Effects Of Vitamin D₃ Supplementation And Exercise On Intramyocellular And Extramyocellular Lipid Accumulation And Energy Metabolism

PurposeSkeletal muscle is an important organ for the utilization of lipids and glucose.Lipid accumulation in the skeletal muscle does not only provide energy for the maintenance of skeletal muscle contraction,but it is also related to the incidence of metabolic diseases.Intramyocellular lipid?IMCL?and extramyocellular lipid?EMCL?play some important roles in skeletal muscle function and insulin resistance.Recent studies have found that the physiological effects of vitamin D have been far beyond the basic function of vitamins,which in its biologically active form,1,25-dihydroxyvitamin D?1,25?OH?₂D?,can play a variety of roles in many tissues.It has been demonstrated that low levels of 25-hydroxyvitamin D?25?OH?D?are associated with immune abnormalities,obesity,and muscle weakness.However,the effects and mechanism of circulating 25?OH?D on IMCL and EMCL in humans are still less understood.We conducted two studies to investigate these issues.In the cross-sectional study,we investigated the relationship of serum 25?OH?D with IMCL and EMCL content and utilization by using ¹H-MRS,and whole body lipid metabolism in healthy adults using the human metabolic chamber.In the randomized,placebo-controlled trial of vitamin D₃ supplementation and exercise intervention,we assessed the effects of vitamin D₃ supplementation alone or concomitant endurance training on IMCL and EMCL accumulation in healthy adults,and tested whether the effects of vitamin D₃ supplementation are associated with the improvement of the whole-body lipid metabolism.Moreover,we investigated whether vitamin D₃supplementation strengthened the effect of endurance training on improving IMCL and EMCL metabolism.Our study provides a new theoretical reference and scientific evidence on the prevention and treatment of skeletal muscle metabolic abnormalities,and associated metabolic disorders.MethodsStudy One:Cross-sectional study?The relationship between vitamin D status and intramyocellular and extramyocellular lipids?Subjects who met the inclusion criteria were recruited.The test content and methods included:?1?The height,weight,body composition,maximum oxygen uptake were measured;a questionnaire survey was also administered.?2?Fasting blood was drawn.?3?Twenty-four-hour human energy metabolic parameters were measured using the human metabolic chamber.?4?Nuclear magnetic resonance spectroscopy?¹H-MRS?was used to test the IMCL and EMCL of the right calf muscles?tibialis anterior,gastrocnemius,and soles?before and after a continuous1-hour moderate-intensity aerobic exercise.?5?ActiGraph GT3X+was used to monitor subjects'daily physical activity for seven consecutive days.Study Two:A single-blind randomized controlled intervention study?Effects of vitamin D₃ supplementation and exercise intervention on intramyocellular and extramyocellular lipids?.Subjects whose serum 25?OH?D concentrations were below 50 nmol/L and met the inclusion criteria were recruited.They were randomly divided into four groups:the placebo control group?CG?,vitamin D supplementation group?VG?,aerobic exercise combined with the placebo group?ECG?,vitamin D supplementation combined with aerobic exercise group?VEG?.Participants in the CG group received daily oral placebo.The VG group were given oral vitamin D drops of 1200 IU/d for 3months.The ECG group received an oral placebo daily and participated in aerobic exercise 3 times/week and 1 hour/session.VEG group took vitamin D drops orally at1200 IU/d,and participated in aerobic exercises(indoor treadmill walking/jogging or power cycling with intensity of 55⁶5%VO_2max for individuals)3 times/wk and 1h/session.Repeated tests were performed before and after the intervention,and the test contents and methods were the same as the cross-sectional study.Results[1]Seventy-four subjects?10 males and 64 females?were recruited for the cross-sectional study,with an overall serum 25?OH?D concentration of 35.0±14.6nmol/L.The subjects were divided into four groups according to the interquartile range of serum vitamin D concentration:Group 1,25?OH?D concentration was less than 24.4 nmol/L;Group 2,25?OH?D concentration ranged from 24.4³2.9 nmol/L;Group 3,25?OH?D concentration ranged from 32.9⁴2.5 nmol/L;and Group 4,25?OH?D concentration was not less than 42.5 nmol/L.The serum 25?OH?D concentration had a significantly negative correlation with FFA?r=-0.273,p=0.020?,TC?r=-0.251,p=0.031?,and FAT%?r=-0.246,p=0.034?,and a positive correlation with VO_2max?r=0.394,p=0.001?,muscle mass?r=0.293,p=0.011?,and resting?RQ??r=0.233,p=0.049?.Subjects in Groups 3 and 4 with higher vitamin D levels,had their 24-hour fat oxidation rate,24-hour carbohydrate oxidation rate,and brisk walking significantly higher than those of Groups 1 and 2 with lower vitamin D levels?p<0.05?.Fifty-six subjects took the ¹H-MRS test for calf muscles.The serum 25?OH?D concentration was significantly negative-correlated to the EMCL in tibialis anterior,gastrocnemius,and soleus muscles?p<0.05?.Regression analysis showed that serum25?OH?D concentration could predict TA-EMCL content??=-0.264,p=0.041?,SOL-EMCL content??=-0.344,p=0.022?,and the changes of ratio of tibialis anterior??=-0.302,p=0.038?.TA-EMCL was negatively correlated with EE/kg body weight?r=-0.270,p=0.044?,and positively correlated with EEwalk/kg FFM?r=0.326,p=0.014?.MG-IMCL was positively correlated with EEwalk/kg FFM?r=0.269,p=0.047?.MG-EMCL was negatively correlated with RMR?r=-0.281,p=0.038?,and positively correlated with EEwalk/kg FFM?r=0.328,p=0.015?.[2]Forty females participated in the intervention study;they were randomly assigned to four groups of ten people each.The mean serum 25?OH?D concentration of the subjects before the intervention was 27.6±9.7 nmol/L,and there was no significant difference among the groups.After the intervention,the serum 25?OH?D concentrations in the four groups significantly increased.Serum 25?OH?D concentrations in the VG and VEG groups were 67.9±15.4 nmol/L and 75.0±15.9nmol/L,respectively,which reached vitamin D sufficiency,and was significantly higher than those in the CG and ECG groups?p<0.05?.In the CG and ECG groups,the serum 25?OH?D concentrations significantly increased after the intervention,but did not reach the sufficiency level.There were no significant changes in body composition and the other indicators before and after the intervention.After the intervention,the resting metabolic rate?RMR?in the VEG group was significantly higher than that in the VG group?p=0.011?;resting respiratory quotient?RQrest?in the VG group was higher than in the ECG group?p=0.036?.The EEwalk/kg FFM was significantly elevated in the VEG group?p=0.009?,and significantly higher than in the VG group?p=0.041?.The carbohydrate oxidation rate of 24 h was negatively correlated with 25?OH?D concentration?r=-0.323,p=0.045?and free fatty acid?FFA??r=-0.454,p=0.004?after the intervention.After the intervention,the TA-IMCL in the VG group decreased significantly?p=0.032?,while that in the VEG and ECG groups increased significantly?p=0.014,p=0.028,respectively?.After controlling the baseline TA-IMCL,the TA-IMCL in the VEG and ECG groups was significantly greater than that in the VG and CG groups?p<0.05?.TA-IMCL/EMCL was significantly reduced in the VG group after the intervention?p=0.015?.After the intervention,TA-IMCL in the VG,VEG,and ECG groups was reduced significantly during the 1-hour aerobic exercise?p<0.05?;TA-IMCL/EMCL in the VG group also significantly decreased?p=0.032?.Conclusions[1]For healthy normal-weight individuals,vitamin D levels were positively correlated with the RQrest.The 24-h fat oxidation rate,24-h carbohydrate oxidation rate,and brisk walking carbohydrate oxidation rate of individuals with higher vitamin D levels were significantly higher than those with lower vitamin D levels.Vitamin D was negatively correlated with TA-EMCL,MG-EMCL,and SOL-EMCL.Vitamin D level is related to the regulation of whole body glucolipid metabolism and local skeletal muscle metabolism,and their relationships had muscle specificity;that is at resting state,there was a correlation among vitamin D,whole body glucolipid metabolism of resting,and soleus EMCL accumulation.Vitamin D and energy expenditure of brisk walking were related to utilization of lipids in the tibialis anterior and changes of IMCL/EMCL in the soleus during brisk walking.[2]Vitamin D supplementation in healthy normal-weight individuals significantly increased their 25?OH?D concentration,but had no significant effect on body weight,BMI,body composition,and so on.Vitamin D supplementation combined with exercise intervention significantly reduced FFA,increased IS,and improved RMR,and increased fat oxidation during brisk walking.Both vitamin D supplementation intervention and exercise intervention had effects on TA-IMCL;vitamin D supplementation significantly decreased TA-IMCL,while exercise intervention could increase TA-IMCL.Vitamin D supplementation alone enhanced the redistribution between IMCL and EMCL in tibialis anterior during the aerobic exercise.Both vitamin D supplementation alone,long-term aerobic exercise training intervention and vitamin D supplementation combined with exercise intervention were beneficial to the oxidative utilization of TA-IMCL during exercise.