Of the 186 patients with mild hyperparathyroidism (45 ≤ PTH < 65 pg/mL), a total of 71.4% had abnormal concentrations of vitamin 25(OH)D < 30 ng/mL: 45/186 (24.1%) had vitamin D deficiency and 88/186 (47.3%) insufficiency, while the remaining 53/186 (29.5%) had vitamin D sufficiency. Here, PTH is linked to hyperparathyroidism.