NEW YORK (Reuters Health) - Older adults who catch a nap on most days may have a higher risk of type 2 diabetes than those who never take a siesta, researchers reported Monday.

In a study of nearly 20,000 Chinese adults age 50 and older, the investigators found that participants who said they usually napped on at least four to six days out of the week had a higher prevalence of type 2 diabetes.

Roughly 15 percent had diabetes, based on blood testing, versus about 12 percent of their counterparts who napped less often or not at all.

When the researchers weighed other factors -- including participants’ ages, physical activity levels and any diagnoses of high blood pressure or heart disease -- frequent napping remained linked to a higher diabetes risk.

Men and women who napped four to six days per week were 36 percent more likely than those who never napped to have diabetes. Similarly, daily nappers had a 28 percent higher risk, according to findings published in the medical journal Sleep.

Before nap lovers become too alarmed, however, the researchers stress that their findings do not prove that napping itself is the culprit.

For one, the study was cross-sectional, meaning it assessed participants at one point in time rather than following them over years. So it is not certain which came first, the frequent napping or the diabetes.

There are also many variables that could account for the napping-diabetes link; people in poorer general health, for example, might sleep more often. While the researchers tried to adjust their data for that -- factoring in participants’ self-reported health conditions, for instance -- they could not measure and control for all variables.

“There is not much to be drawn from the current study until it can be confirmed,” Dr. G. Neil Thomas, one of the researchers on the work, told Reuters Health in an email.

To make a stronger case for cause-and-effect, studies would have to follow a group of diabetes-free people over time, seeing whether those who napped frequently at the outset had a higher risk of developing diabetes, explained Thomas, of the University of Birmingham in the UK.

He suggested that older adults concentrate on lowering their diabetes risk through proven ways.

“Even if the (current) results are confirmed,” Thomas said, “people can do far more for their health by stopping smoking, having a balanced diet and being active. The data for these are unequivocal.”

The findings are based on 19,567 Chinese men and women age 50 and up who were questioned about their health and a number of lifestyle habits. The researchers also measured the participants’ waist circumference and tested their blood sugar levels to diagnose type 2 diabetes or impaired fasting glucose -- abnormal sugar levels that can be a precursor to diabetes.

In general, the researchers found, frequent nappers had a higher risk of both type 2 diabetes and impaired fasting glucose than other study participants.

Regular napping is a common practice in China, for people of all ages, Thomas and his colleagues note. So in comparison with Western countries, where many people may nap only when they are exhausted or ill, routine napping among Chinese adults is less likely to be a marker of health problems.

There are several mechanisms by which napping itself could, in theory, contribute to diabetes development, according to Thomas. Basically, he explained, napping might affect the body’s natural “rhythms” in a way that alters the activity of various hormones.

For example, Thomas noted, waking up is actually stressful for the body, and the nervous system activation it causes may negatively affect the body’s use of blood sugar.

SOURCE: Sleep, March 1, 2010.