Background: Vitamin D is vital throughout pregnancy and lactation for both maternal and infant health. Health Canada recommends women take the AI of 5ug/day of vitamin D during pregnancy, however, it is unknown how much vitamin D is necessary to ensure both mother and baby reach a vitamin D serum concentration of 25OHD>75nmol/L.

Purpose & Hypothesis: This project aims to determine maternal and infant responses vitamin D supplementation in pregnancy and lactation. It is hypothesized that the current AI of 5 μg of vitamin D will be inadequate for women and their infants in Canada to achieve optimal 25OHD concentrations (> 75nmol/L).

Methods: Healthy pregnant women between 18-42 years of age without history of pregnancy complications will be recruited for a double-blind, randomized, controlled trial where they will receive one of three different dosages of vitamin D (10, 25 and 50ug/day) as part of a standard prenatal vitamin. The study at 18 plus/minus 3 weeks gestation and will carry on throughout pregnancy and lactation. Mother and infant vitamin D levels in breast milk and blood will be measured at regular intervals. Skin colour will be measured via light reflectometry. Bone biomarkers such as plasma osteocalcin and urinary n-telopeptide will be assessed. Dietary vitamin D intake and sun exposure will be estimated using a food frequency and lifestyle questionnaire. Data will be analyzed using multiple regression analysis controlling for baseline values.

Expected Results & Conclusions: It is expected that greater vitamin D intakes (25, 50ug/day) will be necessary to raise maternal and infant serum concentrations to 25OHD>75nmol/L to avoid infant supplementation. This data will aid policy makers, mothers and healthcare workers in recommended and appropriate vitamin D dosage throughout pregnancy and lactation.

Inclusion Criteria:

• Women between 18-42 years of age
• within 18 plus/minus 3 weeks gestation
• planning to breastfeed their infant
• a singleton pregnancy

Exclusion Criteria:

• Any co-morbid condition such pre-gestational diabetes, TB, cardiac or renal disease, HIV/AIDS, chronic hypertension, inflammatory bowel disease, autoimmune disease, liver disease, or epilepsy; conditions associated with vitamin D malabsorption: celiac disease, gastric bypass;
• History of previous adverse pregnancy outcome [preterm delivery <37; weeks GA, stillbirth, severe pre-eclampsia, eclampsia, HELLP syndrome (hemolytic anemia, elevated liver enzymes, and low platelet count)];
• Women will also be ineligible if they are taking more than 10 µg day supplemental vitamin D or drugs known to interfere with vitamin D metabolism (i.e corticosteroids).