Most of us can think of dozens of reasons not to exercise. You’re already tired; how can

summon the energy to move more? It takes time out of a busy day. It’s cold out. It is too hot. Your knee hurts.

Study after study shows that exercise combats depression. It lifts your mood, restores your energy, realigns your brain chemistry -- and the price is unbeatable. It costs nothing. Physical activity works at least as well against mild to moderate depression as any other treatment.

Exercise also changes your perception of yourself. It provides a sense of personal mastery and positive self-regard.

We’re not talking here about Olympian levels of activity. When it comes to alleviating depression, it’s not at all necessary to go for the burn. All it takes is 30 minutes of aerobic exercise three times a week. That means walking. Researchers at Duke University have found that 50 minutes of exercise a week brings about a 50 percent decrease in the likelihood of being depressed.

Now, comes new news of what exercise can do. It boosts blood flow to the brain, which allows you to be more mentally engaged. Exercise not only gives you physical energy, it boosts your mental energy. It makes you more alert. These benefits, need I point out, are aside from the ability of exercise to protect the heart and balance body weight.

Exercise also lowers the risk of hypertension and strokes and significantly decrease the incidence of Alzheimer disease that affect 50% of women and one third of men after the age of 85.

Statistically, we have a very high chance of living till we are a hundred, but would you like to be blind or unable to recognize your grandchild when you are older or do you want to be vigorously defending your ideas and sharing your wisdom and life experiences with them. One make you want to die early and one makes you want to be old.

So, do yourself and your brain a favor. Go out for a walk.