The relationship between body mass index and self-reported functional limitation among older adults: a gender difference.

OBJECTIVES: To determine whether there is a gender difference in how body mass index (BMI) relates to self-reported functional limitation. Also, to evaluate whether the method of categorizing BMI changes the observed results.
DESIGN: Cross-sectional cohort study.
SETTING: Rural Pennsylvania. PARTICIPANTS: A total of 7,120 male (n = 3,312) and female (n = 3,808) community-dwelling older adults enrolled in a Medicare managed-risk contract. MEASUREMENTS: All subjects completed a modified Level II Nutrition Risk Screen upon enrollment in the health plan. Height and weight were obtained by nursing personnel during an enrollment clinic visit. Subjects who reported 10 or more pounds weight loss in the previous 6 months were excluded. Logistic regression was used to evaluate the relationship between BMI and self-reported functional limitation separately for each sex, adjusting for age, depression, and polypharmacy. Two schemes were used to categorize BMI: equally distributed sex-specific quintiles and arbitrary division based on National Institutes of Health (NIH) Obesity Guidelines.
RESULTS: How BMI relates to functional limitation depends upon both sex and method of categorizing BMI. When BMI was considered in gender-specific quintiles, women in the highest quintile of BMI had increased risk of functional impairment; there was no relationship between BMI and functional limitation for men. When BMI was categorized by the NIH obesity guidelines, both men and women with BMI >40 had significantly increased risk of functional limitation.
CONCLUSIONS: The mechanisms behind gender discrepancy in self-reported functional limitation remain unclear. Studies may need to consider men and women separately, because how BMI relates to function depends on gender. Further research is needed to evaluate how changes in weight and body composition during middle and old age affect functional status.