A recent research paper from the Netherlands states that a shift from daily exposure to the sun to an intermittent exposure has correlated to an increase in skin cancer, and it suggests that moderate, frequent exposure is the best advice for people living in that country.[1] The researchers also state that frequent exposure is a protective factor against colorectal, cancer, prostate cancer, breast cancer and non-Hodgkin lymphoma, as well as multiple sclerosis and metabolic syndrome.
Interestingly, the paper mentions that the circadian rhythm is affected by light. It postulates that too low levels of light in the daytime and too high levels of light in the evening and at night can weaken and disrupt that rhythm, which could be a risk factor for some types of cancer and for metabolic syndrome. Such ideas have been studied previously, and have indicated that disruption of the circadian rhythm due to night-shift work may lead to increased breast-and/or-colorectal cancer risk in women.[2] [3]
Whatever the reason, which could also be related to vitamin D production among those who are regularly exposed to sunlight, the evidence for the health benefits of safe sunlight becomes clearer by the day. I opine that millions of lives could be saved yearly by regular, non-burning sun exposure for the entire population.
[1] van der Rhee HJ, Coomans CP, van de Velde P, Coebergh JW, de Vries E. [Illness, health and sunlight]. Ned Tijdschr Geneeskd 2013;157(46)
[2] Davis S, Mirick DK. Circadian disruption, shift work and the risk of cancer: a summary of the evidence and studies in Seattle. Cancer Causes Control 2006;17:539-45.
[3] Reparto di Chirurgia Generale A/D, Policlinico Sant’Andrea, Sapienza Università di Roma. [Night work as a possible risk factor for breast cancer in nurses. Correlation between the onset of tumors and alterations in blood melatonin levels]. Prof Inferm. 2007;60:89-93.