According to Dr. Morales, HPS is one of the largest controlled clinical trials (20,000-patient base sample) ever to be conducted to address the following issues: 1) Can high-risk patients with no signs of coronary heart disease (CHD), individuals with diabetes or peripheral vascular disease benefit from cholesterol lowering? 2) Do antioxidant vitamin supplements really reduce the risk of heart disease in these and other high-risk groups? 3) Will people at risk of CHD benefit from cholesterol reduction even if their cholesterol levels are already low?
A total of 15,454 men and 5,082 women were recruited for HPS between July 1994 and May 1997. Eligible patients were aged 40 to 80, and considered to be at elevated risk for CHD due to history of heart attack or other heart disease, generalized arteriosclerosis (clogging of arteries due to fatty deposits), elevated blood pressure or diabetes mellitus.
HPS is the first trial to include sufficient numbers of women , patients over 70 years of age, and diabetics, but without symptoms of heart disease, to determine whether cholesterol-lowering drug simvastatin is worthwhile for them. It is also the first large-scale study to assess the effects of large doses of antioxidant vitamins.
All previous observational studies had indicated lower risks of CHD associated with lower blood cholesterol levels down to 3mmol/l. In an effort to assess the effects of reducing cholesterol among individuals at high risk of CHD even when their cholesterol levels are within the so-called ‘normal’ range, the HPS is studying patients with total cholesterol levels down to 3.5mmol/l. At the study onset, a large number of patients – totaling 7,882 – had total cholesterol levels below 5.5mmol/l.
A lower risk of CHD with higher dietary intake antioxidant vitamins has been suggested by previous observational studies. HPS was designed, therefore, to determine whether antioxidant vitamin supplements are also cardioprotective.
According to Dr. Morales, the HPS started in 1994 now includes patients with a vast range of high-risk factors for cardiovascular events and mortality including those with CHD, stroke, peripheral arteriosclerosis vascular disease and those with diabetes and treated hypertension. "So far, there has been a significant reduction of total cholesterol with a decrease in levels of LDL cholesterol and triglyceride, while an increase in Vitamin E plasma levels were observed," said Dr. Morales.
Morales added that at present there have been no significant excesses of any reported side effects nor in blood biochemical abnormalities. With the study nearing completion and with an observation of 80% good compliance, the study is expected to provide reliable evidence about the effects of cholesterol lowering therapy and of antioxidant vitamin supplements on all-cause or cause specific mortality and major morbidity in a range of different categories of individuals whom uncertainty remains about the balance of benefits and risks of these treatments.
The final results of the HPS will be presented at the American Heart Association Sessions in November 2001.