Sunlight & Cancer

Sunlight prevents cancer, study says

Owen Dyer London

Insufficient exposure to ultraviolet radiation may be an important risk factor for cancer in western Europe and North America, according to the author of a new study that directly contradicts official advice about sunlight.

The research, published this week in the journal Cancer (2002;94:1867-75), examined cancer mortality in the United States. Deaths from a range of cancers of the reproductive and digestive systems were approximately twice as high in New England as in the south west, despite a diet that varies little between regions.

An examination of 506 regions found a close inverse correlation between cancer mortality and levels of ultraviolet B light. The likeliest mechanism for a protective effect of sunlight is vitamin D, which is synthesised by the body in the presence of ultraviolet B.

The studyís author, Dr William Grant, says northern parts of the United States may be dark enough in winter that vitamin D synthesis shuts down completely. While the study focused on white Americans, the same geographical trend affects black Americans, whose overall cancer rates are significantly higher. Darker skinned people require more sunlight to synthesise vitamin D.

"There are 13 malignancies that show this inverse correlation, mostly reproductive and digestive cancers," said Dr Grant. "The strongest inverse correlation is with breast, colon, and ovarian cancer."

Other cancers apparently affected by sunlight include tumours of the bladder, uterus, oesophagus, rectum, and stomach.

The paper estimates that in 2002 insufficient exposure to ultraviolet B among Americans will lead to about 85 000 additional cancers out of 1 285 000 projected cases and 30 000 additional deaths out of 555 000 projected deaths, compared with what would occur if the entire country could obtain the same ultraviolet B levels as the southern states.

The total number of additional deaths that might occur in the United States from melanoma and other skin cancers with the same increased level of ultraviolet B would be about 3000. "Current advice about avoiding sunlight is very parochial," said Dr Grant. "Itís a dermatologistís viewpoint."

Another study by Dr Grant, published in a previous issue of Cancer (2002;94:272-81), looked at rates of breast cancer in 35 countries. That study attributed 25% of cases of breast cancer in Europe to insufficient exposure to ultraviolet B.

"The correlation between breast cancer and latitude in Europe becomes clearest when Scandinavia is removed from the analysis, probably because they get so much vitamin D from fish consumption," he said. "They also put vitamin D in their milk."

Vitamin D supplements in pill form are cheap and readily available, but it is not known whether they can act as a direct substitute for vitamin D synthesised from sunlight.

BMJ 2002;324:696

Response to this study

D. A. Palmer, Industrial Research Scientist

Response from Israel

M. Zilberstain, MD Dermatology

Ecologic Study:Dietary & Solar UV-B & Mortality for Bca

Cancer, 1/02

Study Finds Lower Death Rates:Brast, Colon

Occupational & Environmental Medicine, 4/02

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