We measured serum parathyroid hormone in 8409 Romanian subjects and found a mild seasonal variation with highest levels in March and lowest levels in September. PTH was dependent on serum vitamin D, particularly below 12.82 ng/mL. Together, these suggest that vitamin D supplementation is warranted only in at-risk groups.
Purpose: Seasonal variation of parathyroid hormone (PTH) and its dependency on serum 25-hydroxy vitamin D (25(OH)D) levels are well-described. However, there are few studies from Europe, and genetic, nutritional, and cultural differences are important. We describe the seasonal variation of serum PTH and its relation with serum 25(OH)D levels in Romania.
Methods: We retrieved from our endocrinology center database all PTH measurements between 2011 and 2019 together with age, sex, diagnosis, and date of blood sampling. Simultaneous serum 25(OH)D levels were partially available. Intact PTH was measured using the same electrochemiluminescence assay.
Results: There were 8409 subjects (median age 49 (36, 60) years; 20.5% men) without a diagnosis of hyperparathyroidism (primary or secondary to chronic kidney disease), hypoparathyroidism, or low bone mass. Serum PTH showed a mild seasonal variation with highest levels at the end of March (47.61 pg/mL) and lowest levels at the end of September (43.15 pg/mL). All sex and age subgroups showed highest levels in the spring and lowest levels in the fall. Males had significantly lower PTH levels than females irrespective of season. PTH correlated inversely with serum 25(OH)D with a breakpoint of 12.82 ng/mL in 2800 subjects who had a simultaneous measurement of 25(OH)D. Increasing age was associated with increasing PTH levels independently of serum 25(OH)D.
Conclusions: We showed a mild seasonal variation of serum PTH in Romania, at an inverse sinusoidal pattern than serum 25(OH)D. The breakpoint on the PTH-25(OH)D correlation suggests that vitamin D supplementation is warranted only in at-risk groups.
Keywords: Parathyroid hormone; Romania; Seasonal; Vitamin D.