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. We performed a study 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 were 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, we measured blood pressure at rest and over 24 hours. We measured heart muscle thickness using MRI scans in those patients with a thickened heart muscle. We repeated the MRI scans 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 (Dundee, UK).

When is the study starting and how long is it expected to run for?
The study ran from October 2008 to October 2010.

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 1382 383013

Additional identifiers

EudraCT number 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

Added 16/02/2009:
Ethics Board of Fife, Forth Valley and Tayside Research Ethics Service gave approval in December 2008

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 below 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

Change in office BP, measured at 0, 2, 4 and 6 months.

Secondary outcome measures

Change in LV mass index (measured by cardiac magnetic resonance imaging [MRI]), measured 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

Dept of Clinical Pharmacology
United Kingdom

Sponsor information


University of Dundee

Sponsor details

Research and Innovation Services
11 Perth Road
United Kingdom
+44 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

Not provided at time of registration

Intention to publish date

Participant level data

Not provided at time of registration

Results - basic reporting

Publication summary

2014 results in

Publication citations

Additional files

Editorial Notes

16/11/2016: Publication reference added. 31/08/2016: No publications found in PubMed, verifying study status with principal investigator. 16/02/2009: This record was updated to include amended trial dates; the initial trial dates at the time of registration were: Initial anticipated start date: 01/08/2008 Initial anticipated end date: 31/07/2010