Vitamin D and Hyperparathyroidism
Parathyroid hormone (PTH) rises when calcium falls, keeping serum calcium in the tight physiological range. Vitamin D deficiency lowers calcium absorption, which raises PTH (secondary hyperparathyroidism). Autonomous parathyroid overactivity (primary hyperparathyroidism) raises PTH and calcium simultaneously. Vitamin D dosing differs sharply between the two.
Secondary hyperparathyroidism — vitamin D deficiency driven
The most common cause of elevated PTH. Vitamin D deficiency → reduced intestinal calcium absorption → tendency to hypocalcaemia → parathyroid responds by raising PTH → PTH mobilises calcium from bone. Chronic pattern accelerates bone loss and increases fracture risk. Correcting vitamin D deficiency normalises PTH over weeks to months, protecting bone.
Primary hyperparathyroidism — autonomous
Adenoma or hyperplasia of one or more parathyroid glands produces excess PTH independent of calcium feedback. Serum calcium is high, PTH is inappropriately high or normal. Osteoporosis, kidney stones, and neurocognitive symptoms result. Definitive treatment is parathyroidectomy in symptomatic disease.
Vitamin D deficiency in primary HPT
Many primary HPT patients have concomitant vitamin D deficiency (partly from chronic urinary calcium losses). The traditional concern was that vitamin D supplementation would worsen hypercalcaemia. Recent evidence (Rolighed 2014) shows cautious vitamin D repletion in primary HPT is safe when calcium is monitored — 400–1,000 IU/day maintenance is standard, higher for correction with monitoring.
Tertiary hyperparathyroidism
Long-standing secondary HPT (usually in CKD) leads to autonomous parathyroid overactivity even after the underlying cause is corrected. Treatment options include cinacalcet, active vitamin D analogues, or parathyroidectomy under specialist care.
Practical guide
- Persistently elevated PTH: check serum calcium, 25(OH)D, and renal function.
- Low 25(OH)D + high PTH + normal or low calcium → secondary HPT from deficiency. Correct vitamin D; re-check PTH at 8–12 weeks.
- High calcium + high PTH → primary HPT. Endocrine referral for imaging (sestamibi scan, ultrasound), consideration of surgery.
- Vitamin D correction in primary HPT is generally safe with calcium monitoring; work with endocrinology.