Brain’s Energy Source: Glucose

Although sugar has a bad reputation, the human brain is dependent on glucose (a type of sugar) as its primary source of energy.^1,2 Neurons in the brain have one of the highest energy demands in the body and require quick and continuous glucose supply for all neuronal functions. It is estimated that the human brain consumed nearly 20% of glucose-derived energy despite taking up only about 2% of the body weight. As neuronal function is tightly linked to glucose supply, conditions that alter or negatively impact glucose metabolism can directly affect cognitive function.²

Link Between Diabetes and Brain

The relationship between diabetes and cognitive impairment is undeniable.^2,3 For instance, a 2019 systematic review and meta-analysis of 144 prospective studies concluded that diabetes mellitus is associated with a 1.25-1.91 times higher risk of cognitive impairment and dementia. The trends were similar in those with prediabetes, elevated hemoglobin A1c levels, fasting and postprandial hyperglycemia (ie, high blood glucose levels), and abnormal fasting plasma insulin levels.³

The exact mechanism behind the relationship is still being studied. Diabetes is known to cause adverse changes in blood vessels through atherosclerosis (ie, buildup and hardening of cholesterol plaques) and is a known risk factor for cardiovascular disease and cerebrovascular disease such as stroke.³ Both of which are strongly associated with cognitive impairment and dementia. In addition to the unfavorable vascular changes related to diabetes, some studies suggest that hyperglycemia itself can cause neural damages, disrupt neurohormonal balances, and lead to glucotoxicity that can impair cognitive function.⁴ Hypoglycemia, or low blood glucose levels, can also have detrimental effects on neural capacity.^2,5 Recurrent hypoglycemia associated with advanced diabetes and certain drug use can cause oxidative stress and neural inflammation that result in adverse structural and functional changes in the brain.

How Can Cognitive Function be Affected? 

In addition to increasing risk of Alzheimer’s disease and vascular dementia, diabetes can affect cognitive function in other less serious ways.^6–8 Studies have shown that type 1 and type 2 diabetes mellitus may disturb cognitive function in the following areas:

• Attention
• Information processing speed
• Executive function
• Memory
• Verbal fluency
• Learning
• Psychomotor efficiency
• Mental flexibility
• Visuospatial function

Maintain a Healthy Lifestyle & Ask for Support  

Eating a healthy diet, engaging in regular exercise, monitoring blood glucose levels, adhering to medication plan, managing hypoglycemia, and getting routine checkups are all important in the management of diabetes.⁵ Maintaining a healthy lifestyle and achieving glycemic targets are critical to cognitive health, as is with other diabetes-related complications. It is important to note that those who already experience cognitive impairment may have hinderances in performing the daily self-care required for diabetes management. They may experience poor compliance with lifestyle and medication recommendations and have worse glycemic outcomes and more hypoglycemic episodes. Health care providers, family members, and caregivers should provide adequate support to individuals with cognitive impairment to receive proper care.