Influence of vitamin D on sarcopenia pathophysiology: A longitudinal study in humans and basic research in knockout mice

Vitamin D and Atherosclerosis: Unraveling the Impact on Macrophage Function

Vitamin D plays a crucial role in preventing atherosclerosis and in the regulation of macrophage function. This review aims to provide a comprehensive summary of the clinical evidence regarding the impact of vitamin D on atherosclerotic cardiovascular disease, atherosclerotic cerebrovascular disease, peripheral arterial disease, and associated risk factors. Additionally, it explores the mechanistic studies investigating the influence of vitamin D on macrophage function in atherosclerosis. Numerous findings indicate that vitamin D inhibits monocyte or macrophage recruitment, macrophage cholesterol uptake, and esterification. Moreover, it induces autophagy of lipid droplets in macrophages, promotes cholesterol efflux from macrophages, and regulates macrophage polarization. This review particularly focuses on analyzing the molecular mechanisms and signaling pathways through which vitamin D modulates macrophage function in atherosclerosis. It claims that vitamin D has a direct inhibitory effect on the formation, adhesion, and migration of lipid-loaded monocytes, thus exerting anti-atherosclerotic effects. Therefore, this review emphasizes the crucial role of vitamin D in regulating macrophage function and preventing the development of atherosclerosis.

Lack of vitamin D signalling in mesenchymal progenitors causes fatty infiltration in muscle

BACKGROUND

Recent studies have indicated the importance of muscle quality in addition to muscle quantity in sarcopenia pathophysiology. Intramuscular adipose tissue (IMAT), which originates from mesenchymal progenitors (MPs) in adult skeletal muscle, is a key factor affecting muscle quality in older adults, suggesting that controlling IMAT formation is a promising therapeutic strategy for sarcopenia. However, the molecular mechanism underlying IMAT formation in older adults has not been clarified. We recently found that the vitamin D receptor (VDR) is highly expressed in MPs in comparison to myotubes (P = 0.028, N = 3), indicating a potential role of vitamin D signalling in MPs. In this study, we aimed to clarify the role of vitamin D signalling in MP kinetics, with a focus on adipogenesis.

METHODS

MPs isolated from mouse skeletal muscles were subjected to adipogenic differentiation conditions with or without vitamin D (1α,25(OH)2D3, 100 nM) for 7 days, and adipogenicity was evaluated based on adipogenic marker expression. For in vivo analysis, tamoxifen-inducible MP-specific VDR-deficient (VdrMPcKO) mice were newly developed to investigate whether lack of vitamin D signalling in MPs is involved in IMAT formation. To induce muscle atrophy, VdrMPcKO male mice were subjected to tenotomy of the gastrocnemius muscle, and then muscle weight, myofibre cross-sectional area, adipogenic marker expression, and fatty infiltration into the muscle were evaluated at 3 weeks after operation (N = 3-4). In addition, a vitamin D-deficient diet was provided to wild-type male mice (3 and 20 months of age, N = 5) for 3 months to investigate whether vitamin D deficiency causes IMAT formation.

RESULTS

Vitamin D treatment nearly completely inhibited adipogenesis of MPs through Runx1-mediated transcriptional modifications of early adipogenic factors such as PPARγ (P = 0.0031) and C/EBPα (P = 0.0027), whereas VDR-deficient MPs derived from VdrMPcKO mice differentiated into adipocytes even in the presence of vitamin D (P = 0.0044, Oil-Red O+ area). In consistency with in-vitro findings, VdrMPcKO mice and mice fed a vitamin D-deficient diet exhibited fat deposition in atrophied (P = 0.0311) and aged (P = 0.0216) skeletal muscle, respectively.

CONCLUSIONS

Vitamin D signalling is important to prevent fate decision of MPs towards the adipogenic lineage. As vitamin D levels decline with age, our data indicate that decreased vitamin D levels may be one of the causes of IMAT formation in older adults, and vitamin D signalling may be a novel therapeutic target for sarcopenia.

Advances in sarcopenia: mechanisms, therapeutic targets, and intervention strategies

Sarcopenia is a multifactorial condition characterized by loss of muscle mass. It poses significant health risks in older adults worldwide. Both pharmacological and non-pharmacological approaches are reported to address this disease. Certain dietary patterns, such as adequate energy intake and essential amino acids, have shown positive outcomes in preserving muscle function. Various medications, including myostatin inhibitors, growth hormones, and activin type II receptor inhibitors, have been evaluated for their effectiveness in managing sarcopenia. However, it is important to consider the variable efficacy and potential side effects associated with these treatments. There are currently no drugs approved by the Food and Drug Administration for sarcopenia. The ongoing research aims to develop more effective strategies in the future. Our review of research on disease mechanisms and drug development will be a valuable contribution to future research endeavors.

Low vitamin D levels accelerates muscle mass loss in patients with chronic liver disease

Sarcopenia frequently and progressively occurs in patients with chronic liver disease. This study aimed to clarify the relationship between vitamin D levels and muscle mass loss. A total of 166 patients with chronic liver disease were enrolled in this study. Skeletal muscle mass index (SMI) was measured by bioelectrical impedance analysis at baseline and after 1 year. The rate of change in SMI from baseline after 1 year was calculated: ΔSMI (%) = [(1-year SMI - baseline SMI) / baseline SMI] × 100. Muscle mass loss was defined as ΔSMI ≤ -2%. The median 25-hydroxyvitamin D was 15.2 (11.2-19.3) ng/mL. The median SMI were 6.8 (5.9-7.8) kg/m2 at baseline and 6.7 (5.9-7.6) kg/m2 after 1 year. The median ΔSMI was -1.23% (-2.21% to 1.61%). Multivariate analysis identified low 25-hydroxyvitamin D as an independent factor associated with muscle mass loss. The optimal cut-off value of 25-hydroxyvitamin D to predict muscle mass loss was 12.7 ng/mL. Muscle mass loss was found in 56.4% v.s. 18.0% of patients with 25-hydroxyvitamin D < 12.7 vs. ≥ 12.7 ng/mL, respectively (p = 9.01 × 10-7); with the highest incidence in patients with non-alcoholic fatty liver disease (NAFLD). Specifically, patients with NAFLD and 25-hydroxyvitamin D < 12.7 ng/mL had a significantly higher incidence of muscle mass loss than those with ≥ 12.7 ng/mL (p = 1.23 × 10-3). Low vitamin D levels are associated with muscle mass loss after 1 year in patients with chronic liver disease, especially NAFLD.

Development and Validation of the Meiji Nutritional Profiling System (Meiji NPS) to Address Dietary Needs of Adults and Older Adults in Japan

This study introduces the Meiji Nutritional Profiling System (Meiji NPS), which was specifically designed to respond to age-related shifts in nutrient requirements among Japanese adults (<65 years old) and older adults (≥65 years old). Japan has one of the most aged societies in the world. The health issues of interest are malnutrition and lifestyle-related diseases among adults and frailty among older adults. Two versions of the NPS were developed based on nutrients to encourage (protein, dietary fibers, calcium, iron, and vitamin D), food groups to encourage (fruits, vegetables, nuts, legumes, and dairy), and nutrients to limit (energy, saturated fatty acids, sugars, and salt equivalents). The Meiji NPS for older adults did not include iron or saturated fatty acids. The algorithms were based on the Nutrient-Rich Foods Index (NRF). The convergent validity between the Meiji NPS and the existing NPSs for the same foods was confirmed using Spearman's correlation coefficients (NRF: r = 0.67 for adults and r = 0.60 for older adults; Health Star Rating: r = 0.64 for adults and r = 0.61 for older adults). The Meiji NPS may be useful for nutritional evaluation and reformulation of food products, tailored to adults and older adults to ameliorate health issues in Japan.

Optimal serum 25-hydroxyvitamin D level to prevent sarcopenia in patients with heart failure: Insights from a dose-response relationship

BACKGROUND AND AIMS

Low serum 25-hydroxyvitamin D (25 [OH]D) levels have been associated with sarcopenia, frailty, and risk of cardiovascular disease, whereas high levels negatively impact clinical outcomes. We determined optimal serum 25(OH)D concentrations to minimise the probability of sarcopenia in patients with heart failure (HF) by examining the dose-dependent relationship between serum 25(OH)D levels and sarcopenia.

METHODS AND RESULTS

We enrolled 461 consecutive patients with HF (mean age, 72 ± 15 years; 39% female) who underwent dual-energy X-ray absorptiometry. Serum 25(OH)D levels were measured using a chemiluminescence immunoassay. Sarcopenia was diagnosed according to the 2019 Asian Working Group for Sarcopenia criteria. Overall, 49% of enrolled patients were diagnosed with sarcopenia. Adjusted logistic regression with restricted cubic spline function revealed that the odds ratio (OR) of sarcopenia increased in patients with HF presenting serum 25(OH)D levels <14.6 ng/ml or > 31.4 ng/ml, reaching the lowest OR at ∼20 ng/ml. Multivariate logistic regression revealed that a serum 25(OH)D level below 14.6 ng/mL was independently associated with the presence of sarcopenia (adjusted OR: 2.16, 95% confidence interval [CI]: 1.24-3.78). Incorporating serum 25(OH)D levels <14.6 ng/ml, but not <20.0 ng/ml, in the baseline model improved continuous net reclassification (0.334, 95% CI: 0.122-0.546) in patients with HF.

CONCLUSION

A U-shaped relationship exists between serum 25(OH)D levels and sarcopenia probability in patients with HF. Maintaining serum 25(OH)D levels between 14.6 and 31.4 ng/ml may help prevent sarcopenia in patients with HF.

Implications of Protein and Sarcopenia in the Prognosis, Treatment, and Management of Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is a common cause of chronic liver disease globally, with prevalence rapidly increasing in parallel with rising rates of obesity and metabolic syndrome. MASLD is defined by the presence of excess fat in the liver, which may induce inflammatory changes and subsequent fibrosis in high-risk patients. Though MASLD occurs frequently, there is still no approved pharmacological treatment, and the mainstay of therapy remains lifestyle modification via dietary changes, enhancement of physical activity, and management of metabolic comorbidities. Most nutrition research and clinical guidance in this disease centers on the reduction in fructose and saturated fat in the diet, although the emerging literature suggests that protein supplementation is important and implicates muscle mass and sarcopenia in disease-related outcomes. This review will assess the current data on these topics, with the goal of defining best practices and identifying research gaps in care.

Postnatal Pdzrn3 deficiency causes acute muscle atrophy without alterations in endplate morphology

PDZ domain-containing RING finger family protein 3 (PDZRN3) is expressed in various tissues, including the skeletal muscle. Although PDZRN3 plays a crucial role in the terminal differentiation of myoblasts and synaptic growth/maturation in myogenesis, the role of this molecule in postnatal muscles is completely unknown despite its lifelong expression in myofibers. In this study, we aimed to elucidate the function of PDZRN3 in mature myofibers using myofiber-specific conditional knockout mice. After tamoxifen injection, PDZRN3 deficiency was confirmed in both fast and slow myofibers of Myf6-CreERT2; Pdzrn3flox/flox (Pdzrn3mcKO) mice. Transcriptome analysis of the skeletal muscles of Pdzrn3mcKO mice identified differentially expressed genes, including muscle atrophy-related genes such as Smox, Amd1/2, and Mt1/2, suggesting that PDZRN3 is involved in the homeostatic maintenance of postnatal muscles. PDZRN3 deficiency caused muscle atrophy, predominantly in fast-twitch (type II) myofibers, and reduced muscle strength. While myofiber-specific PDZRN3 deficiency did not influence endplate morphology or expression of neuromuscular synaptic formation-related genes in postnatal muscles, indicating that the relationship between PDZRN3 and neuromuscular junctions might be limited during muscle development. Considering that the expression of Pdzrn3 in skeletal muscles was significantly lower in aged mice than in mature adult mice, we speculated that the PDZRN3-mediated muscle maintenance system might be associated with the pathophysiology of age-related muscle decline, such as sarcopenia.

Navigating sarcopenia in COVID-19 patients and survivors: Understanding the long-term consequences, transitioning from hospital to community with mechanisms and interventions for future preparedness

The coronavirus disease 2019 (COVID-19) pandemic has caused widespread devastation, with millions of confirmed cases and deaths worldwide. Although there were efforts made to develop treatments and vaccines for COVID-19, the coexistence of sarcopenia, a muscle disorder, has been largely overlooked. It is while new variants of this disease (eg, BA.2.86) are challenging the current protocols. Sarcopenia is associated with increased mortality and disability, and shares common mechanisms with COVID-19, such as inflammation, hormonal changes, and malnutrition. This can worsen the effects of both conditions. Furthermore, survived patients with COVID-19 who have elevated risk, as well as aging, which increases the process of sarcopenia. Therefore, addressing sarcopenia in patients with COVID-19 and surviving individuals can be crucial for improving outcomes and preventing long-term disability. During hospital stays, assessing sarcopenia through indicators like muscle wasting and malnutrition is important. Nutritional interventions, such as malnutrition screening and enteral feeding, play a critical role in preventing sarcopenia in hospitals. Mental health and physical activity evaluations and interventions are also necessary. Even after recovering from COVID-19, there is a risk of developing sarcopenia, requiring continued monitoring. Nutrition and physical activity considerations are vital for prevention and management, necessitating tailored training programs and diet therapy. Mental health should not be overlooked, with regular screening, and community-based interventions. Infrastructure should support physical activity, and mental health services must become more accessible. Community engagement through support groups and peer networks can foster resilience and social connection. Efforts are needed to promote healthy diets and ensure access to nutritious foods.

Characteristics of the gut microbiome and metabolic profile in elderly patients with sarcopenia

Introduction: There is growing evidence of research indicating that the gut microbiota is involved in the development of sarcopenia. Nevertheless, there exists a notable deficiency in comprehension concerning the connection between irregularities in the intestinal microbiome and metabolic processes in older individuals suffering from sarcopenia. Methods: To analyze fecal samples obtained from a cohort of 30 older patients diagnosed with sarcopenia as well as 30 older patients without sarcopenia, this study employed 16S rDNA sequencing and liquid chromatography-mass spectrometry (LC-MS)-based non-targeted metabolomics profiling techniques. Results: As a result, we found that 29 genera and 172 metabolites were significantly altered in the sarcopenic patients. Among them, Blautia, Lachnospiraceae_unclassified, and Subdoligranulum were the bacteria with a potential diagnostic value for sarcopenia diagnosis. Correlation analysis between clinical indices and these gut bacteria suggested that the IL-6 level was negatively correlated with Blautia. Function prediction analysis demonstrated that 17 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways differ significantly between sarcopenic and non-sarcopenic patients. The primary classes of metabolites identified in the study included lipids and lipid-like molecules, organic acids and derivatives, and organoheterocyclic compounds. KEGG enrichment analysis showed that purine metabolism, arginine and proline metabolism, alanine, aspartate, and glutamate metabolism, butanoate metabolism, and histidine metabolism may contribute to the development of sarcopenia. The correlation study on gut microbiota and metabolites found that Lachnospiraceae_unclassified was positively associated with seven metabolites that were more abundant in the non-sarcopenia group and negatively correlated with three metabolites that were more abundant in the sarcopenia group. In addition, Subdoligranulum was positively correlated with seven metabolites that were lacking in sarcopenia and negatively correlated with two metabolites that were enriching in sarcopenia. Moreover, Blautia was positively associated with xanthosine. Discussion: We conducted a study on the intestinal microbiota and metabolic profile of elderly individuals with sarcopenia, offering a comprehensive analysis of the overall ecosystem. Through this investigation, we were able to validate existing research on the gut-muscle axis and further investigate potential pathogenic processes and treatment options for sarcopenia.

Locomotor function of skeletal muscle is regulated by vitamin D via adenosine triphosphate metabolism

OBJECTIVES

During musculoskeletal development, the vitamin D endocrine system is crucial, because vitamin D-dependent calcium absorption is a major regulator of bone growth. Because exercise regimens depend on bone mass, the direct action of active vitamin D (1,25-dihydroxyvitamin D3 [1,25(OH)2D3]) on musculoskeletal performance should be determined.

METHODS

To evaluate the effect of 1,25(OH)2D3 on muscle tissue, the vitamin D receptor (Vdr) gene was genetically inactivated in mouse skeletal muscle and the role of 1,25(OH)2D3-VDR signaling on locomotor function was assessed. The direct action of 1,25(OH)2D3 on muscle development was determined using cultured C2C12 cells with myogenic differentiation.

RESULTS

The lack of Vdr activity in skeletal muscle decreased spontaneous locomotor activity, suggesting that the skeletal muscle performance depended on 1,25(OH)2D3-VDR signaling. Bone phenotypes, reduced femoral bone mineral density, and accelerated osteoclast bone resorption were confirmed in mice lacking skeletal muscle Vdr activity. In vitro study revealed that the treatment with 1,25(OH)2D3 decreased the cellular adenosine triphosphate (ATP)-to-adenosine monophosphate ratio without reducing ATP production. Remarkably, protein expressions of connexin 43, an ATP releaser to extracellular space, and ATP metabolizing enzyme ectonucleotide pyrophosphatase phosphodiesterase 1 were increased responding to 1,25(OH)2D3 treatment. Furthermore, the concentration of pyrophosphate in the culture medium, which inhibits tissue calcification, was increased with 1,25(OH)2D3 treatment. In the presence of 1,25(OH)2D3-VDR signaling, calcium accumulation was suppressed in both muscle samples isolated from mice and in cultured C2C12 cells.

CONCLUSIONS

This study dissected the physiological functions of 1,25(OH)2D3-VDR signaling in muscle and revealed that regulation of ATP dynamics is involved in sustaining locomotor function.

The Role of Vitamin D in Skeletal Muscle Repair and Regeneration in Animal Models and Humans: A Systematic Review

Vitamin D deficiency, prevalent worldwide, is linked to muscle weakness, sarcopenia, and falls. Muscle regeneration is a vital process that allows for skeletal muscle tissue maintenance and repair after injury. PubMed and Web of Science were used to search for studies published prior to May 2023. We assessed eligible studies that discussed the relationship between vitamin D, muscle regeneration in this review. Overall, the literature reports strong associations between vitamin D and skeletal myocyte size, and muscle regeneration. In vitro studies in skeletal muscle cells derived from mice and humans showed vitamin D played a role in regulating myoblast growth, size, and gene expression. Animal studies, primarily in mice, demonstrate vitamin D's positive effects on skeletal muscle function, such as improved grip strength and endurance. These studies encompass vitamin D diet research, genetically modified models, and disease-related mouse models. Relatively few studies looked at muscle function after injury, but these also support a role for vitamin D in muscle recovery. The human studies have also reported that vitamin D deficiency decreases muscle grip strength and gait speed, especially in the elderly population. Finally, human studies reported the benefits of vitamin D supplementation and achieving optimal serum vitamin D levels in muscle recovery after eccentric exercise and surgery. However, there were no benefits in rotator cuff injury studies, suggesting that repair mechanisms for muscle/ligament tears may be less reliant on vitamin D. In summary, vitamin D plays a crucial role in skeletal muscle function, structural integrity, and regeneration, potentially offering therapeutic benefits to patients with musculoskeletal diseases and in post-operative recovery.

Interaction of estradiol and vitamin D with low skeletal muscle mass among middle-aged and elderly women

BACKGROUND

Since the connection between muscle atrophy and vitamin D and estradiol status ambiguous, this study was thus conducted to determine whether low skeletal muscle mass (SMM) in middle-aged and elderly women was affected by estradiol and vitamin D levels together.

METHODS

Baseline data from a sub-cohort of the China Northwest Natural Population Cohort: Ningxia Project (CNC-NX) were analyzed. Serum 25-hydroxyvitamin D (25(OH) D) and estradiol were measured by chemiluminescence immunoassay analyzer. Bivariate logistic regression and multiplicative interaction analyses were used to assess the impact of estradiol level and vitamin D status on low SMM, as well as the combined impact of estradiol and low vitamin D status on low SMM.

RESULTS

A total of 287 (9.49%) participants had low SMM, which had lower levels of estradiol and vitamin D concentration than normal SMM group. While, after adjusting the confounding variables, these correlations were maintained in estradiol Q1, Q2, Q3 and vitamin D Q1. Furthermore, the significant combined effect of the highest quartile of estradiol concentrations and non-vitamin D deficiency, and interactions between vitamin D Q1 and estradiol Q2, vitamin D Q1 and estradiol Q3, vitamin D Q2 and estradiol Q1, vitamin D Q3 and estradiol Q3 on low SMM were stably reflected (P for interaction < 0.05).

CONCLUSIONS

Estradiol and vitamin D were interrelated with low SMM in middle-aged and elderly women. Combination of estradiol and vitamin D supplements should be encouraged for middle-aged and elderly women who are at risk of muscle atrophy or experiencing muscle atrophy.

U-Shaped Association of Standardized Serum 25-Hydroxyvitamin D with Risk of Low Muscle Mass: A Population-Based Cross-Sectional Study

Background

In the United States (U.S.) general population, the association between standardized serum 25-hydroxyvitamin D (25(OH)D) concentration and risk of low muscle mass (LMM) remains unclear. Our research aimed to determine whether or not there was a relationship between serum 25(OH)D concentration and risk of LMM.

Methods

We analyzed the cross-sectional data of the US population that participated in the National Health and Nutrition Examination Survey between 2011 and 2014. The relationship between serum 25(OH)D concentration and LMM risk was evaluated using restricted cubic spline (RCS) with multivariate logistic regression model and subgroup analysis.

Results

In all, we included 10,256 people in our analysis. The RCS plot demonstrated a U-shaped relationship between serum 25(OH)D concentration and risk of LMM (P for nonlinearity <0.05). At a Vitamin D concentration of 38.5 nmol/L, LMM risk was at its lowest. Based on analyses stratified by age, sex, hypertension, and diabetes mellitus (DM), serum 25(OH)D concentration and risk of LMM were U-curve correlated for those age 40 or older, male, with hypertension, or without DM. However, LMM risk was positively related to serum 25(OH)D concentration in those younger than age 40 or in women.

Conclusion

There is a U-shaped relationship between serum 25(OH)D concentration and the risk of LMM in the general U.S. population. Careful monitoring and appropriate Vitamin D supplementation might lessen the risk of LMM.

Sarcopenia, osteoporosis and frailty

Muscles and bones are intricately connected tissues displaying marked co-variation during development, growth, aging, and in many diseases. While the diagnosis and treatment of osteoporosis are well established in clinical practice, sarcopenia has only been classified internationally as a disease in 2016. Both conditions are associated with an increased risk of adverse health outcomes such as fractures, dysmobility and mortality. Rather than focusing on one dimension of bone or muscle mass or weakness, the concept of musculoskeletal frailty captures the overall loss of physiological reserves in the locomotor system with age. The term osteosarcopenia in particular refers to the double jeopardy of osteoporosis and sarcopenia. Muscle-bone interactions at the biomechanical, cellular, paracrine, endocrine, neuronal or nutritional level may contribute to the pathophysiology of osteosarcopenia. The paradigm wherein muscle force controls bone strength is increasingly facing competition from a model centering on the exchange of myokines, osteokines and adipokines. The most promising results have been obtained in preclinical models where common drug targets have been identified to treat these conditions simultaneously. In this narrative review, we critically summarize the current understanding of the definitions, epidemiology, pathophysiology, and treatment of osteosarcopenia as part of an integrative approach to musculoskeletal frailty.

Oxidative stress: roles in skeletal muscle atrophy

Oxidative stress, inflammation, mitochondrial dysfunction, reduced protein synthesis, and increased proteolysis are all critical factors in the process of muscle atrophy. In particular, oxidative stress is the key factor that triggers skeletal muscle atrophy. It is activated in the early stages of muscle atrophy and can be regulated by various factors. The mechanisms of oxidative stress in the development of muscle atrophy have not been completely elucidated. This review provides an overview of the sources of oxidative stress in skeletal muscle and the correlation of oxidative stress with inflammation, mitochondrial dysfunction, autophagy, protein synthesis, proteolysis, and muscle regeneration in muscle atrophy. Additionally, the role of oxidative stress in skeletal muscle atrophy caused by several pathological conditions, including denervation, unloading, chronic inflammatory diseases (diabetes mellitus, chronic kidney disease, chronic heart failure, and chronic obstructive pulmonary disease), sarcopenia, hereditary neuromuscular diseases (spinal muscular atrophy, amyotrophic lateral sclerosis, and Duchenne muscular dystrophy), and cancer cachexia, have been discussed. Finally, this review proposes the alleviation oxidative stress using antioxidants, Chinese herbal extracts, stem cell and extracellular vesicles as a promising therapeutic strategy for muscle atrophy. This review will aid in the development of novel therapeutic strategies and drugs for muscle atrophy.

Vitamin D Increases Irisin Serum Levels and the Expression of Its Precursor in Skeletal Muscle

Irisin is a myokine synthesized by skeletal muscle, which performs key actions on whole-body metabolism. Previous studies have hypothesized a relationship between irisin and vitamin D, but the pathway has not been thoroughly investigated. The purpose of the study was to evaluate whether vitamin D supplementation affected irisin serum levels in a cohort of 19 postmenopausal women with primary hyperparathyroidism (PHPT) treated with cholecalciferol for six months. In parallel, to understand the possible link between vitamin D and irisin, we analyzed the expression of the irisin precursor, Fndc5, in the C2C12 myoblast cell line treated with a biologically active form of vitamin D, 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). Our results demonstrate that vitamin D supplementation resulted in a significant increase in irisin serum levels (p = 0.031) in PHPT patients. In vitro, we show that vitamin D treatment on myoblasts enhanced Fndc5 mRNA after 48 h (p = 0.013), while it increased mRNAs of sirtuin 1 (Sirt1) (p = 0.041) and peroxisome proliferator-activated receptor γ coactivator 1α (Pgc1α) (p = 0.017) over a shorter time course. Overall, our data suggest that vitamin-D-induced modulation of Fndc5/irisin occurs through up-regulation of Sirt1, which together with Pgc1α, is an important regulator of numerous metabolic processes in skeletal muscle.

Usefulness of Vitamin D Deficiency Questionnaire for Japanese (VDDQ-J) for Screening of Vitamin D Deficiency and Low Muscle Mass in Relatively Healthy Japanese Anti-Aging Health Checkup Examinees

The Vitamin D Deficiency Questionnaire for Japanese (VDDQ-J) has been developed as an alternative indicator of the vitamin D nutritional status when serum 25(OH)D measurement is unavailable. In the present study, we compared the usefulness of the VDDQ-J with that of serum 25(OH)D concentration and examined the relationship among vitamin D, DXA-based body composition, and muscle strength in 163 anti-aging health check examinees. The median age, 25(OH)D concentration and VDDQ-J score were 62.0 y, 20.1 ng/mL and 22.0 points, respectively. In total, 47.9% of the subjects had serum 25(OH)D concentrations of <20 ng/mL. The VDDQ-J score was significantly negatively correlated with the serum 25(OH)D concentration, and the positive predictive value for vitamin D deficiency was 86.3%. The prevalence of sarcopenia was 6.1%. Low 25(OH)D levels and high VDDQ-J scores were significantly associated with low muscle mass in both univariate analysis and multiple linear regression analysis. The serum 25(OH)D level showed a significant negative correlation with body fat mass. The VDDQ-J score was selected as a significant determinant of low skeletal muscle mass index (<7.0 kg/m2 for men and <5.4 kg/m2 for women) by a multiple logistic regression analysis. In conclusion, the present study showed that a low vitamin D nutritional status as indicated by both low 25(OH)D levels, and high VDDQ-J scores was associated with low muscle mass and the VDDQ-J is considered useful not only for the detection of vitamin D deficiency but also in the screening of individuals with low muscle mass and a high risk of sarcopenia.