The Truth About Vitamin C and Cancer

  • 29 Aug 2017
  • Reading time 18 mins
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Vitamin C reduces your risk of cancer, and high doses are an effective anti-cancer therapy. See the latest compelling evidence.

First shown to be a powerful anti-cancer agent in 1971, it wasn’t until 20 years later that vitamin C started to be accepted by the mainstream medical profession. Eating a vitamin C-rich diet substantially reduces the risk of cancer, and high intakes – above 5000mg a day (the equivalent of 100 oranges) – substantially increases the life expectancy of cancer patients.

The overwhelming evidence is that a high intake of vitamin C correlates with a low risk for cancer. In January 1991, Dr Gladys Block, formerly with the National Cancer Institute, published a review [1] of vitamin C research which concluded that there was very strong evidence of a protective effect of vitamin C for non-hormone cancers. Of the 46 such studies in which a dietary vitamin C index was calculated, 33 found statistically significant protection. After completing a further review in 1991, Dr Block published a review [2] later that year of studies linking vitamin C with cancer prevention, Dr Block concluded:

“Approximately 90 epidemiologic studies have examined the role of vitamin C or vitamin-C-rich foods in cancer prevention, and the vast majority have found statistically significant protective effects. Evidence is strong for ­ cancers of the oesophagus, oral cavity, stomach and pancreas. There is also substantial evidence of a protective effect in cancers of the cervix, rectum and breast. Even in lung cancer there is recent evidence of a role for vitamin C.”

The first ever study in which vitamin C was given to cancer patients was carried out in the 1970s, by Dr Linus Pauling and Dr Ewan Cameron, a cancer specialist, working in Scotland. They gave 100 terminally ill cancer patients 10g (10,000mg) of vitamin C each day and compared their outcome with 1000 cancer patients given conventional therapy. The survival rate was five times higher in those taking vitamin C. By 1978, while all of the 1000 ‘control patients’ had died, 13 of the vitamin C patients were still alive, with 12 apparently free from cancer [3]. Other studies have confirmed these findings. Dr Murata and Dr Morishige of Saga University in Japan showed that cancer patients on 5–30g of vitamin C lived six times longer than those on 4g or less, while those suffering from cancer of the uterus lived 15 times longer on vitamin C therapy [4]. This was also confirmed by the late Dr Abram Hoffer in Canada, who found that patients on high doses of vitamin C survived, on average, ten times longer.

However, Pauling and Cameron’s findings were discredited, largely due to an apparent ‘replication’ of their study by the Mayo Clinic in the US [5]. There was, however, one major difference between the original trial and that of the Mayo Clinic. The ‘terminal’ patients in the original trial kept taking vitamin C every day, while those in the Mayo Clinic trial stopped after an average of 75 days. However, by then, the book was closed and mega-dose vitamin C was considered quackery.

How it works
Of all the antioxidants, vitamin C is the most extraordinary. Vitamin C is believed to help prevent and treat cancer by enhancing the immune system; stimulating the formation of collagen which is necessary for ‘walling off’ tumours; preventing metastasis (spreading) by inhibiting a particular enzyme and therefore keeping the ground substance around tumours intact; preventing viruses that can cause cancer; correcting a vitamin C deficiency which is often seen in cancer patients; speeding up wound healing in cancer patients after surgery; enhancing the effectiveness of some chemotherapy drugs; reducing the toxicity of some chemotherapy; preventing free radical damage and neutralising some carcinogens.

Numerous studies have found a link between vitamin C intake and the incidence of several different cancers, especially non-hormonal cancers [6]. Also, having a high plasma level of vitamin C cuts your risk of dying from cancer [7]. The evidence for the benefits of vitamin C is strongest for cancers of the mouth, oesophagus, stomach, lung, pancreas and cervix. While one analysis of 12 clinical studies found that, ‘Vitamin C intake had the most consistent and statistically significant inverse association with breast cancer risk’ [8], the evidence of an associated decreased risk for breast cancer is not as strong. One study involving 34,000 post-menopausal women, reported no association between the intake of vitamins A, C and E and a reduced risk of developing breast cancer [9].

The WCRF (World Cancer Research Fund) conclude that there is no evidence of a relationship between vitamin C intake and prostate cancer and insufficient evidence for breast cancer. The studies to date do suggest a big difference between the causes and treatment of hormone-related cancers and those of the lung or digestive tract. These lung and digestive tract cancers may be more related to oxidant carcinogens, and prevented by increasing one’s intake of anti-oxidant nutrients. Having an intake above 100mg a day cuts risk of lung cancer substantially [10].

Overall, the research to date strongly supports the importance of eating a diet rich in vitamin C (see below). While ­supplementing 1–5g vitamin C may help prevent some cancers, cancer patients are most likely to benefit from 10 grams or more a day. These higher levels are best taken with the guidance of your health practitioner.

Which foods are best for vitamin C?
Foods are listed in order of those that contain the most vitamin C per calorie of food. The figures in brackets are the amount of vitamin C in 100g, which is roughly equivalent to a cup or serving.


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