The importance of sun exposure for colon cancer
By Marc Sorenson, EdD, Sunlight Institute…
In 1980, Cedric and Frank Garland published a seminal paper showing a relationship between colon cancer and geographical location. They observed dramatically higher rates of colon cancer in the Northeast, where there is a paucity of sun exposure, compared with the South and West where sun is more prevalent. They hypothesized that vitamin D, stimulated in the skin by sun, reduced the risk of colon cancer. They pointed out the correlation between colon cancer and UVR exposure, stating particularly that “New Mexico and Arizona had the highest statewide mean solar radiation values (500 gm-cal/cm2). These states experienced colon cancer rates for white males of 6.7 and 10.1 per 100 000 population, respectively, over the period 1959–61. New York, New Hampshire, and Vermont had the lowest statewide mean solar radiation values (300 gm-cal/cm2) and experienced colon cancer rates for white males of 17.3, 15.3, and 11.3 per 100 000 populations, respectively, during the same period.”
Other studies have corroborated the correlation between high sun exposure and low colon cancer rates. Japanese research demonstrated that people in the areas of highest solar radiation exhibit the lowest rates of colon cancer, with those living in the areas of highest sun exposure having about half the colon cancer rate as those living in the lowest.A significant aspect of this research is that sun correlated to a reduced risk of cancer even where vitamin D consumption was high, indicating that sun exposure (as noted with prostate cancer and breast cancer, above) may have beneficial influences on cancer beyond its stimulation of vitamin D production, or that vitamin D produced in the skin by sun exposure may have advantages over that consumed through food or supplements.
The research by Dr. Mizoue is not the only investigation that differentiated the effects of UV light exposure and vitamin D/colon cancer. A six-week study by Dr. Rebel and colleagues used mice with intestinal tumors—tumors that often progress to cancers. It was shown that the mice given either UV radiation or vitamin-D supplementation reduced the tumor load when compared to mice who received no treatment. However, only the UV treatments prevented the tumors from progressing to cancer. Still other recent research has demonstrated that sun, not vitamin D, may produce all of the positive effects on colon cancer. The researchers performed a 140-day investigation involving rats that had colon adenomas (a precursor to full-blown colon cancer) induced in their colons. The rats were given either vitamin D3 as supplements, or the stored form of vitamin D, 25(OH)D3, in differing amounts. With low dose vitamin D in either form, no reduction in either existing adenomas or emerging tumors were seen. In higher doses, there was a dose-dependent increase in colon tumor numbers in both male and female rats. The researchers said the following in their concluding statement: “Thus, the association between sun exposure and the incidence of colon cancer may involve factors other than vitamin D concentrations. Alternative hypotheses warrant investigation. Furthermore, this study provides preliminary evidence for the need for caution regarding vitamin D supplementation of humans at higher doses, especially in individuals with sufficient serum 25(OH)D3 concentrations.” The takeaway from this research is this: sun is protective against colon cancer in rats (and probably in humans), independent of vitamin D—another reason to safely embrace the sun.
These studies again demonstrate that we cannot substitute vitamin D pills for sun in many cases. UV light from sun or sun lamps is always the best option to cover all prevention and healing possibilities.
 Garland CF, Garland FC. Do sun and vitamin D reduce the likelihood of colon cancer? Int. J. Epidemiol 1980;9:227–31.
 Mizoue, T. Ecological study of solar radiation and cancer mortality in Japan. Health Phys 2004;87:532-38.
 Rebel H1, der Spek CD, Salvatori D, van Leeuwen JP, Robanus-Maandag EC, de Gruijl FR. UV exposure inhibits intestinal tumor growth and progression to malignancy in intestine-specific Apc mutant mice kept on low vitamin D diet. Int J Cancer. 2015 Jan 15;136(2):271-7.
 Irving AA, Plum LA, Blaser WJ, Ford MR, Weng C, Clipson L, DeLuca HF, Dove WF. Cholecalciferol or 25-hydroxycholecalciferol neither prevents nor treats adenomas in a rat model of familial colon cancer. J Nutr. 2015 Feb;145(2):291-8.