British adults who nap during the day and sleep less than 6 hours at night are nearly two times more likely to develop incident type 2 diabetes than those who do not nap and who sleep 6 to 8 hours at night, according to recent study findings.
In a prospective cohort study, researchers also found that daytime napping was independently associated with a 30% increased risk for type 2 diabetes, with adiposity partly explaining the association.
PhD, MPhil, of the Institute of Public Health at the University of Cambridge, U.K., and colleagues analyzed data from 13,465 adults with no known diabetes participating in the European Prospective Investigation into Cancer-Norfolk study (EPIC-Norfolk; 1998-2000), an ongoing, multicenter prospective cohort study. Participants, who completed questionnaires on sleep characteristics as part of the study, reported daytime napping habits and their 24-hour sleep duration; follow-up questionnaires collected information on smoking status, alcohol and drug intake and physical activity. Incident type 2 diabetes cases were identified through multiple data sources until July 2006.
Within the cohort, 3,852 (28.6%) reported napping during the day; 9,285 (67.9%) reported sleeping between 6 and 8 hours daily. Those who reported napping were more likely to be men, older, current or former smokers and physically inactive and have comorbidities and/or lower education.
After adjustment for age and sex, daytime napping was associated with a 50% higher diabetes risk; risk persisted after further adjustment for education, marital status, smoking, alcohol intake, physical activity, comorbidities and hypnotic drug use. However, additional adjustment for BMI and waist circumference attenuated the odds ratio to 1.3 (95% CI, 1.01- 1.69).
For sleep duration, BMI and waist circumference attenuated any association with type 2 diabetes risk; ORs for short and long sleep duration after adjustment were 1.46 (95% CI, 1.10, 1.90) and 1.64 (95% CI, 1.16, 2.32), respectively.
When sleep duration and daytime napping were examined together, the risk for developing diabetes more than doubled for those who took daytime naps and had less than 6 hours of sleep, compared to those who did not nap and had 6 to 8 hours of sleep (OR = 2.57; 95% CI, 1.74-3.78). Long sleep (at least 9 hours per day) was also associated with a 90% increased risk for diabetes, regardless of napping behavior, whereas those who did not nap and slept 6 to 8 hours per day had the lowest risk for developing diabetes.
“Interestingly, participants who took daytime naps but slept for short hours at night had the highest diabetes risk,” the researchers wrote. “It is plausible that short sleep duration and daytime napping were both indicators of sleep disturbance or share a common pathway, leading to an additive combined effect of the two factors.” – by Regina Schaffer
The researchers report no relevant financial disclosures.