The loss of muscle mass and strength, known as sarcopenia, is a significant problem in aging, affecting both healthspan and quality of life. Findings from a recent study suggest that vitamin D affects muscle function through diverse metabolic pathways.
Clinicians determine a person’s vitamin D status by measuring 25-hydroxyvitamin D3, or 25(OH)D3 — the inactive circulating form of vitamin D. However, a new technique, high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS), allows researchers to quantify additional vitamin D metabolites. While these other metabolites, part of what is termed the vitamin D metabolome, are present in low concentrations in the blood, they can perform critical functions in tissues, such as muscles.
Previous research has examined the relationship between vitamin D and muscle function yielding inconsistent results; however, these studies have mainly focused on 25(OH)D3. The current study investigated whether other vitamin D metabolites are associated with muscle function.
The cross-sectional study involved 116 healthy adults who performed handgrip and lower limb strength tests, while a subset of 85 participants consented to thigh muscle biopsies. The authors assessed the participants' vitamin D status using LC-MS/MS, steroid metabolites from urine samples, and the expression of 92 genes from the muscle biopsies. The authors also measured lean body mass and body fat percentages.
Only 14 percent of participants had normal vitamin D levels, while 28 percent had insufficient levels, and 58 percent were found to be deficient. Subjects with a higher percent body fat had lower vitamin D levels. Participants with higher muscle mass had higher active vitamin D levels. Those with higher active, but not inactive vitamin D levels scored better on the muscle strength tests. The authors observed that the expression of 24 skeletal muscle genes correlate with levels of serum 25(OH)D3.
These findings highlight the complex relationship between vitamin D, gene expression, and muscle function. They suggest that the maintenance of muscle mass and strength is complicated, and it may be more appropriate to measure other vitamin D forms rather than just 25(OH)D3.
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