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In matters of the heart, it is wise to never make assumptions. This applies as much to medicine as to love, if not more so.

Proof that seemingly sensible assumptions can be utterly wrong - and even deadly - has come in spectacular fashion in recent weeks.

First, there was news about the blockbuster heart drug Vytorin. A much-anticipated study showed that the medication lowered low-density lipoprotein (LDL, or bad cholesterol) but it had no effect on the buildup of plaque in the arteries, which is what poses the risk of heart attack and stroke.

Vytorin - which is not sold in Canada - is a combination of two drugs, simvastatin (brand name Zocor) and ezetimibe (Zetia). Both drugs reduce cholesterol, the former by regulating production of cholesterol in the liver and the latter by blocking absorption of cholesterol in the intestines.

It was assumed that, combined, the drugs would pack a powerful one-two punch. That assumption - along with a lot of advertising - helped make Vytorin a bestselling drug.

Yet the expensive combo drug works no better than a single statin such as Zocor.

The research tells us that it's not enough to lower cholesterol; how it is lowered seems to matter too.

The study should also draw attention to the fact that Zetia, while it reduces LDL, has not been shown to reduce the risk of death.

In fact, despite the billions of dollars spent annually on drugs that control cholesterol, there is little evidence demonstrating that lowering cholesterol levels reduces heart attacks and death to any significant degree.

In short, cholesterol-lowering statins have been grossly overhyped - but that's a subject for another day.

Last week, another powerful scientific assumption was smashed when the U.S. National Institutes of Health took the rare step of halting part of the massive ACCORD (Action to Control Cardiovascular Risk in Diabetes) study because of the disproportionate number of deaths.

For decades, scientists believed that lowering blood sugar to normal levels would virtually eliminate the risk of heart attack in diabetics.

In the ACCORD experiment, they tested the hypothesis by pushing blood sugar to very levels with an aggressive drug regimen.

The assumption, that lower is always better, appears to be wrong. The rate of death actually increased quite markedly among those at highest risk - and most of them died of heart disease, the very condition that treatment was supposed to prevent.

Patients in the study were taking a lot of drugs, but it is not clear what impact, if any, that had on the results. Some patients took up to five shots of insulin a day, along with medications to lower blood pressure and cholesterol, as well as drugs to control blood sugar such as Avandia - a diabetes drug that has been in the news a lot because it appears to increase the risk of heart attack and heart failure.

(It should be noted too that the ACCORD study, in which Canadians researchers play a key role, has three arms. One aspect has been halted, but the study of the impact of cholesterol drugs and hypertension drugs on diabetics is continuing and will yield important information.)

What is becoming clear, though, is that people with diabetes are different from those without diabetes in ways we do not fully comprehend. Diabetes remains one of our greatest public health challenges.

More broadly, we don't understand the complexities of the heart nearly as well as we pretend.

These two new studies illustrate that point. But there have been many more cautionary tales.

The story of hormone replacement therapy, drugs used to treat the symptoms of menopause, is another example. The idea that bolstering the level of female sex hormones at menopause would make unpleasant symptoms disappear was a sensible assumption. But that simplistic thinking did not take into account that, in the process, rates of breast cancer, blood clots and heart attacks would increase - hardly a good tradeoff.

Similarly, painkillers such as Vioxx were developed to deal with a nasty side effect of traditional painkillers such as ibuprofen: stomach problems. While Vioxx users had marginally fewer stomach woes, they had a lot more heart trouble, not to mention that Vioxx didn't provide any more pain relief that ibuprofen despite costing a lot more.

Doing medical research is expensive. It can be tedious, and sometimes lead to dead ends. There are often complaints that studies demonstrate the obvious.

But in an era when we are so dependent on prescription drugs to manage chronic illnesses, medical research is more crucial than ever.

It is not enough for research to produce breakthroughs and new treatments. Research should test if drugs perform as well in the real world as they do in carefully crafted clinical trials.

Research also has a crucial role in protecting the public from faulty assumptions (no matter how well-meaning and heartfelt) by constantly challenging the current orthodoxy.