Are you getting enough?
Recent research suggests that even those who get plenty of sun exposure – residents of Hawaii who get at least 22 hours of sun per week – can still be vitamin D deficient. Vitamin D deficiency is correlated with many health concerns: depression, heart disease, stroke, cancer, osteoporosis, parathyroid problems, immune function — even weight loss. The RDA for vitamin D has recently been increased from 400 IU to 1 000 IU. Treatment of deficiency can require 2 000-5000 IU per day. Given the widespread deficiency, especially in northern climates like ours, I think it would be prudent to supplement with at least 1 000 IU per day, at least over the cooler months from October through March.