Power napping may raise your productivity at work, but it turns out that it's not so productive for your health, new research suggested.

Napping for more than 40 minutes is linked to an increased risk of developing metabolic syndrome, according to a University of Tokyo study presented at the American College of Cardiology's 65th Annual Scientific Session and Expo and reported in Medical Daily.

Metabolic syndrome manifests as a cluster of conditions — high blood sugar, high blood pressure, excess abdominal fat, and high cholesterol and triglyceride levels — and increases an individual's likelihood of developing cardiovascular disease.

Excessive tiredness during the day is also problematic for health, the scientists found. Daytime sleepiness increased the risk of developing metabolic syndrome by as much as 50 percent, as did napping for 90 minutes or longer. A previous study by the same researchers linked daytime sleepiness and extended naps to Type 2 diabetes.

Tomohide Yamada, lead author of the study, explained:

"Taking naps is widely prevalent around the world. So clarifying the relationship between naps and metabolic disease might offer a new strategy of treatment, especially as metabolic disease has been increasing steadily all over the world."

Believe it or not, the latest napping study was less dire compared to earlier ones. One such study found that middle-aged and elderly adults who napped during the day were 14 percent more likely to die in a 13-year period than their non-napping peers.

The news isn't all bad for nappers: If you simply cut your midday snoozes to less than 30 minutes, you actually decrease your risk of developing metabolic syndrome. Other studies found benefits associated with short naps, including reversing the effects of sleep deprivation, reducing stress (which itself causes a whole slew of health issues), and strengthening immune function.

Naps are a staple of many cultures across the world and are sometimes included in employees' work schedules. (Wouldn't that be nice?) The United States hasn't exactly gotten on board with this whole midday napping thing, but a startup based out of Orange County in California is trying to change that.

Nappify is testing mobile nap pads for Americans wishing to take a 40-minute snooze during the day, for a fee of $12.99, Time reported.

“You take 30, 40 minutes to refresh yourself and then reenergize for the second half of the day,” CEO and co-founder Kevin Pham told Time.

In light of this latest research, however, he may want to consider limiting napping sessions to 30 minutes.