Karhapää P, Pihlajamäki J, Pörsti I, Kastarinen M, Mustonen J, Niemelä 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: 573–580. 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 (β = −0.17, P = 9 × 10 and β = −0.28, P = 6 × 10, 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 (β = 0.17, P = 2 × 10 and β = 0.19, P = 5 × 10, 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 × 10). 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 × 10). CONCLUSION.: Our findings suggest that both eGFR and PTH are significantly associated with vitamin D metabolism in men without known CKD.