Sunshine and Cancer in the USA

A research team at Harvard Medical School have just published the results of a study that monitored the health of 14,916 physicians over an 18 year period to determine whether vitamin D insufficiency increases their risk of prostate cancer. More than two-thirds of the men involved had insufficient vitamin D levels in winter and spring; and almost one-third had a vitamin D deficiency. In summer and autumn, more than 10 per cent were still vitamin D deficient, and more than half had less than optimal amounts of vitamin D in their blood. During the 18 years of follow-up 1,066 doctors developed prostate cancer, and 496 suffered an aggressive form of it. Men whose blood levels of vitamin D were below average were twice as likely to develop aggressive prostate cancer as those in whom levels were above average. The results of the Harvard investigation confirm that insufficient vitamin D is a common problem among men of European-descent in the United States. The relationship between vitamin D and prostate cancer has been investigated before but this is claimed to be the first study to follow a large enough number of men over a long enough period to give a clear picture of the relationship. It seems vitamin D insufficiency significantly increases the risk of prostate cancer, including a lethal form of the disease.
http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0040103#toclink1

Previous research indicates that sun exposure in childhood may protect against prostate cancer in later life. This appears to be the case with other autoimmune diseases too such as multiple sclerosis and insulin-dependant diabetes. A new study carried out at the Mount Sinai Hospital, Toronto, suggests that maintaining adequate vitamin D levels from the sun during adolescence could reduce the risk of breast cancer later in life by over 30 per cent. It seems sun exposure during breast development may be particularly important in preventing the disease. This reduction in breast cancer risk was associated with increasing sun exposure from ages 10 to 19. There was weaker evidence for this in older age groups.
http://cebp.aacrjournals.org/cgi/content/abstract/16/3/422