6 Common Myths About Aging

For instance, studies on the brains of elderly people with and without dementia find significant blood vessel damage in those with hypertension. Such damage shrinks the amount of healthy brain tissue you have in reserve, reducing the amount available if a disease like Alzheimer's hits, Dr. Powers says. That's important, he says, because we're starting to understand that the more brain function you have to begin with, the more you can afford to lose before your core functions are affected.

One way to dodge the dementia bullet? Exercise your body and your brain. Physical activity plays a role in reducing the risk of diseases that cause Alzheimer's. It also builds up that brain reserve. One study found just six months of regular physical activity increased brain volume in 59 healthy but couch-potato individuals ages 60 to 79. Other research finds people who exercised twice a week over an average of 21 years slashed their risk of Alzheimer's in half.

Then there's intellectual exercise. "I encourage regular intellectual stimulation," says Dr. Powers. It doesn't matter what kind, just that you break out of your comfort zone. Even writing letters twice a week instead of sending e-mail can have brain-strengthening benefits, he said. That's because such novel activities stimulate more regions of the brain, increasing blood flow and helping to not only build brain connections, but improve the health of existing tissue.

2. Myth: If you didn't exercise in your 20s, 30s and 40s, it's too late to start in your 50s, 60s or 70s.

Fact: It's never too late! In an oft-cited study, 50 men and women with an average age of 87 worked out with weights for 10 weeks and increased their muscle strength 113 percent. Even more important, they also increased their walking speed, a marker of overall physical health in the elderly.

3. Myth: Sex ends when you age.