Vitamin D: a bright spot in nutrition research

Too little of the sunshine vitamin linked to heart disease, statin-related muscle pain, other conditions.

Heart disease. Falls and broken bones. Breast and prostate cancer. Depression and memory loss. These problems seem to have nothing in common, except that they are leading causes of faltering health and death. Exciting research suggests there is a link — too little vitamin D, the so-called sunshine vitamin, can contribute to all of these.

Millions of Americans, especially older ones, don't have enough vitamin D in circulation. Current national recommendations for daily vitamin D intake — 400 international units (IU) for those aged 51 to 70 and 600 IU for those older than 70 — may not be high enough to reverse this trend.

Making vitamin D

Vitamin D isn't really a vitamin. It is a hormone the body makes in assembly-line fashion. Sunlight striking the skin converts a cousin of cholesterol into pre-vitamin D. As this circulates through the bloodstream, the liver turns it into biologically inactive 25-hydroxyvitamin D. (This is what is measured to determine your vitamin D status.) The kidneys then supply a small chemical tweak, creating the active vitamin D that can affect cells throughout the body.

The amount of 25-hydroxyvitamin D you have in circulation depends on how much sunshine you get, your skin pigmentation (darker skin reduces vitamin D production), your diet (salmon and other fatty fish are rich in vitamin D), and your age (the older you are, the less vitamin D your skin makes).

Experts have defined three categories for vitamin D status: deficient, less than 20 nanograms of 25-hydroxyvitamin D per milliliter of blood (ng/mL); insufficient, from 20 to 30 ng/mL; and sufficient, above 30 ng/mL.

Surveys suggest that at least one-third of American adults, and 75% of adults with cardiovascular disease, fall into the deficient category.

Widespread effects

Vitamin D is best known for helping the digestive system absorb calcium and phosphorus. That's one way it helps build and maintain healthy bones. But it does much, much more.

Coronary artery disease. Deposition of calcium in arteries, a process that stiffens arteries, is more likely to happen in people who are low in vitamin D. In the Harvard-based Health Professionals Follow-up Study, men low in vitamin D were twice as likely to develop heart disease as those with plenty of the vitamin in circulation.

High blood pressure. Active vitamin D decreases the kidneys' production of renin, a hormone that boosts blood pressure. Several studies suggest that low vitamin D contributes to high blood pressure, and that getting more of the vitamin can help control blood pressure.

Heart failure. Most people with heart failure are deficient in vitamin D. Getting more could help strengthen heart contractions.

Statin-related muscle pain. Some people who take a cholesterol-lowering statin stop because of muscle pain. In a study of 128 men and women with statin-related muscle pain, two-thirds of them had 25-hydroxyvitamin D levels under 20 ng/mL. Among those who took a vitamin D supplement while continuing the statin, muscle pain disappeared in 90%.

Infection. Preliminary trials suggest that too little vitamin D can leave the body prone to infection, and having enough in circulation can help the body fight off the flu, tuberculosis, and infections of the upper respiratory tract.

And more. A deficiency in vitamin D has been linked to some types of cancer, type 2 diabetes, depression, osteoporosis, falls, asthma, memory loss, and other chronic conditions.

Getting more D

Food is usually the best way to get vitamins. That's not so for vitamin D. Only a few foods — salmon, tuna, sardines, milk, and fortified cereals — can give you more than 100 IU per serving.

Sunlight is an efficient way to get more vitamin D. Many people can make all they need by getting outside for five to 10 minutes a day without sunscreen. Keep the exposure short because the rays that stimulate vitamin D production are the same ones that, with prolonged exposure, cause sunburn and skin cancer. If you live north of a line connecting San Francisco with St. Louis and Richmond, Virginia, don't bother doing this between November and March — the amount of ultraviolet light hitting your body won't be enough to generate vitamin D.

Supplements are the simplest, safest way to get vitamin D. Multivitamins usually contain 400 IU of vitamin D. Some calcium supplements come with added vitamin D. You can also buy vitamin D by itself. Getting 800 to 1,000 IU from supplements is a good goal.

It makes sense to ask your doctor to test your vitamin D level, and to take a supplement if it is in the deficient or insufficient range. To check your vitamin D status yourself, join Grassroots Health (www.grassrootshealth.org), a nonprofit organization that focuses on vitamin D. For a $40 membership fee, you'll get information on vitamin D and a home test kit.