by Dr. Noel Peterson, ND, DAAPM
With all the emphasis on avoiding sun exposure, the benefits of the sun have been sidelined. It turns out that nonsmokers who stay out of the sun have a life expectancy similar to smokers who soak up the most rays, according to researchers who studied nearly 30,000 Swedish women over 20 years.
The authors write that avoiding the sun “is a risk factor for death of a similar magnitude as smoking,” The study was published March 21, 2016 in the Journal of Internal Medicine.
Pelle Lindqvist, MD, of Karolinska University Hospital in Huddinge, Sweden, and colleagues found that women who seek out the sun were generally at lower risk for cardiovascular disease (CVD) and noncancer/non-CVD diseases such as diabetes, multiple sclerosis, and pulmonary diseases, than those who avoided sun exposure.
One of the strengths of the study was that results were dose-specific — sunshine benefits went up with increasing exposure.
The researchers acknowledge that longer life expectancy for sunbathers seems paradoxical to the common thinking that sun exposure increases risk for skin cancer.
“Longer life expectancy for sunbathers seems paradoxical to the common thinking that sun exposure increases risk for skin cancer.”
In an interview with Medscape, Dr Lindqvist said: “We did find an increased risk of…skin cancer. However, the skin cancers that occurred in those exposing themselves to the sun had better prognosis”.
Some Daily Exposure is as Important for Health
Given these findings, women should not overexpose themselves to sun, but underexposure may be even more dangerous than people think.
“We know in our population, there are three big lifestyle factors [that endanger health]: smoking, being overweight, and inactivity,” he said. “Now we know there is a fourth — avoiding sun exposure.”
Sweden’s restrictive guidance against sun exposure over the past 4 decades may be particularly ill-advised, the study finds, in a country where the maximum UV index is low (< 3) for up to 9 months out of the year. By contrast, Portland Oregon’s UV index is 3 or under for 6 the months of October-March.
Use of sunscreen is also widely misunderstood in the country and elsewhere, Dr Lindqvist said.
“If you’re using it to be out longer in the sun, you’re using it in the wrong manner,” he said. However, “If you are stuck on a boat and have to be out, it’s probably better to have sunscreen than not to have it.”
Women with more pigmentation would be particularly well-served to stop avoiding sunshine, he said, adding that many people in India, for instance, inappropriately follow guidelines like those in Sweden to avoid sun year round.
What about vitamin D and skin cancer?
This study doesn’t resolve the question of the role of vitamin D in health and the amount of it people need. “Whether the positive effect of sun exposure demonstrated in this observational study is mediated by vitamin D, another mechanism related to ultraviolet radiation, or by unmeasured bias cannot be determined.”
“We do know that melanomas are rare among women with darker skin, and sun benefits goes up in those populations when weighing sun exposure’s risk against benefits”, Dr Lindqvist said.
“From Irish studies we know that vitamin D deficiency makes melanomas more malignant,” Dr Lindqvist said.
“This is in agreement with our results; melanomas of [those not exposed] to the sun had a worse prognosis.”
Age and Smoking Habits
The researchers studied sun exposure as a risk factor for all-cause mortality for 29,518 women with no history of malignancy in a prospective 20-year follow-up of the Melanoma in Southern Sweden cohort.
The women were recruited from 1990 to 1992 when they were 25 to 64 years old. Detailed information was available at baseline on sun-exposure habits and potential confounders such as marital status, education level, smoking, alcohol consumption, and number of births.
When smoking was factored in, even smokers at approximately 60 years of age with the most active sun- exposure habits had a 2-year longer life expectancy during the study period compared with non-smokers who avoided sun exposure, the researchers note.
The authors acknowledged some major limitations, including that without exercise data, it was not possible to tell if increased outdoor physical activity or increased sun exposure benefited the patients.
Role of Vitamin D Still in Question
“Whether the positive effect of sun exposure demonstrated in this observational study is mediated by vitamin D, another mechanism related to ultraviolet radiation, or by unmeasured bias cannot be determined. Therefore, additional research is warranted,” the authors write.
This study was supported by the Clintec at the Karolinska Institute; ALF (Faculty of Medicine, Lund University, Region Skane); the Swedish Cancer Society; and the Swedish Medical Research Council. Funding was also received from Lund University Hospital; the Gustav V Jubilee Fund; the Gunnar Nilsson Foundation; the Kamprad Foundation; and the European Research Council. The authors declared no relevant financial relationships.
J Intern Med. Published online March 16, 2016.
Medscape
