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.

• Human milk
• immunoglobulin A
• Kenya
• reproductive ecology

Acknowledgements

We are deeply appreciative of the two anonymous reviewers who improved this manuscript with their suggestions. We would like to thank Z. Cofran, R. Frisancho, W. Leonard, B. Low, J. Mitani and M. Wolpoff for comments on previous versions of this manuscript. We would like to thank field assistants Korea Leala, Rapheala Leado, Selena Gambare and the Abdulai Khalifa for their careful work. Ethical permission for this research was granted by Kenyatta National Hospital Ethical Review Committee and the University of Michigan’s Institutional Review Board. Permission for this research was generously given by the Ministry of Science and Technology of the Republic of Kenya, the District Commissioner of Marsabit District and the chiefs of Karare, Parkishon and Kituruni. Finally, we are deeply indebted to the women and infants who participated in this study.

Declaration of interest

Funding for this project was provided by the Leakey Foundation and the National Science Foundation (BCS-0750779).