Plain English Summary
Background and study aims
South Asians living in the UK are at a particularly high risk of developing heart and blood vessel problems, as well as diabetes. One potential cause of this is a deficiency of vitamin D, which is a hormone produced by the skin in response to sunlight. Low levels of vitamin D are associated with intolerance to glucose (sugar), resistance to insulin and inflammatory chemicals in the blood, all of which can worsen the consequences of heart and blood vessel disease. Many people in the UK have reduced levels of vitamin D, but south Asians living in the UK have especially low levels of vitamin D. The aim of this study is to investigate whether giving supplementary vitamin D to UK south Asians improves their heart and blood vessel function.
Who can participate?
South Asian women aged 18 and over with low vitamin D levels
What does the study involve?
The study lasts for 8 weeks. Participants are randomly allocated to be given either a teaspoon of vitamin D oil or a placebo (dummy) oil once only at the start of the study. Participants are seen at the start and 4 and 8 weeks later. Each visit lasts two hours. At each visit, participants undergo some or all of the following tests depending on which visit it is. Blood pressure is measured and blood samples are taken. The function of the artery in the arm is tested by scanning it with an ultrasound machine before and after inflating a blood pressure cuff on the forearm for 5 minutes, which is then repeated after giving a medication (GTN) spray under their tongue. The stiffness of the arteries is tested using a probe like a pencil that rests on the forearm and neck. The skin blood flow responses to two chemicals called acetylcholine and sodium nitroprusside is measured. A small electric current is used to deliver very small quantities of the chemicals to a small area of skin on the forearm (about the size of a 50 pence coin). This may cause a slight prickling sensation and an area of redness on the skin (which fades after an hour or so), but no pain, and the two chemicals are harmless at these quantities. The blood flow response ismeasured by scanning a laser beam across the surface of the skin whilst a camera looks at the skin.
What are the possible benefits and risks of participating?
Although this dose of vitamin D has been used before and is known to be safe there is a small possibility of side effects. The researchers closely monitor for side effects caused by high calcium levels, such as sickness, diarrhoea, thirst or dizziness. To reduce the chance of vitamin D increasing the calcium level in the blood, participants are asked to not take any other vitamin D supplements or calcium supplements whilst they are taking part in this study. Having blood taken can cause some bruising. The blood pressure cuff causes mild discomfort to some people.
Where is the study run from?
University of Dundee (UK)
When is the study starting and how long is it expected to run for?
January 2009 to July 2010
Who is funding the study?
Heart Research UK
Who is the main contact?
Dr Faisel Khan
Dr Faisel Khan
The Institute of Cardiovascular Research (TICR)
Vascular & Inflammatory Diseases Research Unit
University of Dundee
Ninewells Hospital & Medical School
+44 (0)1382 425574
2007cv23; 2008-003387-18; CTA: 21726/0254/001-0001
The effects of oral vitamin D supplementation on cardiovascular disease risk in UK South Asian women: a randomised, placebo-controlled, parallel-group, double-blinded study
That oral supplementation of vitamin D will improve cardiovascular function and metabolic and inflammatory parameters in South Asian women.
Tayside Research Ethics Committee NHS, 22/10/2008, ref: 08/S1402/55
Randomised placebo-controlled parallel-group double-blinded study
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
Cardiovascular disease risk
Subjects will be given a single dose of 100,000 units of oral vitamin D3 or matching placebo. This dose will be given after baseline assessments. Ingestion will occur in the presence of the research team to ensure 100% adherence to medication.
Vitamin D supplementation
Primary outcome measure
Macrovascular endothelial function, assessed by flow mediated dilation (FMD) according to standard guidelines at the start of the study (i.e., before the intervention) and at 4 and 8 weeks post-intervention
Secondary outcome measures
1. Microvascular endothelial function, tested using iontophoresis according to standard guidelines
2. Arterial stiffness, measured by pulse wave velocity using the validated SphygmoCor pulse waveform analysis system
3. Office blood pressure, measured by oscillometric automatic blood pressure device
4. Metabolic and inflammatory markers:
4.1. Fasting serum lipid profiles, measured using COBAS Bio Autoanalyser
4.2. Fasting glucose, glycosylated haemoglobin (HbA1c) and insulin levels: estimates of insulin resistance calculated using the Homeostasis Model (HOMA) (fasting glucose x fasting insulin/22.5)
4.3. Adiponectin and leptin, measured using a commercially available enzyme-linked immunosorbent assay (ELISA) with good sensitivity and reproducibility
4.4. Plasminogen activator inhibitor-1 and tissue plasminogen activator antigen, both measured by ELISA
4.5. C-reactive protein, measured using a high sensitivity automated turbidimetric assay
4.6. Tumour necrotising factor alpha (TNF-α) and interleukin-6, measured by high sensitivity ELISA
4.7. E-selectin - an adhesion molecule expressed only on activated endothelial cells, measured by ELISA
5. Serum 25 hydroxyvitamin D and parathyroid hormone (PTH) levels
All measurements taken at the start of the study (i.e., before the intervention) and at 4 and 8 weeks post-intervention
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Aged greater than or equal to 18 years
3. Serum 25 hydroxyvitamin D less than 75 nmol/L
4. South Asian ethnicity, as defined by the participant
Target number of participants
Participant exclusion criteria
2. Cardiovascular disease (including previous stroke, transient ischaemic attack [TIA], angina, myocardial infarction, angioplasty, coronary bypass grafting, symptomatic peripheral vascular disease, chronic heart failure, atrial fibrillation)
3. Already taking vitamin D supplements. Consumption of fish oils will not be a contraindication to enrolment as the vitamin D content is very low relative to the dose used in the study.
4. Estimated glomerular filtration rate less than 40 ml/min (by four-variable Modification of Diet in Renal Disease [MDRD] equation)
5. Liver function tests (alanine aminotransferase [ALT], bilirubin, alkaline phosphatase) greater than 3 x normal. These two criteria will ensure that sufficient renal and hepatic function is available to convert vitamin D to the active 1,25 hydroxy form.
6. Unable to give written informed consent
7. Corrected calcium level of greater than 2.60 or less than 2.15 mmol/L
8. Clinical diagnosis of osteomalacia
9. History of renal calculi, sarcoidosis or metastatic malignancy. Excluding these groups will minimise the risk of side effects from vitamin D supplementation.
10. Pregnant or of childbearing age and not taking reliable contraception
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
University of Dundee
Heart Research UK (UK)
Funding Body Type
private sector organisation
Funding Body Subtype
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 (firstname.lastname@example.org). 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 ISRCTN75081811_BasicResults_20Nov17
2013 results in: http://www.ncbi.nlm.nih.gov/pubmed/24075759
Witham MD, Adams F, Kabir G, Kennedy G, Belch JJ, Khan F, Effect of short-term vitamin D supplementation on markers of vascular health in South Asian women living in the UK--a randomised controlled trial., Atherosclerosis, 2013, 230, 2, 293-299, doi: 10.1016/j.atherosclerosis.2013.08.005.
- ISRCTN75081811_BasicResults_20Nov17.pdf Uploaded 20/11/2017