Does Frequent Napping Portend Diabetes?

We’re told that a brief after-lunch nap is good for our memory, which is encouraging news for the millions of older people who enjoy a post-prandial snooze.  However, a report from China in the journal Sleep casts a shadow on this.   

Napping in China is, apparently, a social norm, often starting in childhood. Data from the Guangzhou Biobank Cohort Study was analyzed in a search for a relationship between napping and the occurrence of type 2 diabetes.  There were almost 20,000 men and women over 50 in the database.  Fasting blood glucose levels were used to diagnose diabetes.  The amount of napping was self-reported on a questionnaire.

Overall, diabetes was found in 13.5% of the 20,000 subjects.  It was found in15.1% of those who reported napping daily, and in 14.7% of those napping 4-6 times a week.  These percentages remained essentially unchanged after adjustments were made for age, gender, lifestyle, sleep habits, health status, and overweight.

When a sub-sample of 3,800 participants were re-contacted for additional information, it was found that there was an increased risk of diabetes in those with longer nap duration - 41% higher for those who napped longer than 30 minutes, and 35% higher for those who napped less than 30 minutes, compared with those who never took naps.

How important are these findings for the US population?  The Chinese in the study had an average age of 61 (women) or 64 (men).  So they are somewhat younger than the majority of US people who nap daily, or even 4-6 days a week – I’m assuming that nearly all regular US nappers must be retired i.e. over 65.  Moreover, most US nappers probably have conditions that cause tiredness and increase the urge to nap, whereas the Chinese in the study were “raised to nap”. Nevertheless, the findings may give the regular US napper pause; at the very least, he or she should have an annual blood sugar test (or better, an HbA1c level).