Many natural remedies fall into the category of antioxidants. These include zinc, vitamins A, C, and E, superoxide dismutase, Siberian ginseng, selenium, milk thistle, grape seed extract, ginkgo, garlic, Essiac tea, coenzyme Q10, beta-carotene and astragalus. Whether or not they should be used in cancer patients is controversial.
In a meta-analysis involving 8,521 cancer patients who used vitamins A, C, D, K and E, beta-carotene, selenium, cysteine, B-vitamins, and glutathione in various combinations, one study concluded that antioxidants or other dietary supplements do not interfere with chemo or radiotherapy.
Seeking an expert opinion on the subject is important, and maybe even a few different opinions, as doctors don’t see universally eye-to-eye on the subject. What, then, is the harm with the use of antioxidants in cancer patients? There are several important studies that show harm from taking antioxidants:
One involved 29,133 men (50-69 years who had smoked five or more years) randomized to get vitamin E (50 mg a day), beta-carotene (20 mg a day), alpha-tocopherol plus beta-carotene, or placebo daily for five to eight years. Vitamin E and beta-carotene did not prevent lung cancer in older men who smoked and beta-carotene was found to possibly increase lung cancer in smokers.
In one large study, 18,314 men and women at high risk of developing lung cancer were given the combination of beta-carotene (30 mg) and retinyl palmitate (25,000 IU) each day or placebo. This study was stopped early because of possible harm — 28% more lung cancers and 17% more deaths in those taking the vitamins.
In another study, 540 head and neck cancer patients treated with radiation therapy took either vitamin E (400 IU a day) plus beta-carotene (30 mg a day) or placebo. It found that high doses of vitamin E and beta-carotene during radiation therapy reduced the severity of adverse effects from radiation treatment, but that high doses led to earlier recurrence of tumors. The same group of researchers showed that patients with head and neck cancer who had received vitamin E supplement experienced a higher rate of second primary cancers during the supplementation period.
A study involving 90 women with breast cancer used three to six mega-doses of beta-carotene, vitamin C, niacin, selenium, coenzyme Q10, and zinc on top of the standard cancer treatments. This was compared to 180 well-matched controls who didn’t get the supplements. The results were not good: worse survival in the antioxidant-treated patients.
In 136,000 mostly healthy people in 19 different studies, the single most important conclusion is this: that high dose vitamin E (equal or greater than 400 IU a day) increased the overall mortality and thus should be avoided. In another large study with over 7,000 patients with vascular disease or diabetes randomized to received high-dose vitamin E (400 IU a day) or placebo, the results showed that high-dose vitamin E supplements did not prevent cancer or major cardiovascular events. But they might increase the risk of heart failure.