As many as one in eight people don’t know they have prediabetes and are on the path to developing diabetes. Of Canadian adults, that is nearly 3.5 million people. Both prediabetes and diabetes are important contributors to heart disease.
The findings, published recently in the American Journal of Preventive Medicine (AJPM), aren’t surprising to Kim Twyman, advanced practice nurse in diabetes at the University of Ottawa Heart Institute. Close to 40% of patients treated at the Heart Institute have a history of known diabetes.
“About 60% of our admitted patient population, overall, have elevated blood glucose [sugar]. Of those, 20% are told after screening that they have prediabetes and another 20% are diagnosed with type 2 diabetes,” she said.
It’s clear that many people have prediabetes and didn’t know it beforehand. The numbers not knowing they have prediabetes are higher than what are in the AJPM study because the Heart Institute has a higher risk population.
“I saw a woman the other day who didn’t know she had diabetes—and she had type 2 diabetes. She has perfect cholesterol but came in with a heart attack,” Twyman said.
That’s part of where the confusion lies. There is a lack of awareness of how much blood glucose levels can contribute to heart disease, independent of other known risk factors, such as high cholesterol.
People newly diagnosed with type 2 diabetes are offered an appointment with an endocrinologist at the Heart Institute’s Diabetes Clinic. The team approach in the clinic, which is a collaborative effort with the Division of Endocrinology & Metabolism at The Ottawa Hospital, involves a range of expertise, including cardiologists, an endocrinologist, a diabetes educator, dietitians and rehabilitation specialists, along with community education partners, to provide the complex care that best benefits people with diabetes.
“Keeping blood sugar under control is hugely important. That’s why we approach this fairly aggressively,” said the clinic’s endocrinologist Amel Arnaout, MD. “It’s not only a major risk factor for developing heart disease but makes things worse for those who already have heart disease. People with diabetes have a worse time if they get a cardiac complication. They have higher risks of short- and long-term mortality, and tend to have higher rates of worsening heart disease and additional complications.”
Patients found to have prediabetes are referred to diabetes education programs close to their homes. Once people know they have this risk, most are keen to learn the lifestyle changes they need to undertake to avoid getting diabetes, Twyman said. “For most, having a heart attack is a wake-up call.”
Patients at the Heart Institute are routinely tested for diabetes using the hemoglobin A1C test (also called glycated hemoglobin). This test gives a fuller picture of how well a patient metabolizes sugar than the more commonly used fasting-glucose test, which measures blood glucose after fasting for 10 or 12 hours.
“The A1C test looks at mature red blood cells and gives a picture of how much sugar they have been bathing in over a prolonged period of time,” Twyman said. Fasting-glucose tests give only a snapshot of blood glucose at a moment in time.
Why is prediabetes bad for the heart? The connection between heart disease and high blood glucose is well-established. High blood glucose contributes to making the blood more viscous or thicker; meaning, the heart has to pump harder to push blood through the vessels, she said.
This viscous blood causes mechanical stress on the insides of arteries, making the surfaces uneven and easier for fatty plaque to stick to. The plaque builds up in layers over time, leading to the blockages common in coronary artery disease, Dr. Arnaout said. High blood glucose also causes inflammation, which contributes to the physical damage done to vessel walls.
Detecting high blood sugar and dealing with it early gives the best results, said Heart Institute cardiologist Richard Davies, MD. He pointed out that diet changes alone can have a huge impact on both preventing diabetes in the patient with prediabetes and in keeping those with diabetes healthier.
“I push my own patients with diabetes very hard on diet. I tell them to think of themselves as intolerant of carbohydrates and that they need to limit foods that contain them,” Dr. Davies explained.
By “intolerant to carbohydrates,” he means people prone to high blood sugar don’t process carbohydrates efficiently, so sugars stay in the blood longer. “The body has very little capacity to store sugar and, as a result, high blood sugars are usually the direct result of food eaten within the past 12 hours,” he said.
Reduced ability to process carbohydrates often comes with age as well as with weight gain. Weight loss of just 5%, along with diet changes and moderate exercise, reduces the risk for type 2 diabetes.
Keys to improving blood sugar levels are aiming for foods with a low glycemic index (GI) and limiting carbohydrates. The glycemic index uses a scale of zero to 100 to rank the carbohydrates in food in terms of how they affect blood glucose levels. Those with a low value, 55 or less, are more slowly digested and cause a slower, more steady rise in blood glucose levels (and consequently insulin levels). Higher GI values increase blood glucose levels.
Studies show that low GI diets also improve lipid levels and help with weight management because these foods curb the appetite and delay hunger. Low GI diets also reduce insulin levels and insulin resistance, both pluses in the fight against heart disease. General rules are to avoid foods such as breads, pastas, potatoes and rice.
Dr. Davies noted that exercise is also important, but it can’t offset the effects of a bad diet.