They're the best-selling family of drugs of all time with annual worldwide sales estimated at more than $20 billion. Every year, Canadian doctors write more than 12 million prescriptions for statins, making them the most-prescribed drugs in the country. They're in a class of drugs that has proven very effective at lowering cholesterol levels and reducing the risk of heart attacks.

If we believe the estimate by the Heart and Stroke Foundation that four out of five adults have at least one factor increasing their risk of heart attack, then the potential market for statins is huge.

And that market could easily continue to grow. Statins are being called the Aspirin of the 21st century and a miracle drug — because they might actually do a lot more than just prevent heart attacks.

Studies have suggested that statins might also slow the progression of Alzheimer's disease and help patients with osteoporosis and multiple sclerosis. And new data raise the possibility that statins might also ward off colon, breast and prostate cancer — and lower one's overall cancer risk.

The human body actually needs some cholesterol to help with the building and maintenance of cells. Good — or HDL cholesterol — helps the body absorb vitamins and nutrients from food. It helps produce the hormones the body needs.

Bad — or LDL cholesterol — sticks to the inside of blood vessels and arteries, narrowing the path through which blood flows and increasing the risk of forming clots. That's what leads to heart disease and strokes. Combined, those two diseases make up the leading cause of death in Canada, killing nearly 80,000 people a year, almost 40 per cent of all deaths in this country. Cholesterol is to blame in many of those cases.

At one time, millennia ago, it may have been important for the human body to be able to produce cholesterol — because early humans may have gone long periods between meals, which meant they couldn't count on getting enough cholesterol. But Dr. David Jenkins — a Canada Research Chair in nutrition, and a professor of medicine at the University of Toronto — says that's not the case for the modern couch potato.

"We've got these ancient bodies with these ancient genes which are all destined to make sure that we've got enough cholesterol to fulfill essential functions," Jenkins told CBC Radio's Quirks and Quarks. "Today, unfortunately, we've taken out all those nice things in the diet that take cholesterol out of the body and have brought in a whole load of very nice refined foods that allow us to sit around, not do too much, and just synthesize cholesterol."

Those refined foods help your body produce the bad kind of cholesterol. That's where statins come in. They work by blocking an enzyme in the liver that is involved in producing cholesterol within liver cells.

"This tricks the liver cells into thinking the cholesterol levels are too low within the cell and the cell puts more receptors onto its surface, which drag the bad LDL cholesterol out of the blood," explains Dr. Rory Collins, professor of epidemiology at Oxford University. "The liver then breaks down that cholesterol and it's excreted into the bile and into the gut."

Collins conducted the biggest study of statins to date, covering 20,000 people over five years. The study — published in November 2001 — suggested that a person who has had high cholesterol for decades could reduce their risk of heart attack or stroke by 25 per cent within just a few years of statin treatment. The study also suggested that the risk would continue to decrease, the longer the treatment continued.

The study was a factor in the British government's decision to make statins available over the counter to almost anyone over age 55. Britain's health secretary said the move would encourage more people to start taking statins, even those with a moderate risk of heart disease.

Collins argues that giving statins to more people — even those at lower risk — will prevent even more heart attacks.

A study published in the New England Journal of Medicine's Oct. 11, 2007 edition backs that up. The study was a 10-year follow-up of the West of Scotland Coronary Prevention Study. It found that people who started on statins in the early part of the original study had a significantly reduced risk of heart attack than those who started statin therapy after the original study was completed.

Other studies have suggested that statins may have promise in treating other conditions. One found that cholesterol promotes the development of Alzheimer's disease in rabbits. The researchers wanted to see if lowering cholesterol levels in people with Alzheimer's might slow down the disease. Patients on statins were tested on their cognitive abilities, their memory and their feelings of depression. The study found that the patients who had taken statins seemed to be in better shape.

Health Canada updates safety information on statins

On July 12, 2005, Health Canada issued an advisory warning that some people with pre-existing medical conditions could face a greater risk of developing muscle-related problems, including a serious condition called rhabdomyolysis, if they take statins.

The agency has instructed manufacturers of the drugs to include an updated information sheet detailing its concerns.

Health Canada is advising people to contact their physician if they experience any of the following while on statin therapy:

• Muscle pain they cannot explain.
• Muscle tenderness or muscle weakness.
• Generalized weakness, especially if they do not feel well (i.e. fever or fatigue).
• Brownish or discoloured urine.

For more information, see Health Canada’s advisory

Studies have also suggested that statins may show some promise in the treatment of multiple sclerosis. And, at a meeting of the American Society of Clinical Oncology on June 6, 2004, new research was presented suggesting people who took statins for at least five years appeared to cut their risk of colon cancer in half.

If statins do reduce the risk of cancer, scientists say it may have nothing to do with the drug's effects on cholesterol. One theory is that statins fight off the disease by reducing inflammation. Another theory is statins could block the way some cancer-causing genes work.

Researchers say the evidence is still too weak to recommend taking statins for cancer prevention. They say much more study is needed.

But there is a debate over the widespread use of statins. Some argue that the smaller your risk of developing heart disease, the smaller the benefit you'll get from taking statins. And by taking a pill every day, you might be running the risk of having the harm outweigh the benefits.

Although there are relatively few side effects to statins, they can be quite serious. They include a degenerative muscle disease called myopathy, which can be fatal. Bayer pulled its statin — Baycol — off the market in August 2001 because it caused too many cases of myopathy. Baycol was linked to 52 deaths worldwide, including one in Canada.

According to data obtained by the CBC from Health Canada's adverse drug reaction database, more than 1,000 serious side effects related to statins have been reported in the last 15 years.

While the researchers continue to probe whether statins should be conferred "wonder-drug" status, some doctors are arguing that — wonder drug or not — there's a simple, drug-free way to get cholesterol-lowering benefits similar to what statins bring: watch what you eat and get some exercise.