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Am Fam Physician. 2003;67(3):465

to the editor: The article, “Recent Developments in Colorectal Cancer Screening and Prevention,”1 was good but overlooked one important risk reduction factor for colorectal cancer: vitamin D. Cohort2,3 and ecologic4 studies have shown that serum vitamin D—or solar ultraviolet-B (UV-B) radiation (280–320 nm), which photoinitiates the production of vitamin D—is a significant risk reduction factor for colon cancer and at least 10 other types of cancer.4 Serum 25-OH vitamin D3 was found to be inversely associated with the incidence of colorectal adenoma in a large cohort study5 of nurses among those with consistent vitamin D intakes during the past 10 years. Vitamin D affects calcium metabolism as well as reducing the proliferation of colon cancer cells.6

While an analysis4 did not consider factors other than solar UV-B radiation at the surface at 500 locales in the United States, studies in progress include such potentially confounding factors as urban/rural residence, Hispanic ethnicity, diet (calcium, energy, fat, fiber, protein, and vitamins A, C, and E intake per capita), smoking, and socioeconomic status. For colon cancer, solar UV-B radiation and rural residence (another ecologic surrogate for vitamin D production) accounted for 41 and 51 percent of the variance in mortality rates in women and men, respectively, from 1970 to 1994; fiber accounted for 21 percent (inverse), and vitamin A accounted for 8 percent of the variance for men, in general agreement with the literature.

Vitamin D or its metabolites are not always confirmed as a risk reduction factor for colorectal adenomas or carcinoma; this may be related to the interval between exposure or measurement and disease outcome. Colon cancer is believed to take 10 to 20 years to proceed from initiation to mortality, and vitamin D and its metabolites may be important in certain stages in the process and not in others.

Email letter submissions to afplet@aafp.org. Letters should be fewer than 400 words and limited to six references, one table or figure, and three authors. Letters submitted for publication in AFP must not be submitted to any other publication. Letters may be edited to meet style and space requirements.

This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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