During the first year on study, serum for measurement of 25-OH and iPTH will be drawn monthly and every 2 months during the second study year. Each subject's specimens will be frozen immediately after collection, and transferred to SLRHC where they will be stored at -70 degrees. At one year intervals the each subjects' samples will be assayed in "batched " fashion. On the basis of these annual determinations, subjects with persistent vitamin D deficiency (25-OHD<10ng/l and PTH>73) that lasts throughout both winter and summer months, will be withdrawn from the study and referred to their medical provider.