Vitamin D is one of the most important, yet often misunderstood of all nutrients. Appropriately nicknamed the "sunshine" vitamin, the body produces Vitamin D when exposed to the sun's ultraviolet (UVB) rays. However, it is not abundant in many of today's most popular foods, and almost non-existent in fast foods and processed meals. And as if this weren't bad enough, some of the best sources of vitamin D are ironically some the things we, as humans, tend to avoid the most frequently; exposure to the sun and vitamin D-rich whole milk.

During the winter months, especially for those who reside in cold weather climates, it is important to remain conscious of one's daily vitamin D intake. Days spent under the mind-numbing glow of fluorescent office lights, coupled with our instinctive desire to hibernate indoors, makes it next to impossible to manufacture a respectable amount of vitamin D. And whether we choose to acknowledge it or not, when the body's free reserve runs low, a number of important systems can potentially suffer.

One of the most important roles of Vitamin D is to support bone mineralization by assisting the body in absorbing calcium. It's vital for the growth and maintenance of teeth and bones, and plays a key role in the recovery process after suffering a break or fracture. Poor vitamin D intake has been associated with reduced calcium absorption, bone density loss, and an increased risk for osteoporosis-a condition characterized by low bone mass, bone fragility and susceptibility to fractures, especially of the hip and spine. In 2004, a report published by the Surgeon General listed vitamin D, along with calcium and physical activity, as the three key elements to maintaining optimal bone health.

But In addition, ongoing research has shown that it may help support healthy immune system function, skin cell metabolism, cellular activity, and nervous system health.* The current RDI for Vitamin D is 400 IU daily, however many researchers feel that this is not nearly enough-especially in adults over the age of fifty.

Vitamin D3 has been the subject of many recent studies, and the findings continue to suggest that supplementing this crucial nutrient in higher potencies may offer ever greater health benefits. In addition to its structural support benefits, researchers have examined its effect on dental, colon and breast health, cell abnormalities, nervous system function, mental health, immune system function, and more.*

Vitamin D3 (as Cholecalciferol) is easy absorbed and utilized by the body, and has extremely low toxicity. Vitamin D3 is safe and ideal for healthy adults concerned with supporting strong, healthy bones and teeth. As evidenced by ongoing studies, higher doses of Vitamin D3 may also be beneficial for those individuals seeking support of healthy cardiovascular activity, immune and nervous system function, blood sugar, and metabolism.

Chicago native Jayson Kroner is co-author of the book 7-Syndrome Healing: Supplement Essentials for Body and Mind and an accomplished health and fitness journalist. In addition to regular columns in Chicago Wellness Magazine and Bodybuilding.com, his work has appeared in dozens of national health, fitness and training magazines. He is a member of Citizens for Health, the American Arthritis Foundation, and the Illinois Mountain Bike Association. Jayson resides in Oak Park, IL.