What Aging Can Bring: Forgetfulness, decline in mental agility, risk of Alzheimer’s disease.

What the Research Shows: “Cross-training, by doing things that hit both the left and right sides of the brain, like word puzzles plus mazes and visuals, has been proven to build brainpower,” says Gary Small, M.D., director of the University of California at Los Angeles Center on Aging and author of The Memory Prescription (www.barnesandnoble.com, Hyperion, $17). Swedish researchers believe there’s also a connection between physical activity and cognitive decline. Their study found that subjects who exercised at least 20 minutes two or more times a week at midlife reduced their risk of developing Alzheimer’s and other forms of dementia later by 60 percent. On the nutrition front, a study at the Louisiana State University Health Sciences Center showed that an essential omega-3 fatty acid counteracts the brain’s production of neuron-damaging amyloid proteins.

What You Can Do: Challenge yourself both mentally and physically; as little as 10 minutes of exercise a day may lower your risk of Alzheimer’s, says Small. Eat antioxidant-loaded foods, such as almonds, leafy greens, and blueberries; and if you don’t eat enough fatty fish rich in omega-3 acids, like salmon (at least two servings a week), ask your doctor about taking a daily 1,000-milligram fish-oil supplement.