Cancer Prevention

Higher vitamin C blood levels show protective effect against tumors

Epidemiologic evidence

A search of the medical database PubMed^[1] shows that there is a number of scientific studies looking into the relationship between vitamin C intake from natural food sources and reduced cancer risk. (At least) three meta-analyses summarizing the findings of many pertinent studies are owed to Gladys Block, PhD, who investigated the link between vitamin C, cancer incidence, and cancer prevention.

Dietary vitamin C intake and cancer prevention

Published in the American Journal of Clinical Nutrition in January 1991, Dr. Block's first meta-analysis reviewed here is titled Vitamin C and cancer prevention: the epidemiologic evidence. It is based on 75 studies related to vitamin C intake and cancer protection.

Apparently, at that time Block was working for the US National Cancer Institute's (NCI) Division of Cancer Prevention and Control (which for those who trust the NCI in spite of its less than trustworthy history — see Medical History [scroll to "The National Cancer Institute" or click here] — will lend even more credibility to the results obtained by Dr. Block).

Block found that epidemiologic evidence of vitamin C's protective effect for non-hormone-dependent cancers was strong, with a high percentage of studies which calculated a dietary vitamin C index or assessed fruit intake showing statistically significant protective effects of high versus low intakes of food-derived vitamin C.

For esophageal, laryngeal, mouth and pancreatic cancer, the data revealed consistent evidence for vitamin C (or some other fruit component) exerting a protective effect. Similarly strong evidence was found for stomach, rectal, breast, cervical and lung cancers. Since the author considered it likely that ascorbic acid worked synergistically with other plant components such as carotenoids, she encouraged increased consumption of fruits and vegetables.

Dietary vitamin C intake and cancer protection: more epidemiologic evidence

Published in the American Journal of Clinical Nutrition eleven months after the above paper (in December 1991), Dr. Block's second meta-analysis of vitamin C and cancer studies is titled Epidemiologic evidence regarding vitamin C and cancer. At the time of this and a later publication, Dr. Block apparently was working for the University of California's (Berkeley) School of Public Health.

Reviewing some 90 epidemiologic studies examining the cancer-preventive effect of vitamin C or vitamin-C-rich foods, Block found "extremely strong" data supporting a protective role of vitamin C for stomach, pancreas, mouth and esophageal cancer, and similarly strong evidence for cancer of the cervix and rectum.

While there were conflicting results observed for lung cancer, several more recent studies did find statistically significant protection from higher food-derived vitamin C intakes. Regarding breast cancer, evidence points to a consistent and significant protective effect of elevated dietary vitamin C intake.

A more recent study (from 2018) published in the British Journal of Cancer which had followed more than 24,000 individuals over fifteen years confirmed that those with higher vitamin C blood levels developed less oesophageal cancer and additionally were less likely to develop Barrett’s oesophagus, a precancerous condition. See Dietary antioxidant intake and the risk of developing Barrett’s oesophagus and oesophageal adenocarcinoma (full free text at https://www.nature.com/articles/s41416-018-0113-y).

More summary studies on vitamin C and reduced cancer risk

Gladys Block, PhD, has authored another meta-analysis titled "Vitamin C status and cancer. Epidemiologic evidence of reduced risk" published in the Annals of the New York Academy of Sciences in September 1992 (which can be purchased online), as well as several related studies re the protective effect of vitamin C in collaboration with other researchers.

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Footnotes

1 maintained by the United States National Library of Medicine (NLM), www.ncbi.nlm.nih.gov/PubMed/