Sometimes the cure can be worse than the condition. For thousands of vitamin D-deficient people in the U.S., can obtaining this so-called "sunshine vitamin" actually endanger health?

Vitamin D has been a mainstay in the news recently, with stories claiming it protects against everything from high blood pressure to cancer. Though its ability to prevent these conditions remains unproven, vitamin D is essential for bone health, immune system functioning, and more.

An organic compound, Vitamin D is fat-soluble (meaning some dietary fat is necessary for its absorption). A lack of the vitamin puts us at risk for painful, weak muscles, inadequate bone mineralization, and skeletal deformities in children (rickets), as well as mineral loss and soft bones in adults (osteomalacia).

Ultraviolet (UV) Exposure Is Not the Answer

Our bodies manufacture vitamin D when the sun's ultraviolet B (UVB) rays interact with 7-dehydrocholesterol (7-DHC) present in the skin. "However, we can produce only a limited amount of vitamin D from UVB. A few minutes at midday are sufficient for many Caucasians," says Roy Geronemus, MD, clinical professor of dermatology at New York University Medical Center and director of the Skin/Laser Division at the New York Eye & Ear Infirmary. "After reaching the production limit, further exposure actually destroys the vitamin, decreasing vitamin D levels."

Furthermore, UV exposure is unlikely to produce enough vitamin D in darker skin, so African-Americans and dark-skinned Hispanics relying on UV alone are especially at risk for deficiency. The National Institutes of Health's Office of Dietary Supplements also warns that the elderly have a reduced ability to synthesize vitamin D from sunlight; and between November and February, UV radiation (UVR) is insufficient to produce vitamin D in people living above 42º north latitude, which includes Boston, northern California, and other areas north.

Finally, prolonged exposure to UVR is linked to skin cancer, immune system suppression, photoaging (sun-induced skin aging), cataracts, and other eye damage. Therefore, The Skin Cancer Foundation recommends obtaining vitamin D largely from food or supplements while continuing to follow the Foundation's skin cancer Prevention Guidelines.

How Much Vitamin D Do We Need?

The Food and Nutrition Board of The National Academies has established daily Adequate Intake (AI) levels for vitamin D at 5 micrograms (mcg), or 200 International Units (IU), for those under age 50; 10 mcg (400 IU) for adults 51–70; and 15 mcg (600 IU) for people 71 and older. On nutritional labels, vitamin D quantity is usually listed as Percent Daily Value (DV). This represents the amount as a percentage of your vitamin D needs, based on a diet of 2,000 calories.

But even among physicians there is uncertainty about how much Vitamin D is necessary. Several studies suggest that even 20 mcg (800 IU) of vitamin D may be insufficient to prevent low bone density. If your physician approves, consider increasing your intake. The Office of Dietary Supplements has established tolerable upper intake levels for vitamin D at 25 mcg, or 1,000 IU, for babies under one year old; and 50 mcg, or 2,000 IU, for everyone else. While rare, vitamin D toxicity can cause nausea, weakness, and raised blood levels of calcium, which may lead to mental confusion and heart rhythm problems.

Certain medications can impair vitamin D or calcium absorbency. Consult your doctor about vitamin D intake if you take any medications regularly.

Good Sources of Vitamin D

While oily fish are the best food source of Vitamin D (See "Oily Fish: Your Route to Vitamin D"), several other foods supply significant amounts, including the choices below.

Look for products labeled "for bone health" or "with calcium"; these usually contain vitamin D to aid in calcium absorption.

So maximize your health by getting enough vitamin D the safe way your body will thank you!