CONCLUSIONS Vitamin D supplementation positively affected lower limb muscle strength in athletes , but not upper limb muscle strength or muscle power .
Different muscle groups and functions may respond differently to vitamin D supplementation .
BACKGROUND Vitamin D may play a role in skeletal muscle because of the discovery of VDR in skeletal muscle .
However , vitamin D deficiency is a global problem , including athletes .
Studies examining the effect of vitamin D supplementation on muscle function in athletes have inconsistent results .
Therefore , we aim ed to quantitatively summarize the evidence for the effect of vitamin D supplementation on skeletal muscle strength and explosive power of athletes using a meta- analysis .
Low vitamin D and high parathyroid hormone levels as determinants of loss of muscle strength and muscle mass (sarcopenia): the Longitudinal Aging Study Amsterdam.
The age-related change in hormone concentrations has been hypothesized to play a role in the loss of muscle mass and muscle strength with aging , also called sarcopenia . The aim of this prospect i ve study was to investigate whether low serum 25-hydroxyvitamin D ( 25-OHD ) and high serum PTH concentration were associated with sarcopenia . In men and women aged 65 yr and older , participants of the Longitudinal Aging Study Amsterdam , grip strength ( n = 1008 ) and appendicular skeletal muscle mass ( n = 331 , using dual-energy x-ray absorptiometry ) were measured in 1995 - 1996 and after a 3-yr follow-up . Sarcopenia was defined as the lowest sex-specific 15th percentile of the cohort , translating into a loss of grip strength greater than 40 % or a loss of muscle mass greater than 3 % . After adjustment for physical activity level , season of data collection , serum creatinine concentration , chronic disease , smoking , and body mass index , persons with low ( < 25 nmol/liter ) baseline 25-OHD levels were 2.57 ( 95 % confidence interval 1.40 - 4.70 , based on grip strength ) and 2.14 ( 0.73 - 6.33 , based on muscle mass ) times more likely to experience sarcopenia , compared with those with high ( > 50 nmol/liter ) levels . High PTH levels ( > or=4.0 pmol/liter ) were associated with an increased risk of sarcopenia , compared with low PTH ( < 3.0 pmol/liter ) : odds ratio = 1.71 ( 1.07 - 2.73 ) based on grip strength , odds ratio = 2.35 ( 1.05 - 5.28 ) based on muscle mass . The associations were similar in men and women . The results of this prospect i ve , population -based study show that lower  25-OHD  and higher  PTH levels increase the risk of sarcopenia in older men and women
CONCLUSIONS Vitamin D supplementation positively affected lower limb muscle strength in athletes , but not upper limb muscle strength or muscle power .
Different muscle groups and functions may respond differently to vitamin D supplementation .
BACKGROUND Vitamin D may play a role in skeletal muscle because of the discovery of VDR in skeletal muscle .
However , vitamin D deficiency is a global problem , including athletes .
Studies examining the effect of vitamin D supplementation on muscle function in athletes have inconsistent results .
Therefore , we aim ed to quantitatively summarize the evidence for the effect of vitamin D supplementation on skeletal muscle strength and explosive power of athletes using a meta- analysis .