Sex differences in growth and neurocognitive development in infancy and early childhood.

Undernutrition in early life remains a significant public health challenge affecting millions of infants and young children globally. Children who are wasted, stunted or underweight are at increased risk of morbidity and mortality. Undernutrition at critical periods also impacts on aspects of neurodevelopment, with longer-term consequences to educational performance and mental health outcomes. Despite consistent evidence highlighting an increased risk of neonatal and infant mortality among boys, a common assumption held across many disciplines is that girls are more vulnerable with respect to early-life exposures. In relation to undernutrition, however, recent evidence indicates the reverse, and in contexts of food insecurity, boys are at increased risk of undernutrition in early life compared to girls, with sex-specific risks for neurodevelopmental deficits. These effects appear independent of social factors that may favour boys, such as gender disparities in infant feeding practices and health-seeking behaviours. The observed vulnerability among boys may therefore be underpinned by biological processes such as differential energy requirements during periods of rapid growth. As boys have greater needs for growth and maintenance, then, in times of nutritional hardship, these needs may not be met resulting in risk of undernutrition and subsequent health consequences. In view of this emerging evidence, a greater understanding of the mechanisms behind this vulnerability among boys is needed and policy considerations to protect boys should be considered. This review will explore sex differences in risk of undernutrition and consider these in the context of existing programmes and policies.