Seasonal variations in serum levels, of 25-hydroxyvitamin D and parathyroid hormone but no detectable change in femoral neck bone density in an olderpopulation with regular outdoor exposure
A. Melin et al., Seasonal variations in serum levels, of 25-hydroxyvitamin D and parathyroid hormone but no detectable change in femoral neck bone density in an olderpopulation with regular outdoor exposure, J AM GER SO, 49(9), 2001, pp. 1190-1196
Citations number
46
Categorie Soggetti
Public Health & Health Care Science","General & Internal Medicine
OBJECTIVES. To investigate the influence of season and outdoor daylight exp
osure on serum levels of 25-hydroxy-vitamin D (25OHD), intact parathyroid h
ormone (PTH), ionized calcium, and femoral neck bone mineral density (BMD).
DESIGN: A 12-month, longitudinal, prospective study on a consecutively sele
cted sample of healthy independent older people.
SETTING: Men and women living in their own homes in the inner city of Stock
holm (latitude 59.2 degreesN).
PARTICIPANTS: Sixty-four healthy men (n = 13) and women (n = 51), age 79 to
96 (mean age 83.7) were requested to spend at least 3 hours per week outdo
ors during April through September. Fifteen of these, who failed to comply
with the required time outdoors, constituted a separate group. Subjects wit
h serious diseases and subjects with medication that could interfere with v
itamin D metabolism or bone mineralization were excluded from the study.
MEASUREMENTS: Daily dietary intakes of calcium and vitamin D were recorded
on the basis of the subjects' recall. The participants kept a diary recordi
ng the time spent in sunlight and the area of skin exposed. Fasting blood s
amples were collected and analyzed on four occasions for 25OHD, intact PTH,
and ionized calcium. BMD was determined at 6-month intervals in the femora
l neck, using dual energy x-ray absorptiometry.
RESULTS: At study start in the spring, 6% of the subjects had 25OHD levels
below 10 ng/ml and 78 % had levels below 31 ng/ml. Forty-seven percent had
intact PTH levels above the upper limit of the reference range (8-51 ng/L).
Seasonal variations in the serum levels of 25OHD (P < .001), intact PTH (P
< .001) and ionized calcium (P < .001) were observed only in the group wit
h greater than or equal to3 hours of weekly outdoor daylight exposure. The
25OHD levels in autumn were positively correlated with the number of hours
spent outdoors during the preceding summer (r = 0.63, P < .001). In the who
le group and in the group with weekly outdoor exposure of greater than or e
qual to3 hours, there were no, significant changes detectable in mean value
s of femoral neck BMD during the study year. Femoral neck BMD, expressed as
Z-score, was significantly and positively correlated with serum 25OHD (r =
0.38, P = .003 after summer, r = 0.37, P = .003 after winter).
CONCLUSION: The seasonal changes in serum levels of 25OHD, PTH, and ionized
calcium and the positive correlation between femoral neck BMD and 25OHD in
dicate that regular outdoor daylight exposure during the summer could enhan
ce calcium homeostasis and possibly bone health, even among very old people
living at northerly latitudes.