Low serum calcidiol concentration in older adults with reduced muscular function

OBJECTIVE: To examine the association between muscular function and the ser um concentrations of 25-hydroxyvitamin D (calcidiol) and 1,25-dihydroxyvita min D (calcitriol). DESIGN: A randomized population survey. Baseline measurements of serum calc idiol and calcitriol concentrations and assessment of muscular function (ha nd grip strength, ability to climb stairs, outdoor activity, and fall occur rence). SETTING: The Medical department, Aker University Hospital, Oslo, and subjec ts' homes. PARTICIPANTS: Two hundred forty-six recently hospitalized older patients an d 103 randomly selected older people living at home. MEASUREMENTS: Serum concentration of calcidiol and calcitriol in relation t o muscle function. MAIN RESULTS: Reduced muscle function was associated with low calcidiol lev els. In both the hospital group and the home group, calcidiol concentration s 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 = < .00 1), physical activity (r = -.27, P <.001; r = -.31, P <.001), and the absen ce of fall occurrences (r = -.27, P <.001; r = -.31, P = .004). Calcitriol showed an association with physical activity in the hospital group (r = -.1 9, P < .05), and with fall last month in the home group (r = -.22, P < .05) . CONCLUSIONS: Older people with reduced muscle function often had reduced le vels of calcidiol serum concentration. Low levels of calcidiol were not ass ociated with signs of general undernutrition, such as low body mass, or wit h reduced arm-muscle circumference or triceps skinfold thickness. This find ing may suggest a physiological role for calcidiol in muscle function. Redu ced muscle strength increased disability in our order subjects, which may b e improved by vitamin D supplementation in vitamin D-deficient subjects.