Sleep disorders such as apnea may be linked to the development of Alzheimer's disease, according to a recent study The Washington Post reported.

Researchers from the University of California at San Francisco found that sleep disturbances may increase the risk of Alzheimer's disease. Another study suggests that moderate exercise in middle age and mentally stimulating games, such as crossword puzzles, can prevent its onset.

"I would say that this another important study showing this link between sleep and subsequent diagnosis of dementia," Kristine Yaffe, a psychiatry professor at the University of California at San Francisco, which conducted the study, told the Post.

For the study, researchers collected and analyzed data from nearly 200,000 veterans. They found that those with diagnosed disorders such as sleep apnea or insomnia were 30 percent more likely to suffer dementia than veterans without such problems. Veterans who suffered from sleep problems and post-traumatic stress disorder had an 80 percent greater risk.

In a separate study, researchers at the Wisconsin Alzheimer's Institute and the Wisconsin Alzheimer's Disease Research Center collected data from more than 300 middle-aged people. Forty percent of the subject group carried the gene linked to Alzheimer's and 74 percent had a parent with the illness, two factors known to increase the risk of getting the disease.

The study participants were asked questions about how often the participants read books, visited museums, played games such as checkers or worked on puzzles. They also underwent MRI brain scans to measure the volume of those regions commonly afflicted by Alzheimer's, the Post reported.

The research team found that those who reported a higher frequency of playing games also had greater brain volume in regions affected by Alzheimer's, such as the hippocampus. This finding suggests that stimulating the brain with ordinary diversions such as crossword puzzles may help some people preserve brain tissue and cognitive functions that are vulnerable to dementia.

"The more they play these types of games, the better it is for. . . brain health," Stephanie Schultz, lead author of the study, told the Post.

The findings -- which are set to be released during the six-day Alzheimer's Association International Conference in Copenhagen -- add to previous studies that suggest sleep plays a critical role in the aging brain's health.