Vitamin D and muscle function

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From Osteoporos Int. 2002 Mar;13(3):187-94.

Vitamin D and muscle function.

Pfeifer M, Begerow B, Minne HW.

Institute of Clinical Osteology Gustav Pommer and Clinic Der

Fuirstenhof, Bad Pyrmont, Germany.

The aim of this review is to summarize current knowledge on the relation

between vitamin D and muscle function. Molecular mechanisms of vitamin D

action on muscle tissue have been known for many years and include

genomic and non-genomic effects. Genomic effects are initiated by

binding of 1,25-dihydroxyvitamin D3 (1,25(OH)2D) to its nuclear

receptor, which results in changes in gene transcription of messenger

RNA and subsequent protein synthesis. Non-genomic effects of vitamin D

are rapid and mediated through a

membrane-bound vitamin D receptor (VDR). Genetic variations in the VDR

and the importance of VDR polymorphisms in the development of

osteoporosis are still a matter of controversy and debate. Most

recently, VDR polymorphisms have been described to affect muscle

function.

The skin has an enormous capacity for vitamin D production and supplies

the body with 80-100% of its requirements of vitamin D. Age, latitude,

time of day, season of the year and pigmentation can dramatically affect

the production of vitamin D in the skin.

Hypovitaminosis D is a common feature in elderly people living in

northern latitudes and skin coverage has been established as an

important factor leading to vitamin D deficiency. A serum

25-hydroxyvitamin D level below 50 nmol/l has been associated with

increased body sway and a level below 30 nmol/l with decreased muscle

strength.

Changes in gait, difficulties in rising from a chair, inability to

ascend stairs and diffuse muscle pain are the main clinical symptoms in

osteomalacic myopathy. Calcium and vitamin D supplements together might

improve neuromuscular function in elderly persons who are deficient in

calcium and vitamin D. Thus 800 IU of cholecalciferol in combination

with mg of elemental calcium reduces hip fractures and other

non-vertebral fractures and should generally be recommended in

individuals who are deficient in calcium and vitamin D.

Given the strong interdependency of vitamin D deficiency, low serum

calcium and high levels of parathyroid hormone, however, it is difficult

to identify exact mechanisms of action.