Effect of winter seasonal southward migration on body composition， inflammation， and muscle function in northern migratory elderly

Background　In recent years, the phenomenon of seasonal relocation for elderly care has become increasingly common, more and more elderly people from northern China spend the winter in warmer southern regions. However, research on the nutritional and immune status of migratory elderly based on seasonal migration is relatively rare. Objective　To prospectively observe the impact of short-term seasonal migration on the body composition, inflammatory cytokines, frailty scores and risk of muscle attenuation in northern migratory elderly. Methods　A within-subject pre-post study was conducted among northern migratory elderly, with assessments performed at both arrival (baseline) and departure (endpoint) from the island. Measurements included body composition, blood biochemistry and inflammatory indicators, grip strength, calf circumference, and 6-meter gait speed, along with frailty and sarcopenia risk evaluations. Results　A total of 53 elderly migratory birds were included, including 21 males and 32 females, with an average age of (69.2±5.8) years. Compared with the baseline data, the body composition of the participants after migration was significantly improved, changes in male body composition were manifested in increase in fat free mass (FFM), muscle mass (MM), and skeletal muscle (SM), and the differences were statistically significant (P＜0.05); changes in female body composition were manifested in decrease in body fat percentage (FP), subcutaneous fat weight, and visceral fat area (VFA), and the differences were statistically significant (P＜0.05). Interleukin-2 (IL-2) and tumor necrosis factor-alpha (TNF- α) decreased with statistically significant differences (P＜0.001). IL-4 and IL-10 increased with statistically significant differences (P＜0.001). Linear regression analysis showed that after controlling age, gender, years of migratory life, and baseline levels of IL-2, IL-4, and IL-10, migratory life was independently associated with decrease in pro-inflammatory factors (IL-2) and increase in antiinflammatory factors (IL-4, IL-10). After controlling for age, years of migratory life, and baseline levels of body composition-related indicators, migratory life was independently associated with increases in FFM, MM, and SM in males and decreases in VFA in females. Conclusion　Migrating to a warm environment can significantly improve the body composition of migratory elderly and induce a change in the inflammatory state in the body towards an anti-inflammatory direction.