Michael Craig Miller, M.D., is editor-in-chief of the Harvard Mental Health Letter and an assistant professor of psychiatry at Harvard Medical School. Dr. Miller has an active clinical practice and has been on staff at Beth Israel Deaconess Medical Center for more than 25 years.

Question:

My husband is experiencing increasing forgetfulness over simple things. He has had his thyroid tested (no problems). He doesn't get enough rest and he's under a lot of stress. He doesn't exercise either, and he's a bit overweight. Could these issues be contributing factors?

Answer:

All in all, forgetfulness is a very common problem as we get past 50. When it comes to encoding new memories, our brains tend to get less nimble as we age.

The good news is that over time our brains do get better at putting things in perspective — that is, the parts of our brain that make us wiser become better organized. So there is actually a biological basis for the consolation of getting "older, but wiser."

The brain, however, is very sensitive to general health. A healthier body generally means a healthier and better-functioning brain.

Stress, lack of sleep and lack of exercise could certainly contribute to memory troubles.

Stress, at the very least, is distracting. If you are distracted, you can't pay attention, and you have to be able to pay attention to "encode" or acquire new memories.

Exercising improves memory function and, as a bonus, mood. It actually appears to make the brain function better. Nerve cells become healthier and are better able to make the kinds of connections to one another that support memory and mood.

Sleep researchers have learned in recent years that a good night's sleep is very important for consolidating memories.

So it turns out that lifestyle changes — getting regular exercise and sleeping eight hours per night — can reduce stress, and improve memory and mood.

It's tough to get motivated when you're stressed, of course. People tend to cut back on sleep and exercise if they feel the pressure to get things done. But for most people, that's counterproductive. Exercise and sleep usually help people use their time more efficiently and productively. They'll feel better too.