Winterize Your Diet

Vitamin D is key in the cooler months

By Kathleen Zelman, MPH, RD, LD
WebMD Weight Loss Clinic - Expert Column

Temperatures are dropping, and the days are getting shorter. And shorter days give us less time outdoors to get a healthy dose of sunshine -- and vitamin D.

So in addition to pulling out the wool sweaters, we need to winterize our diets to make sure we get the vitamin D we need this season.

The Role of Vitamin D

This vitamin controls a variety of body functions. One of its fundamental roles is to help absorb calcium into our bones and teeth.

Both calcium and vitamin D are important for bone health and muscle strength. Vitamin D helps maintain muscle strength -- which may explain why we need more with advancing age, as muscles becoming weaker and the tendency for falls becomes greater. In addition, as we age, our ability to produce vitamin D from the sun's ultraviolet (UV) rays becomes less efficient.

Vitamin D deficiency can lead to weak bones and aches and pains. Around the globe, researchers have found that adults over 50 tend to not meet the nutritional requirements for this vitamin -- especially those with dark skin, who are at a higher risk of not absorbing vitamin D from the sun.

Recommendations for vitamin D are 200 international units (IU) for people under 50; 400 IU for people aged 50-70; and 600 IU for those over 70. Some researchers suggest that the elderly may need even more than these recommendation amounts.

Vitamin D is a fat-soluble vitamin, which means it gets stored in the body and can potentially become toxic at high levels. Doses of 1,000 IUs a day are considered safe.

The Sunshine Vitamin

Vitamin D has a unique quality: Sunshine is one of our best sources for it. When our skin is exposed to UV rays, this stimulates a metabolic pathway that produces vitamin D.

This process requires sun exposure without sunscreen (and not through a window). Experts say that if you get 10-15 minutes of strong sunshine on your arms and face at least twice a week, it should meet your vitamin D needs. Dark-skinned people may need more than this amount.

Depending on what part of the country you're in, you may not be able to rely on the sun to provide you with an adequate dose of vitamin D during the winter.

If you live below the imaginary line that runs from Los Angeles to Atlanta, the sun's UV rays are strong enough all year long to help your skin make vitamin D. But north of this line, the UV light is too weak during the fall and early spring to stimulate your skin to make an adequate supply of the sunshine vitamin.

Food Sources of Vitamin D

Basking in the sunshine is certainly one of the most enjoyable (and best) ways to meet your vitamin D requirements. But you can also get vitamin D from multivitamins, many calcium supplements, and some fortified foods.

Because vitamin D is not naturally abundant in our food supply, it generally needs to be added to other foods. Milk is an ideal vehicle for D fortification; without vitamin D, your body can't absorb the calcium in dairy. Two cups of fortified milk will satisfy your requirement for vitamin D if you're under age 50.

Other good sources of vitamin D include fatty fish oils and fish such as salmon, sardines, and tuna, as well as fortified foods such as soy milks, margarines, cereal, eggs, and orange juice.

To make sure you are getting plenty of vitamin D this winter:

  • Enjoy the natural sunlight. A brisk walk outside can lift your mood, even if it does not significantly boost your production of vitamin D.
  • Take your daily multivitamin (which should include around 400 IU of vitamin D).
  • Eat plenty of fish.
  • Enjoy vitamin D-fortified foods such as low-fat milk, cereal, and orange juice.

Published Nov. 10, 2005.


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