Tryptophan is an essential nutrient required to produce niacin (vitamin B3), which is needed for energy metabolism and DNA production. Alterations in tryptophan metabolism could have significant effects on aging and musculoskeletal health. The kynurenine pathway, the main catabolic route of tryptophan, is modulated by inflammatory factors, which are increased in older persons, a process known as inflammaging. Osteoporosis, sarcopenia, osteosarcopenia and frailty have also been linked with chronic increased levels of inflammatory factors. Due to the disruption of the kynurenine pathway by chronic inflammation and/or changes in the gut microbiota, serum levels of toxic kynurenines are increased and have been associated with osteoporosis, sarcopenia and frailty. In contrast, anabolic end products of this pathway, such as picolinic acid, have demonstrated a beneficial effect on bone and muscle. In addition, recent studies have shown that physical activity can modulate this pathway by promoting the secretion of anabolic kynurenines. According to the evidence collected, kynurenines could have a promising role as biomarkers for osteoporosis sarcopenia, osteosarcopenia and frailty in older persons. In addition, some of these metabolites could become important targets for developing new pharmacological treatments for these conditions.

Background: Shorter leukocyte telomere length (LTL) is observed in multiple age-related diseases, which are also associated with vitamin D deficiency (i.e., osteosarcopenia, neurocognitive disorders, cancer, osteoarthritis, etc.), which suggests a close association. In this study, we examined the relationship between vitamin D levels and LTL in older participants of the UK Biobank. Methods: Data were collected from the UK Biobank. Participants aged 60 and older (n=148,321) were included. Baseline LTL was measured using a multiplex qPCR technique and expressed as the ratio of the telomere amplification product (T) to that of a single-copy gene (S) (T/S ratio). Se-rum 25-hydroxyvitamin D (25OHD) was stratified by z score and linked to LTL in a linear regression model adjusting for covariates. Results: Compared to the medium level, a low (in the range of 16.6 nmol/L, 29.7 nmol/L) or extremely low (≤ 16.6 nmol/L) level of serum 25OHD was associated with shorter LTL: 0.018 SD (standardized β= -0.018, 95% CI -0.033 to -0.003, P=0.022) and 0.048 SD (standardized β= -0.048, 95% CI -0.083 to -0.014, P=0.006), respectively. Additionally, the high serum 25OHD groups (> 95.9 nmol/L) had 0.038 SD (standardized β= -0.038, 95% CI -0.072 to -0.004, P=0.030) shorter mean LTL than the group with medium 25OHD levels. The associations above were adjusted for multiple variables. Conclusion: In this population-based study, we identified an inverted U-shape relationship between LTL and vitamin D status. Whether high or low vitamin D-associated shorter LTL is mechanistically related to age-related conditions remains to be elucidated.

Treatment options for sarcopenia are currently limited, primarily relying on two main therapeutic approaches: resistance-based physical activity and dietary interventions. However, details about specific nutrients in the diet or supplementation are unclear. Our objective is to investigate the relationship between nutrient intake and lean mass, function, and strength. Data were derived from the Gothenburg H70 birth cohort study in Sweden, including 719 70-year-olds born in 1944 (54,1 % females). For independent variables, the diet history method (face-to-face interviews) was used to estimate habitual food intake during the preceding three months. Dependent variables were gait speed (muscle performance), hand grip strength (muscle strength) and appendicular lean soft tissue index (ALSTI). Linear regression analyses were performed to analyze the relationship between the dependent variables and each of the covariates. Several nutrients were positively associated with ALSTI, such as polyunsaturated fatty acids (DHA, EPA), selenium, zinc, riboflavin, niacin equivalent, vitamin B12, vitamin D, iron, and protein. After correction for multiple tests, there were no remaining correlations with handgrip and gait speed. Findings of positive correlations for some nutrients with lean mass suggest a role for these nutrients for maintaining muscle volume. These results can be used to inform clinical trials to expand the preventive strategies and treatment options for individuals at risk of muscle loss and sarcopenia.