Effects of vitamin D in skeletal muscle: falls, strength, athletic performance and insulin sensitivity
Clinical Endocrinology, Volume 80, Issue 2, pages 169–181, February 2014
Christian M. Girgis 1,2,*, Roderick J. Clifton-Bligh 2,3,4, Nigel Turner 5, Sue Lynn Lau 1,2,6, Jenny E. Gunton 1,2,6,7,*
Accompanying the high rates of vitamin D deficiency observed in many countries, there is increasing interest in the physiological functions of vitamin D. Vitamin D is recognized to exert extra-skeletal actions in addition to its classic roles in bone and mineral homeostasis. Here, we review the evidence for vitamin D's actions in muscle on the basis of observational studies, clinical trials and basic research. Numerous observational studies link vitamin D deficiency with muscle weakness and sarcopaenia. Randomized trials predominantly support an effect of vitamin D supplementation and the prevention of falls in older or institutionalized patients. Studies have also examined the effect of vitamin D in athletic performance, both inferentially by UV radiation and directly by vitamin D supplementation. Effects of vitamin D in muscle metabolic function, specifically insulin sensitivity, are also addressed in this review. At a mechanistic level, animal studies have evaluated the roles of vitamin D and associated minerals, calcium and phosphate, in muscle function. In vitro studies have identified molecular pathways by which vitamin D regulates muscle cell signalling and gene expression. This review evaluates evidence for the various roles of vitamin D in skeletal muscle and discusses controversies that have made this a dynamic field of research.
Long before the discovery of vitamin D, the sun was revered as a source of physical strength and vitality.
In ancient Greece, heliotherapy (sun exposure) was prescribed as a cure for 'weak and flabby muscles'.1
Sun exposure was considered a performance enhancer; ancient Olympians were instructed to train in sunlight to increase their muscle size.1
In 1938, a Russian group reported significant improvements in 100-m sprint times amongst students receiving UV radiation (7.4% vs 1.7% improvement in controls).38
In 1944, a German group found that medical students receiving UV radiation over 6 weeks had a 13% improvement in performance on a bicycle ergometer.39
In a study from USA, 11 male students experienced a 19% increase in cardiovascular fitness following a course of UV radiation.40
- Vitamin D deficiency is associated with muscle weakness, falls and sarcopaenia
- In general, RCT evidence supports the use of supplemental vitamin D to prevent falls in elderly, institutionalized individuals
- RCT evidence suggests a beneficial effect of supplemental vitamin D in proximal muscle strength in subjects with severe vitamin D deficiency.
However, this area is clouded by nonuniformity in end-points and muscle parameters
- Although vitamin D deficiency is associated with myalgia, the single RCT addressing this question shows no effect of vitamin D supplementation in alleviating myalgia in deficient subjects
- Vitamin D deficiency is surprisingly common in athletes. Two recent RCTs suggest that higher serum 25OHD levels (approximately 100 nM) may be necessary to produce effects in athletic performance
- Vitamin D deficiency is associated with insulin resistance, but this is confounded by adiposity and sedentary, indoor living. There is limited RCT evidence examining the effects of supplemental vitamin D in those with/at risk of insulin resistance, but more studies are currently underway
- VDR polymorphisms are associated with differences in muscle function.
This weighs in to the debate regarding the presence of VDR in skeletal muscle
- Animal studies support a combined role for vitamin D and its associated minerals (calcium/phosphate) in the development of muscle defects in vitamin D deficiency. However, mineral defects appear to be important
- In culture, muscle cells respond directly to 1,25(OH) 2D supporting a molecular basis for itsin vivo effects
- Two intriguing studies have recently emerged, one reporting the activation of VDR in regenerating muscle and another demonstrating that muscle serves as a storage site for 25OHD. The elucidation of vitamin D’s effects in muscle promises to remain a vibrant and evolving field
- Sports benefits from up to 50 ng of Vitamin – meta-analysis - Nov 2012 which has the following chart
- Elderly lower limb muscle strength improved with Vitamin D supplementation - Meta-analysis Oct 2013
- Vitamin D and Muscles – Major review: Feb 2013
- Overview Fractures and Falls and Vitamin D
- Overview Sports and vitamin D has the following summary
Athletes are helped by vitamin D by:
- Faster reaction time
- Far fewer colds/flus during the winter
- Less sore/tired after a workout
- Fewer micro-cracks and broken bones
- Bones which do break heal much more quickly
- Increased VO2 and exercise endurance Feb 2011
- Indoor athletes especially need vitamin D
- Professional indoor athletes are starting to supplement with vitamin D or use vitamin D beds
- Olympic athletes have used UV/vitamin D since the 1930's
- The biggest gain from the use of vitamin D is by those who exercise less than 2 hours per day.
- Reduced muscle fatigue with 10,000 IU vitamin D daily
- Muscle strength improved when vitamin D added: 3 Meta-analysis
- Sports and Vitamin D category