Staying active is a key to a vigorous, healthy body as we grow older. But exercise is just as important for mental health. Walking, biking or swimming helps keep your memory and reasoning ability sharp and your mood bright while it strengthens your heart, arteries — and muscles.

Like every organ, the brain requires a steady supply of oxygen and nutrients to maintain vigor. A sound mind needs a healthy body, and a healthy body needs exercise. Heart disease, diabetes and other illnesses can have a devastating effect on the brain, and exercise cuts the risk that you’ll get them.

In recent years, scientists have learned a lot about what happens inside the brain when we think, form memories and learn new things… and what determines whether our moods are up or down. They’ve found solid evidence that exercise — even a modest amount — can have a positive effect on biological events within the brain cells themselves.

YOUR GROWING BRAIN

Not that long ago, everyone believed that after maturity, no new brain cells were born — your supply of several hundred billion declined gradually but inexorably with advancing years. Now we know that like other parts of the body, the brain constantly renews itself, generating blank cells that, under the right circumstances, can turn into thinking, functioning tissue.

At work are naturally occurring chemicals called growth factors. They are produced by the brain itself and by blood vessels and muscles. They act like fertilizer on a flowerbed, stimulating new brain cells to grow and new blood vessels to support them.

Brain cells are constantly dying, succumbing to a mix of toxins and overstimulation called molecular stress. With age, the balance shifts — growth factors decline, along with the cells’ ability to withstand stress. After age 40, we lose 5% of our brain cells per decade, on average. The network of capillaries feeding the brain withers.

Nothing can stop the effects aging has on the brain, but exercise can dramatically slow it down. Animal experiments have shown that exercise boosts growth factors and the number of new brain cells produced. Other studies found that when animals were active, their brains worked better — exercise increased their ability to learn new things.

KEEP YOUR MENTAL EDGE

There’s evidence that just a modest amount of exercise can have a powerful antiaging effect on the human brain.

A study at the University of Illinois divided 59 sedentary people aged 60 to 79 into groups that did one hour of stretching three times a week, or had sessions of aerobic exercise (activity that gets your heart rate up and keeps it up) for the same amount of time. After six months, magnetic resonance imaging scans found that brain volume had increased in the aerobic exercisers — the frontal and temporal lobes, which are involved in thinking, decision-making and learning, had actually grown bigger.

These results “suggest a strong biological basis for the role of aerobic fitness in maintaining and enhancing central nervous system health and cognitive functioning in older adults,” the researchers concluded.

Looking at actual performance on tests of mental ability, scientists have found that a regular aerobic program can apparently push back age-linked decline in brain function by seven to 10 years.

Exercise also protects against the worst brain-killers of all — diseases such as Alzheimer’s and Parkinson’s. Besides generally strengthening brain circuits, it helps keep arteries healthy and blood sugar under control, cutting the risk for dementia.

IMPROVE YOUR MOOD

Low moods can strike no matter how old you are, but the stresses and losses that frequently come with age — illness, ending a career, retiring to an unfamiliar place — make depression a special danger. Biology also plays a role. The neurotransmitters that carry messages between brain cells dwindle as the years pass. Low levels of these chemicals — serotonin, dopamine and norepinephrine — are associated with depression, and antidepressants appear to work by raising them.

Exercise stimulates neurotransmitter production and can battle depression as effectively as medication. In a Duke University study, an aerobic program proved as potent as the antidepressant Zoloft in relieving depressive symptoms.

You needn’t be clinically depressed to benefit. The neurotransmitter boost of exercise raises mood, increases motivation and can charge up anyone’s zest for life.

AEROBICS AND BEYOND

Your goal should be to get some physical activity nearly every day. But, especially if you’ve been sedentary, get there slowly. The good news is that noticeable benefits start at a much lower level — with as little as an hour a week of exercise.

Important: Check with your doctor before starting any exercise program.

Aerobic exercise appears to be the most beneficial to the brain. Swimming, biking and jogging are good, but for most, brisk walking is perfect.

How hard you should work out: To calculate your “maximum heart rate,” subtract your age from 220. Your goal is walking (or doing another activity) strenuously enough to get your pulse up to 60% to 65% of maximum. Vary your workouts from 30 minutes to an hour, four days a week.

After you’ve become used to exercising, pick up the pace — go for 70% to 75% of maximum for 20 to 30 minutes, then back down to 60% to 65% — during two of the four workouts.

Keep it interesting. Many find that walking is more stimulating out of doors. Team up with a friend so that you can motivate each other and add the pleasures and benefits of social interaction. Variety spices up routine. If you have access to a health club or gym, try the treadmill, exercise bike or elliptical trainer.

Strength training: The brain benefits of strength training (with weights or resistance machines) haven’t been researched as thoroughly as those of aerobics, but it’s well worth the effort anyway — to counter the muscle deterioration that otherwise comes with age. Try to include strength training in your workouts twice a week. If you’re new to it, have a personal trainer design a program for you.

FEED YOUR BRAIN

The same diet recommended for general good health maintains the strong circulation and metabolic balance that protect your brain — lots of fruits, vegetables and whole grains, abundant fiber and limited fats. Particularly beneficial…

  • Berries, broccoli, spinach, beets, garlic and onions, green tea and red wine. These contain antioxidants and other nutrients that activate cellular repair.
  • Omega-3 fatty acids — the kind found in fish — have been linked to a host of health benefits and seem especially vital for brain vigor. The Framingham Heart Study found that a diet with the omega-3s found in three servings of fish weekly cut dementia risk in half. If you don’t like fish, take a daily supplement that includes EPA and DHA, the key fatty acids.