Sun exposure Information by Marc Sorenson, EdD. Sunlight Institute.
There are 62,700 cases of kidney cancer and 14,240 deaths annually. Kidney cancer incidence has tripled since the early 1980s, and some researchers have felt that environmental factors may have played a part in that worrisome increase. One of those factors may be sun exposure, which may be vital to the prevention of the disease. The newest research measured sun exposure, which was based on the average number of hours per day outdoors in the summer, during different periods of life. The researchers also took into consideration the age of the subjects and adjusted the data for other factors that may associate to kidney cancer.
These were some of the research results:
- Higher summer sun exposure at age 40+ years, but not at younger ages, was associated with a significantly lower risk of thyroid cancer. When comparing the highest quartile (fourth) of sun exposure to the lowest quartile, there was a 44% reduction in risk.
- Average lifetime sun exposure was not associated with thyroid-cancer risk.
- Recent summer sun exposure was closely associated with a decreased risk of thyroid cancer.
One of the salient points, in my mind, is that the best sun exposure is that which is habitual or consistent. In the case of kidney cancer, sun exposure in the past does not indicate that the disease will be avoided in the future. Only recent sun exposure provides protection. However, this is not necessarily true of other diseases; in the case of breast and prostate cancers, childhood sun exposure is associated with a lesser risk of the diseases in adulthood.
Previous research has also confirmed the importance of sun exposure on kidney-cancer prevention. There is a strong inverse correlation between sun exposure and kidney cancer. For example, one study that used NMSC as a measure of sun exposure, determined that sun exposure reduced the risk of several cancers, including kidney cancer, from 35% to 42%. Kidney cancer mortality rates were found to be strongly inversely correlated with solar UVB doses in Dr. William Grant’s 2002 and 2006 ecological studies. 
Recent research by Dr. Sara Karami and colleagues, demonstrates that in women, there is a significant reduction in kidney cancer with high levels of sun exposure. Those women with the highest fourth of sun exposure showed a 33% reduction in risk. Interestingly, the data was adjusted for vitamin D intake, and the results still showed sun exposure to have a stand-alone protective influence on kidney cancer—another indication that sun exposure has protective effects beyond vitamin D production.
Remember that a lifetime habit of non-burning sun exposure will always provide the best health outcomes.
 Rachel D Zamoiski, Elizabeth K. Cahoon, D. Michal Freedman, et al. Prospective study of ultraviolet radiation exposure and thyroid cancer risk in the United States. Cancer Epidemiol Biomarkers Prev Published Online First December 2, 2016.
 Tuohimaa P, Pukkala E, Scélo G, Olsen JH, Brewster DH, Hemminki K, Tracey E, Weiderpass E, Kliewer EV, Pompe-Kirn V, McBride ML, Martos C, Chia KS, Tonita JM, Jonasson JG, Boffetta P, Brennan P. Does solar exposure, as indicated by the non-melanoma skin cancers, protect from solid cancers: vitamin D as a possible explanation. Eur J Cancer 2007;43(11):1701-12
 Grant WB. An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet-B radiation. Cancer. 2002 Mar 15;94(6):1867-75.
 Grant WB, Garland CF. The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates. Anticancer Res. 2006 Jul-Aug;26(4A):2687-99.
 Karami S, Colt JS, Stewart PA, Schwartz K, Davis FG, Ruterbusch JJ, Chow WH, Wacholder S, Graubard BI, Purdue MP, MooreLE. Short Report: A case-control study of occupational sun exposure and renal cancer risk. Int J Cancer. 2015 Oct 27.