Iron and fecundity among Tsimane' women of Bolivia.

Elizabeth M Miller,Maie Khalil

doi:10.1093/emph/eoz020

Abstract

Background and objectivesIron is critical for women’s reproduction, and iron-deficiency anemia is a global health problem for mothers. While public health programs have aimed to correct iron deficiency in reproductive-aged women with supplementation, a small group of studies have shown that too much iron also has negative effects on birth outcomes. We hypothesize that women’s iron levels evolved within a narrow optimum, and predict that hemoglobin (Hb) levels would be associated with women’s fecundity.MethodologyWe used the publicly available, longitudinal Tsimane’ Amazonian Panel Study to test the association between -Hb levels and hazard of having a next birth (a measure of fecundity) among 116 parous, reproductive-aged Tsimane’ women of Bolivia. A Cox proportional hazards model was used to model Hb level and other predictors against the event of next birth across the observation period, which began at each woman’s previous birth.ResultsThe higher the Hb level, the lower the hazard of a woman giving birth within the study observation period (hazard ratio=0.82, P = 0.03). However, there was no evidence that low Hb reduced women’s fecundity.Conclusions and implicationsThese results demonstrate that high Hb influences women’s fecundity. These results supports the growing body of literature showing that iron metabolism is critical for understanding the evolution of women’s reproduction. More work is needed to determine the evolved optimal range of iron levels for reproductive-aged women.Lay summaryLower chance of pregnancy among Tsimane’ women with high Hb levels, suggesting evolved optimal Hb levels in women.

Highlights

Iron is essential for life, facilitating oxygen transport throughout the body
The purpose of this study is to test the hypothesis that Hb is associated with fecundity, as measured by hazard of experiencing a birth, in the publicly available Tsimane’ Amazonian Panel Study (TAPS)
When dividing the population in to high, medium, and low categories based on Hb level, there are significant differences in interval between births, with women in the high Hb group having significantly more days between their previous birth and their exit from the analysis, ether via birth or observation period cutoff date

Summary

Introduction

Iron is essential for life, facilitating oxygen transport throughout the body. On the other hand, too much iron is toxic, damaging tissues with oxidative stress and feeding pathogenic bacteria within hosts [1, 2]. Iron is critical for women’s reproduction, and iron-deficiency anemia is a global health problem for mothers. While public health programs have aimed to correct iron deficiency in reproductive-aged women with supplementation, a small group of studies have shown that too much iron has negative effects on birth outcomes. Methodology: We used the publicly available, longitudinal Tsimane’ Amazonian Panel Study to test the association between -Hb levels and hazard of having a birth (a measure of fecundity) among 116 parous, reproductive-aged Tsimane’ women of Bolivia. Conclusions and implications: These results demonstrate that high Hb influences women’s fecundity These results supports the growing body of literature showing that iron metabolism is critical for understanding the evolution of women’s reproduction. Lay summary: Lower chance of pregnancy among Tsimane’ women with high Hb levels, suggesting evolved optimal Hb levels in women

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Discussion

Conclusion