Low serum calcidiol concentration in older adults with reduced muscular function

To examine the association between muscular function and the serum concentrations of 25-hydroxyvitamin D (calcidiol) and 1,25-dihydroxyvitamin D (calcitriol).

A randomized population survey. Baseline measurements of serum calcidiol and calcitriol concentrations and assessment of muscular function (hand grip strength, ability to climb stairs, outdoor activity, and fall occurrence).

The Medical department, Aker University Hospital, Oslo, and subjects' homes.

Two hundred forty-six recently hospitalized older patients and 103 randomly selected older people living at home.

Serum concentration of calcidiol and calcitriol in relation to muscle function.

Reduced muscle function was associated with low calcidiol levels. In both the hospital group and the home group, calcidiol concentrations correlated positively to arm muscle strength (r = .22, P < .001; r = .37, P < .001), ability to climb stairs (r = -.16, P < .05; r = -.42, P = < .001), physical activity (r = -.27, P < .001; r = -.31, P < .001), and the absence of fall occurrences (r = -.27, P < .001; r = -.31, P = .004). Calcitriol showed an association with physical activity in the hospital group (r = -.19, P < .05), and with fall last month in the home group (r = -.22, P < .05).

Older people with reduced muscle function often had reduced levels of calcidiol serum concentration. Low levels of calcidiol were not associated with signs of general undernutrition, such as low body mass, or with reduced arm-muscle circumference or triceps skinfold thickness. This finding may suggest a physiological role for calcidiol in muscle function. Reduced muscle strength increased disability in our older subjects, which may be improved by vitamin D supplementation in vitamin D-deficient subjects.