Dementia: The Risk

by Sherisse Pham

The causes of Alzheimer’s and some other forms of dementia remain incompletely understood, and the flood of research can leave the impression that everything and nothing causes the diseases. Although the list of risk factors changes constantly, several have been isolated as significant predictors of disease.

Some risks may lie within our control. Researchers strongly suspect that behavior and environment influence the development of dementia, though they have not been able to prove it. In fact, an independent government panel advising the National Institutes of Health surprised scientists recently by concluding that there’s insufficient evidence to prove that variables like exercising, quitting smoking, or eating a Mediterranean diet lessen dementia risk. The panel called for continuing research.

Nevertheless, there remains compelling scientific evidence on these fronts: Smoking drives up risk, and current smokers appear more at risk than people who’ve already quit — possibly because smokers are more likely to develop vascular disorders, which affect blood flow to the brain.

Alcohol also affects risk, both increasing and decreasing it. Drinking large amounts of alcohol increases the likelihood of dementia. But people who drink in moderation — roughly half a glass of wine with a meal — are at lower risk than either those who drink excessively or those who don’t drink at all.

Strong evidence also suggests that exercise significantly reduces the risk of vascular dementia and helps prevent other kinds of cognitive loss as well. For inactive elderly individuals who don’t have dementia, Karen Miller, neuropsychologist at the UCLA Memory and Aging Center, recommends walking at least 15 minutes each day. Since diabetes, hypertension, and stroke are also associated with higher dementia risk, doctors and researchers almost universally recommend a healthful lifestyle. “What’s good for your heart is good for your brain,” Miller says.

But many risk factors are beyond our control, the most dangerous being the simple passage of time. Age is the greatest known factor in developing some types of dementia, notably Alzheimer’s, and the affected population will balloon as lifespan increases and the percentage of elderly Americans rises.

Genetics also play a significant role in developing Alzheimer’s. Researchers have identified several genes associated with vulnerability to the disease; the most widely cited is the apolipoprotein E gene, or APOE. APOE comes in several forms, or alleles. The one called E4 is strongly linked to risk, yet many people with E4 never develop the disease. Though blood tests can identify APOE alleles, predicting early in life who will or won’t develop Alzheimer’s is not yet possible.

In 2007, a team led by neurologist Richard Mayeux at Columbia University named another gene, the sortilin-related receptor SORL1, as genetically associated with Alzheimer’s. As with APOE-E4, its relationship with the disease is murky. Mayeux’s team determined there are changes in the gene. “And these changes are associated with the disease,” says Mayeux, “but we don’t understand what that specific change is.”

Family history clearly plays a role. Close relatives of people who develop Alzheimer’s after age 60 are four to ten times likelier to develop the disease. “Risk is particularly high when a parent is affected,” says Lisa Mosconi, a New York University psychiatrist. Adult children of mothers with Alzheimer’s appear to be at higher risk than those fathers have the disease, she adds.

Elderly Hispanics and African-Americans also face higher risk for Alzheimer’s and dementia than Caucasians. Researchers believe genes play a role, although the higher prevalence may also be attributed to such socioeconomic differences as lower education levels, greater stress and poorer nutrition. “Both African Americans and Hipanics have more heart disease, have more diabetes,” says Mayeux. “That’s at least one factor that may contribute to their increased risk.”

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