There isn’t a vitamin more important to your health than vitamin D. You need it to build and maintain strong bones. Your immune system is crippled without it. Vitamin D deficiency appears to raise the risk of almost every chronic disease, from cancer to diabetes to cardiovascular disease to age-related cognitive decline to auto-immune disease. Yet professor and nutrition researcher Peter Horvath at the University of Buffalo School of Public Health and Health Professions in Buffalo, New York, reports that during Buffalo’s winter months, nearly 50% of the population in Buffalo has insufficient levels of vitamin D, while 25% are outright deficient. “Every cell in your body,” he says, “is responsive to vitamin D. If you’re deficient, you won’t see the health effects for years and it could take months to get your levels back up.” Dr. Horvath is probably using the standard definition of vitamin D deficiency—a blood level of less than30 ng/mL (or 75 nmol/L). However other vitamin D e…