Endocrine Abstracts

Introduction: Obesity is a strong risk factor for incident chronic kidney disease (CKD). Furthermore, high body mass index (BMI) is consistently associated with low serum vitamin D in the general population. The aims of the present study were to i) compare vitamin D metabolite levels in overweight/obese versus normal weight individuals with normal to severely impaired renal function and ii) to assess the impact of 25(OH)D on the development of secondary hyperparathyroidism (SHPT).

Methods: Serum 25(OH)D, 1,25(OH)₂D, PTH, calcium and phosphate were measured in 104 CKD outpatients with BMI>25 kg/m². Participants were categorized according to the eGFR (ml/min/1.73 m²): G1: ≥60 (n=53), G2: 30–59 (n=35) and G3: 15–29 (n=16). Fifty normal-weight subjects with comparable eGFR levels composed the control group (G1-nw – G3-nw).

Results: 25(OH)D was lower in overweight/obese G1 patients compared to G1-nw (21.7±6.5 vs 26.5±7.0 ng/ml, P=0.02) and in G2 versus G2-nw (19.0±6.0 vs 25.0±5.2 ng/ml, P=0.005), whereas the level did not differ among G3 groups (15.8±4.7 ng/ml vs 20.3±4.5 ng/ml, P=0.49 in G3 vs G3-nw respectively). Mean 1,25(OH)₂D and PTH levels were similar in obese/overweight versus normal-weight individuals in each eGFR category. Multivariate regression analysis in the entire cohort revealed that factors independently associated with low 25(OH)D levels were BMI>25 kg/m², eGFR<30 ml/min/1.73 m² and female gender whereas low 1,25(OH)₂D levels were associated with eGFR<30 ml/min/1.73 m², older age and increased serum phosphate. Even though serum 25(OH)D levels were suboptimal (<30 ng/ml) in both overweight and controls and in all eGFR groups, significant SHPT was only observed in the groups with eGFR<30 ml/min/1.73 m².

Conclusions: Lower serum 25(OH)D but similar 1,25(OH)2D and PTH levels were observed in overweight/obese compared to normal weight individuals and preserved or moderately impaired renal function. Even though vitamin D insufficiency was a common feature across all eGFR categories, SHPT was only observed in those with severely impaired renal function.