Background: A low or high body mass index (BMI) has been associated with increased mortality risk in older subjects without taking fat mass index (FMI) and fat-free mass index (FFMI) into account. This information is essential because FMI is modulated through different healthcare strategies than is FFMI.
Objective: We aimed to determine the relation between body composition and mortality in older subjects.
Design: We included all adults ≥65 y old who were living in Switzerland and had a body-composition measurement by bioelectrical impedance analysis at the Geneva University Hospitals between 1990 and 2011. FMI and FFMI were divided into sex-specific quartiles. Quartile 1 (i.e., the reference category) corresponded to the lowest FMI or FFMI quartile. Mortality data were retrieved from the hospital database, the Geneva death register, and the Swiss National Cohort until December 2012. Comorbidities were assessed by using the Cumulative Illness Rating Scale.
Results: Of 3181 subjects included, 766 women and 1007 men died at a mean age of 82.8 and 78.5 y, respectively. Sex-specific Cox regression models, which were used to adjust for age, BMI, smoking, ambulatory or hospitalized state, and calendar time, showed that body composition did not predict mortality in women irrespective of whether comorbidities were taken into account. In men, risk of mortality was lower with FFMI in quartiles 3 and 4 [HR: 0.78 (95% CI: 0.62, 0.98) and 0.64 (95% CI: 0.49, 0.85), respectively] but was not affected by FMI. When comorbidities were adjusted for, FFMI in quartile 4 (>19.5 kg/m2) still predicted a lower risk of mortality (HR: 0.72; 95% CI: 0.54, 0.96).
Conclusions: Low FFMI is a stronger predictor of mortality than is BMI in older men but not older women. FMI had no impact on mortality. These results suggest potential benefits of preventive interventions with the aim of maintaining muscle mass in older men.
Alex’s Notes: Numerous observational studies have shown the relationship between BMI and mortality to form a “J” or “U” shaped curve, suggesting that both too high and too low of a BMI is risky. But as we are well aware by now, BMI is a crude measurement that does not account for body composition. In the elderly, Sarcopenia is a serious problem characterized by loss of muscle mass and function with aging. No doubt identifying the relationship between mortality and components of body composition would be of more use than the current BMI relationships.
Thus, the current study examined the relation between BMI, body composition, and all-cause mortality in community-dwelling and hospitalized subjects aged ≥65 years.
Ultimately, 3181 individuals living in Switzerland were included for analysis. Both community-dwelling and hospitalized persons were allowed, body composition was analyzed with BIA, and at the time of the BIA measurement, the Cumulative Illness Rating Scale (CIRS) was completed to provide information on the disease state of 14 organs and systems within the individual. On average, women were healthier (lower CIRS), shorter, and lighter, and had less lean body mass (LBM) and more fat mass (FM) than men. Moreover, community-dwelling men and women were younger, healthier, and had higher BMI and LBM than hospitalized individuals.
The primary causes of death were mostly from cancer (32%), cardiovascular diseases (28%), and respiratory diseases (13%).
For both men and women, mortality decreased with an overweight and obese BMI compared to a normal-weight BMI, as well as with increasing amounts of LBM and FM. Conversely, mortality increased with age, CIRS, past or present smoking, hospitalization, and a BMI <18.5. However, all these associations are unadjusted for one another and are thus influenced by confounding factors. Therefore, the body composition data was entered in a model that also included the CIRS.
Neither LBM nor FM was protective against mortality in women, and only LBM was protective in men.
So what can we do with this information? For women, it suggests that we must look to areas outside of body composition to reduce mortality. Please note that this doesn’t include quality of life, which body composition does influence. For men, the results suggest that interventions to increase LBM would be of great benefit for longevity, but I’m sure you already knew that. ;-)