Condition category
Circulatory System
Date applied
Date assigned
Last edited
Prospectively registered
Overall trial status
Recruitment status
No longer recruiting

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

Trial website

Contact information



Primary contact

Prof Allan Struthers


Contact details

Dept of Clinical Pharmacology
Ninewells Hospital
United Kingdom
+44 (0)1382 383013

Additional identifiers

EudraCT number

2008-002681-63 number

Protocol/serial number


Study information

Scientific title

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


Study hypothesis

That vitamin D supplementation in patients with resistant hypertension and insufficient vitamin D levels will lead to clinically important reductions in blood pressure.

Ethics approval

Ethics Board of Fife, Forth Valley and Tayside Research Ethics Service, 06/08/2008, ref: 08/S1402/31

Study design

Double-blind placebo-controlled parallel-group randomised trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


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

Intervention type



Not Specified

Drug names

Vitamin D supplementation

Primary outcome measures

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


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

Participant type


Age group




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

United Kingdom

Trial participating centre

Ninewells Hospital
United Kingdom

Sponsor information


University of Dundee

Sponsor details

Research and Innovation Services
11 Perth Road
United Kingdom
+44 (0)1382 383359

Sponsor type




Funder type


Funder name

Chest Heart and Stroke Scotland

Alternative name(s)


Funding Body Type

private sector organisation

Funding Body Subtype

professional associations and societies


United Kingdom

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 ( 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

Results - basic reporting

See additional file ISRCTN63688695_BasicResults_06Nov17

Publication summary

2014 results in:

Publication citations

Additional files

Editorial Notes

07/11/2017: Ethics approval details added. The basic results of this trial have been uploaded as an additional file. 06/11/2017: The following changes were made to the trial record: 1. The overall trial start date was changed from 01/10/2008 to 01/03/2008. 2. The overall trial end date was changed from 31/10/2010 to 01/05/2013. 3. Recruitment start and end date added. 4. IPD sharing statement added. 16/11/2016: Publication reference added. 16/02/2009: This record was updated to include amended trial dates; the initial trial dates at the time of registration were: Initial overall trial start date: 01/08/2008 Initial overall trial end date: 31/07/2010