doi:10.1038/nindia.2013.70 Published online 29 May 2013
A paternal genetic contribution could be one factor contributing to the lower birth weights of Indians as compared to Europeans, according to a new study which notes that improved nutrition at birth alone might not wholly resolve this elevated risk. The study is a blow to the traditional blame game that mothers are subjected to for all that goes wrong with Indian babies born with lower birth weights.
The large sample study1 undertaken by researchers in the United Kingdom, however, clarifies that this does not mean that improved nutrition is not critical for health in the Indian population. It may, however, help understand the elevated susceptibility of Indians to type-2 diabetes associated with obesity.
"There is an important public health message from our work: if birth weight is lower for genetic reasons then improved nutrition will not wholly take care of the higher risk. On the other hand, that does not mean improved nutrition is not critical for health", lead researcher Jonathan Wells told Nature India.
Wells, a Professor of anthropology and pediatric nutrition at the Childhood Nutrition Research Centre UCL Institute of Child Health, London says their data, indicating a downwards adjustment of body size in Indians relative to Europeans, is the first evidence in any large population (save for atypical populations such as pygmies) that ethnic groups may differ in body size in part for genetic reasons.
The team, also comprising researchers from Royal Cornwall Hospitals, Cornwall; Imperial College London and London School of Tropical Medicine and Hygiene used data from the UK Office for National Statistics Longitudinal Study (LS) and the Chelsea and Westminster Hospital (CWH), London. Since ethnic groups differ significantly in adult physique and birth weight, the researchers wanted to understand maternal versus paternal contributions to birth weight by comparing the offspring of same-ethnic versus mixed-ethnic unions amongst Europeans and South Asian Indians in the UK.
They found that birth weight of children with mixed-ethnic parentage fell in between that of children with two European or two Indian parents. This, they say, demonstrates a paternal as well as a maternal contribution to ethnic differences in foetal growth.
"This can be interpreted as demonstrating paternal modulation of maternal investment in offspring. We suggest long-term nutritional experience over generations may drive such ethnic differences through parental co-adaptation," the team wrote in their paper.
Wells says most people imagine adaptation to be a response to factors such as food supply and disease after birth. "In contrast, we suggest that adaptation is not only to the environment directly but also to the 'pool of resources' available in the mother during pregnancy." This, he says, links with more general evolutionary models of parent-offspring conflict2.
A recent WHO multi-centre growth study proposed that individuals of high social status in all ethnic groups grow the same but there was a modest reduction of 0.5 cm in birth length in the Indian component of their sample. "Thus, although people have increasingly assumed that growth varies due to environmental pressures, there also appears to be a genetic contribution," he adds.