How low is too low? Blood glucose levels and cardiovascular disease

This study explored the relationship between blood glucose levels and the risk of cardiovascular disease.

In patients with diabetes mellitus (DM), high levels of blood glucose (sugar) can damage the small blood vessels (microvascular disease), leading to eye, kidney and nerve damage. DM management is focused on maintaining ideal blood glucose levels that help to avoid these microvascular complications. There are also macrovascular (that affect large blood vessel or artery) complications caused by DM, such as cardiovascular disease (CVD), which can lead to the clogging of the arteries. This causes blocks in blood flow and can eventually lead to a myocardial infarction (heart attack) or sudden death. It is not known whether there is an ideal blood glucose level that can help patients avoid CVD. The current study examined the associations between blood glucose and CVD. 

6120 DM patients who were not taking glucose-lowering drugs or had been diagnosed with CVD were followed over approximately 9.2 years. At the beginning of the study, patients’ blood pressure, cholesterol levels, fasting blood glucose or FBG (a measure of the blood glucose after 8 hours without food or drink), and 2-hour post-challenge plasma glucose or 2h-PCPG (a measure of how quickly glucose is cleared from the blood) were measured. They were then interviewed by phone once per year to evaluate their cardiovascular health. Patients who experienced a myocardial infarction or angina pectoris (chest pain due to clogged arteries) were said to have coronary artery disease (CAD), while CVD was defined as CAD, stroke, or death. 

There was a significant association found between FBG and death from CVD, while 2h-PCPG was significantly associated with CVD and CAD. These associations were seen when FBG was higher than 5.6 mmol/L and 2h-PCPG levels were higher than 8.0 mmol/L. These blood glucose levels are below the cutoffs at which DM is diagnosed. However, very low blood glucose levels were also associated with CAD and CVD. Therefore, an ideal blood glucose level to avoid CVD may lie between 5.2 and 6.0 mmol/L.

In summary, blood glucose levels lower than those used to diagnose diabetes mellitus are associated with the risk of developing CAD or CVD. The target blood glucose to reduce this risk appears to be between 5.2 and 6.0 mmol/L. 

Patient blood glucose levels were only measured at the beginning of the study. It is not clear from this research how changes in blood glucose levels over time may affect the risk of CAD or CVD.

Discuss with your physician the best way to manage your diabetes.