Cancer antioxidants

The supplements most widely used to protect against cancer are the antioxidants. There have been several studies showing that high doses of antioxidants are beneficial, particularly in those who are deficient. A five-year study of almost 30000 adults in Linxian, China found a 13 per cent reduction in cancer death rates in those given vitamin E, selenium and beta carotene supplements. Several studies suggest that the most beneficial effects are seen when antioxidants are given in combination rather than alone. Antioxidants protect each other from damage and interact in many body functions.

Cancer antioxidantsVitamin A

Lung cancer

Vitamin A supplements have been used to prevent cancer recurrence in smokers who had undergone surgery for lung cancer. In a 1993 study, researchers gave daily doses of 90,000 mcg RE (300,000 IU) to 307 patients took for one year. After a follow-up period of 46 months, the number of patients with either recurrence or new tumors was 56 (37 per cent) in the vitamin A group and 75 (48 per cent) in the control group. Eighteen patients in the treated group developed a second primary tumor, and 29 patients in the control group developed 33 second primary tumors.

Other studies support the use of vitamin A as a cancer preventive in those at high risk of disease. In a 1998 study done in Western Australia, 1024 blue asbestos workers known to be at high risk of diseases such as mesothelioma and lung cancer, were enrolled in a cancer prevention program using vitamin A.

Half the subjects given 30 mg per day of beta carotene and the other half 7500 mcg RE (25,000 IU). The workers were followed up for a five-year period. Four cases of lung cancer and three cases of mesothelioma were observed in those in the vitamin A group, and six cases of lung cancer and 12 cases of mesothelioma in the beta carotene group. In the retinol group, there was also a significantly lower rate of death from all causes. When the researchers compared these results with those workers who had not taken part in the study, they found that those taking part in the study had significantly lower death rates than non-participants.

Leukoplakia

Vitamin A has also been shown to exert protective effects against leukoplakia, a pre-cancerous change in mucous membranes. It often occurs in the mouth and throat and is related to smoking. In a study done in 1997, researchers tested the effects of the retinyl palmitate form of vitamin A on leukoplakia of the larynx. The treatment period was five weeks and the doses used ranged from 90,000 mcg RE per day (300,000 IU) to 270,000 mcg (1,500,000 IU) per day. Complete remission was observed in 15 out of 20 patients and partial response was seen in the remaining five patients.

Cancer antioxidants: Carotenes

Beta carotene supplements have been used in cancer and cardiovascular disease prevention trials including the Finnish Alpha Tocopherol Beta Carotene Cancer (ATBC) Prevention Study, the US Carotene and Retinol Efficacy Trial (CARET) and the US Physicians Health Study. In 1996, these studies reported results which received wide publicity. Results from the ATBC study showed an 18 per cent increase in lung cancer deaths in men who took daily supplements of 20 mg of beta carotene.

The CARET study, which involved 18,000 smokers and people who had been exposed to asbestos was stopped 21 months early due to a 28 per cent increased risk of lung cancer, a 26 per cent increase in the risk of death from cardiovascular disease and a 17 per cent increase in overall deaths in the group receiving the supplements. Results from the 12-year Physicians Health Study suggest that beta carotene supplements have no effect on the risk of cancer. Further analyses of these results support the suggestion that beta carotene is susceptible to oxidative damage by alcohol and the gases in cigarette smoke. Other antioxidants, such as vitamins C and E may help to exert protective effects against this damage. In smokers, dietary vitamin C supplementation should accompany beta carotene supplementation.

Cancer antioxidantsVitamin C

Vitamin C supplements has succesfully been used as cancer antioxidants.

Stomach cancer

Vitamin C supplements may be useful in helping to prevent stomach cancer. In a 1996 study, researchers gave 32 patients 500 mg of vitamin C twice daily for two weeks. Levels in gastric juices and gut tissues were increased, raising the possibility of increased protection against free radicals.

A 1997 Japanese study suggests that vitamin C may inhibit the growth of Helicobacter pylori, a stomach bacterium that increases the risk of ulcers and stomach cancer. Vitamin C-rich diets have been found to decrease the risk of stomach cancer. This has been attributed to the antioxidant ability of vitamin C.

However, vitamin E, which is also an antioxidant, does not inhibit the growth of Helicobacter pylori. This suggests that vitamin C may exert its protective effects through a biochemical mechanism. This research suggests the possibility of a safe, side effect-free alternative to antibiotics for the treatment of ulcers.

Colon cancer

V itamin C supplements may also help to prevent colon cancer. In a 1992 study, twenty patients with colorectal cancer were given vitamins A, C, and E for six months and 21 patients with adenomas received placebo. The results showed that supplementation with vitamins A, C, and E was effective in reducing pre- cancerous abnormalities. Vitamin C supplements may also be beneficial in the treatment of prostate cancer.

Vitamin C and cancer treatment

Controversy surrounds the use of vitamin C in the treatment of cancer. The Nobel Prize winner, Linus Pauling and his colleagues have used vitamin C to improve survival times in cancer patients but these results have not been repeated in other studies. Vitamin C may also benefit cancer patients who are undergoing radiation treatment by enabling them to withstand greater doses of radiation with fewer side effects.

Vitamin E

Vitamin E supplements, especially when combined with selenium, have shown beneficial effects in the prevention of certain types of cancer, including breast cancer. Analysis of results from a 1996 US National Institute on Aging study showed a 22 per cent decrease in the risk of death from cancer in those taking vitamin E supplements.

Prostate cancer

According to more results from the ATBC study published in 1998 in the Journal of the National Cancer Institute, vitamin E reduces the risk of prostate cancer among smokers. Researchers studied the effects of 50 mg (75 IU) in Finnish men and the results showed a 32 per cent decrease in the incidence of prostate- cancer and a 41 per cent decrease in prostate cancer deaths among the men taking vitamin E, compared with those who took no vitamin E.

Selenium

Recent large scale studies in Linxian, China found reduced risk of cancer when selenium supplements were given to those living in selenium-deficient areas. Other studies have shown that selenium supplements protect against some types of cancer such as rectal, ovarian, colon, lung and cervical cancers. However, there are also studies, including the Harvard Nurses Health Study which do not show a protective role for selenium against cancers at any major site. Laboratory studies have shown that selenium can slow tumor cell growth.

Results of a 1996 study showed that selenium supplements were associated with a 50 per cent reduction in deaths from cancer. Researchers at the Arizona Cancer Center set out to test the effectiveness of selenium supplements on the prevention of skin cancer in over 1300 patients. Participants received a placebo or 200 mcg selenium per day over a period of 4.5 years and a total follow-up of 6.4 years. While the results did not show any reduction in skin cancer risk, the selenium group had a 37 per cent reduction in cancer incidence and a 50 per cent reduction in cancer mortality. The effects appeared strongest for prostate (63 per cent lower risk), colorectal (58 per cent lower risk) and lung (53 per cent lower risk) cancers.

Cancer antioxidantsSuggested doses of cancer antioxidants supplements

The doses of antioxidants used in cancer prevention trials are, in many cases, higher than those which could be obtained from the diet. Many nutrition experts recommend taking high daily doses of supplements to help prevent cancer. This may be particularly important in anyone who has a family history of disease or is often exposed to risk factors.

Suggested doses are:

Beta carotene       10 to 30 mg

VitaminE             200 to 800 IU (134 to 536 mg alpha TE)

VitaminC             1000-2000mg

Selenium              200 mcg

Vitamin D

Vitamin D is involved in normal cell growth and maturation, and so may play a part in cancer prevention. Laboratory experiments show that vitamin D can inhibit the growth of human prostate cancer and breast cancer cells. Lung cancer and pancreatic cancer cells may also be susceptible to the effects of vitamin D. Sunlight also seems to be protective against several types of cancer including ovarian, breast and prostate cancers; and this effect may be mediated by vitamin D levels. Synthetic vitamin D-type compounds are being investigatedfor their potential as anticancer drugs.

Colorectal cancer

In a 1996 study, researchers conducted a population-based case-control study examine the relationship between vitamin D intake and disease among 352people with colon cancer, 217 people with rectal cancer and 512 healthy people in Stockholm, Sweden. The researchers used questionnaires to assess the vitamin D intake for the preceding five years. The results showed that those with the highest vitamin D intakes were around half as likely to get cancers of the colon or rectum than those with the lowest intakes.

Results from the Harvard Nurses Health Study published in 1996 suggest a link between vitamin D and colorectal cancer. The study involved 89,448 female nurses and covered the time period from 1980 to 1992 during which 501 cases of colorectal cancer were documented. The results showed a link between intake of total vitamin D and risk of colorectal cancer.

Prostate cancer

In a study published in 1996, researchers in a Boston hospital collected blood plasma samples from 14,916 participants in the Physicians' Health Study and measured vitamin D levels. Their analysis included 232 cases diagnosed up to 1992 and 414 age-matched control participants. Their results showed a slightly reduced risk of prostate cancer in those with high vitamin D levels.

Genes affecting the way a man's body utilizes vitamin D could affect his risk of prostate cancer. A 1996 National Institute of Environmental Health Sciences study found that men with a particular type of vitamin D receptor gene are less likely than others to develop the type of prostate cancer that requires surgery. Researchers looked at the receptor genes in 108 cancer patients and 170 men without cancer. The results showed that 22 per cent of cancer patients had a particular gene while only eight per cent of the cancer-free men did. These findings support the theory that vitamin D plays an important role in prostate cancer development.

Folic acid

Those with diets low in folic acid may have a higher risk of cancer than those who eat large amounts, particularly cancers of the cervix, lung and colon. Folic acid is vital for the maintenance of the genetic code and regulation of cell division in both healthy and tumor tissues. Folic acid deficiency leads to changes similar to those seen in cancer and may affect the repair of DNA and increase chromosome fragility. It may also diminish the ability of the immune system to fight cancer cells and viruses. Deficiency has been shown to affect a gene involved in suppressing tumor formation.

Colorectal cancer

Results from the Alpha-Tocopherol Beta carotene Study published in 1996 suggest a relationship between folate status and colorectal cancer. The study involved male smokers aged from 50 to 69. The researchers measured folate levels in 144 cases of colorectal cancer and 276 healthy people. Those with higher dietary folate intakes had a reduced risk of colon cancer. Men with a high alcohol, low folate, low protein diet were at higher risk for colon cancer than men who consumed a low alcohol, high folate, high protein diet.

Cervical dysplasia

Low blood levels of folic acid may increase the risk of cervical dysplasia (pre- cancerous changes in the cells lining the cervix), possibly by enhancing the effect of other risk factors. Researchers from the University of Alabama investigated the links between folate deficiency and cervical dysplasia in 294 women with the disorder and 170 healthy women. They also assessed the impact of factors such as smoking, oral contraceptive use, human papillomavirus (HPV) infection, and number of sexual partners. The results showed that at low folate levels the risk of dysplasia caused by HPV infection was increased.

Supplements

Folic acid supplements can help to reduce the risk of cancerous changes in several areas such as the cervix, lung and gastrointestinal tract. In a 1997 study, researchers at the Cleveland Clinic investigated the links between folate supplements and cancerous changes in 98 patients with ulcerative colitis. Patients taking the supplements had a 30 per cent lower risk of developing cancerous changes in the bowel. The lower the folate levels the more advanced the degree of cancerous changes in the cells. In a 1997 Italian study researchers also studied the effects of folate supplements on pre-cancerous cell changes in ulcerative colitis. The results showed that folate reduced these changes. Folic acid may also help to prevent the pre-cancerous changes in lung tissue caused by smoking.

Folic acid supplementation may protect abnormal cells from becoming cancerous and may reverse cervical dysplasia in some cases. A 1996 study done at the University of Alabama suggests that supplements may be useful in preventing the initial changes but do not appear to affect the progress of established disease. Some researchers have found a higher risk of abnormalities in cervical tissue in women using oral contraceptives and suggest that folic acid supplements are beneficial in preventing cervical dysplasia in these women.

 
 
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