No Proof Diet, Nutrition Can Prevent Cancer
In August of 2002, the Journal of the American Medical Association (JAMA) reversed their decades long stand against vitamin supplements stating, "Recent evidence has shown that suboptimal levels of vitamins, even well above those causing deficiency syndromes, are risk factors for chronic diseases such as cardiovascular disease, cancer, and osteoporosis." "Pending strong evidence of effectiveness from randomized trials, it appears prudent for all adults to take vitamin supplements. We recommend that all adults take one multivitamin daily." (see http://www.direct-ms.org/pdf/nutritionGeneral/Fletcher%20vitamins%20CA.pdf)
The following article reports findings of researchers who reviewed 59 studies on diet and cancer. They report no proof that dietary supplements or other nutrition strategies are effective for treating or preventing the disease.
It is important to keep in mind several points when considering this report.
- There are literally tens of thousands of research studies on nutrition and cancer. How many studies did these researchers review to find 59 that showed no benefit from diet supplements or nutritional regimens, and what did the other studies report?
- The vast majority of studies reviewed were "poorly designed or poorly executed".
- The failure of these poorly designed or executed studies to find conclusive evidence that dietary supplements or other nutrition strategies help in treating or preventing cancer does not mean that nutrition is not important in preventing or treating the disease; only that these studies did not show such benefit.
- The investigators did not find any conclusive benefit or harm for any of these interventions.
Much of the nutritional research on cancer and other diseases involves the study of free radicals and antioxidant nutrients. Cancer is associated with genetic alterations, and free radicals are one source of such alterations. Antioxidant nutrients, by counteracting such oxidative stress, are believed to help prevent cancer.
Free Radicals" are unpaired electrons of an atom that can disrupt other atomic partners by grabbing one of their outer electrons. Not only does it mess up the normal function of the atomic pair, but it also creates a chain reaction of one atom after another, grabbing someone else's electron. "Radical species" are formed by stress (emotional and physical), pathogens, lack of oxygen, pollutants, inflammation, as well as normal metabolic processes. Free radical damage or "oxidative stress" in the mitochondria of a cell can reduce energy production and cell function. Oxidative damage to the neurons can reduce cognitive, speech, sensory and motor function, and damage to the cell nucleus can cause genetic aberrations. Antioxidants from our diet are the color pigments in grains, vegetables and fruits that absorb solar light. Inside the body these pigments absorb the energy of unpaired electrons and stop the cascade of oxidative stress. http://cancerresourcecenter.com/articles/alt011.html
Inflammation creates free radicals, and inflammation is associated with cancer.
A substantial body of evidence supports the conclusion that chronic inflammation can predispose an individual to cancer, as demonstrated by the association between chronic inflammatory bowel diseases and the increased risk of colon carcinoma.
Ultraviolet light (UVB and UVA) from excessive sunlight exposure can also cause free radicals, and topical application of antioxidant nutrients have been reported to decrease the risk of skin cancer.
DNA damage caused by ultraviolet (UV) irradiation is considered the main etiologic factor contributing to the development of skin cancer. Systemic or topical application of antioxidants has been suggested as a protective measure against UV-induced skin damage. We investigated the effect of long-term oral administration of a combination of the antioxidants ascorbic acid (vitamin C) and D-alpha-tocopherol (vitamin E) in human volunteers on UVB-induced epidermal damage. The intake of vitamins C and E for a period of 3 mo significantly reduced the sunburn reaction to UVB irradiation. Detection of thymine dimers in the skin revealed a significant increase of this type of DNA damage following UVB exposure. After 3 mo of antioxidant administration, significantly less thymine dimers were induced by the UVB challenge, suggesting that antioxidant treatment protected against DNA damage. http://www.nature.com/jid/journal/v124/n2/full/5602688a.html
While there is no conclusive evidence that a healthy diet is beneficial in treating cancer, it certainly can be said that an unhealthy diet will not be beneficial in preventing or treating cancer. We can also say with certainty that a healthy diet is important for general health and well-being and that you can't assume optimal health if the nutrition in insufficient to support or maintain it. This is why good nutrition is important in helping maintain health and preventing cancer and other diseases. Vitamins and dietary supplements are a convenient and, compared to drugs, relatively inexpensive way of assuring this nutritional adequacy.
Because the nausea of chemotherapy and radiation can dramatically affect dietary intake and digestion, nutritional assessment and counseling should be routine during cancer treatment to assure nutritional adequacy. Unfortunately, this aspect of cancer treatment is still largely ignored.
John W. Cartmell, MS
No Proof Diet, Nutrition Can Prevent Cancer
July 18, 2006
By Salynn Boyles http://www.foxnews.com/story/0,2933,204281,00.html
Cancer patients spend billions a year on vitamins and dietary supplements, but there is no proof that these products -- or other nutrition strategies -- are effective for treating or preventing the disease, a new analysis shows.
Researchers who reviewed 59 previous studies assessing a wide range of diet-related approaches found little evidence that specific vitamins, supplements, or foods had any impact on disease-free survival, mortality, or cancer recurrence.
The impact of diet on cancer was either disappointing or could not be determined because most studies conducted to date have been of poor quality, the researchers concluded.
“There is no evidence that dietary modification by cancer patients improves survival and benefits disease prognosis,” they wrote.
Antibiotics vs. Diet Supplements
The analysis was one of two reports on nutrition and cancer, published in the July 19 issue of the Journal of the National Cancer Institute. In an original study from the National Cancer Institute and China’s Peking University, researchers assessed various interventions thought to prevent stomach cancer or precancerous lesions in Chinese people of Linqu County in Shandong Province, where stomach cancer causes 42 percent of cancer deaths. The long-time use (around seven years) of either garlic or vitamin E, vitamin C, and selenium supplements did not result in a reduction in precancerous lesions or in stomach cancers. But a two-week course of antibiotics given to kill Helicobacter pylori bacteria in the stomach was associated with a reduction in precancerous lesions. H. pylori infection is known to be a major cause of stomach ulcers, and it is believed to play a critical role in the development of stomach cancer. Researchers concluded that the H. pylori treatment reduced the occurrence of precancerous stomach lesions, which could prevent stomach cancers.
Studies Show No Impact
The analysis of previous nutrition and cancer studies included 25 studies in patients with cancer and 34 studies in patients with precancerous conditions. Steven Thomas, MD, PhD, and colleagues from the U.K.'s University of Bristol concluded that the vast majority of the studies they looked at were poorly designed or poorly executed. With this caveat, they reported that none of the interventions studied appeared to have an impact on cancer one way or the other. Specifically, vitamin A supplementation did not appear to be beneficial in studies involving patients with lung, cervical, head and neck, and skin cancers, and leukemia.
Other studies examined multivitamins use by patients with a variety of cancers: beta carotene supplementation in patients with skin, stomach, cervical, mouth, and colorectal cancers; fiber for colorectal cancer; and green tea for esophageal cancer.
“We did not find any conclusive benefit or harm for any of these interventions,” Thomas tells WebMD.
More Study Needed
But that doesn’t mean eating a healthy diet with plenty of fruits and vegetables is not important for people with cancer or for cancer survivors, he adds. “People with cancer are increasingly living longer as medical treatments improve. We can certainly say that healthy diets are important for general well-being. But it is more problematic to say that a healthy diet is beneficial in treating cancer. There is some evidence that this is the case, but it is not conclusive.”
Nutrition and cancer researcher John A. Baron, MD, of Dartmouth Medical School, tells WebMD that the studies to date have tended to identify dietary interventions that do not benefit cancer patients.
“We actually do know a lot, but it is mostly about what doesn’t work,” he says. “We now know that antioxidant and fiber supplements are not protective against colorectal cancer, for example.”
In an editorial accompanying the study, Baron wrote that while the studies examining diet and cancer have tended to be negative, there are some “hopeful nuggets of progress” in the search for useful diet plans.
He tells WebMD that his own studies strongly suggest that dietary calcium may help prevent colorectal cancer.
“I do believe that we will have more answers in the near future, but we do need better studies to give us these answers,” he says.
By Salynn Boyles, reviewed by Louise Chang, MD
SOURCES: Davies, A.A. and Wei-cheng, Y. Journal of the National Cancer Institute, July 19, 2006; vol 98: pp 961-980. Steven Thomas, MD, PhD, division of maxiofacial surgery, University of Bristol, U.K. Wei-cheng You, Peking University School of Oncology, Beijing, China. John A. Baron, MD, section of biostatistics and epidemiology, Dartmouth Medical School, Lebanon, N.H.
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