UV exposure in pregnancy boosts fetal bone density

Pregnancy - Mothers' vitamin D levels linked to child bone health.

Children's bone growth in their first decade is affected by maternal exposure to sunlight during pregnancy, University of Bristol research has shown.

Previous studies have suggested that maternal vitamin D levels, which are largely determined by ultraviolet light exposure, affect fetal and infant growth. Poor fetal growth has been associated with low bone mass and raised fracture risk.

Adrian Sayers and Jonathan Tobias measured the bone mineral density and content of 6,955 children in south-west England using dual energy X-ray absorptiometry (DXA). The children were 10 years old on average.

The researchers also used meteorological records to estimate the ultraviolet B light (UVB) exposure of the children's mothers during their third trimester of pregnancy. Vitamin D levels were measured in 355 of the mothers and correlated strongly with the researchers' estimates of UVB levels.

The researchers found that mothers' exposure to ultraviolet light was strongly associated with children's bone mineral density at the age of 10 years. It was also associated with increases in bone mineral content and bone area.

They believe that the finding reflects the fact that exposure to UVB is a major determinant of maternal levels of vitamin D, which is needed for bone formation.

Increasing ultraviolet exposure in winter by the equivalent of four weeks of summer exposure would decrease offspring's fracture risk by around 5 per cent, they say.

'Our findings provide further justification for strategies intended to improve maternal vitamin D status in order to optimise skeletal health of the child, for example through vitamin D supplementation during pregnancy,' the researchers write.


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