Archief Roodbont

Hypertension

Vitamin D deficiency and insufficiency have been observed to upregulate the renin-angiotensin-aldosterone system (RAAS), resulting in hypertension, a well-known risk factor for CVD.^[21] In an animal study emulating vitamin D deficiency, vitamin D receptor knockout mouse models showed increased blood pressure, increased serum angiotensin-converting enzyme levels, and tissue renin content.^[8,22] Human studies have shown that 1,25(OH)₂D has an inhibitory effect on renin synthesis, which decreases blood pressure.^[23] It has also been demonstrated that exposure to UVB, but not UVA, radiation on a regular basis both elevated serum 25(OH)D levels above 100 nmol/L and decreased blood pressure by 6 mmHg in hypertensive patients.^[24] (In this study, patients were exposed to UVB radiation in a tanning bed, 3 times per week, for a total of 3 months.) Another study in elderly women demonstrated that supplementation with vitamin D and calcium, compared to calcium alone, resulted in a significant increase in 25(OH)D concentrations (P <.01), a decrease in PTH levels (P <.05), a decrease in blood pressure by 9.3% (P <.025), and a decrease in heart rate by 5.4% (P <.025).^[25] Furthermore, the NHANES III study found that those individuals with higher serum 25(OH)D concentrations had a self-reported mean systolic blood pressure approximately 3 mmHg lower compared to patients with lower concentrations.^[8]

In contrast, several smaller studies noted no such benefits of vitamin D supplementation on blood pressure decline.^[5] The Women's Health Initiative study, recently conducted in the U.S., revealed that no blood pressure changes were noted in women randomized to receive vitamin D (400 IU) and calcium at the end of a 7-year follow-up period.^[26] It should be noted, however, that the vitamin D dose administered to study subjects was lower than recommended in clinical practice (for adults >70 years, supplementation is recommended to be at least 800 IU daily).^[27] In addition, the authors also reported that study subjects had low adherence to the study drug. Nevertheless, these results should not be ignored; further studies are needed to clarify the clinical importance of vitamin D supplementation as an antihypertensive agent.