Influence of physical mobility and season on 25-hydroxyvitamin D-parathyroid hormone interaction and bone remodelling in the elderly.
OBJECTIVE
To investigate influences of physical mobility and season on 25-hydroxyvitamin D-intact parathyroid hormone (iPTH) interaction in the elderly.


METHODS
We examined 188 frail institutionalized elderly at the expected nadir of their serum vitamin D concentrations (winter). This group was compared with 309 healthy ambulatory elderly at the expected time of maximum vitamin D repletion (summer), to accentuate the influences of season and physical activity.


METHODS
Serum concentrations of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, iPTH and urinary deoxypyridinoline (DPD) were measured.


RESULTS
Vitamin D metabolites were significantly lower in the institutionalized elderly (P<0.0001), with an 82.5% prevalence of vitamin D deficiency (25-hydroxyvitamin D <12ng/ml) in institutionalized elderly in wintertime and 15.5% in ambulatory elderly in summertime. Overall, median iPTH did not differ between groups. However, median iPTH secretion in the presence of low vitamin D serum concentrations (5-30ng/ml) was greater in ambulatory elderly. This could be explained by lower mobility status being correlated with greater serum calcium concentrations (r=0.24, P=0.02 in women; r=0.35, P=0. 001 in men) and greater urinary excretion of DPD (r=0.41, P=0.0001 in women; r=0.42, P=0.0002 in men), independent of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and iPTH.


CONCLUSIONS
These data support the hypothesis that immobility, even in the presence of vitamin D deficiency, acts as an overriding influence on bone metabolism by promoting bone resorption (measured as urinary DPD) and increasing serum calcium independent of iPTH. Therefore mobility status may substantially affect 25-hydroxyvitamin D threshold values and the degree to which patients benefit from vitamin supplementation.
Theiler
R
R
Departments of Rheumatology, University of Basel, Switzerland.
Stähelin
H B
HB
Kränzlin
M
M
Somorjai
G
G
Singer-Lindpaintner
L
L
Conzelmann
M
M
Geusens
P
P
Bischoff
H A
HA
D000368:Aged; D000369:Aged, 80 and over; D016723:Bone Remodeling / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007326:Institutionalization; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D009752:Nutritional Status; D010281:Parathyroid Hormone / Q000097:blood*; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D