Does Sugar Cause Dementia?

More than 150 million Americans have blood sugar levels that may boost the threat of dementia, new research suggests. People whose blood sugar levels are at the high end of “normal” are more likely to have brain shrinkage in areas involved with memory and cognitive skills, reports a new study published in Neurology.

The study adds to growing scientific evidence that dementia—irreversible memory loss that occurs with disorders like Alzheimer’s disease—may be triggered by “brain diabetes,” excessive sugar circulating in the brain’s blood vessels. The researchers were the first to discover that key brain areas show shrinkage tied to aging and dementia even before blood sugar hits the levels currently classified as diabetic or pre-diabetic.

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In the study, adults ages 60 to 64, with normal fasting blood sugar, as defined by the World Health Organization, had brain scans. When the scans were repeated four years later, those with higher blood sugar showed greater atrophy in areas of the brain’s hippocampus and amygala--both of which play a key role in memory and mental skills— compared to did people with lower blood sugar.

Higher (but still “normal” blood sugar) accounted for up to 10 percent of the shrinkage observed, even when other risk factors, such as age, smoking, high blood pressure, and alcohol use were taken into account. More than 150 million Americans have “high-normal” blood sugar, prediabetes, or diabetes, so may be at risk for accelerated brain aging or dementia.

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"Numerous studies have shown a link between type 2 diabetes and brain shrinkage and dementia," said study author Nicolas Cherbuin, PhD, with Australian National University in Canberra. “(Our) findings suggest that even for people who do not have diabetes, blood sugar levels could have an impact on brain health.”

Like many other scientists, Cherbuin believes that the numbers that define “normal” blood sugar urgently need to be re-evaluated. Other recent studies indicate that blood sugar levels at the high end of “normal” mark the start of insulin resistance (IR), a disorder in which the body produces insulin, but doesn’t use it properly. IR is the root cause of type 2 diabetes.

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Why Does High-Normal Blood Sugar Harm the Brain?

“Once people become insulin resistant, they start to develop microvessel disease, the leading cause of dementia,” reports Bradley Bale, MD, medical director of the Heart Health Program at Grace Clinic in Lubbock, Texas. “Small blood vessels become damaged, reducing the amount of oxygen and other nutrients that flow to the brain.”

Many people with IR aren’t aware of their danger, adds Dr. Bale. “Most patients with insulin resistance aren’t diagnosed until they become diabetic.” The CDC reports that one-third of America’s nearly 26 million diabetics and 87 million adults with pre-diabetes are currently undiagnosed, as high blood sugar silently damage their brain and blood vessels, more than tripling risk for heart attacks and strokes.

What Causes Insulin Resistance?

The leading risk factors for insulin resistance include a large waist (greater than 40 inches for a man or 35 inches for a woman, even if your weight and BMI are normal), high blood pressure, high triglycerides, low levels of HDL (good) cholesterol, obesity and a sedentary lifestyle.

The more of these risks you have, the more likely you are to become insulin resistant. Some of the best ways to protect your health—and your brain—are exercising vigorously every day, losing even a little weight, and eating a diet that’s high in antioxidant-rich, colorful fruits and vegetables, fiber, and foods that provide omega-3, such as oily fish like tuna and salmon, while limiting or avoiding sweets.

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How Sugary Foods Harm Your Brain

Once you develop IR, a diet that’s high in sugar worsens the problem, says Dr. Bale. “If you’re insulin resistant, the insulin-producing beta cells in your pancreas have already lost at least 60 percent of their function. Eating sugary foods puts more demand on these already exhausted cells, so can aggravate the problem, which in turn increases the likelihood that you’ll develop microvessel disease.”

A recent study shows that high-fructose sweeteners, in particular, may be driving the development of brain-harming microvessel disease. This type of sugar, which is ubiquitous in processed foods, appears to raise levels of a cell-damaging toxin called uric acid, the researchers report, increasing potentially risk for vascular dementia, chronic kidney disease, stroke, and coronary heart disease. 

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