Does Green Tea Aid in Cancer Prevention?October 2001
By Ivy Greenwell, Photography by Matthew Pace
one million people every year
worldwide. This is especially
tragic in view of our knowledge
that stomach cancer is relatively
easy to prevent. The great
majority of stomach cancer
cases could be eliminated.
Antioxidants other than green tea polyphenols also play an important role in helping protect against gastric cancer, even in the presence of H. pylori. In fact, antioxidant deficiencies may be a crucial factor in susceptibility to the infection, while antioxidant supplements may be an effective means to diminish the bacterial load (Bennedsen 1999). In fact, Tsubono, the same author who led the recent negative study on green tea and gastric cancer, earlier conducted an interesting comparison of gastric cancer mortality in various regions of Japan, and found a distinct relationship between gastric cancer mortality and plasma levels of various antioxidants, including especially alpha-tocopherol and beta carotene, as well as other carotenoids and ascorbic acid. Thus it comes as no surprise that a recent joint Chinese and U.S. National Cancer Institute interventional study showed that supplementation with vitamin E, beta-carotene and selenium significantly lowered gastric cancer mortality (Yang 2000).
Several studies have found diminished risk of gastric cancer with higher plasma levels of antioxidants and selenium. An Italian study found increased survival in gastric cancer patients with a high intake of alpha-tocopherol. A Spanish case-control study found that those in the highest quartile of flavonoid intake had only 44% risk of gastric cancer compared to those in the lowest quartile (flavonoids are phenolic compounds found in vegetables and fruit). Synthetic antioxidants may also help somewhat: a Dutch study found a non-significant trend for decreased risk of gastric cancer with higher intake of BHA and BHT.
Thus, a variety of antioxidants appear to be effective in the prevention of gastric cancer: green tea polyphenols (based on the findings of studies other than Tsubono’s), vitamin C, vitamin E, carotenes (including beta-carotene and astaxanthin, a carotenoid found in algae and seafood, also available as a supplement), flavonoids, selenium and possibly BHA and BHT.
Of special interest is an interventional study that compared the effectiveness of antioxidants and standard anti-H. pylori therapy in prevention of gastric dysplasia (a serious precancerous condition that is likely to progress to cancer). This study was conducted in a rural area in Colombia. Persons diagnosed with various types of precancerous gastric lesions were assigned to anti-H. pylori therapy, vitamin C therapy, beta-carotene therapy or placebo groups. Gastric biopsy specimens were collected at baseline and after 72 weeks. Those 74% of the subjects in the anti-H. pylori therapy in whom the treatment succeeded in eradicating the infection showed a marked regression in their lesions. However, subjects who received antioxidant therapy also showed excellent results, with vitamin C and beta-carotene being about equal in effectiveness. Combination of treatments did not produce a statistically significant increase in the rate of regressions (Correa 2000). Considering the low cost of vitamin C and beta carotene supplements, together with their safety, their effectiveness in regressing precancerous stomach lesions and preventing gastric cancer cannot be ignored.
Those who consider themselves at risk of stomach cancer may incorrectly assume that they shouldn’t be using aspirin. Interestingly, aspirin, even though it can lead to damage to gastrointestinal mucosa, has been shown to lower the risk of gastric cancer (and colon cancer), most likely because of its anti-inflammatory action (Akre 2001). Chronic inflammation can lead to cell abnormalities and eventually to cancer. It is possible that selective COX-2 inhibitors will prove even better as NSAID-based cancer prevention, to be used in conjunction with other preventive measures. It should be remembered that green tea polyphenols also have anti-inflammatory activity, which is likely to be a very important part of their anti-cancer mechanism.
The fact that the incidence of stomach cancer has declined dramatically in the Western world leads to the conclusion that this type of cancer is largely preventable. It appears that the major factor associated with the drop in incidence of gastric cancer in the West has been the wide use of refrigeration, basically ending the demand for salt-preserved foods such as salted herring. At the same time, antioxidant-rich vegetables and fruit became available year-round, together with nutritional supplements.
Currently, stomach cancer kills one million people every year worldwide. This is especially tragic in view of our knowledge that stomach cancer is relatively easy to prevent. The great majority of stomach cancer cases could be eliminated. We can minimize the risk of stomach cancer by eradicating H. pylori infection, avoiding heavily salted foods, smoked foods, nitrite-containing and pickled foods, and by consuming an antioxidant-rich diet based on fresh rather than processed food, together with supplements known to have anticarcinogenic benefits, including vitamins C, E and beta-carotene, selenium and green tea extract.
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