When your blood glucose level falls, you shouldn’t be behind the wheel. Hypoglycemia poses a serious hazard to you and to others on the road.

People who take insulin or pills for their diabetes should always try to keep their blood glucose (sugar) from dropping too low. One example of when this is especially important is when planning to drive. Low blood glucose (hypoglycemia) can impair your judgment, slow your reactions, and even cause you to lose consciousness.

If your glucose level falls to 70 milligrams per deciliter (mg/dL) of blood or lower, the level is lower than desired for you to think and react quickly. Researchers have studied the effects of hypoglycemia on the driving skills of people with type 1 diabetes. In one experiment, they temporarily lowered the blood glucose levels of study participants, and then had them pretend to drive using simulators—devices that re-create road conditions. The person reacts as though he or she is at the wheel.

In that study, mild hypoglycemia (a blood glucose level of 64.8 mg/dL) did not appear to affect driving. However, once blood glucose dropped to 46.8 mg/dL—moderate hypoglycemia—the participants did much more swerving and spinning on the pretend roads. They also crossed over into other lanes more often and went off the road more often.

These moves would have been very dangerous had they occurred on actual roads. Yet, only half of the participants said they would not drive with a similar blood sugar level.

In another test, the individuals were told to have a glucose drink or stop pretend-driving if they thought it was necessary. Although 79% of the drivers were aware that they were experiencing low blood sugar, only 32% took the glucose drink or “pulled over.”

Driving restrictions in diabetes

In many European countries, people with diabetes may have to undergo frequent medical examinations or tests of hypoglycemia awareness. The European Union, an association that includes many European countries, recommends not permitting people with diabetes to drive buses, trucks, and vehicles that transport heavy goods.

Here in the United States, doctors in California must report any individual who loses consciousness due to hypoglycemia. The state then takes away the person’s driver license. In most states, people who use insulin can’t get an interstate commercial driver license, although temporary exceptions are often made.

The hypoglycemia hazard

You might feel that these restrictions are not necessary, and that other types of drivers (for example, those who are inexperienced or very old) pose a greater risk to the public. It’s true that diabetes won’t always interfere with a person’s driving ability. However, studies of driving and diabetes have found that

• up to 40% of insulin-dependent drivers have had symptoms of low blood sugar while driving
• 31% of drivers with type 1 diabetes and 8% with type 2 diabetes had driven in a hypoglycemic stupor in the preceding 2 years, and 28% with type 1 diabetes and 6% with type 2 diabetes had experienced hypoglycemia while driving in the preceding 6 months
• 13.6% of insulin-dependent drivers had been involved in an accident since beginning insulin treatment
• drivers with type 1 diabetes reported more crashes and tickets than drivers with type 2 diabetes or drivers without diabetes.

On the other hand, in many studies the accident rate per mile for people with diabetes is no higher than that of the general population. Indeed, some studies have found that the accident rate is actually lower among people with diabetes. And hospital admission rates from car accidents are no higher for drivers with diabetes than for drivers without.

Why take a chance?

Overall, medical conditions cause very few accidents. The additional risks for most drivers with diabetes appear to fall well within the level of risk accepted for all drivers, at least according to some researchers.

But rather than play the odds, use common sense instead. If your blood glucose readings have been too high or too low, consider driving less frequently, for shorter distances, only in daylight, and/or only in good weather. Continue taking these precautions until you’re able to bring your blood glucose under control.

From Diabetes Care