only for adults below the age of 60 lends some support to the first hypothesis, as older people are less likely to be involved in heavy physical work.

TABLE 6. Pearson's correlation coefficients between the anthropometric status of preschool children and of adults from the same household

Correlations are between the HA and WH z scores of children and the BMls of adults in the same household at the same season, and between the changes in the children's scores and those in the adults' BMls.

*p < . 10. **p < .05.

Table 6 gives the correlation coefficients of the mean BMI of adults and the mean HA or WH of children from the same households at both seasons. With age as a control variable, child HA was not significantly correlated with adult BMI at either season. In contrast, a low but significant positive correlation was seen between child WH and adult BMI. Comparable ranges of correlation coefficients have been reported between parents' and school-age children's weights in 11 non-European samples [28]. The only relationship found in the changes in adult and child indices between the seasons was a tendency (p < .10) for changes in women's BMI to correlate with WH changes in the children. This suggests that season may influence women's and children's nutrition status in the same way.

The changing relationship between household dietary adequacy and Individual nutrition status

The correlations between household dietary adequacy and child or adult anthropometric status were low at both seasons (table 7). Child anthropometric indices were unrelated to household energy adequacy, except that HA Z scores tended to be negatively correlated with household energy adequacy at nonharvest. This suggests that energy adequacy would not help to screen households with malnourished children in the study community. The lack of relationship between the two values is in agreement with findings of other studies [1-3]. It may be that intrahousehold distribution of food is not commensurate with individuals' specific nutritional requirements. Furthermore, as shown elsewhere [29, 30], other child-specific factors such as morbidity may also be strong determinants of child nutrition status together with diet. Another reason might be that the household food consumption as measured over two days was not representative of usual food intake at the period of the survey, or else that the estimates of household energy requirements were inaccurate, as the energy expenditure of the adults was not measured directly.

TABLE 7. Correlation coefficients between the percentage adequacy of household intake of nutrients and the nutritional status of children and adults

Pearson's correlation coefficient was used for assessing the relationships of the adequacy of energy, protein, and iron intake; spearman s correlation coefficient was used for that of vitamin A.

*p<.10. **p<.05.

In contrast, a positive significant relationship was seen between adult BMI and household energy adequacy, although only at the non-harvest season. This suggests that adult BMI may be a somewhat better indicator of household energy balance than child anthropometric status, but, to assess the adequacy of household energy intake, seasonal patterns of physical activity must be determined carefully. Changes in adult body weight have been found to be consistent with variations of household energy intake in one report [4], but others have found no direct relationship [3].

Household protein adequacy appeared to be unrelated to individual anthropometric indices at either season. Iron adequacy was significantly correlated (p < .05) with adult BMI at non-harvest, which reflects the high and significant correlation of energy and iron adequacy (p < .001, r = .71).

At the harvest season a significant positive correlation (p < .05) was observed between household vitamin A adequacy and both child and adult anthropometric indices. As energy and vitamin A adequacy were significantly correlated (p < .001, r = .33 and .45 at non-harvest and harvest respectively), their relative contribution to the variance of child or adult anthropometric indices was assessed by multiple regression analyses (table 8). The age of the child and adult BMI were also included in the analysis as potential explanatory variables of child anthropo metric status. The WH and HA Z scores were introduced together with household dietary adequacy in the regression of adult BMI.

TABLE 8. Multiple linear regression coefficients of child and adult anthropometric status on individual and house hold variables

Child HA, child WH, and adult BMI arc dependent variables. Partial R² refers to the contribution of the significant variable.

*p<.10. **p < .05. ***p < .01. **** p < 0.001

At non-harvest, neither household energy nor vitamin A adequacy was a predictor of the child or adult anthropometric indices. Adult BMI and child WH were significant predictors of each other, accounting alone for 14% of the observed variation in the dependent variable. This means, for instance, that child WH increased on average by a value of 0.28 (corresponding to 280 g) as adult BMI increased by one unit (approximately 3 kg). Indeed, at that season more adults with chronic energy deficiency (BMI < 18.5), particularly women, were likely to be found in households with at least one wasted child than in households with no malnourished child (relative risk = 2.75). Household energy adequacy tended to be associated negatively with HA Z score, as shown in table 7. Not even child age could significantly explain the variation in HA Z scores in the regression model. This is likely due to the narrow range of height for age in our sample. Mean HA Z scores were below -2 in all age groups except 0-11 months, but there were only eight children in this group (table 4).

At harvest, child WH Z scores and adult BMI could no longer predict one another, and there was no household clustering of low adult BMI and child wasting. However, household vitamin A adequacy then explained 7% (p<.05) of the observed variation in WH Z scores and 16% (p < .001) of the variation in adult BMI, and this was still significant even when energy adequacy was controlled for. Vitamin A would therefore exert an effect that cannot be explained only by its association with energy intake. Vitamin A adequacy made only a small contribution to explaining the HA of children, compared with child age (R2=.19 for the combined model). The positive coefficient of age is surprising, considering that, by two years of age or so, height deficits are difficult to reverse [16]. It may merely reflect the seasonal, but likely transient, improvement of HA observed in children over three years of age.

The relationship between household vitamin A adequacy and individual anthropometric indices changed with the season. Adult BMI and child WH were significantly related to household vitamin A adequacy only at harvest, when mean vitamin A intake improved over the non-harvest season as a consequence of increased availability of foods containing vitamin A, notably milk and spirulina. Despite this increased intake, some households were still deficient in vitamin A, perhaps because of poor dietary habits or limited access to the necessary foods. At non-harvest, sources of the vitamin were scarce, as shown by low median intake, and such a relationship might not have been seen because most households, with or without malnourished individual members, were affected by this low supply.

The relationship between household vitamin A adequacy and the anthropometric indices, although significant on one occasion, should be interpreted with caution. Even if day-today variation in vitamin A intake is likely much smaller in the community studied than in industrialized countries [31], partly owing to the monotony of the diet, the intake measured over two days may not be representative of the usual intake during the whole season.

The association between child (and adult) anthropometric indices and household vitamin A adequacy does not necessarily imply a causal relationship. Many variables other than food supply may explain children's nutrition status and were considered in our study (these will be discussed at length in a forthcoming paper). Our results nonetheless suggest that child growth indices, if at all related to household food consumption, are likely to reflect diet quality, notably vitamin A content, more than quantity (energy sufficiency), at least where household energy supply is not very limiting but vitamin A deficiency is suspected and child protein-energy malnutrition is widespread, as in the study community. In such areas, monitoring the consumption of major local food sources of vitamin A, at the household as well as at the child level, may be useful. Some evidence links vitamin A deficiency and its ocular manifestations to stunted linear growth and wasting in young children, although this relationship has not been observed consistently [32].

Household vitamin A adequacy was also a better predictor of adult BMI at harvest than energy adequacy, even when the latter was controlled for. Determination of vitamin A adequacy was less prone to error than of energy adequacy since it is not dependent on the estimation of the level of physical activity. Moreover, vitamin A, independent of energy, may play a role in preventing infections in adults. Impaired immune responses have been reported in people with vitamin A deficiency as well as in deprived laboratory animals [33]. However, in the past, most human studies have focused on children; therefore, little is known about adult response. Vitamin A adequacy may also be a reflection of the socioeconomic status of the household [34]. These are additional reasons for advocating that the household consumption of foods containing vitamin A should be monitored, using, for instance, a simple food frequency questionnaire.

In conclusion, this study showed that dietary adequacy as well as child and adult anthropometric status are all indicators of household nutrition. However, when taken individually, they cannot reflect the overall food and nutrition status of the household. It also showed that the weak association between household dietary adequacy and individual nutrition status changed with the seasons, and that vitamin A intake was a better predictor of individual anthropometric indices than energy intake. The relationship between adult and child anthropometric indices also changed with the seasons. This suggests that seasonality should be taken into account when appraising the household food situation from the nutrition status of some of its members or vice versa.

The fact that children's nutrition status was not consistently related to that of adults, in conjunction with the higher magnitude of seasonal changes in women than in men, argues in favour of monitoring the anthropometry of both preschoolers and adult women in households. Further investigation may be called for to study the link between adult anthropometric status and vitamin A intake and to examine the relevance of monitoring household consumption of major sources of vitamin A to identify malnourished households where the energy supply is not limiting but vitamin A is.

Acknowledgements

The authors gratefully acknowledge the participation of the Mao households in this study. Helpful comments were received from Edward Frongillo and Vivian Krause. Support for this research was provided by a grant from IDRC, Ottawa. Acknowledgement is also made to the Canadian Public Health Association, Ottawa, and the Centre Sahel, Quebec, for covering travel expenses.

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