A study published online by the International Journal of Cancer on April 26 found incidence rates of 12 types of cancer inversely correlated with solar erythemal UV doses in July.
The study drew from the National Institutes of Health-AARP (NIH-AARP) cohort of 450,934 white, non-Hispanic subjects aged 50-71 years. During up to nine years of follow-up to the end of 2006, 75,917 cases of cancer were identified. The UVB index was solar erythemal UV incident at the surface in July determined from the NASA satellite instrument, Total Ozone Mapping Spectrometer (TOMS) between 1978-1993 and 1996-2005. Erythemal UV includes the UVB region for vitamin D production, but also extends into the UVA region where no vitamin D is produced. Participants in the study were from six states California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania and two metropolitan regions (Atlanta and Detroit).
Those with cancer were divided into four quartiles of July erythemal UV dose with approximately equal numbers of cases. Many cancer risk-modifying factors such as BMI, physical activity, and smoking were shown to be nearly equally present among those in the four quartiles. However, the authors admitted that there could be unaccounted for confounding factors not included in the study, such as moving from the residential location at time of enrollment.
The 12 types of cancer are bladder, colon, kidney, lung, pancreas, pleura, prostate, rectal, thyroid cancer, diffuse large B-cell, T-call, and non-Hodgkin’s lymphoma. In addition, non-significant inverse correlations were also found for gall bladder, larynx, small intestine, and stomach cancer and follicular lymphoma. Increased risk of lip cancer (nonsignificant) and melanoma and other non-epithelial skin cancer (significant) provided support for the UV index used. These findings largely support the findings in many ecological studies. 1
Surprisingly, cancers of female organs, breast, ovary and uterus, were not inversely correlated with the UV index. A possible reason is that women spend less time in the sun than men. Other studies have found significant inverse correlations for solar UVB doses for men but not women such as an ecological study of cancer mortality rates in California in the period 1950-64.2
As the authors note, this study provides additional strong support for the role of vitamin D in reducing risk of cancer as no other factor has been proposed to explain the link between solar UVB irradiance and cancer risk reduction, and there is good support for vitamin D reducing the risk of cancer in other studies.
3. Lin SW, Wheeler DC, Park Y, Cahoon EK, Hollenbeck AR, Michal Freedman D, Abnet CC. Prospective study of ultraviolet radiation exposure and risk of cancer in the U.S. Int J Cancer. 2012 Apr 26. doi: 10.1002/ijc.27619. [Epub ahead of print]