Current impediments to acceptance of the ultraviolet-B-vitamin D-cancer hypothesis.

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Anticancer Res. 2009 Sep;29(9):3597-604.

Current impediments to acceptance of the ultraviolet-B-vitamin D-cancer hypothesis.
 
Grant WB, Boucher BJ.

Sunlight, Nutrition, and Health Research Center (SUNARC), San Francisco, CA 94164-1603, USA.

The
ultraviolet-B (UVB)-vitamin D-cancer hypothesis was proposed in 1980.
There have been numerous ecological, observational and other studies of
the hypothesis. There are about 14 types of cancer for which it seems
to apply: bladder, breast, colon, endometrial, esophageal, gallbladder,
gastric, ovarian, pancreatic, rectal, renal and vulvar cancer and both
Hodgkin's and non-Hodgkin's lymphoma. Nonetheless, the hypothesis has
not yet been accepted by public health agencies. Some of the reasons
for this include a distrust of ecological studies, some mistrust of
observational studies, and the existence of just one positive
randomized controlled trial, an analysis of a vitamin D and calcium
supplementation study involving post-menopausal women in Nebraska.
Paradigm shifts such as this generally take time, in part due to
opposition from those content with the status quo. In this paper,
results of ecological studies in the United States using summertime
solar UVB as the index of vitamin D production, which is highly
asymmetrical with respect to latitude, and indices for other cancer
risk-modifying factors (air pollution, alcohol consumption, dietary
iron and zinc, ethnic background, socioeconomic status, smoking and
urban/rural residence) are discussed in terms of supporting the
hypothesis. These studies were not considered while other ecological
studies were examined in recent critiques of the hypothesis. While
additional randomized controlled trials would, of course, be helpful,
the current evidence seems to satisfy the criteria for causality as
outlined by A. Bradford Hill.