People who exercise regularly swear that it gives them a wonderful sense of well-being. They say it makes them feel good.
One explanation is that because we feel healthier, look better and feel positive about setting and achieving new goals, we feel good.
Other, more scientific factors contribute to the effect. Exercise causes the brain and other parts of the body to produce several chemicals that promote feelings of pleasure and well-being. Some of these chemicals actually prevent and relieve pain. Psychiatrists sometimes prescribe exercise to treat depression, therapy that is most likely effective for the same reasons.
The brain produces many chemicals that alter mood and level of alertness. The catecholamines -- epinephrine (adrenaline) and norepinephrine (noradrenaline) -- are hormones that promote alertness, preparing you for the "fight or flight" reaction. Your body tenses, and you feel alert and ready for action.
Other mood-altering hormones include the endorphins, which are natural opiates (in that they prevent and relieve pain). Endorphins and another chemical, serotonin, promote a sense of satisfaction and pleasure. Exercise raises the brain's level of these hormones, making you feel better.
All of these natural physical reactions constitute another reason to exercise.
Q: My fiance is in great shape, but I'm worried about the big, blue veins on his arms and legs. He says they are signs that he's in good condition. They look a lot like varicose veins to me. Are they?
A: There is a big difference between the enlarged veins of an athlete and varicose veins. Normal veins are straight like pipes. Varicose veins look like worms bending in many different directions, and they can hurt.
Varicose veins are caused by a problem with the tiny valves inside the blood vessels. These valves are supposed to help keep your blood moving steadily in one direction, back toward your heart. If they don't work properly, gravity can cause blood to remain in your legs instead of moving toward the heart. Blood remaining in the legs causes the veins to bulge.
In athletes, like your fiance, veins in the arms and legs can become en- larged because those veins are used to carrying the extra blood needed to supply exercising muscles with oxygen and fuel. The width of the veins also enables them to carry warm blood from the body's exercising muscles to the skin, where cooling takes place so overheating doesn't occur during a vigorous workout.
Q: I drink a soft drink or two almost every day. Does that increase my chances of developing osteoporosis when I get older? Also, are soft drinks hard on the stomach?
A: In 1989, a study from researchers at Harvard Medical School appeared to show that consuming large amounts of carbonated drinks causes osteoporosis, or bone thinning, which -- to some extent -- affects most women and some men as they grow older.
The study's authors reasoned that carbonated drinks contain large amounts of phosphates. Phosphates bind to calcium from other sources in the intestines and prevent the calcium from being absorbed into the bloodstream. Calcium is essential for strong bones.
However, other data does not support this study. A recent study from Sinai Hospital in Baltimore showed that rats which had consumed tremendous amounts of soft drinks did not suffer from a loss of calcium from their bones.
If women who drink a lot of carbonated drinks develop osteoporosis, it is because they are not getting enough calcium in their diet. They should be eating more dairy products or taking calcium supplements.
Soft drinks are not particularly hard on the stomach -- unless you have stomach ulcers. Soft drinks do not cause intestinal gas. The gas in the drinks is absorbed long before it reaches the end of your 30-foot gastrointestinal tract.
Nevertheless, people who have too much stomach acid and/or stomach ulcers should avoid carbonated drinks. The bubbly drinks cause the acid to regurgitate from the stomach and erode the inner lining of the esophagus.
In essence, you should be more concerned about tooth decay. The carbon dioxide in the drinks make the beverages acidic; teeth are alkaline. Acidic soft drinks form a chemical reaction that neutralizes the alkaline teeth and punches tiny holes in their surface.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.
United Feature Syndicate