Harvard University gave workers the excuse they were looking for last week when they said a nap after lunch may reduce the risk of heart attack.

But time-conscious managers may have a rebuttal: Though much forgotten in the press, another Harvard study, published several years earlier, made its own news splash by arguing that naps are associated with a higher incidence of heart attack.

So, who to believe?

The most recent article, published in the Archives of Internal Medicine, studied 23,000 Greek men and women ages 20 to 86 for an average of six years. After controlling for differences in body size, diet, exercise and smoking, subjects who napped three times a week for half an hour had a 37 percent lower death rate from heart disease. The effect on men was more pronounced than on women.

The conclusion seemed to contradict a study published in 2000 in the Journal of Epidemiology by a researcher in the department of nutrition at Harvard’s School of Public Health. That study compared approximately 500 Costa Ricans who had survived heart attacks with a nearly equal number of healthy people. Those who suffered heart attacks were 50 percent more likely to have taken a daily siesta.

Parsing the two contradictory conclusions, Martin Moore-Ede, a physiologist and the chief executive of Circadian Technologies, a research firm specializing in managing shift workforces, says: “Napping is a great solution if you are energetic and active and if you have adequate exercise during the day, but it’s not a great solution if you are a couch potato.”

Moore-Ede says the research done on the Greek workers was more thorough, especially since it followed them over time rather than retroactively determining what caused the Costa Rican subjects’ heart attacks.

Whether or not napping reduces the risk of heart attack, during the past decade some employers have started promoting napping. This trend will only accelerate, Moore-Ede says, as the number of people with flexible work schedules who work on the road and who work outside the normal 9-to-5 hours increases. Nearly one in four workers, or 24 million people, fall into this category.

“If you have an active lifestyle, whether you’re running through airports or digging ditches, then napping is a good solution,” Moore-Ede says. “Sleep deprivation itself is associated with cardiovascular risk.”

—Jeremy Smerd