Two papers reported reduced risk of several types of internal cancers in China with respect to higher latitude [Grant, 2007] or solar UVB doses [Chen et al., 2010].
Chen W, Clements M, Rahman B, Zhang S, Qiao Y, Armstrong BK. Relationship between cancer mortality/incidence and ambient ultraviolet B irradiance in China. Cancer Causes Control. 2010 Oct;21(10):1701-9.
Grant WB. Does solar ultraviolet irradiation affect cancer mortality rates in China? Asian Pac J Cancer Prev. 2007 Apr-Jun;8(2):236-42.
Competing interests declared:
I receive funding from Bio-Tech Pharmacal (Fayetteville, AR), and the Sunlight Research Forum (Veldhoven) and have received funding from the UV Foundation (McLean, VA), the Vitamin D Council (San Luis Obispo, CA), the Vitamin D Society (Canada).