extreme prematurity (\<28 weeks gestation)

infants \<12 months of age

breastfed infants with no vitamin D supplementation

recent (\<1 year) immigrants from countries where rickets and malnutrition prevalent

other chronic respiratory disease (broncho-pulmonary dysplasia; cystic fibrosis)

endocrine disorder of calcium/ vitamin D metabolism

disorder/ disease with associated malabsorption (inflammatory bowel disease)

kidney/ liver disease

sickle cell anemia

medications known to interfere with bone metabolism/ vitamin D levels

vitamin D supplementation \>1000 IU/ day in past 3 months

unable to attend medical visit in 3-4 months

plan to leave the province during the next 6 months.

Vitamin D to Reduce Colds and Asthma Attacks in Young Children