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Meta-study: vitamin D supplementation boosts muscle strength

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.

Vitamin D
Vitamin D
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.

Meta-study: vitamin D supplementation boosts muscle strength

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.

Meta-study: vitamin D supplementation boosts muscle strength

"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."

J Sci Med Sport. 2014 Aug 11. pii: S1440-2440(14)00163-7.

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