By Helen Chin Lui of The Healing Place in Medfield, MA
It's time to think about stocking up on your Vitamin D for the fall and winter. Vitamin D, calciferol, is a fat-soluble vitamin. It is found in food, but also can be made in your body after exposure to ultraviolet rays from the sun. Vitamin D exists in several forms, each with adifferent activity. Some forms are relatively inactive in the body, and have limited ability to function as a vitamin. The liver and kidney help convert vitamin D to its active hormone form.
The major biological function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. It promotes bone mineralization in concert with a number of other vitamins,minerals, and hormones. Without vitamin D, bones can become thin, brittle, soft, or easily broken.
One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for this vitamin in adults. Although milk is fortified with vitamin D, dairy products made from milk such as cheese, yogurt, and icecream are generally not fortified with vitamin D. Only a few foods naturally contain significant amounts of vitamin D, including fatty fish and fish oils. Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin. Season, latitude, time of day, cloud cover, smog, and suncreens affect UV ray exposure. For example, in Boston the averageamount of sunlight is insufficient to produce significant vitamin D synthesis in the skin from November through February. The lack of sun during the winter months can also lead to depression and Seasonal Affective Disorder. Sunscreens with a sun protection factor of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen whenever sun exposure is longer than 10 to 15 minutes. If you are prone to depression during the winter months, please talk to your health care provider, you may be vitamin D deficient.