Evaluation assessment of the cut-off point of vitamin D in the population older than 64 years old

Serum 25(OH)D(3) is the best indicator of vitamin D status, although some controversy remains regarding "normal" and "abnormal" values. The objective was to identify the 25(OH)D(3) serum concentration threshold which allows to know the 25(OH)D(3) serum levels correlated to PTH(i) increase and to describe the prevalence of hypovitaminosis D. Cross-sectional population study in subjects over 64 years of age residing in the basic healthcare areas in our hospital's area of reference. A total of 239 persons -mean age (standard deviation) 72 (5.4) years- were evaluated. Mean serum concentrations of 25(OH)D(3) and PTH(i) were 17 (7.5) ng/ml and 60.5 (26.1) pg/ml, respectively. 32% of the subjects showed an increase in the serum concentration of PTH(i) > 65 pg/ml. 96% of the cases with an increase in PTH(i) had serum concentrations of 25(OH)D(3) < or = 25.5 ng/ml. In 70% of the subjects, the serum concentration levels of 25(OH)D(3) ranged between 11 and 25 ng/ml and in 17% the levels of 25(OH)D(3) were lower than 10 ng/ml. The normal ranges for our population could correspond to levels of 25(OH)D3 > or = 25 ng/ml, with a 95% of sensibility to detect secondary hyperparathyroidism.