The human brain is delicate and sensitive to the amount of sugar or glucose used as fuel. In both type 1 and type 2 diabetes, uncontrolled hyperglycemia and occasional hypoglycemia during treatment can damage the brain.
Risk of hyperglycemia
The effects of diabetes on the brain, especially those associated with hyperglycemia, do not show symptoms quickly.
Joseph C. Masdeu, MD, of the Methodist Neurological Institute in Houston, says, “Over time, people with diabetes have an increased risk of vascular damage, including damage to small blood vessels in the brain, and this damage affects the white matter of the brain.”
The white matter of the brain is part of the nerves in the brain. When nerves in the brain are damaged, patients have changes in the way they think, i.e., they develop vascular cognitive impairment or vascular dementia.
Diabetes can induce inflammation
Joel, MD, PhD, director of the Clinical Diabetes Center at a New York (Montefiore) medical center, says that you can get vascular cognitive impairment with either type 1 or type 2 diabetes, but there are some differences in risk.
“In general, the longer you have diabetes, the more likely you are to develop dementia, but for people with type 1 diabetes who have well-controlled disease, the chances are much smaller,” he said.
People with type 2 diabetes can face a double whammy because they often have other problems, and those problems can also lead to blood vessel damage.
“These patients have a poorer metabolism overall, have low levels of HDL cholesterol (good cholesterol), high triglycerides and high blood pressure, and are more likely to be obese,” Joel said.
He said diabetes encapsulates these problems and can induce inflammation that damages blood vessels, so it’s important to manage the condition.
Sometimes, patients want to try different therapies before they go on insulin injections or other diabetes medications,” Joel said. The last thing they want to try is an injection.” But it’s important for patients to start lowering their blood sugar early in the disease, rather than spending 5 years fighting the disease.
Low blood sugar can cause sudden problems
A patient is more likely to have hypoglycemia if he or she has tightly controlled diabetes. The effects of hypoglycemia on the brain are more immediate and more pronounced than hyperglycemia.
The lower the blood sugar, the more severe the hypoglycemia symptoms. Hypoglycemia can affect mood and make it hard for the brain to think, as well as cause headaches, dizziness, poor coordination, and difficulty walking or talking. Severe hypoglycemia can cause a person to have seizures or convulsions, faint, or pass out.
Non-sensory hypoglycemia
Recurrent episodes of hypoglycemia can have serious effects, said Gail Musen, MD, assistant professor of psychiatry at Harvard Medical School in Boston, USA.
“Occasional hypoglycemia may not have a major effect on the brain,” she said, “but if a person has frequent hypoglycemia, he or she will not be aware of the crisis, and that state is most frightening.”
This condition, called unperceived hypoglycemia, occurs when the brain is unable to notice low blood sugar levels. When this happens, the person is also unable to perceive the early symptoms of hypoglycemia, such as nausea, hunger, shivering, cold or clammy skin, and a violent heartbeat.
Usually these symptoms are enough to wake the person with diabetes from sleep, but if the person is imperceptibly hypoglycemic, the person does not wake up, but the blood sugar continues to drop until a critical situation occurs.
Absent hypoglycemia can also cause a patient to have an accident while driving a car, or to fall while walking.
Effects of hypoglycemia
The jury is still out on whether recurrent hypoglycemia can cause memory problems or increase the risk of dementia. A large study called the Diabetes Control and Complications Trial showed no long-term effect of hypoglycemia on memory or on the ability to think in people with type 1 diabetes. But another study showed that among older adults with type 2 diabetes, those with a history of severe hypoglycemia were at higher risk for dementia.
Joel said it’s important to get serious about controlling diabetes in the first place. “Hypoglycemia may not make a patient develop dementia, but hypoglycemia can be extremely uncomfortable. High blood sugar may not be uncomfortable, but it can cause related conditions such as dementia.”
A possible link to Alzheimer’s disease?
Studies do show a link between diabetes and Alzheimer’s disease. people with type 2 diabetes are twice as likely to develop Alzheimer’s disease as non-diabetics. But researchers are still trying to answer the question of whether diabetes actually causes Alzheimer’s disease.
“Alzheimer’s disease is characterized by a buildup of beta-amyloid, an abnormal brain protein, in the brain,” said Peter Butler, M.D., director of the Larry Hillblom Islet Research Center at the University of California, Los Angeles.
In some people with Alzheimer’s disease, beta-amyloid forms clumps that interfere with the ability of nerve cells to communicate with each other.
“In the pancreas, which synthesizes insulin, there are similar proteins that cause cell damage and death,” Peter said, “and this may be a common risk for developing Alzheimer’s disease or type 2 diabetes, because the proteins that go wrong are very similar in both diseases.”
But Peter added that vascular cognitive impairment (a possible complication of diabetes) is another causative factor in Alzheimer’s disease. This adds to the tedium and complexity of the problem. There seems to be a lot of unanswered questions about which disease occurs first, whether one triggers the other, and how the diseases are linked.
“It’s hard to distinguish between these diseases, which are all chronic diseases in which the body’s cells don’t function,” Peter said, “and it would seem very ignorant.”