Do Supplemental Forms of Choline, Methionine, Betaine, Vitamins B2, B6, B9 and/or B12 Increase Cancer Risk in Humans? A Systematised Narrative Review
By Marie Harrison - Nutrition Science and Practice
Abstract
Background:
Although dietary sources of choline, methionine, betaine, and vitamins B2, B6, B9 and B12 may decrease cancer risk, recent studies postulate that supplemental forms may increase this risk. This resulted in internet pages, social media, blogs and online discussion forums advising individuals to avoid B-vitamin supplementation. The proposed fortification of UK flour with folic acid makes this systematised narrative review particularly timely and relevant.
Aim and objectives:
The review aim is to amalgamate the multiple research on whether supplemental choline, methionine, betaine, vitamins B2, B6, B9 and B12 increase cancer risk in humans; concentrating on how the intervention may or may not work in different circumstances. This will be accomplished by a systematised narrative review, focusing on the quality of the studies.
Methodology:
Searches were conducted in major research databases for the keywords and alternative names for the supplements, methylation and cancer within the Title, Abstract and Keyword fields. Papers were accepted/rejected based on the predetermined inclusion and exclusion criteria. These were critically appraised using the Joanna Briggs Institute checklists and then compared and contrasted to ascertain any overall patterns in the data.
Findings:
26 papers (eight RCTs, 17 cohort and one case-control study) were reviewed. All but two studies concluded a nil or beneficial effect on cancer risk from B-vitamins. No studies found increased risk for breast cancer. One study found increased risk for colorectal and lung cancers. Miscellaneous cancers showed increased risk in two studies. However, these findings should be viewed with caution due to the very small risk/benefit levels involved combined with high risk of bias, non-conducive primary outcomes and numerous comorbid conditions, which could skew results.
Conclusion:
The original hypothesis was confirmed, that vitamins B2, B6, B9 and B12 have no effect (or slight beneficial effects) on cancer risk.
