Background: Aging sarcopenia characterized by low muscle mass with low muscle strength affects men and women differently. The contribution of interleukin-6 (IL-6) to sarcopenia has been suggested based on a negative correlation between plasma IL-6 and muscle function described by some studies. However, no consensus regarding clinically relevant cut-off criteria has been reached. Another question arises whether pooling male and female data is an accurate way to determine the predictive value of IL-6 in sarcopenia. The present meta-analysis was designed to assess: (1) whether plasma IL-6 in aged populations in fact correlates negatively to muscle strength; (2) whether such a correlation exists both in men and in women; and (3) whether plasma IL-6 shows a gender difference in old age.
Methods: We applied the preferred reporting items for systematic review and meta-analysis protocols (PRISMA). We searched PubMed and Embase for papers that reported data on individuals over 65 without inflammatory diseases. We extracted either separate male and female data on plasma IL-6 along with at least one muscle parameter or correlation coefficient between plasma IL-6 and these parameters. Random effect models calculated with DerSimonian and Laird weighting methods were applied to analyze correlation coefficients and gender difference in plasma IL-6. Egger's test was used to assess the small study effect.
Results: Twenty articles out of 468 records identified were suitable for analyses. Plasma IL-6 correlates negatively with grip strength in mixed populations and also separately in men [- 0.25 with 95% confidence interval (CI): - 0.48, - 0.02] and in women (- 0.14 with 95% CI: - 0.24, - 0.03). However, contrary to expectations, men with better muscle condition have higher plasma IL-6 than women of similar age with worse muscle condition (plasma IL-6 male-female difference: 0.25 pg/mL with 95% CI: 0.15, 0.35).
Conclusion: This is the first study to demonstrate that a higher predictive IL-6 cut-off level should be determined for aging sarcopenia in men than in women.
Keywords: Gender; Grip strength; Inflammation; Interleukin-6; Sarcopenia.