Walking can reduce the risk of anxiety by about 25% to 50% too. One study found that over 10 weeks, a physical activity regimen was as effective in reducing anxiety in patients as was standard anti-anxiety medication. Another found enhanced creativity after just one walking session.
Some studies suggest that longer bouts -- 30 minutes of walking each day versus three 10-minutes bouts -- bring about the greatest mood improvements.
How does it work? Scientists think that the well-exercised brain produces more opioids (such as endorphin) and is better able to use neurotransmitters (such as norepinephrine, serotonin and dopamine) -- all of which works to improve brain functioning in much the same way as antidepressant drugs.
Sleep: Future sleep troubles might be warded off by walking at least 11 minutes a day, one study suggests -- with greater benefits for even longer stints. Another found that sedentary people who sleep poorly who tried brisk walking for 35 minutes four times a week were able to fall asleep faster and sleep longer. Some researchers suspect that exercise, as well as influencing mood, might help calibrate the body's circadian clock.
Alzheimer's disease and cognition: Brisk walking for at least 15 minutes at least three days a week might reduce risk of dementia and Alzheimer's by about 40%, researchers say. In the Nurses Health Study, gentle walking for 1.5 hours each week was associated with higher cognitive functioning -- and less decline -- in women 70 and older.
Experiments with mice on the exercise wheel have shown that physical activity decreases harmful plaque buildup in the brain and increases growth of neurons in the memory areas.
Parkinson's disease: The evidence is mixed, but a few studies suggest that regular physical activity might prevent or lessen the effects of Parkinson's. Researchers suspect that exercise might affect brain levels of dopamine, a chemical affected by the disease.
Stroke: In two large studies (the Nurses Health Study and the Harvard Alumni Study), women who walked an hour a day and men who walked 1.75 miles a day had a 40% drop in stroke risk -- and women who walked briskly had their risk cut in half. Even one brisk, 20-minute walk triggers enzymes that help break down small blood clots. The effect can last an hour.
Sexual function: The Massachusetts Male Aging Study found that sedentary men who started the equivalent of briskly walking two miles a day had a 70% lower risk of erectile dysfunction than those who stayed inactive; In the Health Professionals Follow-Up Study, even walking only 2.5 hours a week reduced the risk by 20%. Researchers suspect that physical activity affects the availability of the key chemical nitric oxide as well as generally enhancing blood flow in the penis.
In women, low rates of physical activity have been linked to low sexual desire and difficulties with sexual arousal. How walking aids sexual function in women is still mostly a mystery.
Staying alive: Studies following large groups of people have found that walkers simply live longer. Some examples: Death rates dropped by 22% for 10,000 Harvard alumni who walked at least nine miles a week; by 50% for 700 retired Hawaiian men who walked at least two miles a day; by 29% for 9,500 women who walked about 10 miles a week. One study estimated that daily 30-minute walks can extend life by 1.3 years for men and 1.5 years for women older than 50.