Body Mass Index and Cognition

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Ghaderpanahi et al.1 reported an interesting cross-sectional study from Tehran of 108 elderly adults classified according to body mass index (BMI) into four groups: underweight (<18.5 kg/m2), normal (18.5–24.9 kg/m2), overweight (25.0–29.9 kg/m2), and obese (≥30.0 kg/m2). When Mini-Mental State Examination (MMSE) score was less than 22, a psychiatrist confirmed the diagnosis of dementia using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. They used normal BMI for the reference group. Multivariate adjustment showed that the overweight group had the lowest relative risk for dementia (0.24) and that the obese group had the highest (1.43). The underweight group had a relative risk of 0.43 for dementia. A 12-month longitudinal study to assess cognitive decline relative to BMI is reported herein. Ninety-four community-dwelling individuals attending a memory clinic and residing 100 km north of Sydney Australia who were free of dementia at baseline were selected in a consensus conference of a geriatrician (PR) and clinical nurse consultant (EH). Participants had initial MMSE scores of 22 to 30. At baseline and 6 and 12 months, the MMSE,2 Montreal Cognitive Assessment,3 Frontal Assessment Battery,4 and Addenbrooke Cognitive Assessment5 were administered—a total of 12 comparisons. Table 1 shows that the underweight group had the lowest cognitive scores of the four groups in all 12 comparisons (chance would suggest 3/12 comparisons), whereas the overweight group had the highest cognitive scores in nine of 12 comparisons. Thus these results are consistent with those of Ghaderpanahi and colleagues' study1 for overweight but not underweight individuals, although the current study did not attempt multivariate adjustment for age, sex, education, smoking, serum cholesterol, diabetes mellitus, hypertension, and cardiovascular disease. Ghaderpanahi and colleagues did not adjust for apolipoprotein E genotype. Recently the Health in Men Study6 reported on 4,227 men aged 70 to 89 who were free of dementia according to hospital diagnoses for a mean of 5.8 years. The reference group was 1,450 men (34.4% of the total sample) with a BMI less than 25.0 kg/m2. Two thousand one hundred forty-six men (50.9% of the sample) were overweight (BMI 25.0–29.9 kg/m2). They had hazard ratio (HR) of 0.66 for incident dementia. The 617 obese men (BMI ≥ 30.0 kg/m2; 14.7% of the sample) had a HR of 0.84 for incident dementia. Conflict of Interest: Dr. Paul Regal and Eileen Heatherington declare no conflict of interest with employment, affiliations, grants, funding, honoraria, speaker's forum, consultancy, stocks, royalties, expert testimony, board membership, patents, or personal relationships. Author Contributions: Paul Regal: study concept; study design; acquisition of subjects; data management, analysis, and interpretation; and preparation of the manuscript. Eileen Heatherington: patient assessment. Sponsor's Role: There was no sponsor.