Children of women who maintained high Vitamin D levels while pregnant have bigger, stronger and more calcium-rich bones than those of other children at age 9, new research finds.

The study suggests Vitamin D levels in pregnant women may have a greater impact on children’s eventual risk of osteoporosis and bone fractures than drinking more milk or other common approaches to building bones.

Previous studies have shown that women with larger bodies, better nutritional habits and good exercise habits have babies with greater bone mass – a major protective factor against bone-weakening osteoporosis later in life. At least one study had also shown that Vitamin D supplements given to prematurely born babies during their first year resulted in stronger bones at age 12. But no one had tested the effects of prenatal Vitamin D levels.

How to get maternal Vitamin D levels up? Only two factors appeared useful in the study: living in a place with a high number of sunny days (the body needs ultraviolet light to make Vitamin D) or taking vitamin supplements.