Vanguard Neurologist

wsj.com

Spring forward with caution, a study suggests.

Researchers found that since 1987, heart attacks increased 6% in Sweden the day after a “spring forward” to daylight saving time.

By contrast, on the day after “falling back” an hour in the autumn, Swedes had 5% fewer heart attacks.

The reason: waking up earlier “can be hypothesized to have an adverse cardiovascular effect in some people,” wrote Imre Janszky and Rickard Ljung, the two Swedish doctors who reported the findings in a letter in this week’s New England Journal of Medicine.

The findings come from an analysis of Swedish national health records from 1987 to 2006.

The calculations compared the Monday after a change in daylight saving time with the corresponding Mondays two weeks before and two weeks after, and skipped years when the switch occurred on Easter.

“It has been postulated that people in Western societies are chronically sleep deprived, since the average sleep duration decreased from 9.0 to 7.5 hours during the 20th century,” Drs. Janszky and Ljung wrote. “Our data suggest that vulnerable people might benefit from avoiding sudden changes in their biologic rhythms.”

On average, about 1,735 Swedes had heart attacks the day after the switch, compared with 1,636 the Monday two weeks earlier or later. Sweden has about nine million people.

After “falling back” and getting an extra hour of sleep, Swedes had about 2,038 heart attacks the next Monday, compared with 2,140 on surrounding weeks.

The negative effects of “springing forward” seemed to continue for multiple days after the transition, increasing heart attacks by 5% over the entire week.

The beneficial effects of “falling back” were more modest.