Reviewers assessed 10 papers on 11 studies published between 1950 and September 2016, involving a total of 520 colorectal cancer patients and 5,981 healthy controls, in order to analyse the link between serum vitamin E and the risk of developing the cancer.
They found that the colorectal cancer patients had lower serum vitamin E levels than the healthy controls, but only in the hospital-based studies; they subsequently found no relationship between serum vitamin E concentration and colorectal cancer risk from the population-based studies.
Additionally, ethnicity-based subgroup analysis in nine of the studies showed that European colorectal cancer patients tended to have lower serum vitamin E levels than the healthy controls.
However, no significant difference in serum vitamin E levels between colorectal cancer patients and healthy controls was observed in the other two studies, which had assessed Asian subjects. The review attributed this to the small number of subjects in the latter two studies.
Colorectal cancer is the world’s fourth most common cause of cancer death, the third most common cancer in men, and the second most common cancer in women. The five-year survival rate for patients is much lower in developing countries than in developed countries, and worryingly, the possible causes of colorectal cancer are still not fully understood.
The reviewers acknowledged the limitations of their meta-analysis: it included only papers published in English and Mandarin, which might have skewed its results toward English-speaking countries.
The studies also mainly used a case-control design, with few based on cohort studies regarding the link between vitamin E and colorectal cancer. As such, the causality suggested in the analysis “could not be firmly established”.
The review concluded that while serum vitamin E deficiency might be associated with a higher risk of developing colorectal cancer, “necessary prospective cohort studies should be conducted to assess the effect of serum vitamin E” on the risk of colorectal cancer.
“Link between risk of colorectal cancer and serum vitamin E levels”
Authors: Yonghai Dong, et al.