A Spoonful of Sugar…
For at least 20 years, epidemiologists have been wondering about what exactly the point is of.... well, what we do. Should we just do the “science bit” and present our results in worthy journals that nobody (except other epidemiologists) reads? Or push the powers that be into using our research to make society a better place? Have we made health policy shortcomings into individual medical issues when they needn't be?
A new BMJ paper published this week on “pre-diabetes” brings this idea back to the fore - who do we diagnose as “pre-diabetic” and what do we do with them once we've decided they fit the bill? Is it a medical problem, or something we need to address in society? Or neither? John Yudkin of UCL and Victor Montori of The Mayo Clinic claim that a disagreement over definitions and numbers may be at the heart of the “pre-diabetic epidemic”, and that it may well be no more than a storm in a tea cup (milk, no sugar, thanks).
It all started in 1979 with the Glucose Tolerance Test. After fasting overnight, patients drink 75ml of glucose solution, and two hours later their blood glucose level is measured. The result is given in mg/dL – how many milligrams of glucose are found in one tenth of a litre of blood. Less than 140 mg/dL? Great, your body is processing sugar well. Above 200 mg/dL? Sorry, but your body is struggling to process all that sugar. You're already diabetic and need treatment. And the bit in between? That 140 – 200mg/dL...well, it's risky. You're not diabetic yet but you're showing some signs and you need to be careful.
By 1997 we realised that the tolerance test was inconvenient both for staff and patients, who could spend half a day just waiting around. So the test was reduced to cut out the “drink” bit, and the idea of “raised fasting glucose” was introduced. You would simply be tested on an empty stomach without having to metabolise a thing. Because you weren't having any glucose this way, the levels expected in your blood were reduced. The new “normal” was 70 – 110 mg/dL, diabetics would show a reading above 126 mg/dL and those pesky folk with what was called “impaired fasting glucose” were between 110 and 126 mg/dL.
And this is where the quibbling began. In 2003 the American Diabetes Association decided to lower the threshold where “normal” ended and “pre-diabetes” began to 100mg/dL, but the World Health Organisation didn't agree, worried that the change would medicalize twice the number of people with no evidence for concern. The ADA have also created a lower threshold for the newest method – a test that detects the amount of glycated haemoglobin (the amount of glucose “stuck” to your red blood cells) and can be done at any time of day without fasting. The standard measure for a “pre-diabetes” reading was initially 6 – 6.5 mmol/L (millimoles per litre), but in 2003 the ADA announced that their own benchmark would start at 5.7 mmol/L. This last test, increasingly common, leads to the biggest overdiagnosis of all.
According to Yudkin and Montori, this leads to huge differences when it comes to classifying people in large numbers (as epidemiology does). For instance, a study of 98 658 people in China puts more than 50% of them into the “pre-diabetic” category using the ADA numbers – three times what “pre-diabetic” levels would be under the WHO standard. In a US study of 3627 people, 13.5% of people were found to have impaired glucose tolerance using the good old fashioned drink method. But researchers figured out that if the Fasting Glucose test had been used instead, 6.8% of people would have been classified as pre-diabetic with the WHO.... and a whopping 25% using the ADA guideline levels. What we read in the headlines becomes less about health, and more about the politics of numbers.
The WHO dislike the term “pre-diabetic” anyway, arguing that it implies there's no escape from a steady progression, and that people WILL go on to develop diabetes. People may suffer the same stigma as if they had full Type 2 diabetes, getting poorer deals in health insurance, employment prospects and suffering general anxiety over the medicalization of their condition. Yet less than half of people with pre-diabetes, as judged by the Fasting Test, actually go on to develop Type 2 diabetes within ten years. It's early days, but studying the outcomes of glycated haemoglobin tests seem produce similar figures. An international committee of experts convened in 2009 concluded that classifying people on a continuum is a bad idea anyway, as it implies that we know exactly when risk begins or becomes clinically important. And the fact is, we don't.
Aside from the numbers, the biggest question becomes “what do we do with all the people we've diagnosed?” Traditionally “lifestyle intervention” is most effective. In a Chinese study, a personalised diet and exercise plan with individual coaching was linked to a downturn of up to 46% in the relative risk of developing diabetes, while a Finnish study found that risk reduction was directly related to how much participants changed their lifestyle. But if we were to use the ADA guidelines to decide who was pre-diabetic, these interventions would grind to a halt under sheer weight of numbers.
And this is where epidemiology's existential crisis comes in, and the individual medical approach to diabetes falls down. Instead of helping a select group of people to swim against the tide and maintain a healthy lifestyle in an unhealthy world, should we not try and influence policy to make society healthier in the first place? Telling people to exercise is all very well, but we need to give them safe spaces to do it – cycle lane systems and open spaces alike. Telling people to eat more healthy food is great, but what if your nearest supermarket's processed foods are on special offer when the fresh fruit section is too pricey for your five a day?
We need to not only give people information about healthy choices, but the power to change their habits. If we don't, we just come across as busybodies and people ignore us. And arguments about seemingly arbitrary medicalization do us no favours at all when the way we live is the issue.