ReviewDoes sunlight prevent cancer? A systematic review
Introduction
The interest in the effects of sunlight and ultraviolet rays on health in man has until now mainly been focused on the negative aspects. The steady rise in the incidence of skin cancer during the last decades, largely caused by increased sun exposure, has in most western countries led to public health recommendations that sun exposure should be avoided.
There is a linear relationship between the degree of sun exposure and squamous cell carcinoma of the skin.1 The relationship between melanoma, the most aggressive type of skin cancer, and sunlight, however, is more complicated.1 Intermittent sun exposure at young age causing severe sunburn is the most important exogenous risk factor, whereas a certain degree of chronic exposure might have a preventive effect.2, 3 Moreover, sun exposure might be associated with increased survival from melanoma.4, 5, 6
For many years it has been known that sun exposure has positive effects on bone metabolism. In recent years, a growing list of other possible beneficial effects has been added, such as a reduced risk on multiple sclerosis, diabetes type 1, schizophrenia and several types of cancer.7, 8, 9, 10, 11
These new data could make it necessary to reconsider the health recommendations on sun exposure. But first these new data have to be evaluated. In the present paper, we reviewed all studies concerning sun exposure and cancer other than skin cancer.
Section snippets
Search strategy
A search was performed in 2 electronic databases: EMBASE (1980 to February 2006) and MEDLINE (1966 to February 2006). Text words (or mesh terms) that were used included cancer (NOT skin cancer) and, separately, the 20 most frequently occurring types of cancer in Western Europe (prostate, bladder, breast, colon, rectal, pancreas, gall bladder, stomach, oesophageal, liver, lung non-small cell, ovary, uterine cervix, uterus, pharynx, larynx, brain, and oral cavity cancer; non-Hodgkin lymphoma,
Results
A total of 2431 titles were found. When it was obvious from the title or the abstract that studies were not relevant to our subject, they were excluded. Based on the title and abstract, 94 studies were reviewed completely, of which 27 were selected in accordance with our criteria. Sixty-seven publications were excluded, either because they did not present original data, or because they did not present effect estimates with p-value or confidence intervals, or because they were re-analyses of a
Discussion
From our review, it becomes clear that there is an increasing evidence of sunlight having a preventive effect on the initiation and/or progression of different kinds of cancer.
Conflict of interest statement
There is no conflict of interest. The researchers have not been funded by any external organisation.
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