Low 25-Hydroxyvitamin D in Primary Hyperparathyroidism: Enhanced Conversion Into 1,25-Hydroxyvitamin D May Not Be...

Area of Science:

• Endocrinology and Metabolism
• Bone and Mineral Research

Background:

• Vitamin D deficiency is frequently observed in patients with primary hyperparathyroidism (PHP).
• Low serum 25-hydroxyvitamin D [25OHD] levels in PHP may result from increased conversion to the active form, 1,25-dihydroxyvitamin D [1,25(OH)D].

Purpose of the Study:

• To investigate vitamin D metabolism in individuals diagnosed with primary hyperparathyroidism.
• To analyze the relationship between parathyroid hormone (PTH), calcium, 25OHD, and 1,25(OH)D levels in PHP patients.

Main Methods:

• Serum calcium, PTH, 25OHD, and 1,25(OH)D levels were measured in 210 adults (102 with PHP, 40 with normal 25OHD, 68 with vitamin D deficiency).
• Measurements were repeated in 37 PHP patients post-vitamin D supplementation and 43 post-surgery.
• Statistical analyses included Student's t-test, ANOVA, and correlation assessments.

Main Results:

• PHP patients exhibited significantly higher calcium, PTH, and 1,25(OH)D levels compared to controls.
• 25OHD levels were lower in PHP patients, comparable to those with vitamin D deficiency.
• Vitamin D supplementation in PHP patients increased 1,25(OH)D and calcium without reducing PTH; normalization occurred post-surgery.
• Significant correlations were found between PTH and calcium, 25OHD, 1,25(OH)D, and the 1,25(OH)D/25OHD ratio in PHP patients.

Conclusions:

• Subnormal 25OHD in PHP is likely due to enhanced conversion to 1,25(OH)D, not necessarily true vitamin D deficiency.
• Vitamin D supplementation can exacerbate hypercalcemia in individuals with PHP.
• Surgical correction of PHP leads to normalization of vitamin D metabolites and mineral levels.