High blood sugar puts you at risk for memory loss and cognitive problems, according to a new study out of Japan.

In this study, 1017 people in Japan, all under the age of 60, were given an oral glucose tolerance test (OGTT). In a glucose tolerance test, the person is given a fixed amount of glucose (sugar) and then their blood levels are monitored for several hours so that doctors can track how quickly and efficiently the glucose is “cleared” from their bloodstream. (The test is frequently given as part of a diagnostic workup for diabetes and insulin resistance.)

Based on their glucose tolerance tests, the researchers were able to classify the subjects as diabetic, pre-diabetic, or non-diabetic.

What the researchers found was that even after adjusting for variables like age and sex, the incidence of Alzheimer’s Disease, vascular dementia and all-cause dementia were significantly higher in subjects with diabetes. Remember, by definition, diabetics have blood sugar issues and don’t do well on glucose tolerance tests, so this study clearly links blood sugar issues with an increased risk of dementia.

Diabetics in this study had a whopping 74% increased chance of winding up with dementia from any cause whatsoever (“all-cause dementia”).

But here’s what’s interesting. Of the 308 people who started the study with pre-diabetes, a very significant 25% of them ultimately developed dementia. The American Diabetes Association estimates that 79 million people are walking around with pre-diabetes, which is defined as the state that occurs when a person’s blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes.

As many of you may know, cardiologist Steve Sinatra and I are currently at work on a book about heart disease. In reading the copious amount of research on fat, cholesterol, sugar and the heart, it’s become stunningly clear to me that we have been barking up the wrong tree for thirty years by trying to reduce fat in the diet and bring down our cholesterol.

What we should have been looking at is sugar. (You’ll see why when the book comes out.)

But sugar isn’t just a culprit in heart disease. Cancer cells feed on sugar. High glycemic (sugar) diets are implicated in heart disease, diabetes, and nearly any condition in which there’s a lot of inflammation.

This new study adds dementia and cognitive problems to the long and growing list of conditions you don’t want to have that are negatively impacted by a high-sugar diet.