Glomerular filtration rate and parathyroid hormone are associated with 1,25-dihydroxyvitamin D in men without chronic kidney disease

Karhapaa P, Pihlajamaki J, Porsti I, Kastarinen M, Mustonen J, Niemela O, Tuomi H, Kuusisto J (University of Eastern Finland, Kuopio; University of Tampere, Tampere; Finnish Medical Agency, Kuopio; and University of Tampere, Tampere, Finland). Glomerular filtration rate and parathyroid hormone are associated with 1,25-dihydroxyvitamin D in men without chronic kidney disease. J Intern Med 2012; 271: 573580. Background and aim. Vitamin D, estimated glomerular filtration rate (eGFR) and parathyroid hormone (PTH) are related to cardiovascular disease risk. We examined the associations between the levels of 25-hydroxyvitamin D (25-D) and 1,25-dihydroxyvitamin D (1,25-D) and both eGFR and PTH. Design and setting. Cross-sectional population-based study in Kuopio, Eastern Finland. Subjects. A total of 909 men without known chronic kidney disease (CKD) and not receiving antidiabetic medication, aged from 45 to 73 years, were included in the study. Main outcome measures. Fasting levels of 25-D, 1,25-D, creatinine and PTH were measured, and an oral glucose tolerance test (OGTT) was performed. Results. High levels of 25-D were associated with low levels of eGFR and PTH (beta = -0.17, P = 9 x 10-7 and beta = -0.28, P = 6 x 10-17, respectively, adjusted for age, body mass index and levels of calcium, phosphorus and glucose in a 2-h OGTT, and also for either eGFR or PTH). By contrast, high 1,25-D levels were associated with high levels of eGFR and PTH (beta = 0.17, P = 2 x 10-6 and beta = 0.19, P = 5 x 10-8, respectively, adjusted as mentioned earlier and additionally for 25-D). Eighteen per cent of men in the highest 25-D quartile were in the lowest 1,25-D quartile and also had a lower eGFR than men with high levels of both 25-D and 1,25-D (P = 4 x 10-5). Finally, 15% of men in the lowest 25-D quartile were in the highest 1,25-D quartile and also had higher PTH levels than men with low levels of both 25-D and 1,25-D (P = 2 x 10-3). Conclusion. Our findings suggest that both eGFR and PTH are significantly associated with vitamin D metabolism in men without known CKD.