This is a randomized, placebo-controlled trial of vitamin D supplementation with 20mcg cholecalciferol (to achieve a total intake of 25mcg/day), with or without 500mg calcium to assess vitamin D requirements in lactating women and to ascertain whether vitamin D supplementation at levels sufficient to achieve defined thresholds of maternal serum 25-hydroxyvitamin D will increase the vitamin D content of maternal milk. The study will also report serum 25-hydroxyvitamin D in maternal-cord dyads over a 12-month period and describe the relationship between them. Information on maternal iPTH levels, anthropometry, diet and sun exposure will also be reported.

Inclusion Criteria:

• Pregnant women intending to breast feed their infant for at least 12-weeks
• Pregnant women >20 weeks gestation
• Pregnant women >18 years of age
• Pregnant women in good general health

Exclusion Criteria:

• Consumption of a vitamin D-containing supplement(>10µg/day) in the 3 months prior to commencing the trial
• Consumption of a vitamin D or calcium containing supplement during the 12- week trial
• Mothers taking a vacation to a sunny climate or using a solarium during the 12-week trial
• Mothers with pre-existing type 1 or type 2 diabetes
• Mothers with pre-existing hypertension
• Mothers with diagnosed hypercalcemia
• Mothers with diagnosed intestinal malabsorption conditions
• Mothers with multiple fetuses (e.g. twins)
• Consumption of medications known to interfere with vitamin D metabolism.