Serum vitamin D in obese and overweight subjects according to estimated glomerular filtration rate.

OBJECTIVE

Obesity and renal disease are both associated with low serum 25(OH)D. The aims of the present study were to (a) assess vitamin D status and compare serum vitamin D levels in overweight/obese versus normal-weight individuals according to eGFR and (b) assess the role of 25(OH)D in the development of secondary hyperparathyroidism (SHPT).

DESIGN

Serum 25(OH)D, 1,25(OH)2D, parathyroid hormone (PTH), calcium, and phosphate were measured in 104 subjects with BMI > 25 kg/m2. Participants were categorized according to eGFR (ml/min/1.73m2): G1 ≥ 60 (n = 53), G2 30-59 (n = 35), and G3 15-29 (n = 16). Fifty normal-weight individuals with comparable eGFR served as controls: G1-nw (n = 23), G2-nw (n = 18), and G3-nw (n = 9).

RESULTS

25(OH)D levels were lower in G1 compared to those in G1-nw (21.7 ± 6.5 vs 26.5 ± 7.0 ng/ml, p = 0.005), G2 versus G2-nw (19.0 ± 6.0 vs 25.0 ± 5.2 ng/ml, p = 0.001), and G3 vs G3-nw (15.8 ± 4.7 vs 20.3 ± 4.5 ng/ml, p = 0.030). 1,25(OH)2D and PTH levels were similar in obese/overweight versus normal-weight individuals in each of the eGFR categories. Factors independently associated with low 25(OH)D levels were BMI > 25 kg/m2, lower eGFR, and female gender. Mean 25(OH)D levels were < 30 ng/ml in both overweight and controls, in all eGFR groups. SHPT was universally observed when eGFR was < 30 ml/min/1.73m2.

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. Even though vitamin D insufficiency was common across all eGFR categories, secondary hyperparathyroidism was more prevalent as eGFR declined.