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Normal-Weight Obesity and Disability in Older Adults: Data from the National Health and Nutrition Examination Study 1999-2004

2016; Wiley; Volume: 64; Issue: 6 Linguagem: Inglês

10.1111/jgs.14157

1532-5415

John A. Batsis, Todd A. MacKenzie, Francisco López-Jiménez, Stephen J. Bartels,

Body Composition Measurement Techniques

Current body mass index (BMI) strata misrepresent the accuracy of true adiposity in older adults. Sensitivity of BMI in diagnosing obesity drops with age, approaching 30% in individuals aged 80 and older.1 A subset of individuals was previously identified that would be overlooked in clinical practice as being at low risk who had a normal BMI and high percentage of body fat (normal-weight obesity (NWO)).2 This group is at high risk of cardiometabolic risk and mortality.3 Although these factors can ultimately affect longevity and quality of life, functional status is often more important to adults as they age. The association between NWO and impairments, measured using self-reported measures of physical limitations, activities of daily living (ADLs), and instrumental activities of daily living (IADLs), was examined. This was a secondary analysis of National Health and Nutrition Survey 1999 to 2004 data using methods described elsewhere1 and identified subjects aged 60 and older with a BMI of 18.5 to 25.0 kg/m2 who had dual-energy X-ray absorptiometry measures of body composition. High percentage of body fat was classified as 25% and greater in men and 35% and greater women.2 Questionnaires assessed physical limitations, three ADLs, and four IADLs, consistent with methods used previously.4 Aggregate measures were assessed. The aim was to examine the relationship between NWO and each impairment (reference normal BMI, normal body fat). Rates were assessed in subjects with a normal BMI and high or low percentage of body fat. Sex-specific multivariable logistic regression analyses were performed, adjusting for age, race, smoking, comorbidity, and appendicular lean mass (ALM). An exploratory analysis determined whether NWO differed according to sex. One thousand three hundred four individuals were included (52.1% female, 66.9% with NWO). Mean age was 72, mean BMI was 23.0 kg/m2 in both sexes (men, P = .38, women, P = .37), and waist circumference was 93.1 in men and 95.2 cm in women (P < .001). Percentage body fat was higher in women (39.6%) than men (28.9%) (P < .001). For participants with NWO, ALM was higher in men (20.2 kg) than women (13.7 kg) (P < .001). In men with and without NWO, rates of physical limitations were 41.6% and 34.4% (P = .23), rates of IADL impairment were 25.3% and 20.5% (P = .24), and rates of ADL impairment were 34.2% and 33.1% (P = .84), respectively. In women with and without NWO, rates of physical limitations were 55.1% and 50.6% (P = .45), rates of IADL impairment were 31.3% and 36.7% (P = .32), and rates of ADL impairment were 44.7% and 43.0% (P = .72). Sex-specific differences were found in those with NWO in physical limitations (P = .005), ADL impairment (P = .001) and IADL impairment (P = .002). Regression models are presented in Table 1. Irrespective of the covariates, no association between NWO and limitations was observed in either sex. Significant associations between NWO and ADLs were seen with women, who were more likely to have limitations than men. After adjusting for ALM in all models, no associations were observed between NWO and any type of limitation. Although older adults with NWO have greater cardiometabolic dysregulation, including dyslipidemia, inflammation, and metabolic syndrome, than those without, these results suggest no association with functional impairments. ALM attenuates the magnitude of results, indicating the importance of the interaction between muscle and adipose tissue. These results have considerable implications. First, individuals with a normal BMI but a high percentage of body fat may succumb to death first3 and not experience a longer period of disability than their counterparts with a lower percentage of body fat may face. Their cardiometabolic dysfunction may promote earlier death, as shown in an earlier analysis.2, 3 Second, the importance of ALM in older adults cannot be overstated. Sarcopenia is a natural phenomenon of aging that is associated with considerable morbidity and mortality.4, 5 As body composition changes with age, clinicians need to be aware of this process. Although muscle mass has been shown to be related to impairments,6 the National Health and Nutrition Examination Study lacked data on muscle strength, which may be more of an indicator of long-term health.7 Third, the differences observed according to sex within the NWO category are important. Women were at greater risk of impairments than men, consistent with the fact that they live longer than men. This study has the limitations of any cross-sectional study, including inability to prove causation. This may explain the discordant results observed in a cohort of subjects with and at risk of osteoarthritis, in whom NWO was associated with greater risk of functional decline. The questionnaires used in the interview consisted of incomplete ADL assessment and were based on self-reported data, not allowing for full ascertainment of IADLs or ADLs. Last, all questions on physical limitations were aggregated, which could have introduced bias to the results. Future cross-sectional and longitudinal studies should use standardized functional assessments to determine whether individuals with NWO are at greater risk of functional impairment over time. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: All authors contributed to this letter. Sponsor's Role: None.