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Let's walk through the evidence

Exactly how much good does that daily stroll do? For starters, it's terrific for the heart.

March 12, 2007|Regina Nuzzo | Special to The Times

STUDIES investigating the health wonders of exercise keep rolling in. But just like with eating habits, physical activity habits are tough to study in gold-standard, randomized clinical trials -- after all, who would agree to be assigned to a marathoners' group for 20 years? Instead, most researchers do the next best thing: study people's exercise habits and see how they fare, health-wise, down the line.

Here's a snapshot of some high-profile studies that have focused on walking or other moderate-intensity physical activity:

Cardiovascular system: This is where the mother lode of walking benefits have been found.

Some examples: The Women's Health Initiative study (tracking 74,000 women ages 50 to 79) found a 30% lower risk of cardiovascular problems (such as heart attack or stroke) for those who walked briskly for at least 22 minutes a day.

Another study of 39,000 women (the Nurses Health Study), found half the risk of coronary heart disease for women who walked at least one hour a week. Time spent walking was more important than pace.

Men benefit too: A study of 2,700 retired men (the Honolulu Heart Program) found that those who walked at least 1.5 miles a day halved their risk of coronary heart disease.

Another, of 44,000 men (the Health Professionals Follow-Up Study), found an 18% lower risk of coronary heart disease for those who walked at least 30 minutes a day. In this case, how fast they walked was more important than how long.

How does it work? Moderate-intensity activity boosts levels of high-density lipoproteins (the "good" cholesterol), lowers levels of low-density lipoproteins ("bad" cholesterol), increases oxygen supply and improves heart contractions and blood pressure.

Type 2 diabetes: With 30 minutes of walking a day, you might lower your risk for developing diabetes by one-third to one-half, scientists say. At work are the same heart-healthy mechanisms, plus extras: weight loss, improved insulin response and better blood-sugar control.

Even a single bout of brisk walking can greatly improve glucose metabolism for up to 18 hours afterward; it does so by helping muscles take up glucose from the blood without using insulin (perhaps in the same way as the diabetes drug metformin.)

And if you already battle diabetes, walking might help extend your life. In a decade-long study of 1,600 people in Southern California, diabetics who walked more than a mile a day were half as likely to die of any cause than those who walked less -- even after adjusting for other factors such as sex, age, weight and smoking and drinking habits.

Cancer: Colon cancer appears especially affected by walking: Risk for the disease could drop by about 35% with 30 to 60 minutes a day of physical activity, scientists say. Walking might help with treatment too. In one study of 600 women, those who increased their activity levels after diagnosis lowered their risk of dying by one-half.

Breast cancer is also on the list. In the Women's Health Initiative study, women who did the equivalent of two hours a week of brisk walking dropped their risk of breast cancer by 18%. In the Nurses Health Study, breast cancer patients who walked from three to five hours a week were half as likely to die from the disease as those who didn't walk.

Scientists are planning a clinical trial to test a moderate-intensity physical activity program for breast cancer survivors.

Some studies have suggested that moderate exercise might help prevent stomach cancer, endometrial cancer and prostate cancer, but researchers say more research is needed.

Why physical activity helps fight or prevent cancer isn't clear, but the key might be in the way physical activity affects hormones or the immune system.

Bones and joints: Walking or other weight-bearing activity builds bone strength and slows the rate of bone-mineral loss as we age. In one study, postmenopausal women who walked four hours a week dropped their risk of hip fracture by about 40%, with brisk walkers experiencing the greatest benefit. But some researchers think that simply walking may not be enough to prevent osteoporosis: Strength training might be needed, too.

Knee osteoarthritis may also benefit from walking, but more data are needed.

Mood: Active folks are 30% to 50% less likely to be depressed or to develop depression down the road, researchers say. In one study, a walking program was just as effective in treating symptoms of depression as a jogging program. But more patients stuck with the walking program.

In other studies, regular exercise has sometimes been found to be as effective as psychotherapy for depressed patients; some researchers think that the combination of physical activity and medication might be more effective than medication alone.

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