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Diabetes and Driving

U of T study finds that diabetics who keep strict control of their blood sugar are more likely to be involved in a car accident, not less

Laws that require diabetics to keep tight control of their blood sugar level in order to hold onto their drivers’ licence are not only unfair, they are counterproductive. Patients with the best glycemic control, it turns out, are more than twice as likely to be in a crash as patients with the worst.

Donald Redelmeier, a professor in the department of medicine at the University of Toronto, and his colleagues, examined every diabetic driver reported to the Ontario Ministry of Transportation Medical Advisory Board in the years 2005 and 2006 who had a documented blood sugar history. Fifty-seven had been in motor vehicle accidents and 738 were there for other reasons, including challenging a licence suspension and mandatory annual reviews of people with commercial licences.

Diabetic drivers in Ontario, and many other jurisdictions around the world, are required to document their blood sugar history. One commonly used blood test indicates a patient’s glycemic control over a two-to-three month period and does not rely on the patient to self-report. A healthy person has a reading of around 6 on this test — and people insist diabetics should strive for that too.

Good control of blood sugar is important for long-term health, making eye and kidney problems less likely, for instance. Driving laws are based on the idea that people who control their sugars are likely to suffer such problems. But well controlled blood sugar does not make a diabetic a safer driver, the researchers found. They published their work in the journal PLoS Medicine this week.

“Tighter glycemic control is associated with increased risk of motor vehicle crash,” says Dr Redelmeier. “The finding calls into question the laws in Ontario that restrict drivers licencses based on these tests.”

Maybe people who are sticklers about blood sugar also happen to be unusually reckless drivers or maybe they drive in more dangerous places. But Dr Redelmeier thinks it is more likely to be the fact that keeping blood sugar low sometimes backfires, leading to hypoglycemic episodes where blood sugar is so low that people black out while at the wheel.

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