title: Change in Body Mass Index Associated With Lowest Mortality in Denmark, 1976-2013.
abstract: OBJECTIVE
  Research has shown a U-shaped pattern in the association of body mass index (BMI) with mortality. Although average BMI has increased over time in most countries, the prevalence of cardiovascular risk factors may also be decreasing among obese individuals over time. Thus, the BMI associated with lowest all-cause mortality may have changed.
  
  
  OBJECTIVE
  To determine whether the BMI value that is associated with the lowest all-cause mortality has increased in the general population over a period of 3 decades.
  
  
  METHODS
  Three cohorts from the same general population enrolled at different times: the Copenhagen City Heart Study in 1976-1978 (n = 13,704) and 1991-1994 (n = 9482) and the Copenhagen General Population Study in 2003-2013 (n = 97,362). All participants were followed up from inclusion in the studies to November 2014, emigration, or death, whichever came first.
  
  
  METHODS
  For observational studies, BMI was modeled using splines and in categories defined by the World Health Organization. Body mass index was calculated as weight in kilograms divided by height in meters squared.
  
  
  METHODS
  Main outcome was all-cause mortality and secondary outcomes were cause-specific mortality.
  
  
  RESULTS
  The number of deaths during follow-up was 10,624 in the 1976-1978 cohort (78% cumulative mortality; mortality rate [MR], 30/1000 person-years [95%CI, 20-46]), 5025 in the 1991-1994 cohort (53%; MR, 16/1000 person-years [95%CI, 9-30]), and 5580 in the 2003-2013 cohort (6%;MR, 4/1000 person-years [95%CI, 1-10]). Except for cancer mortality, the association of BMI with all-cause, cardiovascular, and other mortality was curvilinear (U-shaped). The BMI associated with the lowest all-cause mortality increased by 3.3 from the 1976-1978 cohort compared with the 2003-2013 cohort. [table: see text] The multivariable-adjusted hazard ratios for all-cause mortality for BMI of 30 or more vs BMI of 18.5 to 24.9 were 1.31 (95%CI, 1.23-1.39;MR, 46/1000 person-years [95%CI, 32-66] vs 28/1000 person-years [95%CI, 18-45]) in the 1976-1978 cohort, 1.13 (95%CI, 1.04-1.22; MR, 28/1000 person-years [95%CI, 17-47] vs 15/1000 person-years [95%CI, 7-31]) in the 1991-1994 cohort, and 0.99 (95%CI, 0.92-1.07;MR, 5/1000 person-years [95%CI, 2-12] vs 4/1000 person-years [95%CI, 1-11]) in the 2003-2013 cohort. CONCLUSIONS AND RELEVANCE Among 3 Danish cohorts, the BMI associated with the lowest all-cause mortality increased by 3.3 from cohorts enrolled from 1976-1978 through 2003-2013. Further investigation is needed to understand the reason for this change and its implications.
authors.affiliation: Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark2Copenhagen General Population Study, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark3Section for Molecular Gen.
authors.forename: Shoaib
authors.initials: S
authors.lastname: Afzal
authors.affiliation: Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark2Copenhagen General Population Study, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark3Section for Molecular Gen.
authors.forename: Anne
authors.initials: A
authors.lastname: Tybjærg-Hansen
authors.affiliation: Copenhagen City Heart Study, Frederiksberg Hospital, Copenhagen University Hospital, Frederiksberg, Denmark.
authors.forename: Gorm B
authors.initials: GB
authors.lastname: Jensen
authors.affiliation: Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark2Copenhagen General Population Study, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark3Section for Molecular Gen.
authors.forename: Børge G
authors.initials: BG
authors.lastname: Nordestgaard
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002318:Cardiovascular Diseases / Q000401:mortality; D002423:Cause of Death / Q000639:trends*; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000401:mortality; D016016:Proportional Hazards Models