Study one: Tea corrects endothelial dysfunction

Both short- and medium-term consumption of tea improves abnormal endothelial function, according to the results of a recently published American study. The effect was not due to the caffeine in the tea.

Subjects: 66 patients with proven coronary artery disease

Method: Randomised, controlled cross-over intervention study. Subjects drank either black tea (450 ml) or water on a single occasion and had brachial artery vasomotor function assessed using ultrasound. The subjects then consumed either tea or water for 4 weeks.

Results: Tea consumption was associated with improved flow-mediated dilation (FMD) of the brachial artery. FMD is a measure of endothelium-dependent endothelial function. Water had no effect.

The benefits on endothelial function were seen in both the immediate and the 4 week time periods (p< 0.001 by repeated-measures ANOVA). An equivalent oral dose of caffeine had no short-term effect on FMD.

Reference: Circulation. 2001;104:151

Study two: Vitamin C and angina

Vitamin C given intravenously improves endothelial function in angina patients, according to a study from Japan.

Subjects: 28 patients with variant angina and 24 controls.

Method: Flow mediated dilation of the brachial artery was measured in both groups. 17 of the angina subjects were randomised to receive intravenous vitamin C or placebo.

Results: FMD was significant less in the angina patients than in the controls (1.8% vs 6.4%, p <0.001). Administration of intravenous vitamin C significantly improved FMD (from 2.2% to 4.5% p <0.01), whereas placebo had no significant effect .

Reference: Am J Cardiol 2001;87:1154-9

Study three: Vitamin E and diabetics

High dose vitamin E supplementation improves endothelial function in patients with type I diabetes mellitus, according to Australian research.

Subjects: 41 subjects with type I diabetes.

Method: Randomised placebo-controlled intervention trial in which active treatment was oral vitamin E supplementation (1,000 IU for three months).

Results: Subjects on vitamin E supplementation had significant improvement in FMD (from 2.6% to 7.0%, p < 0.005). Placebo treatment produced no significant change.

The improvement in endothelial function associated with vitamin E supplementation was correlated with the changes in LDL vitamin E concentration (r = 0.42, p < 0.05) and with changes in the oxidative susceptibility of LDL (r = 0.64, p < 0.0001).

Reference: J Am Coll Cardiol 2000;36:94-102

COMMENTS

You may recall that we have discussed the relationship between homocysteine and arterial endothelial function. We pointed out that deterioration in endothelial function is one of the mechanisms which is thought to be involved in the development of ischaemic cardiovascular disease (atherosclerosis).

The endothelial cells lie between the blood and the vascular wall, and are involved in regulating the tone of the arterial muscle.

These three studies are just a few of many that have been published over the last two years on the impact of nutritional intervention on endothelial function. The subject is currently of great interest. Other nutrients that have been involved in recently published intervention trials on endothelial function include: coenzyme Q, folate and red wine.

Clinical situations in which such trials have been conducted include patient groups with: diabetes (types I and II), coronary artery disease, hypertension, hypercholesterolaemia, renal transplantation, smokers and healthy subjects.

Not all results have been as positive as the three trials summarised above. In some cases no benefit or only short term benefit was found.

But on balance the results from the trials published over the last two years have been promising, even though they have so far only involved small numbers of subjects and short term interventions.

If we continue to see a trend of positive results from such trials, it will be a significant step in the story of nutrition and ischaemic heart disease.

Firstly, it will almost certainly help us to better understand the mechanisms which lie behind the epidemiological associations between diet and heart disease. For example, the apparent protective effects of red wine and tea, the role of various types of fat etc.

Secondly, it may enable us to identify in advance which patients are likely to respond to certain kinds of nutritional interventions.

We know only too well how inconsistent have been the results of the various prospective trials of supplements (such as vitamins E and C) in protecting against heart disease. One possible explanation is that this is due in part to differences in the type and severity of endothelial dysfunction that is found in such patients.

If this turns out to be true, it may then be feasible to identify those patients who are most likely to respond to such nutritional treatments by conducting short term `intervention trials’ on them using these nutrients, and monitoring the response of endothelial function.

This is currently just a hypothesis. But it is an intriguing one, and much work is now underway to see if further progress can be made.

Thirdly, people will not arbitrarily be put on the ‘statin’ drugs all the time since cholesterol is and has never been the problem.

SEE ALSO: Tea Cuts Risk of Heart Disease