RESUMEN
PURPOSE: Emerging data supports an association between parathyroid hormone (PTH) and aldosterone. It has been speculated, that potential adverse cardiovascular effects of vitamin D insufficiency may partly be caused by the development of secondary hyperparathyroidism with increased activity of the renin-angiotensin-aldosterone system (RAAS). We aimed to investigate the effect of normalizing vitamin D status and/or reducing PTH levels on RAAS activity and other markers of cardiovascular health. METHODS: In a double-blinded study during wintertime, we randomized 81 healthy postmenopausal women with secondary hyperparathyroidism (PTH > 6.9 pmol/l) and 25-hydroxy-vitamin D (25(OH)D) levels < 50 nmol/l to 12 weeks of treatment with vitamin D3 70 µg/day (2800 IU/day) or identical placebo. Markers of cardiovascular health were defined as changes in the plasma RAAS, glycated hemoglobin, lipids, and lipoproteins, blood pressure, vascular stiffness, heart rate, and cardiac conductivity. RESULTS: Compared to placebo, vitamin D3 treatment significantly increased plasma levels of 25(OH)D and 1,25(OH)2D by 230% (95% CI: 189-272%) and 58% (190-271%), respectively. Vitamin D3 treatment reduced PTH by 17% (11-23%), but did not reduce RAAS activity. Compared to placebo, vitamin D3 treatment increased plasma levels of high-density lipoproteins (HDL) by 4.6% (0.12-9.12%), but did not affect other measured indices. CONCLUSIONS: Vitamin D3 supplementation normalized vitamin D levels and reduced PTH. The supplement increased levels of HDL, but had no effects on RAAS activity or other indices of cardiovascular health.