title: Body mass index and cognitive function: the potential for reverse causation.
abstract: OBJECTIVE
  Higher late life body mass index (BMI) is unrelated to or even predicts lower risk of dementia in late life, a phenomenon that may be explained by reverse causation due to weight loss during preclinical phases of dementia. We aim to investigate the association of baseline BMI and changes in BMI with dementia in a large prospective cohort, and to examine whether weight loss predicts cognitive function.
  
  
  METHODS
  Using a national cohort of adults average age 58 years at baseline in 1994 (n=7029), we investigated the associations between baseline BMI in 1994 and memory scores from 2000 to 2010. We also examined the association of BMI change from 1994 to 1998 with memory scores from 2000 to 2010. Last, to investigate reverse causation, we examined whether memory scores in 1996 predicted BMI trajectories from 2000 to 2010.
  
  
  RESULTS
  Baseline overweight predicted better memory scores 6 to 16 years later (β=0.012, 95% confidence interval (CI)=0.001; 0.023). Decline in BMI predicted lower memory scores over the subsequent 12 years (β=-0.026, 95% CI= -0.041; -0.011). Lower memory scores at mean age 60 years in 1996 predicted faster annual rate of BMI decline during follow-up (β=-0.158 kg m(-2) per year, 95% CI= -0.223; -0.094).
  
  
  CONCLUSIONS
  Consistent with reverse causation, greater decline in BMI over the first 4 years of the study was associated with lower memory scores over the next decade and lower memory scores was associated with a decline in BMI. These findings suggest that preclinical dementia predicts weight loss for people as early as their late 50s.
authors.affiliation: Department of Social and Behavioral Sciences, Harvard School of Public Health, Boston, MA, USA.|Discipline of Geriatrics, University of Sao Paulo Medical School, Sao Paulo, SP, Brazil.
authors.forename: C K
authors.initials: CK
authors.lastname: Suemoto
authors.affiliation: Department of Social and Behavioral Sciences, Harvard School of Public Health, Boston, MA, USA.
authors.forename: P
authors.initials: P
authors.lastname: Gilsanz
authors.affiliation: Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, CA, USA.
authors.forename: E R
authors.initials: ER
authors.lastname: Mayeda
authors.affiliation: Department of Social and Behavioral Sciences, Harvard School of Public Health, Boston, MA, USA.|Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, CA, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Glymour
mesh_terms: D000375:Aging / Q000523:psychology; D015992:Body Mass Index; D003071:Cognition; D003704:Dementia / Q000453:epidemiology* / Q000209:etiology* / Q000503:physiopathology / Q000523:psychology; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory; D008875:Middle Aged; D009765:Obesity / Q000150:complications* / Q000453:epidemiology* / Q000503:physiopathology / Q000523:psychology; D011237:Predictive Value of Tests; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D015431:Weight Loss