The trouble is, most of us—53 percent of women, 41 percent of men, and 61 percent of kids—have insufficient levels. Though our bodies naturally produce the vitamin from the sun's UV-B rays, these days we don't absorb nearly enough sunlight to manufacture an adequate amount—and during winter, most of the country gets so little sun, doing so is impossible. But don't sweat it: With a few easy moves, you can boost your D levels. We've gathered the latest info on the vitamin everyone's suddenly talking about.
High levels of vitamin D are linked to...
High levels are linked to...
Greater resistance to viruses
During a recent study, researchers at the Yale University School of Medicine discovered that people with high levels of vitamin D got sick about half as often as people with low levels. And when they did fall ill, they recovered in fewer days. The reason: Vitamin D instructs your white blood cells to manufacture a protein that kills infections.
Specifically, a 30 to 50 percent lower chance of breast cancer, and a 50 percent lower chance of colon cancer. D regulates some of the genes responsible for cellular growth and survival, says Holick, and it does its job cleverly: "It helps shut down any out-of-control growth to prevent malignancy. If that doesn't work, it will help kill the cell. And if a tumor grows anyway, it will work to cut off blood supply."
Higher cancer survival rate
At the Dana-Farber Cancer Institute, researchers found that colon cancer patients with high levels of D had a 39 percent lower chance of dying from the disease. And this might actually apply to all cancers, says Edward Giovannucci, MD, ScD, professor of nutrition and epidemiology at the Harvard School of Public Health.
Reduced risk of Parkinson's
Researchers believe the correlation, which Archives of Neurology reported in July, may have to do with D's protective effect on the brain: It regulates calcium levels, enhances the conduction of electricity through neurons, and detoxifies cells, among other handy functions.
Low levels are linked to...
Low levels are linked to...
People with insufficient D levels have an 80 percent greater risk of narrowing of the arteries, according to a long-term study at Johns Hopkins. This might have to do with D's role in regulating more than 200 genes and controlling inflammation, and its possible involvement in modulating blood pressure.
Since D stimulates insulin production, it's no surprise that too little is associated with diabetes. Research has also shown that kids who are deficient in D have a 200 percent greater chance of developing type 1.
A 2008 study showed that more than 25 percent of chronic pain patients have low D levels, which could be because D helps control neuromuscular function. And a 2010 study correlated low levels of the vitamin with migraines and headaches. A dearth of D may prevent blood vessels from constricting and dilating properly, which can lead to throbbing pain.
D may help stimulate serotonin production, which could explain why people who don't get enough are more susceptible to the blues.
Higher risk of death
After analyzing D levels of more than 13,000 people, researchers at Johns Hopkins found that those with the lowest levels had a 26 percent greater chance of dying—from any cause.
Next: 5 things that increase your risk of vitamin D deficiency