Two recent studies have found a correlation between elevated blood sugar levels and Alzheimer’s disease (AD). One study involved individuals with type-1 diabetes while the other mimicked type-2 diabetes in mice.
Type-1 diabetes is an autoimmune disorder in which the pancreas does not produce enough insulin, resulting in reduced glucose uptake by cells and increased blood sugar. This condition most often develops in childhood.
Type-2 diabetes is more prevalent and occurs as a result of either reduced insulin production or loss of sensitivity to insulin, because of which glucose uptake in cells decreases. This causes increased blood sugar. The onset of this condition commonly occurs in adulthood.
Alzheimer’s disease is a condition marked by β-amyloid plaques and neurofibrillary tangles in the brains of patients, leading to neuro-cognitive problems.
In this study conducted by Dr. Rosano’s research team at University of Pittsburgh, middle-aged patients with and without type-1 diabetes were compared to non-diabetic individuals. The results showed:
- White matter hyperintensities, a common outcome of the normal aging process as well as some neurocognitive disorders, was moderate to severe in 33% of diabetic individuals, compared to 7% in control subjects (as seen with Magnetic Resonance Imaging or MRI)
- Those with diabetes had lower average scores in three cognitive tests to assess
- Information processing speed
- Manual dexterity
- Verbal intelligence
- The results were not dependent on age, education, or other factors
- Prevalent neuropathy and smoking tripled the odds of having white matter hyperintensities; this did not depend on age or duration of the disease
- High blood pressure or elevated blood sugar were insignificant factors in the increase in hyperintesities
- Type-1 diabetes appeared to hasten brain aging
Scientists from Washington University at St. Louis, led by Dr. David Holtzman, investigated the effects of increased blood sugar in a mouse model of Alzheimer’s disease. The mice were subjected to increased glucose in blood over 4 hours. The results showed that:
- There was a significant increase in β-amyloid in the brains of AD mice. β-amyloid is the precursor for plaques in the brain observed in AD
- High sugar produces more β-amyloid
- A channel called ATP-sensitive potassium channel, when opened, reduced β-amyloid synthesis
According to the Alzheimer’s Association, numerous studies have deduced that patients with diabetes tend to have a lower level of cognitive function and a higher level of dementia. Those observations, taken together with the studies discussed here, seem to suggest that diabetes, be it type-1 or -2, and Alzheimer’s disease have a correlation. Larger studies will be needed in patients with Alzheimer’s disease suffering from diabetes to arrive at a definitive association.
Written by Mangala Sarkar Ph.D.