The investigators proposed a pilot study preparatory to developing a randomized trial of vitamin D for the prevention of TB infection. The specific aims are presented below:

1. To recruit subjects, obtain consent, distribute vitamin D supplements to the children in the schools, obtain blood samples and transport them to the United States.
2. To test the hypothesis that daily vitamin D supplementation will increase plasma levels of 25(OH)D, and restore TLR-induced antimicrobial activity in monocytes/macrophages tested in vitro.

Inclusion Criteria:

• Eligible subjects will be children age 12 to 15 years inclusive in public school, located in Songino-Khairhan district, who are residents of Ulaanbaatar, and whose parents have given informed consent and who accent to participate in the study.

Exclusion Criteria:

• Individuals with pre-existing calcium, parathyroid conditions, or type I diabetes, sarcoidosis, or who require chronic diuretic therapy including calcium channel blockers, or who are cognitively impaired.