title: Association of Body Mass Index with Depression, Anxiety and Suicide-An Instrumental Variable Analysis of the HUNT Study.
abstract: OBJECTIVE
  While high body mass index is associated with an increased risk of depression and anxiety, cumulative evidence indicates that it is a protective factor for suicide. The associations from conventional observational studies of body mass index with mental health outcomes are likely to be influenced by reverse causality or confounding by ill-health. In the present study, we investigated the associations between offspring body mass index and parental anxiety, depression and suicide in order to avoid problems with reverse causality and confounding by ill-health.
  
  
  METHODS
  We used data from 32,457 mother-offspring and 27,753 father-offspring pairs from the Norwegian HUNT-study. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale and suicide death from national registers. Associations between offspring and own body mass index and symptoms of anxiety and depression and suicide mortality were estimated using logistic and Cox regression. Causal effect estimates were estimated with a two sample instrument variable approach using offspring body mass index as an instrument for parental body mass index.
  
  
  RESULTS
  Both own and offspring body mass index were positively associated with depression, while the results did not indicate any substantial association between body mass index and anxiety. Although precision was low, suicide mortality was inversely associated with own body mass index and the results from the analysis using offspring body mass index supported these results. Adjusted odds ratios per standard deviation body mass index from the instrumental variable analysis were 1.22 (95% CI: 1.05, 1.43) for depression, 1.10 (95% CI: 0.95, 1.27) for anxiety, and the instrumental variable estimated hazard ratios for suicide was 0.69 (95% CI: 0.30, 1.63).
  
  
  CONCLUSIONS
  The present study's results indicate that suicide mortality is inversely associated with body mass index. We also found support for a positive association between body mass index and depression, but not for anxiety.
authors.affiliation: Department of Public Health, Faculty of Medicine, Norwegian University of Science and Technology, 7491, Trondheim, Norway; Forensic Department and Research Centre Bröset St. Olav's University Hospital Trondheim, Trondheim, Norway.
authors.forename: Johan Håkon
authors.initials: JH
authors.lastname: Bjørngaard
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom; MRC Integrative Epidemiology Unit at the University of Bristol, Bristol, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Carslake
authors.affiliation: Department of Human Movement Science, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Tom Ivar
authors.initials: TI
authors.lastname: Lund Nilsen
authors.affiliation: Neurobiology of Stress and Behaviour Research Group, School of Clinical Sciences, University of Bristol, Bristol, United Kingdom.
authors.forename: Astrid C E
authors.initials: AC
authors.lastname: Linthorst
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom; MRC Integrative Epidemiology Unit at the University of Bristol, Bristol, United Kingdom.
authors.forename: George
authors.initials: G
authors.lastname: Davey Smith
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Gunnell
authors.affiliation: Department of Public Health, Faculty of Medicine, Norwegian University of Science and Technology, 7491, Trondheim, Norway.
authors.forename: Pål Richard
authors.initials: PR
authors.lastname: Romundstad
mesh_terms: D000293:Adolescent; D000328:Adult; D001007:Anxiety / Q000209:etiology*; D015992:Body Mass Index; D002648:Child; D003863:Depression / Q000209:etiology*; D005220:Fathers / Q000523:psychology / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D009035:Mothers / Q000523:psychology / Q000706:statistics & numerical data; D009765:Obesity / Q000150:complications / Q000523:psychology; D010287:Parent-Child Relations; D016016:Proportional Hazards Models; D011569:Psychiatric Status Rating Scales; D012307:Risk Factors; D013405:Suicide / Q000706:statistics & numerical data*