Grant: Operating Grant

Pregnant and breastfeeding women need to have adequate vitamin D levels because low vitamin D in the mother's blood can be bad for the health of the mother and baby. Scientists have observed that Canadian women of childbearing age (for example, ages 15 to 45 years) have low levels of vitamin D. This suggests that women are not getting enough of this vitamin. Humans get a small amount of vitamin D from the food we eat, but most of it is made in our skin when it absorbs sunlight. In winter in Canada, there is not enough sunlight to make this happen. So it is important for pregnant and breastfeeding women to take extra vitamin D in a pill (a vitamin supplement). So far, however, we do not know how much pregnant and breastfeeding women need to take to ensure good health for themselves and their babies. Two Canadian recommendations differ by 10 times (5 versus 50 units). Also, when human skin is darker (naturally or because of a tan) it has lower light absorption and so makes less vitamin D. We do not yet know if a woman's skin colour affects the amount of vitamin D she needs to take. In this study, we want to find out how much extra vitamin D pregnant and breast¬feeding women need to take in order to need to achieve an appropriate level in themselves and their babies. To try to answer these questions, we propose to study 210 pregnant women who will take a vitamin D supplement (5, 25, and 50 units per day) from pregnancy through breastfeeding. We will measure the effect of vitamin D supplements on the growth of the baby and on the bone health of mother and baby. We will also determine if there is any effect of skin colour, which we will study using a device called a colorimeter that measures how might light is reflected by the skin. The results of this study will important for women and their doctors and for the organizations and government (Health Canada) who make the recommendations about vitamin supplements in pregnant and breastfeeding women.