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Aim Serum C-peptide is an active peptide that has important physiological functions and characteristics in the elderly. The present study aimed to investigate the association between physical activity and serum C-peptide level independent of insulin level among the elderly. Methods The study included 1700 elderly participants aged ≥65 years. Stratified analysis of covariance was used to compare serum C-peptide levels in participants with different physical activity levels. Two separate multiple linear regression models were created to estimate the association between physical activity and serum C-peptide level. Results The results of analysis of covariance stratified by sex, body mass index and serum insulin level showed that those who engaged in vigorous physical activity had lower serum C-peptide levels than those who engaged in light or no physical activity. Separate multiple linear regression analysis showed that in those with low serum C-peptide levels (≤0.621 nmol/L), physical activity was significantly positively associated with the serum C-peptide level. In contrast, physical activity was negatively associated with the serum C-peptide level among those with serum C-peptide level >0.621 nmol/L. Conclusions The serum C-peptide level showed a significant two-way association with physical activity. The present findings suggest that physical activity modification is important for improving serum C-peptide levels among the elderly. Geriatr Gerontol Int 2014; 14: 647-653. [ABSTRACT FROM AUTHOR]

Aim: The changes in body composition and biomarker levels that occur during the aging process are complex and remain poorly understood. The present study aimed to evaluate changes in serum C-peptide levels and fat mass-tolean mass ratio (FM/LM ratio) with increasing age, and to explore the associations between serum C-peptide levels and FM/LM ratio. Methods: This was a population-based cross-sectional study that included 3912 participants aged 30-85 years. Body composition was measured using dual-energy X-ray absorptiometry. Analysis of covariance was used to evaluate how the serum C-peptide level and FM/LM ratio change with increasing age, as well as how the FM/LM ratio changes in line with increasing serum C-peptide level. A multiple linear regression analysis was carried out to determine the association between serum C-peptide level and FM/LM ratio. Results: Analysis of covariance showed that serum C-peptide levels, and most regional FM/LM ratios tended to increase in line with increasing age. Total fat mass, total lean mass, percentage total fat mass and total FM/LM ratio were significantly elevated, and percentage total lean mass decreased significantly with increasing serum C-peptide levels in both men and women. Multiple linear regression analysis showed that serum C-peptide level was strongly associated with the total FM/LM ratio. Conclusions: The findings showed that both serum C-peptide level and FM/LM ratio increased with increasing age, and the serum C-peptide level was closely associated with changes in the total FM/LM ratio. [ABSTRACT FROM AUTHOR]