Vitamin D is like calcium's personal assistant. Its primary function is to open the proper channels so that your intestines can allow calcium to be absorbed and your kidneys can reabsorb calcium that has already been filtered for excretion. Vitamin D's association with calcium means that it plays a vital role in assisting in the same functions that calcium provides. A deficiency in vitamin D can result in rickets, osteomalacia and muscle pain and weakness. There are two ways to obtain vitamin D: through sunlight and dietary consumption.
Dietary Sources
Vitamin D is one of the less common vitamins when it comes to food sources, according to the Office of Dietary Supplements. The dearth of vitamin D in common foods has prompted manufacturers to fortify their products with this essential nutrient. Milk, cereal margarine and soy foods are among the many products fortified with vitamin D. Fatty fish, egg yolks, cheese and mushrooms have naturally occurring vitamin D. Vitamin D supplements, in the form of D-2, or ergocalciferol and D-3 or cholecalciferol are also effective at increasing blood levels of vitamin D.
From the Sun
Sunlight doesn't just feed plants; it also gives your skin the ability to produce vitamin D. When your epidermis absorbs ultraviolet radiation, it causes a substance called 7-dehydrocholesterol to be converted to cholecalciferol, or vitamin D-3. In fact, most of the vitamin D humans receive is through sun exposure.
Getting the D Without the Damage
The Linus Pauling Institute states that to minimize your risk of skin damage due to sun exposure, light-skinned persons should limit exposure to 5 to 10 minutes of sun three times per week between 11:00 am and 2:00 pm during the spring, summer and fall. This exposure must be direct, as sunlight through a glass window will not have the same effect. This amount will provide ample vitamin D stores to last throughout the winter. If you have dark skin or live in latitudes with less sunlight, your needs may vary.
Considerations
Using sun block, though a wise health choice, hinders vitamin D synthesis. Clothing that blocks skin exposure has the same effect.
Epidermal synthesis of vitamin D decreases with age, and elderly people may require more dietary vitamin D to make up for this shortfall. Breastfed infants may also have difficultly obtaining enough vitamin D, as this nutrient is not well represented in breast milk.
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