Vitamin D not only plays a key role in maintaining bone strength, it also plays an important role in muscle growth. Because almost everyone suffers from a vitamin D deficiency, you’d expect that average people would gain strength if they took extra vitamin D. British sports scientists analysed data from 6 previously published studies and concluded that vitamin D supplementation does indeed boost muscle strength.
Most scientists now agree more or less that elderly people can gain strength by taking vitamin D. Vitamin D levels in many old people are alarmingly low. But scientific opinion is divided as to whether vitamin D supplementation increases muscle strength in young, healthy people.
Sports scientists at the Queen Mary University of London dug up 6 good studies in which a total of 370 healthy men and women aged between 18 and 40 had participated. The subjects had taken daily doses of about 4000 IE vitamin D in these studies.
More details on the subjects and the studies are shown in the table below.
LP = leg press; CP = chest press; LC = leg curl; BP = bench press; LPID = leg press isokinetic dynamometer; BPID = bench press isokinetic dynamometer; GSIK = gastrocnemius-soleus strength via an isokinetic dynamometer; HG = handgrip on isokinetic dynamometer; PG = pinch grip on isokinetic dynamometer; IMQ = isometric quadriceps contraction.
As you can see, the subjects in some of the studies were athletes. But whether the subjects were athletes or not, vitamin D supplementation resulted in an increase in muscle strength.
The first figure shows the effects on muscle strength of the lower body; the second on the upper body.
“Vitamin D3 supplementation improves upper and lower limb muscle strength in a healthy, adult, athletic and non-athletic population between the ages of 18 and 40”, the Brits write. “Nevertheless, the evidence was based on a restricted total number of included studies, suggesting that further, randomized controlled trials should establish optimal dosing regimen, control for gender differences and consider effects in larger athletic populations. There is a need for further investigation into muscular power and endurance with vitamin D supplementation.”
“Research has suggested that it may be necessary to increase serum concentrations above the optimal concentrations (>50 nmol/L (20 ng/ml)) of vitamin D in order to suitably improve muscle strength. Although all of the studies used managed to increase their subjects serum levels to adequate concentrations, none reported ‘optimal’ levels.”
“No symptoms of vitamin D toxicity (>375 nmol/L(150.2 ng/ml)) were mentioned in any of the studies, suggesting the regimen used in these studies were safe.”
Effects of vitamin D supplementation on upper and lower body muscle strength levels in healthy individuals. A systematic review with meta-analysis.
To investigate the effects of vitamin D supplementation on muscle strength in healthy individuals.
A systematic review with meta-analysis.
In October 2013 a computerised literature search of three databases (PubMed, Web of Knowledge and Scopus) was performed. Included in the review were controlled and randomised controlled trials, published in English, which measured muscle strength and serum vitamin D concentration in participants 18-40 years old. References of identified articles were then cross-checked and citations scanned for additional articles. Quality was assessed using the PEDro scale. Muscle strength and vitamin D levels were extracted for a meta-analysis on upper and lower limb strength with standardised mean differences calculated to analyse effect.
Six randomised controlled trials and one controlled trial were identified and quality assessment showed all seven trials were of ‘good quality’. Data was extracted from 310 adults, 67% female, with mean ages ranging from 21.5 to 31.5 years. Trials lasted from 4 weeks to 6 months and dosages differed from 4000IU per day to 60,000IU per week. Upper and lower limb muscle strength had a standardised mean difference of 0.32 (95% CI=0.10, 0.54) and 0.32 (95% CI=0.01, 0.63) respectively, suggesting vitamin D supplementation significantly increased muscle strength in the experimental group for upper (P=0.005) and lower limbs (P=0.04).
Vitamin D supplementation increases upper and lower limb strength. Further research should focus on its effect on muscle power, endurance and maximal strength.
PMID: 25156880 [PubMed – as supplied by publisher]