Medical Matters: John, a middle-aged man with a family history of heart disease and a tendency to high cholesterol, is very careful about his diet.
He has always been scrupulous about dairy products, concentrating on low-fat milk and cheese. Recently he came to see me perplexed about research in Science magazine contending that full-fat products are more effective at lowering blood pressure and reducing obesity than low-fat products, especially when combined with lots of fruit and vegetables. I was as flummoxed as John. I muttered something about "ongoing research" and made a mental note to look up the article. It is the dilemma of what is known as evidence-based medicine.
The explosion of medical research, knowledge and information is so extensive that it is hard to keep up to date. The proponents of evidence-based medicine believe best practice is based on the best evidence at the time. This may seem obvious, but it is impossible to read up on everything, so one has to be judicious and choosy in what one wants to know.
Research follows a standard pattern. A hypothesis or theory is considered, such as testing the efficacy and safety profile of a new drug. Work is done in small groups of patients, results are collected and analysed and the hypothesis is advanced or refuted (very little is proven). To confuse the issue, no sooner is a piece of research completed than another team will often provide evidence suggesting the opposite. Who is to be believed?
Statistics can clarify or confound things also. Every doctor has a wealth of experience in individual cases, but single anecdotes do not make convincing statistics. The more numbers there are, the more convincing the hypothesis. The term meta-analysis has been coined to describe analysis of pooled research with enormous numbers - and the results, in theory, should be more convincing.
Take passive smoking. Even the most diehard smoker will admit the wealth of evidence associating smoking with a host of cardiac, respiratory and malignant disorders. Given the presence of more than 4,000 noxious substances in tobacco smoke, the common perception is that non-smokers exposed to it would be at greater risk of illness than those not exposed. A recent report in the British Medical Journal from California, however, based on a meta-analysis of passive smoking, implies that the risks are far lower than previously thought.
Predictably this report has been criticised by the anti-smoking lobby, and with good reason: the data is derived from the effects of smoking on spouses of smokers rather than from the effects of smoke exhaled by smokers, which is considered more toxic than inhaled smoke. Also, the study was partly funded by the tobacco lobby. Were it to be further corroborated, it would be sweet music to the tobacco industry and the licensed trade, which object to the likely ban on smoking in pubs.
Another condition that has undergone a sea change is peptic ulceration. For many years the cause, excessive secretion of gastric acid, was thought to be due to "stress". I well recall a distinguished physician in the 1970s advising patients with ulcers to "cultivate the art of relaxation" by downsizing jobs and moving to the country. Treatment at the time included selective vagotomy, an operation in which the nerve facilitating acid secretion was cut.
The development of powerful acid suppressors, known as H2-blockers, in the late 1970s made surgery almost redundant. In the 1980s research showed the presence in the stomach of bacteria known as H pylori was a major factor. The accepted treatment is now triple therapy of a protein pump inhibitor (an even stronger suppressor than H2-blockers) and two antibiotics to eradicate H pylori.
Any medical student who put forward such theories 30 years ago would have been told to reread his textbooks. Have we any idea how ulceration will be managed in 30 years and how quaint our current management might appear then?
Even bed rest, traditionally recommended for many illnesses, has been reappraised. A generation ago treatment of heart attacks included up to six weeks in bed. Many patients with back pain found themselves immobilised on traction for long periods. Today patients with uncomplicated coronaries can be home within a week, and patients with back pain are encouraged to mobilise rapidly.
Prolonged bed rest can lead to sluggish blood flow, deep-vein thrombosis, muscle wasting, osteoporosis and kidney stones. Unless they are severely ill or incapacitated, hospital patients are advised to stay out of bed as much as they can.
Doctors, like lawyers, can work only with the evidence they have. Last year's can become inadmissible, but medicine must carry on. I rest my case.
Dr Muiris Houston is on leave