Plain English Summary
Background and study aims
People who have high blood pressure despite taking three or more blood pressure lowering medications have a condition called resistant hypertension. This group of patients struggle to find medications that reduce their blood pressure effectively, and thus remain at higher risk of future heart attack and stroke. Persistently high blood pressure also leads to thickening of the heart muscle, which can lead to impaired heart function and rhythm disturbances. Vitamin D levels are low in many people in Scotland, and low vitamin D levels have been found to be associated with higher blood pressure. The aim of this study is to test whether vitamin D supplements could improve blood pressure and reverse the thickening of the heart muscle that is common in people with resistant hypertension.
Who can participate?
Men and women aged over 18 with resistant hypertension
What does the study involve?
Participants are randomly allocated to receive either a large dose of vitamin D every 2 months, or a dummy (placebo) dose. At the beginning of the study, blood pressure is measured at rest and over 24 hours. Heart muscle thickness is measured using MRI scans in those patients with a thickened heart muscle. The MRI scans are repeated after 6 months, and measured blood pressure at 2, 4 and 6 months.
What are the possible benefits and risks of participating?
The benefit of taking part is that a new way of treating difficult-to-treat high blood pressure might be found. The risks are very small as vitamin D is very safe. It can very rarely increase the risk of kidney stones, although whether it really does this or not is controversial.
Where is the study run from?
Ninewells Hospital (UK)
When is the study starting and how long is it expected to run for?
March 2008 to May 2013
Who is funding the study?
Chest Heart and Stroke Scotland (UK)
Who is the main contact?
Prof. Allan Struthers
Prof Allan Struthers
Dept of Clinical Pharmacology
+44 (0)1382 383013
Does vitamin D reduce blood pressure and left ventricular (LV) mass in resistant hypertensive patients with vitamin D insufficiency? A double-blind, placebo-controlled, parallel-group randomised trial
That vitamin D supplementation in patients with resistant hypertension and insufficient vitamin D levels will lead to clinically important reductions in blood pressure.
Ethics Board of Fife, Forth Valley and Tayside Research Ethics Service, 06/08/2008, ref: 08/S1402/31
Double-blind placebo-controlled parallel-group randomised trial
Primary study design
Secondary study design
Randomised controlled trial
Patient information sheet
Not available in web format, please use the contact details to request a patient information sheet
100,000 units of oral vitamin D3 every two months or placebo.
Total treatment duration: 4 months
Total follow up: 6 months
Vitamin D supplementation
Primary outcome measure
Office BP, measured at 0, 2, 4 and 6 months
Secondary outcome measures
LV mass index, measured by cardiac magnetic resonance imaging [MRI] at 0 and 6 months
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Aged greater than 18 years, either sex
2. Serum 25-hydroxy vitamin D less than 75 nmol/L
3. Office blood pressure (BP) greater than 140/90 mmHg despite three or more anti-hypertensives
Target number of participants
Participant exclusion criteria
1. Hypertension known to be due to a correctable underlying medical or surgical cause
2. Estimated glomerular filtration rate less than 40 ml/min (by four variable Modification of Diet in Renal Disease [MDRD] equations)
3. Liver function tests (alanine aminotransferase [ALT], bilirubin, alkaline phosphatase) greater than 3 x normal
4. Corrected calcium greater than 2.60 mmol/L or less than 2.15 mmol/L
5. Known metastatic malignancy or sarcoidosis
6. Clinical diagnosis of osteomalacia
7. History of renal calculi
8. Diagnosis of heart failure with left ventricular systolic dysfunction
9. Atrial fibrillation
10. Already taking vitamin D supplements. Consumption of fish oils will not be a contra-indication to enrolment
11. Unable to give written informed consent
12. Pregnant or of childbearing age and not taking reliable contraception
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Chest Heart and Stroke Scotland
Funding Body Type
private sector organisation
Funding Body Subtype
Associations and societies (private and public)
Results and Publications
Publication and dissemination plan
The protocol is available from the authors on request but is not available online.
IPD sharing statement
The datasets generated during and/or analysed during the current study are/will be available upon request from Dr Catrina Forde (email@example.com). Study data are available for non-commercial, bona-fide academic analyses in collaboration with the authors; decisions on data access will be made between the investigators and the Sponsor (University of Dundee). Participant consent for unrestricted sharing of individual participant data was not obtained.
Intention to publish date
Participant level data
Available on request
Basic results (scientific)
See additional file ISRCTN63688695_BasicResults_06Nov17
2014 results in: https://www.ncbi.nlm.nih.gov/pubmed/24420547
- ISRCTN63688695_BasicResults_06Nov17.pdf Uploaded 07/11/2017