Monday, March 30, 2009

Prolong life with exercise after age 50

Men who start or increase their exercise programs after age fifty live longer than those who remain at their present activity levels, according to a study in the British Medical Journal (March 2009). More than 2200 men were checked at ages 50, 60, 70, 77 and 82 years. The greater the increase in exercise duration over that span, the longer their lives were extended. The reduction in early death from increasing exercise was the same as for men who stopped smoking.

Lack of exercise is associated with obesity, diabetes, heart attacks, strokes, osteoporosis, and cancer. Exercising regularly more than halves your chance of dying prematurely (Archives of Internal Medicine, December 2007). Yet more than 50 percent of North Americans do not exercise.

Exercise prevents disease and increases life span by many mechanisms. The major benefit probably comes from the contracting muscles themselves. A high rise in blood sugars and fats after meals damages cells. When blood sugar levels rise too high, sugar sticks to the surface of cell membranes. Once there, it can never get off, eventually killing the cells and leading to blindness, heart attacks, strokes and the other consequences of uncontrolled diabetes. Contracting muscles draw sugar and fat so rapidly from the bloodstream that they usually prevent blood sugar levels from rising too high. This effect is maximized during exercise. The effect is maintained for about half hour after you stop exercising and gradually tapers off until it disappears after about 18 hours. That explains why you get maximum benefit by exercising every day (rather than three times a week), and why greater benefit is gained by exercising more intensely for longer durations. How to start an exercise program

Monday, March 23, 2009

Can't lose weight? New research on thyroid may solve your problem

Diets rarely help people to lose weight permanently, so exercise gives you your best chance to lose excess weight and keep it off. However, some people cannot lose weight, no matter how much they exercise. Researchers at the University of Pittsburgh showed that overweight people who do not lose weight when they follow an exercise program are likely to suffer from low thyroid function, and therefore should be able to lose weight if they take thyroid hormones (Medicine & Science in Sports & Exercise, February 2009). I think this is a very important study so this issue of the eZine is a little longer than usual.

When you eat, blood sugar levels rise. Your pancreas responds by releasing insulin into your bloodstream which drives sugar into cells where it can be used for energy. As you gain weight, fat cells fill with fat. This blocks insulin receptors so your cells cannot respond adequately to insulin and blood sugar rises to higher levels. This causes your pancreas to release even more insulin. Too much insulin can harm you. It acts on your brain to make you hungry, eat more and gain more weight. It constricts the arteries leading to your heart to cause heart attacks.

As I explained last week, muscles become extraordinarily responsive to insulin when you exercise so you need far less insulin to drive sugar from your bloodstream into cells. Insulin levels go way down with exercise, but the effect gradually tapers off in about 18 hours. So you have to exercise every day to maintain the benefit of lowered insulin levels, and overweight people who exercise every day usually lose weight.

However, some overweight people cannot lose weight no matter how much they exercise. This study shows that many of these people have low thyroid function which prevents the cells from responding to insulin and drives both insulin and blood sugar to very high levels.

Doctors do not diagnose low thyroid function by measuring thyroid hormone levels. Instead, they do a blood test called TSH that measures the brain's response to thyroid hormone levels. The brain produces TSH to stimulate the thyroid gland to make more thyroid hormone. TSH rises to high levels when the brain senses that there is not enough thyroid hormone in the body.

For many years, doctors have argued among themselves whether to treat people who have normal levels of thyroid hormones and very high levels of TSH (called subclinical hypothyroidism). This exciting new study shows that people who have high levels of TSH but have normal levels of thyroid hormone have muscles that do not respond to insulin adequately when they exercise. This means that they develop high levels of insulin and blood sugar, become overweight, diabetic, and often die of heart attacks.

If you are person who has extreme difficulty losing weight, ask your doctor to draw a blood test called TSH. If it is above 3.0, you probably will benefit from taking thyroid hormone. However, you must be careful not to take too much because overdoses of thyroid cause osteoporosis. Your thyroid dose should be adjusted to keep your TSH values between 0.3 and 3.0. Free weekly Fitness & Health eZine

Sunday, March 15, 2009

Bone Density May Not Measure Bone Strength

A study from Manchester Metropolitan University in the UK shows that sprint cyclists have denser bones than long distance cyclists who have denser bones than sedentary control subjects (Medicine & Science in Sports & Exercise, March 2009). While cyclists have less dense bones than weight lifters and football players, they still have denser bones than people who do not exercise. The greater the force on bones during exercise, the denser the bone. So any type of exercise is good for your bones and a sedentary lifestyle is bad for bones.

When I reported on this study, several readers responded by quoting other studies that showed competitive cyclists have lower bone mineral density in their spines than moderately-active, aged-matched men (Medicine & Science in Sports & Exercise, February 2009; Osteoporosis International Reports, August 2003). These studies have been interpreted to mean that cycling increases risk for bone fractures beyond what you would expect from just falling off the bike.

I cannot find any studies showing that cycling weakens bones to increase fracture risk. Bone density is associated with bone strength, but does not measure it. The only way to measure bone strength is to see how much force it takes at break a bone. For example, birds have strong bones that are not very dense.

The theory that the act of cycling weakens bones flies in the face of our current understanding of bone metabolism. If indeed cyclists suffer from weak bones (and I do not believe that they do), the cause would be something other than riding a bicycle. Bones are constantly remodeling. Cells called osteoblasts bring in calcium to bones while cells called osteoclasts take calcium out. Any force on bones increases, and lack of force decreases, the rate of bone formation. Astronauts in space lose bone because lack of force blocks their ability to respond to Insulin Like Growth Factor-1 that stimulates bone growth (Journal of Bone and Mineral Research, March 2004). All competitive cyclists know that hammering on the pedals while pulling up on their handle bars puts tremendous force on every muscle and bone in their bodies, and this should stimulate bone growth.

Sunday, March 08, 2009

Weight Training Benefits the Heart

Most authorities recommend both endurance and resistance exercise for heart health, even for people who have recovered from heart attacks. Now a study from The University of Athens in Greece shows how resistance exercise may help prevent heart attacks (Medicine & Science in Sports & Exercise, February 2009). Nine healthy, untrained male volunteers performed leg presses, with eight sets of six repetitions and three-minute rest intervals. One day later their blood fat levels were lower than normal after a high-fat meal. This shows that a single bout of weight lifting can prevent a high rise in blood fats one day later. A high rise in fat or sugar after meals increases risk for heart attacks. Exercising and exercised muscles help to remove sugar and fat from the bloodstream and this effect can last as much as twenty-four hours.