Objectives: Recent epidemiological studies have reported inverse associations between vitamin D status and blood pressure. The study aim is to determine if exposure to ultraviolet B radiation, which synthesizes vitamin D, lowers blood pressure, compared with ultraviolet A radiation.
Methods: Men and women (n = 119) with low vitamin D levels [serum 25-hydroxyvitamin D [25(OH)D] <50 nmol/l], completed a randomized clinical trial carried out during winter. Blood pressure was measured for 12–14 h with an ambulatory monitor at baseline and 12 weeks. In between, participants received 24 whole body exposures of either ultraviolet B (n = 58) or ultraviolet A (n = 61) over 12 weeks.
Results: Mean (SD) 25(OH)D increased from 43.7 (9.7) to 92.6 (16.9) nmol/l in the ultraviolet B arm after 12 weeks, and from 45.4 (9.2) to 64.9 (11.3) nmol/l in the ultraviolet A arm. However, mean blood pressure, which was similar for the ultraviolet B and ultraviolet A at baseline (134.9/79.2 vs. 132.9/77.8 mmHg; P = 0.59 and 0.56, respectively), did not change from baseline to 12 weeks in either group. The mean change [95% confidence interval (CI)] in blood pressure over this period in the ultraviolet B group compared with the ultraviolet A group was −2.2 (−7.8, 3.3) mmHg for systolic (P = 0.42) and −2.7 (−6.5, 1.0) mmHg for diastolic (P = 0.15).
Conclusion: Exposure to ultraviolet B did not lower blood pressure. Our results suggest that if vitamin D protects against cardiovascular disease, it involves some mechanism other than blood pressure.
aSchool of Population Health, University of Auckland
bEpsom, Auckland, New Zealand
Correspondence to Professor Robert Scragg, Epidemiology and Biostatistics, School of Population Health, University of Auckland, Private Bag 92019, Auckland, New ZealandTel: +64 9 3737 599 ext 86336; fax: +64 9 3737 503; e-mail: firstname.lastname@example.org
Abbreviations: 25(OH)D, 25-hydroxyvitamin D; PTH, parathyroid hormone; UV, ultraviolet
Received 22 February, 2011
Revised 4 May, 2011
Accepted 1 June, 2011