Early-life nutritional and environmental determinants of thymic size in infants born in rural Bangladesh

Abstract

Aim: The aim was to assess the impact of nutritional status and environmental exposures on infant thymic development in the rural Matlab region of Bangladesh.

Methods: In a cohort of N(max) 2094 infants born during a randomized study of combined interventions to improve maternal and infant health, thymic volume (thymic index, TI) was assessed by ultrasonography at birth and at 8, 24 and 52 weeks of age. Data on birth weight, infant anthropometry and feeding status were also collected.

Results: At all ages, TI was positively associated with infant weight and strongly associated with the month of measurement. Longer duration of exclusive breastfeeding resulted in a larger TI at 52 weeks. TI at birth and at 8 weeks correlated positively with birth weight, but by 24 and 52 weeks and when adjusted for infant weight this effect was no longer present. Thymic size was not affected by pre-natal maternal supplementation or by socioeconomic status but was correlated to arsenic exposure during pregnancy.

Conclusion: In this population of rural Bangladeshi infants, thymic development is influenced by both nutritional and environmental exposures early in life. The long-term functional implications of these findings warrant further investigation.

Figure 1

Mean thymic index (open circles) and thymic index expressed in relation to body weight (closed circles) by age. Data are expressed as means and 95% CIs.

Figure 2

Relative size of thymus variation with time of year plotted at birth and at 8, 24 and 52 weeks of age. The curves are the seasonal component of equation (1) fitted by multiple regression. They show the mean TI difference from the overall average at different times of the year. Post-natally, the thymus is largest in the first half of the year and smallest in the second half of the year. The picture is rather different at birth where there appeared to be two peaks: at the turn of the year and at mid-year. The difference between the patterns at the different post-natal ages is not significant but these do differ significantly from the pattern at birth.