THE DETAILS: The researchers used participants of the Framingham Heart Study, a group of people whom medical scientists have been studying since 1948. They narrowed down the original 5,209 participants to a group of 949 adults, average age 79, who were free of dementia at the start of the study. Of the patients diagnosed with depression at the start of the study, tests given about nine years later showed that 21.6 percent developed dementia, compared with just 16.6 percent of people who were not depressed. The researchers also saw a 50 percent increase in the risk of developing dementia with each 10-point increase in score on depression tests administered at the start of the study. The risks were similar for Alzheimer's disease, for which there was a 40 percent increase in risk for each 10-point increase in depression score. For both dementia and Alzheimer's disease, depressed adults were 1.5 times more likely to develop one of the two diseases than nondepressed adults.
WHAT IT MEANS: "Depression needs to be taken very seriously," says the study's lead author Jane Saczynski, PhD, assistant professor of medicine at the University of Massachusetts Medical School. "It's a very serious medical condition that is known to be related to other medical conditions." But what her study can't show, she says, is whether depression causes dementia, whether it's a risk factor, or whether people who have depression have some other sort of chemical imbalance that turns up as dementia later in life. But it's becoming more and more obvious that the two are linked.
In the same issue of Neurology, two other studies examined the relationship between the two disorders. One of the two additional studies found that a single depressive episode was associated with an 87 to 92 percent increased risk of dementia and that two depressive episodes doubled the risk. The second study focused more on the "cause and effect" question, and found that depressed adults who ultimately fell prey to Alzheimer's disease scored the same on depression tests before and after their Alzheimer's diagnosis, suggesting that depression is not a cause of these disorders but an underlying factor.
"We're leaning more and more towards the theory that depression is a risk factor for dementia," says Saczynski. But treating the depression may not lower the risk. In Saczynski's study, she looked at a subset of people who were considered "depressed" based only on the fact that they were taking antidepressants. Those adults were just as likely to develop dementia as those not taking antidepressants. What Saczynski suggests is to modify lifestyle behaviors that can put you at risk for dementia, whether or not you're currently depressed.
Here are some ways to protect yourself from depression and dementia:
• Exercise. Research has shown that exercise can improve your ability to concentrate and carry out complex tasks, and a recent study found some evidence that aerobic activity can delay and possibly prevent Alzheimer's in people who are at highest risk for the disease. Other studies have found that even in people not at risk for Alzheimer's, exercise can improve cognitive function by up to 15 percent.
• Eat like the Greeks. Among the numerous benefits of the oft-touted Mediterranean diet, researchers are finding that it keeps your brain healthy. A study published last August in the Journal of the American Medical Association found that strict adherence to the diet (composed primarily of fish, fruits, vegetables, whole grains, nuts, beans, legumes, and very little meat or dairy) was associated with a 32 to 40 percent reduction in risk of Alzheimer's. Even following the diet to a lesser extent lowered one's risk by 2 to 14 percent.
• Get enough sleep. Sleep deprivation has a profound impact on the brain, including reducing short-term memory function, and that can have long-term effects on cognitive function and dementia. Keep your brain healthy by getting eight hours of sleep a night, or more if need be.
• Stay socially engaged. Social engagement, along with all of the aforementioned activities, wards off both dementia and depression, says Saczynski. Whether it's working after retirement or taking a dance class, remaining connected to your friends and family wards off loneliness, a major risk factor for dementia.