Last year, I changed my recommendation for vitamin D and began encouraging everyone to supplement with at least 1,000 IU a day, up from the 400 to 800 IU I’d previously advised. I made this change because I had become convinced that people aren’t getting enough of this nutrient for optimum health. Since then, evidence has continued to accumulate that vitamin D offers a tremendous variety of health benefits beyond its most well known one, building bones. These helpful effects range from preserving muscle strength and preventing falls to protecting against cancer and autoimmune disease.
Sometimes called the “sunshine vitamin” because your skin produces it when exposed to sunlight, vitamin D is actually a hormone. It’s also in some foods, including oily fish (like salmon and sardines) and fortified milk, soy milk, orange juice, and cereals. Vitamin D allows your bones to take up calcium, but there are receptors for this hormone all over the body, including the brain, heart, breast, prostate, and immune cells. This helps to explain why vitamin D has such widespread effects.
The body’s ability to manufacture vitamin D declines significantly with age, so older people are more likely to be deficient. Also at high risk are individuals with dark skin (which produces less vitamin D in response to sunlight) and those who live in northern climates and spend winters mainly indoors. Obesity also increases the risk of vitamin D deficiency because it’s stored in body fat, making the nutrient less available for use by other tissues.
Benefits Beyond Bone Health
You’re probably already aware that vitamin D is helpful for preventing and treating osteoporosis and osteopenia. Here I’ll discuss several benefits that are less well known, with help from Walter Willett, MD, chairman of the Department of Nutrition at the Harvard School of Public Health, who has coauthored numerous studies on the vitamin.
Muscle weakness and falls.
Vitamin D deficiency has been linked with muscle weakness, and a study of some 4,000 adults aged 60 to 90 found that those with higher blood levels of vitamin D had stronger leg muscles and better mobility (American Journal of Clinical Nutrition, September 2004). Vitamin D’s muscle-strengthening effects may explain why it helps prevent falls: An analysis of five studies concluded that supplementing with vitamin D reduces the risk of falls by more than 20 percent; daily doses of 700 to 800 IU were more protective than 400 IU (Journal of the American Medical Association, April 28, 2004).
Vitamin D helps regulates cell growth and may lower the risk of many cancers. A new review of 63 previous studies concludes that taking 1,000 IU of vitamin D a day can cut the risk of colon cancer by 50 percent and reduce the chances of breast and ovarian cancer by 30 percent (American Journal of Public Health, February). Also, a study of men in San Francisco revealed that those with the highest amount of sun exposure had half the risk of prostate cancer than those with little sun exposure (Cancer Research, June 15, 2005). At least a dozen studies are now under way to test vitamin D’s effectiveness at cancer prevention.
There’s also evidence that vitamin D may improve the prognosis of cancer patients. In one study, people who had surgery for early-stage lung cancer in the summer (when their production of vitamin D from sunlight would be highest) and also had the highest intake of vitamin D from food and supplements were more than twice as likely to surpass the five-year survival mark as those who had winter surgeries and the lowest intake of vitamin D (Cancer Epidemiology, Biomarkers & Prevention, October 2005). Other researchers are looking at vitamin D as a potential treatment for prostate cancer.
Blood pressure tends to be higher during the winter and in people living farther from the equator or with dark skin—all of which are associated with lower production of vitamin D from sun exposure. Recent studies in Europe found that elderly people with low blood levels of vitamin D were more likely to have a stroke, and a German study suggests low levels of the nutrient may contribute to the development of congestive heart failure (Journal of the American College of Cardiology, January 1, 2003).
Vitamin D also helps to regulate immunity. Multiple sclerosis (MS) and other autoimmune disorders—in which immune responses are directed against the body’s own tissues—are much less common near the equator, where people get more sunlight and produce more vitamin D. Supplementation also appears to be protective: Women who took at least 400 IU of vitamin D per day were 40 percent less likely to develop MS (Neurology, January 13, 2004) and one-third less likely to develop rheumatoid arthritis (Arthritis & Rheumatism, January 2004). In other research, infants given vitamin D supplements had a lower risk of type 1 diabetes, another autoimmune disorder.
More evidence suggests women with the highest intake of vitamin D from food and supplements (about 700 IU per day) have a 40 percent lower risk of developing PMS than those with the lowest intake (Archives of Internal Medicine, June 13, 2005). Higher blood levels of vitamin D were recently linked with better lung function (Chest, December 2005) and a lower risk of gum disease (American Journal of Clinical Nutrition, September 2005). And an unpublished study suggests that women who get the most vitamin D from food and supplements are about 25 percent less likely to develop type 2 diabetes.
Getting Enough Vitamin D
If you can get vitamin D from sunlight and food, why bother with supplements? For one thing, excessive sun exposure can cause skin cancer. Although sunscreen can help protect your skin, it also blocks vitamin D formation. I think it’s fine to get moderate sun exposure—10 or 15 minutes without protection a few days a week—in order to boost vitamin D production. But I would still recommend supplementing with 1,000 IU of vitamin D a day as insurance.
As for food, it’s difficult to get enough vitamin D from diet alone: You’d have to eat two or three servings of salmon a day or drink 10 glasses of fortified milk to get 1,000 IU of the vitamin. Recently, a bakery in Wisconsin (naturalovens.com) developed a whole-grain bread with 1,000 IU of D per slice and dark chocolates that deliver 2,000 IU per piece, but these highly fortified products are being marketed as dietary supplements.
To get at least 1,000 IU of vitamin D from pills, you have a few options. You can take an isolated vitamin D supplement. Or you can take a multivitamin (most contain 400 IU of D) plus a vitamin D supplement to make up the difference. Or women can take a multivitamin plus supplements that combine calcium and vitamin D. (Men are probably better off getting calcium from food, because some research suggests a high intake of calcium may increase prostate cancer risk.)
Look for supplements containing the D3 (cholecalciferol) form of vitamin D, which is better utilized than the D2 (ergocalciferol) form. Because vitamin D is fat soluble, take it with a meal containing some fat to enhance absorption.
although cod liver oil (available as a liquid and in gelcaps) is rich
in vitamin D, I’m wary of recommending it. Many products are so high in
vitamin A that toxic amounts could build up in your system.
For more on the health benefits of vitamin D, visit cholecalciferol-council.com.
D is Key to Using Calcium
Vitamin D may be more important than calcium for bone health, suggests a recent study. Researchers in Iceland analyzed levels of parathyroid hormone (PTH), which regulates calcium metabolism, in 944 healthy adults. They found that higher blood levels of vitamin D were more closely associated with normal levels of PTH than a high calcium intake. They concluded that getting more than 800 mg of calcium a day from food and supplements may be unnecessary as long as vitamin D levels are normal (Journal of the American Medical Association, November 9, 2005). To me, this study shows that the main issue with calcium is absorbing it and using it, rather than not getting enough in. Vitamin D is the key to absorbing and using calcium.