Uncontrolled diabetes can lead to memory loss. The brain's most important fuel is glucose. The entry of glucose into the brain is regulated at the blood-brain barrier. This barrier, which is formed by the cells that line brain capillaries (very small blood vessels), controls the brain's environment. It regulates the transport of nutrients into the brain as well as the exit from the brain of chemically charged particles and by-products of brain metabolism. Storage of glucose in the brain is very limited. This means that a person needs a constant supply of glucose from their blood for normal brain functioning. However, high blood glucose levels do not make the brain function even better. Both extended periods of elevated glucose levels (hyperglycemia) and very low glucose levels (hypoglycemia) are believed to contribute to the development of memory problems in people with diabetes.

The brain's high metabolic rate and the corresponding need for a constant supply of sugar from the bloodstream are required to fuel neurotransmission. Since learning and memory depend on neurotransmission taking place, any lapse in the system will affect the ability to learn and remember. Prolonged low or high blood glucose causes your hippocampus to malfunction biochemically, and the result is often impaired concentration and attention, memory loss, and slowing of information processing speed.