Low blood sugar levels overnight may contribute to life-threatening changes in heart rhythm, a major risk for patients with diabetes, experts warn.
The findings, which will be published in the May issue of the journal Diabetes, also shed new light on the “dead in bed” syndrome—where young people without any history of long-term complications die suddenly from the disease.
Few of the patients taking part in the present study reported symptoms of low blood sugar levels or irregular heartbeats. They were only detected through continuous glucose monitoring and electrocardiograms, which tracked blood glucose levels and heart rates over a week in a group of older patients with Type 2 diabetes and a history of cardiovascular disease.
“We don’t want to alarm patients, but what we’ve found is potentially important in explaining a possible mechanism by which low overnight blood sugars lead to prolonged, slow heart rates that could disturb blood flow to the heart, causing life-threatening heart attacks,” says Simon Heller, professor of clinical diabetes at the University of Sheffield, who led the study.
Previous studies had apparently ruled out a direct effect of hypoglycaemia (very low levels of sugar in the blood) as a cause of death in patients with Type 2 diabetes.
History of Heart Problems
“While we expected to find some low overnight blood sugars, we were startled to find how extensively it was occurring overnight and that it was sometimes lasting for several hours. When this occurred, we also saw evidence of prolonged periods of very slow heart rate rhythms in patients.
“While a cause for concern, these slow heart rates were not associated with any very serious heart rhythm disturbances in the study. But the findings suggest that even those on standard insulin therapy who are not aiming for intensive glucose targets should be aware of the risk of running low sugars overnight, particularly if they have known cardiovascular disease.”
Previous research has focused on the effects of high blood sugars on patients with diabetes, so more research was needed to understand how low blood sugars in patients with Type 2 diabetes caused irregular heartbeats, Heller says.
“In an older group with a known history of cardiovascular disease this might turn out to be something to be very concerned about, but further investigation is needed to confirm the link between overnight low blood sugar levels and abnormal heart rates that disturb the flow of blood to the heart,” Heller points out.
“If patients are aware they have low blood sugar levels, they can act accordingly, perhaps by checking their blood glucose in the middle of the night every now and then and talking with the doctor to change insulin type or the timing of the dose to minimize the risk of prolonged episodes of hypoglycaemia overnight.
“Clinicians responsible for the care of patients using insulin to treat Type 2 diabetes need to be more aware of the potential for prolonged nocturnal episodes of hypoglycaemia at night. They need to check for it and alter therapy to reduce the risk, especially for those who have known history of cardiovascular disease.”
The National Institute for Health Research supported the research.