Iatrogenic hypoglycemia is the most frequent acute complication of insulin therapy in people with type 1 diabetes (T1DM). Recurrent hypoglycemic events initiate a process of habituation, characterized by suppression of hypoglycemic symptoms and lead to hypoglycemia unawareness, which in itself defines a particularly high risk of severe hypoglycemia. Recent evidence suggest a pivotal role for increased brain lactate transport capacity in the pathogenesis of hypoglycemia unawareness. However, there is uncertainty about the magnitude of this effect and whether such excess brain lactate is oxidizes as a glucose-sparing alternative energy source or acts as a metabolic regulator controlling brain glucose metabolism, oxygen consumption and cerebral blood flow.

Objective: The primary objective of this study is to investigate the effect of hypoglycemia on brain lactate accumulation and regional cerebral blood perfusion in humans. The secondary objective is to assess whether this effect is a related to hypoglycemia unawareness or a consequence of T1DM per se.

Hypothesis: The investigators hypothesize that hypoglycemia stimulates lactate transport over the blood-brain barrier leading to cerebral lactate accumulation and that this lactate accumulation is a function of prior hypoglycemic exposure frequency contributing to clinical hypoglycemia unawareness. Furthermore, the investigators expect that this effect of hypoglycemia on brain lactate accumulation is related to changes in cerebral blood flow (CBF).

Inclusion criteria for healthy subjects

• Age: 18-50 years
• Body-Mass Index: 18-30 kg/m2
• Blood pressure: <160/90 mmHg

Inclusion criteria T1DM patients with normal hypoglycemic awareness

• Diabetes duration ≥ 1 year
• Age: 18-50 years
• Body-Mass Index: 18-30 kg/m2
• HbA1c: 42-75 mmol/mol (6-9%)
• Outcome Clarke questionnaire: 0-1
• Blood pressure: <160/90 mmHg

Inclusion criteria T1DM patients with hypoglycemia unawareness

• Diabetes duration ≥ 1 year
• Age: 18-50 years
• Body-Mass Index: 18-30 kg/m2
• HbA1c: 42-75 mmol/mol (6-9%)
• Outcome Clarke questionnaire: >3
• Blood pressure: <160/90 mmHg

Exclusion criteria for healthy subjects

• Inability to provide informed consent
• Presence of any medical condition that might interfere with the study protocol, such as brain injuries, epilepsy, a major cardiovascular disease event or anxiety disorders
• Use of any medication, except for oral contraceptives
• MR(I) contraindications (pregnancy, severe claustrophobia, metal parts in body)

Exclusion criteria for all T1DM patients

• Inability to provide informed consent
• Presence of any other medical condition that might interfere with the study protocol, such as brain injuries, epilepsy, a major cardiovascular disease event, anxiety disorders, or complications of T1DM (including neuropathy and retinopathy)
• Use of any other medication than insulin, except for oral contraceptives or stable thyroxine supplementation therapy
• MR(I) contraindications (pregnancy, severe claustrophobia, metal parts in body)