Sacred Cow Tipping It's a brave man, they say, who first ate an oyster. That earliest oyster-eater may have also improved his metabolic responses during moments of physical exertion, according to a new study. In other words, he wouldn't have tired as quickly as his non-oyster-eating buddies. But this study isn't about oysters; it's about a multi-tasking mineral (abundant in oysters) that may improve endurance while also giving your body a very healthy vision-improving boost. The mineral is zinc, and as I mentioned earlier this week (in the e-Alert "No Shrinking Violet" 6/14/05) zinc is one of the key tools in DNA reproduction and repair. There are also zinc-containing enzymes that are believed to regulate energy expenditure, although the effect of dietary zinc on metabolic response during exercise has not yet been thoroughly studied. Enter a team of researchers from the U.S. Department of Agriculture in North Dakota. The USDA team set out to examine what effect low zinc intake has on cardiorespiratory function and the activity of the carbonic anhydrase enzyme during exercise. (The carbonic anhydrase enzyme helps red blood cells deliver carbon dioxide to the lungs; a function that muscle cells require to produce energy.) The researchers recruited 14 men between the ages of 20 and 31. For the first phase of this crossover study, half the group ate a low-zinc diet (about 4 mg per day) and half ate a high zinc diet (about 19 mg per day) for nine weeks. All the men returned to normal diets for a six week washout period, and then began the second phase in which they crossed over to either a low-zinc or a high-zinc diet for another nine weeks. Peak work capacity of each subject was determined with a 45-minute physical test conducted during the second and ninth weeks of each of the two study phases. Work capacity was recorded with a cycle ergometer, which measures the effectiveness of muscles and muscle groups. As reported in the May 2005 issue of the American Journal of Clinical Nutrition, the authors of the study write: "These findings indicate that low dietary zinc is associated with significant reductions in zinc status, including red blood cell carbonic anhydrase activities, and impaired metabolic responses during exercise." In short: An inadequate intake of zinc may impair physical performance. In addition to improving metabolic response, research shows that zinc provides other key health benefits, such as enhancement of the immune system, assistance in the repair of damaged tissues, and inhibition of the abnormal clotting that contributes to cardiovascular disease. And a daily zinc intake of 80 mg has been shown to help improve vision, while also reducing the risk of age-related macular degeneration (AMD). In the e-Alert "Oyster Goggles" (10/11/04), I told you about a clinical trial called the Age-Related Eye Disease Study (AREDS) sponsored by the National Eye Institute. For more than eight years, researchers tracked nearly 3,600 participants between the ages of 55 and 80 to examine the effects that antioxidant supplements have on AMD. The results: High levels of zinc and antioxidants significantly reduced the risk of AMD, and the same supplements (if administered in the early stages of AMD) may also significantly inhibit the total amount of vision loss that would normally be caused by advanced AMD. The AREDS team recommended that anyone at high risk of developing AMD should consider taking daily supplements in the amounts used in the study:
Zinc (as zinc oxide) - 80 mg
Vitamin C - 500 mg
Vitamin E - 400 IU
Beta-carotene - 15 mg
For those who do include zinc in their daily supplement intake, it's also a good idea to add a little copper as well. In the e-Alert "Aim High" (5/7/03), HSI Panelist Allan Spreen, M.D., noted that zinc can create a copper deficiency, and vice versa. And Jonathan V. Wright, M.D., agrees, stating that, "Zinc supplements should usually be offset by a small amount of copper, 1-2 mg daily." Fortunately, many multivitamins already provide a low dose of copper, taking care of the necessary zinc/copper ratio. And to add more zinc to your diet all you need to do is increase your intake of the food that has the highest zinc content: oysters. But if the prospect of swallowing an oyster makes you green around the gills, then you can also get zinc from red meat, poultry, beans, nuts, whole grains and dairy products. Zinc is generally best absorbed when the diet is rich in animal protein. Sources:
"Low Dietary Zinc Decreases Erythrocyte Carbonic Anhydrase Activities and Impairs Cardiorespiratory Function in Men During Exercise" American Journal of Clinical Nutrition, Vol. 81, No. 5, May 2005, ajcn.org "Low Zinc May Impact Physical Performance" NutraIngredients.com, 6/6/05, nutraingredients.com "Milk, Does a Body Bad?" ABC News, 6/9/05, abcnews.go.com | 
