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 42 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 Skin Cancer Foundation supports The Institute of Medicine of the National Academies’ Recommended Dietary Allowance (RDA) for vitamin D, which is 600 IU (International Units) a day for people between the ages of 1 and 70, and 800 IU a day for people ages 70 and older. For children under 1 year, adequate intake (AI) is 400 IU a day.
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!
|Food||Serving Size||IUs Per Serving|
|Cod liver oil||1 tbsp.||1,360|
|8 oz.||Up to 120|
|Vitamin D-fortified orange juice||8 oz.||98|
|Vitamin D-fortified milk||8 oz.||98|
|Vitamin D-fortified yogurt||6 oz.||Up to 80|
|Vitamin D-fortified margarine||1 tbsp.||60|
|Egg yolk||1 yolk||41|
|Beef liver, cooked||3.5 oz.||15|
Published on November 6, 2008