People with well-controlled diabetes are at greater risk for car crashes and other driving mishaps, according to two recent studies.

Diabetes patients strive for tight control of blood sugar, aspiring for glycosylated hemoglobin (hbA1c) levels of 6.5-7. However, the methods used to stay at these levels, including regular blood tests and treatment with insulin and drugs can cause episodes of hypoglycemia, leading patients to lose concentration or even consciousness.

One 2-year study in the Public Library of Science compared the Hba1c levels of 795 drivers with diabetes who had or hadn’t been in an accident. The researchers found that lower HbA1c levels were tied to a higher risk of a motor vehicle crash. Those in previous accidents had an average HbA1c level of 7.4, compared with 7.9 among those who had not. The authors claim that the increase risk of lower HbA1c might account for about one-third of the 57 accidents in the study.

A 1-year study in Diabetes Care screened 452 drivers with type 1 diabetes for mishaps such as collisions, citations, and losing control, as ell as self-reported hypoglycemic episodes. More than half the drivers (52%) reported at least one hypoglycemia-related driving mishap, 32% reported two or more, and 5% reported six or more. Additionally, almost (41%) said they had experienced disruptive moderate hypoglycemia that impaired driving. Participants using pump therapy to manage their glucose were 35% more likely to record a hypoglycemia-related fender bender than those using insulin injections.

Both results suggest the need for laws that restrict driving in patients with diabetes. Countries that permit people with diabetes to drive (which is most) require that the drivers have no eyesight problems and can document their glycaemic control.