Body mass index trajectories preceding first report of poor self-rated health: a longitudinal case-control analysis of the English Longitudinal Study of Ageing
BackgroundStudies have consistently found that obesity is associated with poor self-rated health, but how body mass index (BMI) developed in the lead up to poor self-rated health is unknown.\n\nMethodsWe nested a longitudinal case-control study in the English Longitudinal Study of Ageing (1998-2015) to investigate BMI trajectories in the years preceding a first self-report of poor health. Participants rated their health at each data collection; every other collection included a BMI assessment by a nurse. Case status was defined as a first report of poor health during follow-up. Three age- and sex-matched controls were identified per case using density sampling. BMI trajectories were fitted to time backwards prior to first report of poor health using mixed-effects models. Age and sex were potential modifiers. We conducted subgroup analyses of those not reporting certain chronic diseases or smoking.\n\nResultsWe identified 732 cases and 2195 controls. Age, but not sex, modified the association between BMI and self-rated health. Participants reporting poor health at age 60 had a 1.5 kg/m2 (95%CI: 0.8 to 2.1) higher BMI at the time of reporting than controls, and their BMI had previously increased sharply. After age 75, cases no longer had higher BMI than controls, and their BMI had decreased sharply prior to reporting poor health. Age was also an effect modifier among those without diabetes, however BMI trajectories were more similar among the middle-aged.\n\nConclusionDevelopment of BMI was associated with poor self-rated health; however, the nature of the association depended markedly on age.\n\nO_TEXTBOXWhat is already known on this subjectO_LIStudies based on a single body mass index measurement have consistently found that being underweight or obese was associated with poor self-rated health.\nC_LIO_LIHow body mass index developed in the lead up to poor self-rated health was unknown.\nC_LI\n\nC_TEXTBOX\n\nO_TEXTBOXWhat this study addsO_LIIn the present study, body mass index trajectories leading up to poor self-rated health were strongly dependent on age at first report of poor health. Middle-aged participants with poor self-rated health had higher body mass index than controls; both groups had increasing body mass index over time.\nC_LIO_LIIn contrast, a report of poor health at age 75 or later was preceded by a decrease in body mass index; controls were 10 years older than cases before they started to lose body mass index.\nC_LIO_LIOur results suggest that future prospective studies and clinical decision making should take into account the age-dependent association between development of body mass index preceding poor self-rated health.\nC_LI\n\nC_TEXTBOX