so is length of exposure," says Wang. The study was published in Carcinogenesis in 2008.
A Balance of Nutrients
The Dietary Guidelines for Americans recommend eating a variety of foods. In addition, some studies have shown that supplementing individual nutrients indiscriminately can disturb the balance of nutrients in the body. "More research needs to be done in this area," says Wang. "But focusing too much on getting inordinate amounts of a few single nutrients might increase cancer risk."
Folic acid, for example, is the manmade form of folate, a natural B vitamin found in many vegetables, beans, fruits, and whole grains. Folate is essential for DNA synthesis. Some consumers might start the day getting 200 micrograms (mcg) of folic acid from a fortified breakfast cereal and another 400 mcg from a multivitamin. For them, it would take just one fortified "energy drink" with an additional 400 mcg of folic acid to reach the upper level of 1,000 mcg per day. Any further enriched foods consumed, such as bread, rice, or pasta, would result in the consumer exceeding the amount thought to be well tolerated biologically. The recommended dietary allowance for folate is 400 mcg daily.
"Precancerous and cancerous cells divide rapidly, so they require a lot of building blocks for synthesis of new copies of DNA," says Joel Mason, director of the ARS-funded Vitamin and Carcinogenesis Laboratory. "It has been shown that under select circumstances, an overabundance of folic acid promotes tumor growth. Studies in laboratory animals substantiate this." Mason described these concerns in the journal Nutrition Reviews in 2009.
The laboratory is part of the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts University in Boston, Massachusetts.
Another Double-Edged Sword
Also in Boston, Jeffrey Blumberg, director of HNRCA's Antioxidants Research Laboratory, tackled the question of whether supplemental antioxidants, including vitamins C and E and beta-carotene, while protecting healthy cells, may also protect tumor cells during chemotherapy or radiation therapy. He and colleagues reviewed published data from randomized clinical trials addressing benefits versus risks of such antioxidant
The researchers concluded that the use of supplemental antioxidants during cancer therapies should be discouraged because of the possibility of tumor protection. The commentary was published in the Journal of the National Cancer Institute in 2008.
Phytochemicals and other food components affect genes that trigger specific molecular mechanisms. Depending on the concentration and exposure over time, some of these mechanisms are similar to detoxification and some promote stress. For example, the food compounds that "turn on" detoxifying phase I and phase II enzymes can help clear the carcinogens.
Consuming a varied diet that provides adequate levels of all recommended nutrients from foods is the best way to eat well without upsetting the balance of individual nutrients in the body. A personalized eating plan and assessment of individual food choices based on the Dietary Guidelines for Americans can be found at MyPyramid.gov.--By Rosalie Marion Bliss, ARS.
This research is part of Human Nutrition, an A RS national program (#107) described at www. nps.ars.usda.gov.
To reach scientists mentioned in this article, contact Rosalie Bliss, USDA-ARS Information Staff 5601 Sunnyside Ave., Beltsville, MD 20705-5129; (301) 504-4318, firstname.lastname@example.org.
|Gale Copyright:||Copyright 2010 Gale, Cengage Learning. All rights reserved.|