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Sun Exposure and Vitamin D Debate: How much is enough?

sept07-sunworshipper.jpgby Kevin S. Liu, M.D.

Question
On the matter of sun exposure as an important source of vitamin D, what level of light intensity is most desirable? And what’s the most sensible approach to getting sun?

— Sterling, New York

Answer
This topic has received quite a bit of coverage in the last several years, as experts have tried to decide just what to recommend. It is true that sunlight exposure provides a good source of vitamin D. However, it’s important to understand a few points about that very issue.


HOW VITAMIN D IS MADE

The skin contains a chemical that changes into an inactive form of vitamin D upon exposure to ultraviolet radiation, type B. The liver and kidneys then convert it into an active form.


How Much Vitamin D Do You Need?

Though there’s controversy over whether these guidelines are adequate, the Institute of Medicine (IOM) currently recommends that people up to age 50 get 200 international units of vitamin D through diet daily. Those 51 to 70 should get 400, and people 71 and older should get 600. A few good sources:

  • Cooked salmon, 3 1/2 ounces: 360 IU
  • Cooked mackerel, 3 1/2 ounces: 345 IU
  • Vitamin-D-fortified milk, 1 cup: 98 IU
  • Egg, one whole (vitamin D is in the yolk): 20 IU

Source: Dietary Supplement Fact Sheet: Vitamin D, National Institutes of Health Office of Dietary Supplements


HOW MUCH SUN DO YOU NEED?
Most fair-skinned people produce their maximum levels of vitamin D after just a few minutes of direct sunlight. So one idea is to expose as much skin as possible to midday sun (when UVB is most prevalent) for about 10 to 15 minutes, using no sunscreen. The elderly and people with darker complexions require longer.

As you might imagine, dermatologists don’t like this idea since sun exposure also increases your risk for skin cancer and causes your skin to age more quickly. And anyway, that brief amount of sun still isn’t enough to produce ample vitamin D on cloudy or smoggy days. (Window glass also blocks UVB rays.)

However, other experts are concerned that food alone doesn’t yield enough vitamin D to keep you from being deficient.


THE COMPROMISE: SUN AND FOOD FOR VITAMIN D
As a compromise, many currently recommend exposing your hands, face and arms to direct sunlight for about 10 to 15 minutes a day, three times a week, using no sunscreen. In addition to that, get more vitamin D through supplements and/or foods, such as vitamin-D-fortified orange juice and milk.


KEVIN S. LIU, M.D.,
is a member of our print magazine editorial board and a board-certified family doctor in Keller, Texas.

Last updated and/or approved: March 2010. Original article appeared in summer 2007 former print magazine. Bio current as of summer 2007. This article is not meant as individual advice. Please see our disclaimer.

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