Could staying out of the sun actually increase your cancer risk?

New research has found that women with high concentrations of vitamin D have a much lower chance of developing cancer. But even more striking is this: avoiding the sun may be as dangerous as smoking.

Nonsmokers who stayed out of the sun had a life expectancy similar to smokers who soaked up the most rays, according to a recent study involving nearly 30,000 Swedish women over 20 years.

Avoiding the sun “is a risk factor for death of a similar magnitude as smoking” the authors wrote in a recent issue of the Journal of Internal Medicine. Compared with those with the highest sun exposure, life expectancy for those who avoided sun dropped by 0.6 to 2.1 years.

Meanwhile, a study published recently in the journal PLOS ONE found a 67 per cent reduction in risk for all cancers in women with higher vitamin D levels.

The authors of this study noted the importance of sunlight in vitamin D absorption. While ancestors spent a lot of time outdoors in direct sunlight, today more time is spent indoors and behind computer screens.

Spending more time outside, though, is something North Americans have been taught to avoid; the dangers of too much sun exposure are well-known.

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But experts say we need to have a better understanding of the risks and benefits of being in the sun.

The researchers of the Swedish study acknowledged that longer life expectancy for sunbathers seems paradoxical to the common thinking that sun exposure increases risk for skin cancer.

“We did find an increased risk of…skin cancer,” lead author Pelle Lindqvist noted. “However, the skin cancers that occurred in those exposing themselves to the sun had better prognosis.”

Reinhold Vieth, scientific advisor for the non-profit Vitamin D Society and professor at the University of Toronto, points out that for people concerned about vitamin D, most dermatology societies recommend taking vitamin D supplements: at least 1000 IU/day.

“My own advice is that every person needs to understand how their own skin responds to sunshine,” Vieth says. “Never stay in the sun long enough to allow your skin to turn red. For a person with white, unshielded skin, this means spending no more than about 10 to 15 minutes in sunshine at a UV index of 7. For a person with very black skin, the time needed to produce the same amount of vitamin D can be six times longer. Very black skin functions like a built-in SPF of 6.”

Government advisory groups state that for adults, intakes of vitamin D up to 4,000 international units per day are safe.

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“But for context, recognize that 10 minutes of full body sun exposure–lying on a lawn chair with a bathing suit on in summer sun–produces the equivalent of 10,000 international units in one day, and that is a natural amount and safe.”

According to the Canadian Cancer Society, skin cancer is the most common cancer in the country. While the rate of new cases and death rate for many types of cancer are going down, melanoma rates have been increasing significantly in both men and women since 1986.

The society urges people to plan outdoor activities before 11 a.m. and after 4 p.m., when the sun is not at its strongest, and to use sunscreen, among other measures

And it emphasizes the dangers of indoor tanning. The amount of radiation emitted has been documented to be many times more than natural sun at midday in summer. The World Health Organization classifies tanning beds as a known factor that causes cancer in humans. People who start using indoor tanning equipment before the age of 35 have a 59 per cent increased risk of melanoma, the deadliest form of skin cancer.