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How Exercise Prolongs Life by Making You Stronger

As you age, you become progressively weaker. If you exercise regularly, you will not become as weak as other people your age who do not exercise. The same mechanism that makes you stronger will also help you to live substantially longer than people who do not exercise.

Harvard researchers have proven that exercise prevents loss of the connections between nerves and the muscles that they innervate caused by aging (Proceedings of the National Academy of Sciences, published online August 29, 2010). The researchers studied genetically engineered mice with nerve cells that glow in fluorescent colors. Muscles are made up of millions of individual muscle fibers. Every muscle fiber is innervated by a single nerve. If the nerve dies, the muscle fiber innervated by that nerve also dies. With aging, all humans and mice lose nerves that cause their corresponding muscle fibers to die also. However, mice placed on just one month of exercise in later life actually regained some of the lost connections between nerves and muscle fibers. This is the same mechanism that helps revive nerves in the brain to slow down and even stop the loss of mental function associated with aging. Exercise also prevents loss of strength associated with aging that causes falls, broken bones and injuries in older people.

Researchers at The University of Western Ontario in London just reported that competitive runners with an average age of 65 had the same number of nerves and muscle fibers as younger recreational runners, and far more muscle fibers and nerves than non-exercising age-matched controls (Medicine & Science in Sports & Exercise, September 2010).

This helps explain why exercisers live more than 12 years longer than those who do not exercise (British Journal of Sports Medicine, March 2008). Many other studies show that lifelong physically active older mammals have greater numbers of muscle fibers and their associated nerves than comparable-age mammals that do not exercise. Intense exercise is far more effective than casual exercise to:
• Prevent and treat diabetes (Circulation, July 2008; J. Applied Physiology, January 2006)
• Prevent heart attacks in obese people without weight loss (MSSE, October 2006)
• Prevent heart attacks (MSSE, July 1997)
• Reduce belly fat (MSSE, November 2008)
• Prevent premature death (Heart, May 2003)
• Prevent metabolic syndrome and heart attacks (Exercise and Sports Sciences Reviews, July 2009)
• Raise HDL cholesterol (Journal of Strength and Conditioning Research, March 2009)
(Caution: Exercise can cause heart attacks in people with blocked coronary arteries.)

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Dear Dr. Mirkin: How does drinking fruit juice increase risk for heart attacks?

The CARDIA study shows that all sugared drinks, including fruit juices, raise total cholesterol, the bad LDL cholesterol, triglycerides, and blood pressure (American Journal of Clinical Nutrition, August 13, 2010). People who drink fruit juice also have much larger waist circumferences. Abdominal obesity means that a person has high insulin levels and is at markedly increased risk for heart attacks and diabetes.

Taking sugar in drinks when you are not exercising increases risk for heart attacks, diabetes and premature death. Before food can pass from the stomach into the intestines, it must be converted to a liquid soup. No solid food passes into the intestines. When solid food enters your stomach, the pyloric sphincter at the end of the stomach closes and the stomach continuously squeezes the food until it is turned into a liquid soup. This can take up to four hours which markedly delays the rise in blood sugar. Since fruit juice is already a liquid, it passes immediately into the bloodstream to cause a high rise in blood sugar.

Here's how high rises in blood sugar cause heart disease: When blood sugar levels rise too high:
• your pancreas releases huge amounts of insulin which
• converts sugar to triglycerides (high triglycerides), which clog up your bloodstream to increase risk for clots, so
• you use up huge amounts of your good HDL cholesterol (low HDL cholesterol) in carrying triglycerides and your bad LDL cholesterol from your bloodstream into your liver.
• Low HDL (good) cholesterol causes heart attacks because HDL is not available to carry cholesterol and triglycerides from your bloodstream.
• High insulin levels constrict arteries to cause heart attacks.
• High blood sugar levels cause sugar to stick to the surface membranes of cells to destroy them and cause all the horrible side effects of diabetes.
• High triglycerides in your liver cause a fatty liver that can lead to diabetes.

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Dear Dr. Mirkin: Should I avoid sunlight to prevent skin cancer?

Not unless you have a medical reason, very light skin, or already have skin damage from excess exposure to sunlight. A review of the world's literature on vitamin D production by the skin from sunlight shows that it is almost impossible for most people to maintain adequate blood vitamin D3 levels with just casual exposure to sunlight (Photodermatology, Photoimmunology and Photomedicine, July 13, 2010)

Researchers measured vitamin D3 levels in 824 elderly people from 11 European countries (The Lancet. 22 July 1995). A normal D3 level is more than 75 nmol/L. One third of men and half of women had severely lowered levels below 30. Those who took supplements or used sun lamps were still deficient, averaging only 54. Wearing long-sleeved clothes in sunshine was a very strong predictor of severe vitamin D deficiency.

Vitamin D levels are lowered by:
• reduced sunlight exposure;
• aging, which decreases the skin's ability to make vitamin D;
• reduced dietary intake of vitamin D;
• obesity, in which fat deprives the rest of the body of vitamin D; and
• using too much soap, which removes the vitamin D from the skin's surface before it can be absorbed into the bloodstream.

If your vitamin D3 blood level is below 75 nmol/L (30 ng/ml), you are deficient and should check with your doctor about taking vitamin D pills, or getting exposure to sunlight on your legs. An editorial in the September 1, 2010 issue of NEJM recommends no indoor tanning and regulation of the tanning industry.

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Recipe of the Week:

Extra Quick Chili

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June 21st, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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