Antioxidants Important in Exercise, Against Breast Cancer

TEL HASHOMER, Israel & BETHESDA, Md.--Two studies releasedin the April 29 Proceedings of the National Academy of Sciences (www.pnas.org)implicated antioxidants for two conditions of opposite sides of the human healthspectrum. Researchers at the Heller Institute of Medical Research in Israellearned that the body's natural antioxidant defenses may not be able to scavengethe increased free radicals that occur as a result of strenuous exercise, andresearchers at the National Cancer Institute determined antioxidants may havechemopreventive effects against breast cancer.

The first study (100, 9:5119-23, 2003) was conducted based on the hypothesisthat strenuous exercise leads to an increased metabolic rate, heightenedproduction of reactive oxygen species and a compromised antioxidant defensesystem. To test this theory, researchers recruited 31 men who followed asix-month training schedule of working out five days a week. Participants alsocarried 35 kg of weight during two extreme marches, which were separated by atwo-week regular training schedule. Only 29 men finished the 50 km march, and 16completed the 80 km march.

Blood samples taken after the 50 km and 80 km marches showed a respective25-percent and 37-percent increase in uric acid (the body's tool for expellingmetabolic nitrogen; levels too high can cause gout), perhaps due to theincreased metabolism. The marches also caused a 10-fold boost in leakage ofcreatine phosphokinase (an enzyme found in muscle tissue released in increasingamounts when muscle is damaged), and a four-fold increase in plasma levels ofaspartate transaminase (a marker of liver injury). Researchers concluded theelevated respiration rate that occurs during exercise leads to the production ofmore reactive oxygen species than the body's antioxidant system can scavenge.

In the second study (100, 9:5390-5, 2003), researchers at the National CancerInstitute, in cooperation with a team from Seattle's Pacific Northwest ResearchInstitute, found antioxidants may protect against breast cancer. Theyinvestigated cell toxicity and mutagenicity of 4-hydroxyestradiol (4-OHE2), anoxidative metabolite of estrogen, in human MCF7 and TK-6 lymphoblast cells.

The cytotoxicity of estrogen increased when there was a deficiency ofintracellular glutathione, an antioxidant amino acid compound. However,ascorbate and cysteine (a non-essential amino acid precursor of glutathione)were found to protect against cytotoxicity and decrease mutation induction.Researchers concluded oxidation is necessary to induce the damaging effects ofestrogen, and a diet rich in vitamins and synthetic antioxidants could decreasethe risks associated with estrogen exposure and perhaps prevent breast cancer.