Cardiovascular disease. Consider this scenario: Two people enter the emergency room complaining of chest pain. One has suffered a heart attack in the past. The other has diabetes.
Who is more likely to be having a heart attack? The one with diabetes, Primack says, explaining that this situation is commonly used in medical schools to demonstrate how diabetes acts as a “coronary artery disease equivalent.” “If you have diabetes, you basically already have coronary artery disease, even if it hasn’t been diagnosed,” he says.
While experts used to believe that dietary cholesterol was the main culprit behind artery-clogging plaque, current research suggests excess levels of sugar in the blood likely play a larger role, Primack says. High blood sugar levels increase the production of free radicals, highly reactive molecules that cause premature cell death and reduce the availability of nitric oxide, a compound that’s needed for blood vessels to relax and allow blood to flow freely despite plaque buildup.
Heart disease is the leading cause of death among people with diabetes, according to the International Diabetes Foundation.
Sexual dysfunction. With high blood sugar levels, the same factors that decrease blood flow to the heart reduce blood circulation to the sexual organs, Primack says.
According to the Joslin Diabetes Center, an affiliate of Harvard Medical School in Boston, more than one-half of men who have diabetes for 10 years also suffer from erectile dysfunction, and those with poorly controlled blood sugar levels are more likely to have sexual side effects compared with those who have their blood sugar under control. While they have been less studied, sexual issues are also common in women with chronically high blood sugar levels, according to the Cleveland Clinic. Side effects such as vaginal dryness, low levels of sexual interest and difficulty reaching orgasm can occur.
Cognitive decline. “In recent years, we have begun to call Alzheimer’s disease diabetes of the brain,” Primack says. Others have called it Type 3 diabetes. Either way, the link between high blood sugar and cognitive decline is strong, no matter your diabetes diagnosis. For example, a 2018 study published in the journal Diabetologia, which tracked 5,189 people over the course of 10 years, showed that those with the highest blood sugar level had the fastest rate of cognitive decline.
Researchers don’t yet know the full explanation between the sugar-brain connection, but reduced blood flow is likely to play a role, Primack says.
Bone and joint problems. Most people have heard of diabetic neuropathy, in which chronically high blood sugar levels damage nerve cells throughout the body, leading to a pins-and-needles sensation and even numbness in the hands, feet, arms and legs. But here’s a lesser-known fact: This nerve damage can also deteriorate the body’s joints, explains Dr. Jeff E. Sellman, a family and sports medicine physician with the Florida Orthopaedic Institute in Tampa. Called Charcot joint or diabetic arthropathy, it can cause instability and deformations in the joints, commonly in the feet.
Meanwhile, excess levels of glucose in the blood can adhere to joint surfaces, degrade collagen and reduce joint mobility.
Kidney disease. By damaging blood vessels in the kidneys, chronically high blood sugar levels can also reduce kidney function and contribute to renal disease. The longer someone has diabetes, and the longer that diabetes goes uncontrolled, the greater the risk of resulting kidney disease. According to the Centers for Disease Control and Prevention, one-third of people with diabetes have chronic kidney disease.
The kidneys help balance fluid levels and remove waste from the body, and thus are vital to overall health. If you have Type 2 diabetes or have had Type 1 diabetes for more than five years, the National Institute of Diabetes and Digestive and Kidney Diseases recommends having your kidney function checked every year.
Depression. Experts used to think it was the day-to-day doldrums of managing diabetes that increased the risk of depression in people with Type 1 and Type 2 diabetes, but emerging research suggests that blood sugar levels may be a far greater depressant than taking blood sugar readings and insulin shots.
For example, 2015 research published in The Journal of Neuroscience shows that, for those with Type 1 diabetes, high blood sugar levels increase the brain’s levels of a neurotransmitter associated with depression. The study also found that high sugar levels alter connections between regions of the brain that control emotion, potentially contributing to mental health issues.