Vitamin D: Are You Getting Enough?

What do you think of when you think of vitamin D? Osteoporosis? Rickets? The sun? How about colon cancer? High blood pressure? Muscle aches? Multiple sclerosis?

The truth is, vitamin D, more commonly known as the "sunshine vitamin" because sunlight provides our greatest source, may be one of the most important vitamins we know of in terms of long-term health. Unlike other nutrients, it acts more like a hormone than a vitamin, directly affecting genes responsible for controlling nearly every aspect of a cell's development. Low levels put women at risk of numerous health problems, including osteoporosis, colon cancer, high blood pressure, multiple sclerosis, lupus, type 1 diabetes, schizophrenia, depression and infectious diseases like colds and the flu. Vitamin D helps immune system cells destroy the bacterium that causes tuberculosis, increases production of insulin and enables heart cells to contract. Low levels may even be a risk factor for preeclampsia, a potentially fatal condition that occurs in late pregnancy. In fact, nearly every cell in the body expresses receptors for vitamin D, meaning the vitamin plays some role in the normal activities of that cell.

If women maintained high levels of vitamin D, they could reduce their risk of breast cancer as much as 50 percent; colorectal cancer up to 253 percent; and heart disease, stroke and peripheral artery disease more than 100 percent, says vitamin D expert Michael F. Holick, MD, PhD, of Boston University Medical Center. In one of the few studies to look at the direct benefits of vitamin D supplementation on disease, 18 people with hypertension exposed to ultraviolet B light three times a week for up to 10 minutes at a time for three months not only increased their vitamin D levels about 180 percent, but reduced their blood pressure to normal levels.

Unfortunately, D is not an easy vitamin to get these days. We've been trained to avoid the best source (the sun) by covering our body and using sunscreen. Even if you skip the sunscreen, it's nearly impossible to get enough D from sun exposure between October and April, no matter where you live, said Dr. Holick. The only good dietary source—wild-caught (not farmed) oily fish like salmon and mackerel—is expensive and often high in mercury.

That's why an estimated 50 percent or more of the world's population have a vitamin D deficiency. In the United States, 42 percent of African-American girls and women ages 15 to 49 and about 35 percent of all women ages 20 to 69 have low blood levels of vitamin D. Overall, women are more than twice as likely as men to have low levels of this important vitamin.

How to Get More Vitamin D

The Institute of Medicine (IOM) recently raised its recommended daily level of vitamin D to 600 international units (IUs) for anyone up to 71 years old, including children, and as much as 800 IUs for those 71 and older. Dr. Holick and some other experts think children and adults should have blood levels of 30 ng/ml (nanograms per milliliter). To get there, he recommends that everyone supplement with 1,000 IUs a day. You should always tell your health care professional about any supplements you take. Extreme levels of vitamin D can damage the kidneys and heart and may be associated with other chronic diseases and even death. The IOM established maximum safe levels of vitamin D at 2,500 IUs per day for children ages 1 through 3; 3,000 IUs daily for children 4 through 8 years old; and 4,000 IUs daily for all others.