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[Determination of 25-hydroxyvitamin D serum levels and its seasonal variations in healthy young people].

BACKGROUND
25-hydroxyvitamin D has a longer half life and its serum levels have less daily variations than calcitriol. Thus, its measurement is a better indicator of vitamin D status.


AIM
To measure 25-hydroxyvitamin D levels in normal subjects during summer and winter.


PATIENTS AND METHODS
Vitamin D was measured using a competitive protein binding radioassay in 61 subjects (27 male) aged 21 to 57 years old, during July and August (winter) and February and March of the next year (summer).


RESULTS
25-hydroxyvitamin levels were 28.8 +/- 1.5 and 30.9 +/- 2.3 ng/ml during winter and summer respectively. No differences were found between men and women. Ninety five percent confidence levels were between 13 and 50 ng/ml. Levels in one patient with malabsorption were 9.3 ng/ml, in 2 patients with hypophosphatemic osteomalacia were 2.1 and 9.3 ng/ml, in 12 patients with alcoholic cirrhosis were 16.4 +/- 1.3 ng/ml, in 4 patients with primary osteoporosis were 23.3 +/- 0.7 and in three patients receiving vitamin D were 334 +/- 33.2 ng/ml.


CONCLUSIONS
Normal levels of 25-hydroxyvitamin D range from 13 to 50 ng/ml in normal adults, there are no differences between men and women and seasonal variations are minimal.