Epidemiology of vitamin D and colorectal cancer: casual or causal link?
BACKGROUND
Since Garland and Garland hypothesized that better vitamin D status lowered risk of colorectal cancer in 1980, the relation between vitamin D status and colorectal cancer risk has been investigated in epidemiologic studies. These studies are reviewed.


METHODS
Various approaches have been used to estimate vitamin D status, including direct measures of circulating 25(OH)vitamin D levels, surrogates or determinants of vitamin D (including region of residence, intake, and sun exposure estimates, or a combination of these). These measures of vitamin D status have been studied in relation to colorectal adenoma, cancer incidence and mortality.


RESULTS
In general, all lines of inquiry from observational studies indicate that an association between better vitamin D status and lower colorectal cancer risk exists. While most of the studies have examined vitamin D status in relation to risk of cancer, some evidence suggests that vitamin D may be additionally important for colorectal cancer progression and mortality.


CONCLUSIONS
Although confounding factors cannot be entirely excluded, the consistency of the association using various approaches to measure vitamin D, for diverse endpoints and in diverse populations shows high consistency and is suggestive of a causal association. Thus, improving vitamin D status could be potentially beneficial against colorectal cancer incidence and mortality.
Giovannucci
Edward
E
Harvard School of Public Health, and Channing Laboratory, Brigham and Women's Hospital, Boston, MA 02115, USA. egiovann@hsph.harvard.edu
D000236:Adenoma / Q000378:metabolism*; D000818:Animals; D002112:Calcifediol / Q000378:metabolism*; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000378:metabolism* / Q000401:mortality; D004032:Diet; D019587:Dietary Supplements; D018450:Disease Progression; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D016032:Randomized Controlled Trials as Topic; D012306:Risk; D014807:Vitamin D / Q000378:metabolism*
D014807:Vitamin D; D002112:Calcifediol