What's In It For You?: Exercise is important for everyone, but not always for the same reasons.

For starters, how about happiness and long life? Exercise offers a wide range of benefits. It helps control weight, lowers blood pressure, lowers cholesterol, cuts the risk of heart attack, strengthens your immune system,eases arthritis pain, protects against osteoporosis, fends off some forms of cancer, keeps your thinking sharp in old age, and even brightens your mood.

As if all of this were not enough, exercise can also improve blood glucose control.

Moderate exercise can reduce the need for diabetes medicines or insulin. It can also can slow the progression from prediabetes to type 2 diabetes.

But “moderate” means just that. Don't try to run a marathon on your first outing. A brisk walk, for 15 minutes twice a day—or even a shorter walk, if you've been a couch potato for years—will do you more good than you imagine.

If you change your routine and start to exercise, tell your doctor. He or she will want to monitor you more closely and may want to change your medicines.

It's never too late to start. It's never too early, either. Through the life span, exercise can:

• Fight childhood obesity. An estimated 15 percent of American children and teens aged 6 to 19—roughly 9 million kids—are obese. Families and schools are urged to establish healthy diets, cut junk food and sugary sodas, and promote exercise. Limit kids' TV time, send them out to play, and encourage schools to expand physical education programs.

  The payoff for children will be reduced risk of type 2 diabetes. Exercise also will reduce their risk of developing other diseases, either as children or as adults, and will improve their emotional health.

• Improve teens' physical and mental health. For teens, physical activity strengthens bones and joints, builds lean muscle mass, and can delay the development of high blood pressure. For girls, exercise in their teens or even earlier builds stronger bones, which protects against osteoporosis later in life.

  Exercise also can reduce teens' depression and anxiety, heighten self-esteem, and provide a feeling of social well-being.

• Reduce stress and increase well-being in midlife. For adults in the high-stress midlife years when family, career, and financial pressures gang up, exercise can be a marvelous mood-enhancer. People who are physically active are far less likely to be depressed, tense, confused, stressed out, and anxious.

  Midlife is also the time when such killers as heart disease and cancer first begin to strike broadly, so midlifers may have the most to gain from the lower death rates that come with regular exercise. In addition to protecting against heart disease, exercise appears to cut the risk of colon cancer,breast cancer, endometrial cancer, and prostate cancer.

• Keep seniors healthy. For seniors, the most important benefit from exercise probably is that it helps them stay mobile and independent. Regular exercise can fight the muscle wastage and frailty that makes it impossible for some elders to care for themselves. Exercise can even help to rebuild weakened muscles. It can also improve balance, helping seniors avoid falls and broken bones.

  The worst fear of many seniors is loss of their mental sharpness. Exercise may help here, too. Studies have shown that physical training improves mental function in seniors with dementia. In fact, merely walking may reduce the risk of dementia in people who are in their 70s or older.

  Why exercise improves mental function isn't known. Maybe human beings,young to old, just work better when they move around.

When you decide to start exercising, it's easiest to do something you already know how to do. That's why walking is a good first step. But a well-rounded physical activity program includes other elements as well. The major exercise groups are:

• Endurance exercises, such as brisk walking, bike-riding, dancing,stair-climbing, or even heavy yard work. These pump up breathing and heart rate, increase energy, build stamina, and improve heart health.

• Strength or resistance exercises, such as weightlifting,weightpushing, or resistance-band stretching. These help tone muscle, build muscles, improve bone health, and reduce the risk of falling.

• Stretching exercises, such as side hip rotation or trying to touch your toes. These improve flexibility and freedom of movement.

• Balance exercises, such as side leg raising or standing on one foot for as long as you can. These are particularly important for seniors.