Professor Law and his colleagues of the University of London searched scientific literature in order to calculate the effect of LDL cholesterol reduction on the risk of a heart attack. Given a pre-treatment LDL cholesterol level of 190 mg/dL (4.8 mmol/L), which was the average value of all the patients investigated, they discovered the following:
- Statins must be taken continuously for years. The longer period they are taken, the better chance of lower a person's risk of a heart attac. The researchers also discovered that a long-term reduction of 40 mg/dL (1 mmol/L) of LDL cholesterol translates to a risk reduction of 11% in the first year, 24% in the 2nd year, 33% in the 3rd to 5th year and 36% in the 6th and subsequent years.
- If LDL cholesterol is reduced by even more than 40 mg/dL (1 mmol/L), the effect on heart attack rates is higher: a reduction of 60 mg/dL (1.5 mmol/L) of LDL cholesterol (which can be achieved with low doses of certain statins such as 20 mg/day of simvastatin) halves the risk of a heart attack after 2 years.
- On average, the reduction in LDL cholesterol was even higher with statin treatment in the studies investigated: 70 mg/dL (1.8 mmol/l). After years of treatment, this decreased the risk of heart attack by 60% and the risk of stroke by 17%.
Long-Term Benefits Are Also Age-Dependent
Cohort studies involving a large number of patients who were studies for a long period of time suggest even higher benefits of low LDL cholesterol. After prolonged treatment with statins, these studies suggest that the following reductions in heart attack risks (over the lifetime of a patient) are achievable:
% Reduction of Heart Attack Risk
LDL cholesterol reduction in mg/dL (and mmol/L):
Age: 50 years
Age: 60 years
Age: 70 years
Please note that these results aren't applicable to any drugs other than statins. Statins may have beneficial effects in addition to their ability to lower cholesterol levels.
This means that a similar reduction in LDL cholesterol levels achieved with fibrates or phytosterols may not result in as high a reduction of a heart attack risk if the same reduction was achieved with statins.
How Many Patients Must Be Treated To Prevent 1 Heart Attack?
Since patients who already experienced a heart attack are more likely to have another one than a healthy individual, the number of patients required to treat varies.
It is estimated that approximately 20-30 patients with previous heart attacks (or 50-60 individuals with no previous heart attacks) must be treated to prevent 1 heart attack (numbers obtained from the study of Simons and Sullivan, 2005).
This number is sobering for many, since one would normally assume that a risk reduction of 25 to 30% (which is readily achievable with long-term statin use) would have a larger effect on the heart attack-rate. In other words one would intuitively think that to prevent one heart attack with statins, only a small number of people required treatment.
Here is why the effect is relatively small:
Assume the overall risk for a group of people (say 50 year old smokers) to suffer a heart attack within the next 10 years is 8%. A reduction of that risk by 25% would lower the overall risk to 6%. Therefore, treatment of 100 patients would prevent heart attacks in 2 individuals (8 ot of 100 before the statin-treatment, 6 out of 100 thereafter).