A recent study suggests that sarcopenic obesity is not associated with any greater mortality risk than sarcopenia alone. Weight and muscle loss presents the greatest mortality risk.
Sarcopenia, defined as the decline of skeletal muscle tissue and muscle strength with age, is one of the most common causes of functional decline in older adults. Typically, age-related loss of muscle mass is accompanied by an increase in adipose tissue (weight-gain) leading to sarcopenic obesity. The co-existence of obesity and low muscle mass is thought to increase mortality risk more than the two factors acting alone.
The English Longitudinal Study of Ageing (ELSA) published in the American Journal of Clinical Nutrition examined the association of sarcopenic obesity, changes in muscle strength and weight with the risk of mortality. The sample consisted of 6864 community-dwelling men and women with a mean age of 66.2 years. Baseline clinical assessment of handgrip strength and body mass index (BMI) was conducted between 2004 and 2005. An identical clinical assessment was repeated 4 years later, between 2008 and 2009. Individual participant data were linked with death records from National Health Service registries up to February 2012. Sarcopenic obesity was defined as a BMI > 30 in the lowest tertile of sex-specific grip strength (< 35.3 kg for men and < 19.6 kg for women). Covariates such as physical activity, depressive symptoms, and socioeconomic status were also recorded at baseline.
There were 906 deaths over a mean follow-up of 8 years. The researchers observed a U-shaped association between BMI and mortality, with the overweight category showing the lowest risk of mortality. There was a linear increase in the risk of mortality for the middle and lower tertiles for grip strength compared to the highest tertile.
The risk of all-cause mortality increased with reducing grip strength within each BMI category compared with the reference group (normal BMI and highest handgrip strength). For participants in the lowest handgrip tertile, there was no significant difference observed between normal BMI, overweight, and obese, after adjusting for covariates. Compared with the reference group (nonobese and nonsarcopenic), the increased risk of all-cause mortality was found to be similar in sarcopenic and sarcopenic obese participants. On the contrary, the risk of all-cause mortality was significantly higher in participants who had a weight loss and /or loss of handgrip strength (muscle loss) over 4 years than in those who maintained stable weight and grip strength. Thus, the mortality risk was found to be highest in participants with weight loss and reduced strength, signifying muscle loss.
The main findings of the study show that sarcopenic obesity does not confer any greater risk of mortality than sarcopenia alone. The results indicate that weight and muscle loss combined pose the greatest risk. Evidence from previous studies suggests that muscle mass is more strongly associated with mortality than being overweight or obese. This study reaffirms that obesity is not associated with mortality when compared with a reference category of normal weight.
ELSA included participants that were younger and healthier than the overall cohort because of a loss of older and disadvantaged participants. Therefore, the findings of this study might represent a conservative estimate of the true effects. In addition, the covariates information collected was self-reported and could have led to imprecise measurement.
In conclusion, sarcopenic obesity is not associated with a greater risk of mortality compared with sarcopenia alone. Weight loss combined with a loss of muscle strength presents the greatest risk. Therefore, identification of affected older patients should be an important objective for clinicians.
