Low vitamin D, high parathyroid hormone levels linked in hyperparathyroidism
Adults with primary hyperparathyroidism and low vitamin D levels are likely to have high levels of serum parathyroid hormone, indicating more severe disease; however, more severe disease does not affect bone structure or volumetric bone mineral density, according to research in The Journal of Clinical Endocrinology & Metabolism.
“The fact that vitamin D had so little effect upon indices of skeletal health in [primary hyperparathyroidism], assessed using advancing imaging techniques, was unexpected and in contrast with our hypotheses,” Marcella D. Walker, MD, MS, of the College of Physicians and Surgeons at Columbia University, and colleagues wrote. “Likewise, active vitamin D was also not strongly associated with microarchitecture in univariate analyses and was not significant in multiple regression models.”
Marcella D. Walker
In a cross-sectional study, researchers analyzed data from 99 patients with primary hyperparathyroidism (PHPT; 79% women; mean duration of PHPT, 4.3 years). Within the cohort, 18 patients had vitamin D deficiency (defined as 25-hydroxyvitamin D values < 20 ng/mL); 35 patients had vitamin D insufficiency (defined as 25-[OH]D values 20-29 ng/mL); and 46 patients had normal levels (25-[OH]D values 30 ng/mL). Researchers measured bone microarchitecture and strength with high-resolution peripheral quantitative computed tomography (HR-pQCT), microfinite element analysis and trabecular plate and rod parameters with individual trabecula segmentation (ITS), as well as serum calcium, phosphate, creatinine, serum 25-(OH)D, 1,25(OH)D and parathyroid hormone levels.
Researchers found that patients with vitamin D deficiency had higher serum parathyroid hormone levels than patients with vitamin D insufficiency or normal levels (mean parathyroid level, 127 pg/mL vs. 81 pg/mL and 72 pg/mL, respectively; P < .0001). In addition, patients with vitamin D deficiency were younger (mean age, 57 years vs. 59 and 67 years, respectively; P = .001) and weighed more (mean weight, 181 lb vs. 174 lb and 157 lb; P = .053). Researchers found no between-group differences in HR-pQCT, microfinite element analysis or ITS indices across the three vitamin D categories after adjustments for age, weight and sex.
Due to the small sample size of patients with vitamin D deficiency, researchers also assessed differences comparing those with vitamin D levels less than 30 ng/mL with those with levels of 30 ng/mL or greater. After adjusting for sex, patients’ vitamin D levels of less than 30 ng/mL had marginally lower cortical volumetric BMD (3.1%; P = .08) and marginally higher cortical porosity (7.5 vs. 6.6; P = .07) at the tibia, but not at the radius.
In multiple regression analysis, vitamin D level accounted for only 3% of the 49.2% known variance in cortical volumetric BMD and was not significant in the model for cortical porosity at the tibia.
“We believe the negative results are reassuring and helpful in guiding management of PHPT patients with regard to vitamin D levels,” the researchers wrote. “Our work suggests 25-(OH)D levels 20 ng/mL in PHPT may be considered adequate based on [parathyroid hormone], bone microarchitecture and bone strength outcomes.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.