Abstract
ABSTRACTVitamin D is commonly prescribed to normalize deficiencies and to treat osteoporosis. However, the effect vitamin D supplements have on skeletal muscle health is equivocal. Although vitamin D is known to play a role in the various processes that maintain muscle integrity and function, recent studies utilizing high bolus dose vitamin D supplementation has demonstrated an increased risk of falls. Thus, the aim of this study was to investigate the effects of high vitamin D supplementation on skeletal muscle function with and without exercise enrichment. Four‐week old C57BL/10 mice (n = 48) were separated into either normal vitamin D (1500 IU/kg diet; unsupplemented) or high vitamin D (20,000 IU/kg diet; supplemented) treatment groups. Each dietary group was further separated into interventional subgroups where mice either remained sedentary or received exercise‐enrichment for 8 weeks in the form of voluntary running. Following the intervention period, whole body in vivo and ex vivo contractile analysis were performed. High vitamin D supplementation decreased force production in the slow‐twitch soleus muscles of sedentary mice (p < .01); however, exercise normalized this effect. Eight weeks of exercise did not improve fatigue resistance of the extensor digitorum longus (EDL) or soleus muscles in unsupplemented mice, likely due to low levels of activation in these muscles. In contrast, fatigability was improved in the EDL (p < .01) and even more so in the soleus (p < .001) in the supplemented exercise‐enriched group. Our data highlights that increasing vitamin D levels above normal reduces postural muscle force as seen in the soleus. Thus, unnecessary vitamin D supplementation may contribute to the increased risk of falls observed in some studies. Interestingly, when vitamin D supplementation was combined with exercise, force production was effectively restored, and fatigue resistance improved, even in muscles lowly activated. Regular exercise may modulate the effects of vitamin D on skeletal muscle, and be recommended for individuals receiving vitamin D supplements. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.
Highlights
Vitamin D is a key hormone that regulates many bodily functions and, importantly, plays a major role in the maintenance of bone and muscle integrity.[1,2,3,4,5,6,7] For example, vitamin D regulates bone metabolism through the control of mineral ion homeostasis, calcium and phosphate
Vitamin D supplementation produces the greatest health benefits to deficient individuals when serum levels are normalized, optimal dosages and regimens are still yet to be determined.[4,5,6,10,13,14,15] Many vitamin D supplementation studies have demonstrated “nonskeletal” benefits, including decreased severity of autoimmune diseases, such as rheumatoid arthritis,(16,17) and decreased symptoms of depression.[18] research conducted over the past decade has focused on the effects of intermittent high-dose vitamin D administration consisting of single boluses between 300,000 and 600,000 international units (IU) of vitamin D that are aimed at delivering a yearly dosage (for review see Sanders and colleagues[19])
Whole body weight changes were observed with the EXER UNSUPP and EXER VITD mice having a significantly smaller total body weight posttreatment compared to SED UNSUPP and SED VITD mice, which was accompanied with a lower overall weight gain (p < .0001, Table 2)
Summary
Vitamin D is a key hormone that regulates many bodily functions and, importantly, plays a major role in the maintenance of bone and muscle integrity.[1,2,3,4,5,6,7] For example, vitamin D regulates bone metabolism through the control of mineral ion homeostasis, calcium and phosphate. Vitamin D supplementation produces the greatest health benefits to deficient individuals when serum levels are normalized, optimal dosages and regimens are still yet to be determined.[4,5,6,10,13,14,15] Many vitamin D supplementation studies have demonstrated “nonskeletal” benefits, including decreased severity of autoimmune diseases, such as rheumatoid arthritis,(16,17) and decreased symptoms of depression.[18] research conducted over the past decade has focused on the effects of intermittent high-dose vitamin D administration consisting of single boluses between 300,000 and 600,000 international units (IU) of vitamin D that are aimed at delivering a yearly dosage (for review see Sanders and colleagues[19]) Even though these studies demonstrated rapid increases in serum 25(OH)D (inactive vitamin D) levels, these annual high doses have been found to be problematic, with reports of increased risk of falls and fracture.[20,21] the mechanisms behind this effect are still unknown, skeletal muscle weakness, leading to increased tripping, has been suggested, and our recent study demonstrated a decrease in ex vivo muscle force production in mice receiving a single yearly dose.[22]. In this study we investigated whether a gradual administration of high vitamin D would improve exercise performance, and whether there is a synergistic effect of vitamin D and exercise on muscle function
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