Obesity causes 20 percent of all cancer, low vitamin D may be the connection – meta-analysis - Sept 2014

Obesity and cancer: the role of vitamin D.

BMC Cancer. 2014 Sep 25;14:712. doi: 10.1186/1471-2407-14-712.
Shanmugalingam T1, Crawley D, Bosco C, Melvin J, Rohrmann S, Chowdhury S, Holmberg L, Van Hemelrijck M.

BACKGROUND:
It is estimated that 20% of all cancer cases are caused by obesity. Vitamin D is thought to be one of the mechanisms underlying this association. This review aims to summarise the evidence for the mediating effect of vitamin D on the link between obesity and cancer.

METHODS:
Three literature searches using PubMed and Embase were conducted to assess whether vitamin D plays an important role in the pathway between obesity and cancer:

• (1) obesity and cancer;
• (2) obesity and vitamin D; and
• (3) vitamin D and cancer.

A systematic review was performed for (1) and (3), whereas a meta-analysis including random effects analyses was performed for (2).

RESULTS:

• (1) 32 meta-analyses on obesity and cancer were identified; the majority reported a positive association between obesity and risk of cancer.
• (2) Our meta-analysis included 12 original studies showing a pooled relative risk of 1.52 (95% CI: 1.33-1.73) for risk of vitamin D deficiency (<50 nmol/L) in obese people (body mass index>30 kg/m2).
• (3) 21 meta-analyses on circulating vitamin D levels and cancer risk were identified with different results for different types of cancer.

CONCLUSION:
There is consistent evidence for a link between obesity and cancer as well as obesity and low vitamin D. However, it seems like the significance of the mediating role of vitamin D in the biological pathways linking obesity and cancer is low. There is a need for a study including all three components while dealing with bias related to dietary supplements and vitamin D receptor polymorphisms.

PMID: 25255691

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