Taking Naps Increases Risk for Diabetes 28-36%

Even intentional napping may increase older adults’ risk of Type 2 diabetes, according to a large cohort study.

A siesta most days of the week appeared to elevate the likelihood of diabetes by a significant 28% to 36% in adults ages 50 and older, after adjustment for other sleep habits, health status, and other important factors, according to a published article.

The association persisted after exclusion of participants with ill health and daytime sleepiness, G. Neil Thomas, PhD, of the University of Birmingham, England, and colleagues reported.

Daily napping is a longstanding tradition across age groups in China, whereas diabetes is a fairly new phenomenon in the population, suggesting that diabetes is not responsible for inducing daytime sleepiness, the researchers said.

Prior studies from Germany and the U.S. also showed a link between napping and diabetes; another indicated higher all-cause mortality in older American women who snoozed each day. But “in these populations napping is not the norm and could be the result of underlying health problems,” Thomas’ group wrote.

Given the rapidly rising incidence of diabetes in China and the planned, routine naps common there, the researchers examined baseline Type 2 diabetes status (fasting blood glucose measurement) and napping, self-reported by 19,567 Chinese men and women ages 50 years or older in the Guangzhou Biobank Cohort Study.

Most of the participants — 67.2% — took at least one nap per week. The 59.4% who took a nap daily actually slept slightly more at night than non-nappers (6.4 versus 6.2 hours for those who napped less than once a week, P=0.004).

About two-thirds of the nappers took their nap within an hour after lunch and another 16.3% as a siesta in the afternoon. Naps averaged 60 minutes.

The overall prevalence of Type 2 diabetes was 13.5% in the cohort, but rose in a dose-dependent manner from 11.7% among never-nappers, 14.7% in those who napped four to six days per week, and 15.1% with daily napping. Longer naps appeared more strongly linked to diabetes (P=0.006 for trend).

The association was attenuated somewhat by adjustment for other sleep characteristics, such as insomnia and snoring, as well as age, sex, occupation, exercise, smoking, health status, adiposity,and metabolic markers. But it remained significant, with odds of diabetes elevated 36% for four to six naps per week and 28% for daily naps.

Daily naps had an even stronger effect in another analysis including only those who perceived themselves as in good health and reported physical activity, no daytime sleepiness, and no recent hospital admissions, cardiovascular disease, or hypertension .

Even individuals who had undiagnosed diabetes, according to fasting glucose levels, showed a similar association.

The researchers cautioned that the study could not determine causality, but because diabetes rates in China were under 1% until 1978, when economic reform started, napping habits likely predated diabetes in the cases included in the study.

“Both sleep homeostatic and circadian processes have profound influences on multiple physiological functions including the release of and sensitivity to metabolic hormones (e.g., insulin), and sympathetic-parasympathetic balance,” the authors noted.

Practice Pearl: Caution interested patients that although the study suggested that a nap habit predating diabetes may have increased Type 2 diabetes risk, the study could not prove causality.

Lam K-BH, et al “Napping is associated with increased risk of Type 2 diabetes: The Guangzhou Biobank Cohort Study” SLEEP 2010; 33: 402-07.