Effect of vitamin D nutrition on disease indices in patients with primary hyperparathyroidism

In patients with primary hyperparathyroidism, the size of the adenoma is a major determinant of biochemical indices, disease severity, and manner of presentation. However, the large variation in adenoma weight, both within and between populations and a steady decline in parathyroid adenoma weights over time remain largely unexplained. Based on the results in a small number of patients almost two decades ago we proposed that vitamin D nutritional status of the patient explains both the disease manifestations and much of the variation in adenoma size. Accordingly, we examined the relationship between vitamin D nutrition, as assessed by serum levels of 25-hydroxyvitamin D, and parathyroid gland weight, the best available index of disease severity, in a large number of patients (n = 440) with primary hyperparathyroidism. A significant inverse relationship was found between serum 25-hydroxyvitamin D level and log adenoma weight (r = -0.361; p < 0.001). Also, the adenoma weight was significantly related directly to serum PTH, calcium, and alkaline phosphatase as dependent variables. In patients with vitamin D deficiency (defined as serum 25-hydroxyvitamin D levels 15 ng/mL or lower), gland weight, PTH, AP, and adjusted calcium were each significantly higher than in patients with 25-hydroxyvitamin D levels of 16 ng/mL or higher, but serum 1,25-dihydroxyvitamin D levels were similar in both groups. We interpret this to mean that suboptimal vitamin D nutrition stimulates parathyroid adenoma growth by a mechanism unrelated to 1,25-dihydroxyvitamin D deficiency. We conclude that variable vitamin D nutritional status in the population may partly explain the differences in disease presentation.