Low serum vitamin A mothers breastfeed daughters more often than sons in drought-ridden northern Kenya: a test of the Trivers–Willard hypothesis

Breastfeeding over two years is associated with longer birth intervals, but not measures of growth or health, among children in Kilimanjaro, TZ

OBJECTIVES

Breastfeeding has been associated with numerous health and well-being benefits for both children and their mothers, including prolonging the birth interval to the subsequent sibling. The clearest associations between breastfeeding and health outcomes, per se, reflect exclusive breastfeeding in the first months of postnatal life and are most evident during infancy. Fewer studies explore the consequences of breastfeeding for multiple years. In this article, we ask whether breastfeeding for more than 2 years is associated with discernible health and well-being benefits to children.

METHODS

Data were collected from 315 children, aged 2 to 7, and their caretakers residing in Kilimanjaro, Tanzania. Basic demographic and health information was solicited, and anthropometric and blood markers of health were evaluated.

RESULTS

Our results indicate a strong positive relationship between breastfeeding for 2 or more years and interbirth interval, but little evidence for a relationship between prolonged breastfeeding and several indicators of child growth and health.

CONCLUSIONS

We suggest that these relationships may support the recently rekindled birth spacing hypothesis, positing selection for longer interbirth intervals, rather than, or in addition to, more direct health benefits associated with breastfeeding for 2 or more years. Our results may indicate attenuating health benefits associated with longer breastfeeding.

Milk immunity and reproductive status among Ariaal women of northern Kenya

Abstract Background: The immune factors in human milk protect infants from infection and promote immune development. Evidence suggests that the production of milk-specific immunoproteins is energetically costly, making them a form of maternal investment in offspring health that is subject to life history trade-offs.

AIM

This research tests the relationship between measures of reproductive effort and the production of milk immunoglobulin A (IgA) among Ariaal women, a settled northern Kenyan pastoralist population that experiences nutritional and disease stress.

SUBJECTS AND METHODS

Two hundred and forty-three lactating Ariaal women participated in a questionnaire, anthropometric measurement and milk collection. Milk IgA was analysed using ELISA.

RESULTS

There was a significant U-shaped relationship between post-partum months and milk IgA, reflecting decreasing investment in the current offspring over the early post-partum period and subsequent recovery of maternal energy status near the end. There was also a significant inverse U-shaped relationship between milk IgA and parity, with high parity women showing a drop in milk IgA. In contrast, anthropometric measures of energy status were not associated with the production of milk IgA.

CONCLUSION

This research shows that patterns of reproductive investment can be demonstrated in milk IgA in the absence of measured energy changes.

Nutrient intakes associated with elevated serum C-reactive protein concentrations in normal to underweight breastfeeding women in Northern Kenya

OBJECTIVES

Low-grade elevation of C-reactive protein (CRP) is a non-specific inflammatory marker, used as a predictor for cardiovascular disease development and chronic inflammatory risks. Research investigating dietary influences on inflammation has focused primarily on the relationship between dietary characteristics, CRP elevation and BMI in the populations at greatest risk for cardiovascular disease, namely those in the overweight and obese ranges, often in clinical settings and/or among those middle aged or older, leaving little information about normal to underweight populations of reproductive age in ecological settings. This study evaluates impacts of dietary nutrients on serum CRP levels in a population of predominantly underweight to normal weight adult women experiencing the additional nutritional demands of lactation.

METHODS

Data from non-overweight breastfeeding Ariaal women of Kenya collected in 2006 were used (n = 194). Logistic regression models were applied using low-grade CRP elevation (hsCRP > 3 mg/L) as the outcome variable and dietary nutrients, age, BMI, and serum retinol as predictors.

RESULTS

Models showed that energy intake (Kcal) and age were positive predictors of CRP elevation while folate intake, total vitamin A intake, and serum retinol concentration were protective against CRP elevation. Unlike previous studies among higher BMI populations, this study found no significant effect of dietary lipids/fatty acids or BMI on CRP elevation.

CONCLUSIONS

The effects of specific dietary nutrients on inflammatory status may vary with BMI or, in women, reproductive status. Further research should investigate the role of dietary fats, fatty acids, and antioxidant vitamins across populations with a wide range of BMI, including postpartum women.

The evolutionary ecology of early weaning in Kilimanjaro, Tanzania

Public health recommendations promote prolonged breastfeeding of all children; however, parental investment (PI) theory predicts that breastfeeding will be allocated among a mothers' offspring to maximize her reproductive success. We evaluated PI in terms of risk for weaning before age two among 283 children in Kilimanjaro, Tanzania. Results demonstrate: (i) a Trivers-Willard effect--high socioeconomic status (SES) females and low SES males were more likely to be weaned early; (ii) later-born children were less likely to be weaned early; (iii) higher birthweight children were less likely to be weaned early, and (iv) no effect of cattle (a source of supplementary milk) ownership. These associations were largely independent and remained significant in models controlling for potential confounders; however, the inverse association between early weaning and birth order lost significance in the model containing birthweight. These patterns were observed despite public health recommendations encouraging breastfeeding for at least two years.

Dietary diversity score is a useful indicator of vitamin A status of adult women in Northern Kenya

OBJECTIVES

Diets consisting of diverse food items provide a wide range of nutrients that can enhance nutritional quality of the diet. Few studies have, however, assessed dietary diversity and its effects on micronutrient health in rural populations in field settings. This study assesses how well Dietary Diversity Score (DDS), an indicator of dietary diversity based on a simple count of food groups consumed, predicts the micronutrient status, focusing on serum vitamin A concentration.

METHODS

We used cross-sectional data from women in food-insecure northern Kenya where dietary diversity is likely critical for micronutrient health yet under-studied. A linear regression model was applied to examine the relationships between DDS and serum retinol concentration. A logistic regression model was used to test DDS as a predictor of vitamin A insufficiency (serum retinol < 1.05 μmol/l).

RESULTS

DDS had a significant positive effect on serum retinol concentration (t = 2.01, P = 0.045) after adjusting for age, wealth, acute phase reaction, hemoglobin, vitamin A intake and vitamin A supplementation. A one unit increase in DDS by adding an extra food group in one's diet was significantly less likely to have vitamin A insufficiency (OR = 0.64, P = 0.026) after adjusting for the covariates.

CONCLUSIONS

Our results indicate that diversified diets enhance vitamin A status relative to narrower diets with equivalent vitamin A content. DDS shows a potential as a low-cost, field-friendly method for exploratory assessments of vitamin A status, and a potential as a research tool for human biologists and anthropologists interested in dietary quality and micronutrient health.