— Eva-Lotta Jansson/Corbis

Once relegated to a plain-jane role as calcium's helper in building strong bones, vitamin D has blossomed into a superhero among vitamins. The sunshine vitamin can boost the body's ability to ward off infections, contribute to a strong and healthy heart, help prevent several forms of cancer and protect against autoimmune diseases and diabetes.

But to reap these benefits older adults must have sufficient levels of vitamin D, and scientists caution that most don't get enough of this nutrient.

Why? With age, it becomes harder for the body to make vitamin D from sunlight, plus older adults stay inside more during daylight hours and protects themselves more from the sun. Often they fail to eat vitamin D-rich foods or take vitamin D pills. Judicious sun exposure, the right foods, and adequate supplements can bring levels up to where they should be.

Here is some recent research that underscores the importance of vitamin D.

• Protect your mind

A new British study found that low levels of vitamin D can cause problems with memory, attention, and logic. The researchers looked at data from more than 3,000 adults and found that those who were severely vitamin D-deficient were nearly four times more likely to perform poorly on tests of memory and attention.

Another British study had similar results. Compared with men and women who had sufficient levels of vitamin D, those who were severely deficient experienced a substantial decline in thinking and in the ability to organize thoughts, make decisions and plan ahead.

• Guard against heart disease

Research has targeted low levels of vitamin D as an independent risk factor for heart attack, stroke, and congestive heart failure even after accounting for age, blood pressure, and cholesterol levels, says Johns Hopkins University cardiologist Erin Michos, M.D.

Two recent studies from the Intermountain Medical Center Heart Institute in Utah show that correcting the deficiency may reduce the risk. In the first study, the researchers examined more than 9,000 people whose blood tests revealed low levels of vitamin D and who had a repeat test within a year. At that time nearly half of them had raised their vitamin D levels to what's considered normal. This group had much less heart disease than those whose levels were still below normal.

In the second study, the researchers divided the records of more than 40,000 people into three categories based on vitamin D levels: normal, moderately deficient, and severely deficient. As expected, patients with a severe deficiency were most likely to have been diagnosed with heart disease or stroke.

"The critical question now is whether vitamin D can actually prevent heart disease," says Michos. "We don't have a definitive answer yet."

• Ward off Parkinson's

In the first long-term analysis of the relationship between vitamin D and Parkinson's, Finnish researchers found that low levels of vitamin D increased the risk and high levels protected against the disease.

They tested blood levels of vitamin D in more than 3,000 men and women ages 50 to 79 who were free of the disease from 1978 to 1980 when the study began. Over the next 29 years, 50 in the group were diagnosed with Parkinson's. Those with the lowest levels of vitamin D were three times more likely to develop the disease than those with the highest.

• Bone up on bone health

A position paper of the International Osteoporosis Foundation says vitamin D can improve bone strength, reduce the risk of falling and help prevent fractures. "Supplementing with vitamin D is safe, well-tolerated, and inexpensive," says Tufts University's Bess Dawson-Hughes, M.D., lead author of the paper.

• Chase the blues away

The National Institute of Aging in Baltimore found women with low vitamin D levels experienced more mood declines compared with women who had sufficient D. And women with too little vitamin D who were not depressed at the start of the study were twice as likely to become depressed as those who had healthy levels.

• Stay active

Researchers at Wake Forest University measured levels of vitamin D in more than 2,600 older adults. Four years later the team found physical abilities — such as how quickly each participant could walk a short distance, rise from a chair five times or maintain balance — remained significantly better among those who had the highest vitamin D levels at the beginning of the study.

Nissa Simon, a health writer, lives in New Haven, Conn.