title: Napping and the risk of type 2 diabetes: a population-based prospective study.
abstract: OBJECTIVE
  Some studies indicate an association between napping and increased risk of type 2 diabetes. We studied this prospectively in a sample representative of general population.
  
  
  METHODS
  A questionnaire was administered to the Finnish Twin Cohort in 1990 (response rate 77%, age 33-60 years). The study population included 12,244 subjects who replied to the question "Do you sleep during the daytime (take naps)?" with five response alternatives ranging from "no need" to "every or almost every day." Information on incident cases of diabetes was obtained by linkage to nationwide registers. Logistic regression models were used to obtain odds ratios (ORs) (95% confidence intervals) for incident type 2 diabetes risk in 1991-2004 by napping category. Adjustments were made for 11 socio-demographic and lifestyle covariates. For subjects aged 33-45 years at baseline, a questionnaire in 2011 provided information on prevalent diabetes.
  
  
  RESULTS
  Thirty-four per cent had no need for napping, and 15% did so on ≥3 days weekly. There were 356 incident type 2 diabetes cases during the follow-up. Using the 'no need' category as the reference, the risk of type 2 diabetes was significantly increased only among those napping most frequently [OR 1.86 (1.29-2.67), age- and sex-adjusted]. After adjusting for other covariates, the results were essentially the same, but when adjusted for body mass index, the association decreased (to about 1.3) and was statistically non-significant. Analysis of 2011 self-reported type 2 diabetes was in line with the register data.
  
  
  CONCLUSIONS
  Frequent napping is associated with future risk of type 2 diabetes. This association is largely explained by obesity.
authors: Finnish Institute of Occupational Health, Helsinki, Finland; Department of Public Health, University of Helsinki, Helsinki, Finland. Electronic address: christer.hublin@ttl.fi.
authors: Christer
authors: C
authors: Hublin
authors: Institute for Molecular Medicine Finland, University of Helsinki, Helsinki, Finland.
authors: Mikko
authors: M
authors: Lehtovirta
authors: Department of Public Health, University of Helsinki, Helsinki, Finland; Helsinki Sleep Clinic, Vitalmed Research Centre, Helsinki, Finland.
authors: Markku
authors: M
authors: Partinen
authors: Department of Public Health, University of Helsinki, Helsinki, Finland.
authors: Markku
authors: M
authors: Koskenvuo
authors: Department of Public Health, University of Helsinki, Helsinki, Finland; Institute for Molecular Medicine Finland, University of Helsinki, Helsinki, Finland; National Institute for Health and Welfare, Helsinki, Finland.
authors: Jaakko
authors: J
authors: Kaprio
mesh_terms: D000328:Adult; D000367:Age Factors; D015992:Body Mass Index; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology*; D005260:Female; D005387:Finland; D006306:Health Surveys; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications*; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D012890:Sleep / Q000502:physiology*
keywords: Follow-up; Napping; Population; Type 2 diabetes