A question of personal risk
Cholesterol conspiracy theorists queue up to decry the pharmaceutical industry’s promotion of statins, but the truth is much more complex, writes Norman Swan.
Everyone loves a good conspiracy. Emails regularly land in my inbox challenging me to expose the cholesterol myth and how it has been perpetuated by the pharmaceutical industry to sell statins, a family of cholesterol lowering medications. The challengers’ argument is a one, two punch. First it demolishes cholesterol as a risk factor for heart disease and stroke; second it dismisses the effectiveness of statins, the cholesterol-lowering medication. Like all conspiracy theories, there’s a bit of truth in these ideas, but not enough to give them oxygen.
First, cholesterol. Conspiracy theorists argue that most evidence linking cholesterol levels with heart disease and stroke is “associative” – the studies do not prove cause and effect. Perfectly true. Observational studies, like the Framingham Study in Massachusetts, followed the health of thousands of people for years. It showed that people with high cholesterol have a higher risk of a heart attack or stroke. Other so-called “case-control” studies compared people with and without disease to see what factors stand out. Again, cholesterol is one.
These studies do not prove cause and effect but they can reveal risk factors. That the link between smoking and lung cancer and heart disease was just an association, albeit a very strong one, was exploited for years by the tobacco industry.
Nailing a causative relationship between a risk factor and a disease needs an experiment – for example a clinical trial where the risk factor is removed to see whether the disease incidence changes.
Here’s where the studies have not always been consistent. Dietary interventions aimed at lowering cholesterol have been disappointing, especially one called MRFIT that tested multiple risk factor reduction. It failed to show a net benefit largely because the control group changed their lifestyle to lower their risk. But when cholesterol has been reduced using medications, rates of heart attacks and deaths have fallen significantly.
A second source of confusion is that most people who have a heart attack or stroke don’t have sky-high cholesterol or blood pressure. They have a combination of moderately raised risk factors such as gender, age, family history, smoking, blood pressure and cholesterol, which multiply together to give a high personal risk (also called absolute risk).
A third argument made is that if cholesterol is so important, why aren’t cholesterol-raising saturated fats as bad for us as we used to think? Well, in fact saturated fats are bad for us, but they don’t raise cholesterol levels as much as we thought. Nevertheless, they’re still important. If you look at the population as a whole, saturated fat reduction has helped to reduce average risk and contributed to the 2% a year reduction in deaths from coronary heart disease for 30 years in the US and Australia.
So there’s no doubt that cholesterol is an important risk factor for cardiovascular disease, but no more so than blood pressure, probably less than smoking and certainly less than diabetes. Cholesterol is perceived as more important than evidence suggests because it’s easier to reduce and because of efforts of pharmaceutical firms to sell more statins. But that doesn’t mean it is innocent.
So let’s go to statins.
The anti-cholesterol camp says they’re not as effective as doctors tell us, with unacceptable side effects that the industry plays down. They also say women don’t benefit from them.
When cholesterol has been reduced ... rates of deaths have fallen significantly
For those of you who are perplexed, don’t be. The evidence is clear and it’s all about working out your personal risk.
Statins are only worth taking if your risk of a heart attack or stroke is high. At highest risk are people who’ve already had a heart attack, stroke, angina, a coronary procedure, diabetes, genetically high cholesterol, or have an Aboriginal or Torres Strait background. Repeated studies show statins significantly reduce coronary events and premature death at these risk levels. The debate is over people who have not had a heart attack or stroke but whose personal risk score is high.
But how high does that risk score need to be before it’s worth taking statins? At least a 2% per year risk, say heart health authorities. That means 10-15% over five years.
As to side effects, it’s true that some company-funded trials have under-measured side effects. Around one in 10 people experience muscle aches and pains and some people find they are a bit foggy on statins. But all drugs have side effects.
The message is that you need to know your risk, so ask your general practitioner to do an absolute risk score on you and repeat it every few years to ensure your risk isn’t edging upwards. And be careful which conspiracy theory you believe. Me, I’ll stick to those funny aliens with triangular faces in the American desert.