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Mild Dehydration Does Not Impair Exercise Performance

The Gatorade Sports Science Institute in Barrington, Illinois published a study showing that 46 percent of recreational exercisers are dehydrated (Applied Physiology, Nutrition and Metabolism, June 2006). However with good reason, the study does not say that they are harmed. There is no data anywhere to show that this mild dehydration affects health or athletic performance. Another study from the University of Connecticut shows that a person must lose a tremendous amount of fluid before it affects his performance (Medicine & Science in Sports & Exercise, October 2006).

When you exercise for more than an hour, you may need to take fluid, but not too much. Excessive fluid can cause a potentially fatal condition called hyponatremia. Normally, the amount of salt and other minerals in your bloodstream should equal the same total mineral content in every tissue in your body. If the mineral concentrations are not equal, they try to become equal. Fluid moves from the area of lower mineral content to that of the higher concentration. If you take in so much fluid that it lowers the mineral level in your blood, levels in your brain are higher than those in your bloodstream. This causes fluid to move from your bloodstream into your brain, which increases pressure in your brain and can cause seizures and unconsciousness. The swelling can cause permanent brain damage.

Hyponatremia is a disease seen almost exclusively in people who are not exercising near their maximum. The major risk factor is having more time to drink than to concentrate on pushing the pace, no matter what the sport or the duration of the event. Top athletes drink very little fluid during competitions such as bicycle racing, marathon running or cross country skiing, because it is so difficult to drink while you are exercising near your maximum. On the average, a world-classes marathon runner drinks less than a cup an hour during a race. This is far less than the amount recommended by the American College of Sports Medicine just a few years ago. On the basis of our present knowledge, it may not be safe for mediocre athletes to take in more than 800cc per hour (3.5 cups).

Recent studies show that fit humans can tolerate significant fluid loss before their performance suffers, and that most cases of muscle cramps are not caused by dehydration or salt loss. They are caused by muscle damage itself and can be controlled by stopping exercise and stretching the cramped muscle.


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Dear Dr. Mirkin: Why do I become uncoordinated when I'm tired?

Fatigue reduces both strength and accuracy. There's a physiological reason why tiredness weakens muscles. Muscles are made up of thousands of fibers. Each fiber stores sugar. and when it runs out of its stored sugar, it cannot contract effectively. As you tire, your muscles have fewer fibers to contract and you become weaker and less coordinated. This means that a pitcher who is warmed up and fresh will have more active fibers in his muscles and be able to throw more accurately and faster than when he is tired. A fresh football player can kick further and more accurately than when he is tired. That's why professional and college sports teams have large rosters, so they always have plenty of fresh players. The same principle applies to boxers, wrestlers, tennis players and so forth, but they do not have the luxury of calling in a substitute. If you compete in an individual sport that requires both endurance and coordination, take it easy early in your competition and save something for the end.


Dear Dr. Mirkin: How could smoking increase risk for cervical cancer?

Cervical cancer is a venereal disease caused by the human papilloma virus called HPV. Nineteen different strains of HPV have been associated with cervical cancer. HPV-16 is the most carcinogenic. As solid cancers grow, they produce angiogenesis factors that increase blood flow to them to supply nutrients and energy. Tobacco contains nicotine, a potent angiogenesis factor. A study from Sweden shows that women who smoke are far more likely to suffer cervical cancer than their non-smoking counterparts (Cancer Epidemiology, Biomarkers & Prevention, November 2006).

Researchers compared the medical records of 375 women who had cervical cancer to those of 363 women who did not. Pap smears taken an average of nine years before cervical cancer occurred showed which women were infected with HPV- 16. Blood tests showed the number of viruses in their bloodstream. Smokers infected with HPV-16 were 14.4 times more likely to suffer cervical cancer. Smokers with high blood levels of HPV-16 were 27 times more likely to get cervical cancer. Cervical cells undergo a series of changes as they pass from normal toward cancerous, so all pre-menopausal women should get yearly Pap smears. Check with your doctor.


Nutrition Note:
It's gotten a lot easier to find a healthful breakfast cereal! Most major manufacturers have removed partially hydrogenated oils from their popular brands. When Diana last did this list there were 56 brands that contained trans fats; this month she found just 13!!! Only Kellogg's still has a large number of cereals which contain trans fats, and there are hopeful signs that they will change their recipes too.

The 2007 updated Cereals List

Here's a cereal bar "cookie" recipe that you can make with oatmeal or a mixture of your favorite cereals:

Oatmeal Bars

You'll find lots of recipes and helpful tips in The Good Food Book - it's FREE

June 26th, 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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