Jury Still Out on Vitamin C's Effect on Cancer

For many people, breakfast includes a routine glass of orange juice, a good source of vitamin C. However, the controversy about vitamin C and its effect on cancer is anything but routine. While early studies claimed efficacy, later vitamin C studies revealed little influence as a cancer prevention measure and have questioned whether it interferes with chemotherapy and radiation.

Much of the controversy emerged in the 1970s when two-time Nobel Prize winner Linus Pauling, PhD, elevated vitamin C in the media by claiming that high doses could prevent the common cold. Then in 1979, Pauling and Ewan Cameron, MB, ChB, authored Vitamin C and Cancer, stating that high doses of the vitamin were also effective in cancer prevention.

Since then, many studies have disproved Pauling’s theories. Large clinical trials revealed that vitamin C, at best, might lessen the severity of a cold but does not prevent it. Three doubleblind studies conducted by the Mayo Clinic showed that patients with advanced cancer who were given high daily doses of vitamin C fared no better than patients who were given a placebo.

I have to adhere to the voice of caution and advise my patients about the components of a healthful diet rather than relying on supplementation.

More recently, in a randomized controlled trial of beta carotene and vitamins C and E (Women’s Antioxidant Cardiovascular study), duration and combined use of the antioxidants had no effect on cancer incidence or cancer mortality. Other studies have shown no link between oral vitamin C supplementation and prevention of prostate, lung or gastrointestinal cancers, although a small study in Korea linked it to reduced risk for cervical cancer.

“The debate is still ongoing,” says dietitian D. Milton Stokes, MPH, RD. Stokes says another area of concern is that vitamin C’s antioxidant behavior may protect cancer cells from the effects of chemotherapy and radiation. For that reason, the American Cancer Society recommends cancer patients discuss their vitamin C intake with their healthcare provider.

Even though the jury is still out on whether vitamin C can prevent cancer, it remains an essential vitamin for maintaining healthy bones and tissue. Vitamin C helps form collagen, a protein that is the main component in skin, blood vessels, tendons and scar tissue. It is also needed to repair and maintain bones, cartilage and teeth.

Also known as ascorbic acid, vitamin C is a watersoluble vitamin, which means that the body absorbs what it needs and then eliminates the rest through urine. Because of this, a continuous supply of vitamin C is needed in the diet. The recommended dietary allowance is 90 milligrams per day for men aged 19 and older and 75 milligrams per day for women aged 19 and older, although pregnant and breastfeeding women need higher amounts.

Stokes recommends dietary vitamin C as the “safest way to go” because of possible interactions with cancer therapies and since the purity of supplements can be questionable. He says 100-percent fruit juices, such as orange or tomato, are easy sources of vitamin C. It is also found in numerous fruits and vegetables, such as red peppers, broccoli, papayas and strawberries.

Until more research is completed, Stokes says, “I have to adhere to the voice of caution and advise my patients about the components of a healthful diet rather than relying on supplementation. I counsel them to eat real food containing antioxidants and take only a multi-vitamin or mineral supplement instead of mega-doses of anything. And above all else, I strongly urge all my patients to inform their oncologist of any supplements. The medical team needs to know.”