Prevalence of sarcopenia, influencing factors, and serum beta-2 microglobulin levels in the elderly

Introduction: Sarcopenia is a skeletal muscle disease characterized by progressive loss of muscle mass and muscle strength. The increasing elderly population raises the potential for sarcopenia to become a significant public health issue. One of the most critical problems for sarcopenia is the uncertainty and difficulty in the diagnosis process. This study aimed to determine the prevalence and risk factors of sarcopenia in individuals aged 65 and over and to investigate the role of serum beta-2 microglobulin level as a biomarker in the diagnosis/screening of sarcopenia. Method: This nested case-control study was conducted between 2023 and 2024 on 251 elderly individuals recruited at the Department of Public Health of Faculty of Medicine in Çukurova University and family health centres affiliated to the Department located in Doğankent, Karataş and Havutlu Districts; Physical Medicine and Rehabilitation Department of Balcali Hospital of Cukurova University; and the Department of Geriatrics at Adana City Hospital. Participants completed a physical activity questionnaire, the FRAIL frailty scale, and the SARC-F sarcopenia screening test. Muscle strength was measured using a hand dynamometer, and muscle mass was assessed using the bioelectrical impedance method. Individuals with low muscle strength and low muscle mass were evaluated as having definitive sarcopenia. Serum beta-2 microglobulin levels were measured in both the sarcopenia and control groups. The data were analyzed using t-tests, Mann-Whitney U tests, Pearson correlation tests, Spearman correlation analysis, chi-square tests, logistic regression analysis, multivariate linear regression analysis, mediation analysis, and ROC analysis. P<0.05 was considered statistically significant. Results: The average age of the 251 elderly individuals included in our study was 72.19±6.11 years. Of the participants, 62.2% were female, and 37.8% were male. The prevalence of sarcopenia in individuals aged 65 and over was found to be 5.2%. The most important predictors for the risk of sarcopenia were age and the average daily dietary energy (kcal) intake, while the content of the diet (amounts of carbohydrates, fats, proteins) was not found to be significant. Each unit increase in age led to a 0.118 unit decrease in appendicular muscle mass, while each unit increase in average daily dietary energy intake led to a 0.02 unit increase in appendicular muscle mass. It was found that frail elderly individuals had significantly lower muscle mass compared to normal elderly individuals. When examining the mediator role of frailty in the relationship between age and muscle mass, frailty was not found to be significant, but the direct effect of age on muscle mass (reduction in muscle mass) was found to be significant. Serum beta-2 microglobulin levels were statistically significantly lower in sarcopenic participants compared to the control group. The optimal cutoff value for serum beta-2 microglobulin level was found to be 2.26 ug/mL, and values lower than this were found to be diagnostic for sarcopenia. For this cutoff value, sensitivity was 92.31%, specificity was 80.77%, positive predictive value was 70.59%, negative predictive value was 95.45%, Youden index was 0.731, and the area under the curve was 0.901. Individuals with a beta-2 microglobulin level below 2.26 had a 5.66 times higher risk of having low appendicular muscle mass. Conclusion: The prevalence of sarcopenia in the elderly was 5.2%. Age was the most significant risk factor for sarcopenia. Increasing the daily dietary energy intake in elderly individuals might be effective in preventing low muscle mass and strength. A low serum beta-2 microglobulin level has the potential to be an important candidate biomarker for the diagnosis of sarcopenia. Key words: sarcopenia, beta-2 microglobulin, elderly