Your afternoon naps could be killing you. Noooooooooo.

Researchers at the University of Tokyo have found a correlation between taking regular naps of 40 minutes or longer, and an increased risk of health conditions such as obesity and high blood pressure.

The findings are based on more than 20 studies, comprising over 300,000 participants. At the American College of Cardiology’s annual conference, it was reported that taking lengthy daytime naps is linked to the development of a range of metabolic syndromes.

The research involved asking people whether they regularly nap, whether they feel sleepy during the day, what time they nap, and for how long. This information was then compared with their medical history. While a relationship was found between napping and health complications for naps 40 minutes or longer, shorter naps had no such link. So it looks like 40 is the magic number – any longer, and your risk of metabolic syndromes dramatically increases.

The researchers described their findings as a ‘J-shaped trend’ between time spent napping and health risk. That is, while naps under 40 minutes had no effect on ones risk for metabolic conditions, once naps were longer than 40 minutes, risk rose substantially. And participants who napped for 90 minutes were 50% more likely to suffer from a metabolic syndrome, as were people who reported being excessively tired during the day.

Goodness me. All this information is making me sleepy.

In discussing the research, lead author Dr Tomohide Tamada said, "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."

The theory behind the findings (which are a little troubling if, like me, you're fond of a good siesta) is that during naps that are longer that 40 minutes, the body prepares for deep sleep, which disrupts ones metabolism. Shorter naps don't have the same effect.

In fact, researchers were surprised to see a decreased risk for metabolic disease among those who napped for less than 30 minutes.

Note to self: Set alarm for 29 minutes from now.

Metabolic conditions like high cholesterol, obesity, and high blood pressure, all put a person at risk of premature death, so the effects of taking long naps during the day could be potentially life-threatening.

However, there are a few things to keep in mind when considering this research. First, it's correlational, so the researchers can't definitively say that napping causes metabolic conditions, just that the two are associated. It could be that people who are at risk of developing high blood pressure or high cholesterol simply tend to be more tired. Also, the data is based on self-reported information, which may or may not be entirely accurate.

A lot more research is needed to clarify the link between napping and poor health outcomes, but in the meantime, I'm going to stick to my 29 minute nap plan.

Speaking of health, not many of us know how much sugar is in our favourite drinks.