Defining Vitamin D Deficiency and Its Relationship to Hypertension in Postmenopausal Korean Women

Background: Inconsistent results regarding the association between low vitamin D level and hypertension (HTN) have led to uncertainty in clinical practice as to the use of vitamin D cutoff value. The aims of this study were to investigate the association between vitamin D deficiency and HTN in postmenopausal women and to determine the clinically significant cutoff value for vitamin D deficiency. Methods: We analyzed data from the Korean National Health and Nutrition Examination Survey 5 database (4107 postmenopausal women, aged 50-79 years). The cutoff value for vitamin D deficiency was based on the changes in parathyroid hormone (PTH) level according to serum 25(OH)D value. Results: PTH levels were significantly higher in groups with serum 25(OH)D <15ng/mL (p<0.001). When a serum 25(OH)D value of 15ng/mL was used as a cutoff value, 35.2% of the subjects were found to be vitamin D deficient. Although the association between 25(OH)D level <15ng/mL and systolic blood pressure did not remain significant after adjusting for season (p=0.30), multiple logistic regression analysis revealed that 25(OH)D level <15ng/mL was an independent risk factor for HTN (adjusted odds ratio [OR] 1.285, 95% confidence interval [CI] 1.024-1.614, p=0.031). Conclusions: Using serum PTH level, we defined vitamin D deficiency as 25(OH)D <15ng/mL in postmenopausal women. Vitamin D deficiency [25(OH)D <15ng/mL] was a significant risk factor for HTN in postmenopausal women.