By Mary Brophy Marcus, USA TODAY

Improved living and diet habits - including lots of  physical activity, regular tea-drinking and sufficient vitamin D levels - could reduce the risk of brain decline, according to three studies presented Sunday.

"These are encouraging," says William Thies, chief medical and scientific officer of the Alzheimer's Association. "These types of studies make people think, 'Well gosh, maybe I can do something about this disease.' "

The studies were presented at the Alzheimer's Association International Conference in Honolulu.

One of the studies is from the Framingham, Mass., cardiovascular risk study, in which researchers from Brigham and Women's Hospital in Boston, among others, tracked more than 1,200 elderly people over 20 years, 242 of whom developed dementia.

The researchers found that participants who had moderate to heavy levels of physical activity had about a 40% lower risk of developing any type of dementia. Those who reported the least amount of activity were 45% more likely to develop dementia compared with those who logged higher levels of activity.

In a second study, including data on more than 4,800 men and women ages 65 and older, participants were followed for up to 14 years. Tea drinkers had less mental decline than non-tea drinkers. Those who drank tea one to four times a week had average annual rates of decline 37% lower than people who didn't drink tea.

Coffee didn't show any influence except at the highest levels of consumption, researchers say. Author Lenore Arab of UCLA says, "Interestingly, the observed associations are unlikely to be related to caffeine, which is present in coffee at levels two to three times higher than in tea."

In a third study, British researchers looked at vitamin D's effect on brain health. They examined data from 3,325 U.S. adults ages 65 and older from the NHANES III study. Vitamin D levels were measured by blood test, and cognitive tests were administered. Odds of cognitive impairment were about 42% higher in those deficient in vitamin D, and 394% higher in people severely deficient.

"Vitamin D is neuro-protective in a number of ways, including the protection of the brain's blood supply and the clearance of toxins," says author David Llewellyn of the University of Exeter Peninsula Medical School.

"More and more studies are suggesting that lifestyle changes may be able to silence the expression of risk genes, a phenomenon called epigenetics," says Duke University's Murali Doraiswamy, an expert on aging. He says learning how to tap into that is going to be a high priority.