Malignant melanoma is as much as 35% more common among people who live in Gothenburg and the region's coastal municipalities than those who live inland. Researchers at Sahlgrenska Academy, University of Gothenburg, Sweden, have found that the number of malignant melanoma cases in the Västra Götaland region has quadrupled since 1970.

Malignant melanoma has become increasingly common in the Western world over the past few decades. One of the biggest factors has been excessive and unprotected sunbathing despite widespread awareness of the health risks.

Melanoma takes a long time, sometimes several decades, to develop. For that reason, sunbathing habits from many years ago still affect a person's risk level.

According to a new study by researchers at Sahlgrenska Academy, University of Gothenburg, the number of melanoma cases in the Västra Götaland region has quadrupled among men and tripled among women since 1970.

"This represents a relative increase of more than 3% per year," says Magdalena Claeson, a researcher at Sahlgrenska Academy who participated in the study. "The increase in the region was considerably above average for the entire country."

The study found that 35% more men and 25% more women developed malignant melanoma in Gothenburg than in the inland municipalities. Fifteen per cent more women developed the disease in the coastal municipalities than inland.

One explanation is that inhabitants of Gothenburg and the coastal municipalities are exposed to the sun for more hours a day. A 2007 study conducted by the Swedish National Board of Health and Welfare found that inhabitants of Gothenburg and the coastal municipalities tend to take longer summer holidays in sunny countries and spend more time outdoors when abroad. Meanwhile, they are more likely to work indoors when they are in Sweden.

"The latest research suggests that melanoma is caused by this type of intermittent exposure to the sun," Magdalena Claeson says. "In other words, people get sunburned during their summer holiday and spend a lot of time indoors for the rest of the year."

The results have convinced the researchers that more preventive resources should be appropriated for the Västra Götaland region, particularly Gothenburg and the coastal municipalities.

"Among the measures likely to prove effective are educational initiatives among schoolchildren and sun protection information for people who travel abroad," Claeson says.

The article, entitled "Incidence of Cutaneous Melanoma in Western Sweden, 1970-2007," has been accepted for publication in Melanoma Research.