Skeletal muscle accounts for approximately 40% of human body weight. Sarcopenia is the age-related atrophy or progressive decline of skeletal muscle. Older adults, especially the elderly, are at a much higher risk of sarcopenia, as muscle mass and strength begin to steadily decline in the third decade of life. Nearly 50% of an individual’s muscle mass may be lost by age 70, unless it’s sustained by regular exercise and resistance training. Muscle loss leads to functional decline and loss of independence, and it is associated with increased risk of falls, fractures, immobility, acute and chronic illness, frailty, and even mortality.
Studies show a strong association between sarcopenia and osteoporosis (“osteosarcopenia”), and they often coexist in elderly populations, particularly older women. Musculoskeletal decline is linked to multiple factors, including vitamin D and calcium availability, protein intake, and physical inactivity. Vitamin D deficiency is a common health concern for postmenopausal women and elderly populations and has been associated with muscle weakness and an increased risk of falling. Similarly, elderly populations are more susceptible to vitamin D deficiency due to poor dietary intake, decreased exposure to sunlight, and nutrition-related conditions. Postmenopausal women with vitamin D deficiency have been shown to have significantly reduced appendicular muscle strength and physical performance compared to those with normal vitamin D levels in a multicenter retrospective study.
Vitamin D plays a vital role in calcium homeostasis and uptake in myocytes, which promotes muscle protein synthesis (through mammalian target of rapamycin complex 1 signaling) and calcium and phosphate transport that are important for muscle contraction and strength. According to systematic reviews and meta-analyses, vitamin D supplementation may support muscle strength and muscle mass in both elderly and frail populations, in addition to healthy adults. In another report, a mere 20 µg (800 IU) per day of vitamin D supplementation in the elderly lowered the risk of falling by 22% compared to a placebo or calcium supplementation alone. Other clinical studies have shown that vitamin D supplementation led to significant reductions in muscle pain and proximal myopathy, especially in subjects with severe vitamin D deficiency.
Moreover, a recent prospective, cohort observational study (n = 1,915) published in The Journal of Clinical Endocrinology and Metabolism determined that aging men with vitamin D deficiency have a twofold increased mortality risk compared with men with vitamin D levels in the normal range. From a group of 1,915 community-dwelling men ages 40 to 79 years old, 469 died during a mean follow-up of 12.3 ± 3.4 years. The men with a total serum 25(OH)D <20 µg/L had an increased mortality compared to those with vitamin D values greater than 30 µg/L; and men in the lowest three free 25(OH)D quintiles had a higher mortality risk compared to the men in the highest quintile.
Although the research shows a correlation between vitamin D deficiency and sarcopenia, and there were some improvements in clinical outcomes with supplementation, results are still controversial. Further clinical research is needed to determine the optimal interventional dose and duration for promoting optimal musculoskeletal health as part of the natural aging process. Encouraging patients to consume more foods rich in vitamins D and K, and to increase resistance training and adequate sunlight exposure may help slow the progression of age-related muscle decline.
By Caitlin Higgins, MS, CNS