Last Updated: 2003-06-03 13:00:36 -0400 (Reuters Health)

OSLO (Reuters) - Temperature jumps in north Sweden seem to trigger heart attacks, scientists said on Tuesday.

"Warmer weather over Scandinavia ... was associated with an increase in the incidence and mortality in northern Sweden," the scientists said in a report published in the June edition of the Journal of Internal Medicine.

Their study looked at 1985-1999 hospital records in Sweden's two northernmost counties, where 510,000 people live.

"Meteorological factors could be one of the so far neglected factors" in explaining heart attacks, the report said.

A possible explanation was that people became more active when temperatures rose and had heart attacks after exerting themselves. "When it's warmer you go out and shovel away the snow or mow the lawn," one of the authors, Torbjoern Messner of Kiruna Hospital, told Reuters.

"We don't know if the findings would hold up in other regions. We'd like to see similar studies in other parts of the Arctic," he said.

People in northern Sweden and other parts of the Arctic have higher levels of cholesterol in their blood than people further south. Messner said their genetic make-up might be different.

The study did not exactly match temperature changes to the frequency of heart attacks. Instead, it tracked complex shifts in barometric pressure known as the Arctic Oscillation that regulates temperature, humidity and winds.

The Oscillation index ranged between -4.1 to plus 4.1, indicating extremes of low and high pressure, over the period. A one point rise on the index was found to cause 8.3 percent more heart fatalities than normal.