What happens during a low?

Daniel Sher discusses the psychological perspective behind what happens during a low: what happens in the brain and how are people with diabetes affected psychologically and behaviourally?

Low blood-glucose levels, or hypoglycaemia, is the most common side effect of insulin. Insulin use, as you probably know, is a life-saving treatment for people living with diabetes, especially people with Type 1 diabetes. People with Type 1 and Type 2 diabetes are at risk of low blood glucose.

How is the brain affected?

The brain, unlike other organs, doesn’t store glycogen. This means that the brain doesn’t have its own energy supply. Rather, the brain depends on glucose in the blood for fuel. In other words, when blood glucose levels drop, the brain is essentially being starved of energy and oxygen.

When blood glucose drops, the hypothalamus and brain stem sense the low, triggering a counter-regulatory response in the brain. The brain’s fight-or-flight system is activated; adrenaline and stress hormones (cortisol) are released. The liver is signalled to increase supply of glucose into the bloodstream and you suddenly find yourself feeling intensely hungry.

How is cognition (thinking) affected?

Research shows that multiple aspects of thinking become impaired during a low. In particular, the functioning of the frontal lobes is affected, with negative effects on multi-tasking and complex thinking/ problem solving. Processing speed and concentration also tend to be negatively affected.

This means that during a hypo, it’ incredibly difficult to perform any task that requires complex thinking. Fortunately, these effects are temporary. Importantly, though: research shows that these symptoms can persist for up to 75 minutes even after your blood glucose has come back to normal.

Please take a moment to let that sink in: the cognitive effects of a low can last for long after the low has been treated. How might this impact on a student writing an exam, a surgeon in the operating theatre or a teacher trying to teach a lesson?

We also know that the hippocampus, which is the brain’s memory centre, is vulnerable to low blood glucose. This means that studying during a low may well be a significant waste of time and energy. Rather use that time to fold your laundry and tidy your desk and return to your studies when your brain has the fuel it needs to learn and analyse.

Low blood glucose and anxiety

Sweaty palms. Heart palpitations. Dry mouth. Fear and irritability. Headache. Confusion. Trembling. A feeling of impending doom. Are these symptoms of anxiety or low blood glucose? Ultimately, these symptoms can be caused by both: there is a huge  overlap between hypoglycaemia and anxiety.

Why is anxiety such a common side effect of low blood-glucose? We have already discussed how the brain compensates for lows: the fight-or-flight response gets triggered, with adrenaline and cortisol being released. The side effect of all this is an anxiety response. Biology aside, lows are psychologically scary and uncomfortable and can be anxiety-provoking for this reason.

If you have ever been diagnosed with an anxiety disorder, though (such as generalised anxiety disorder or panic disorder), lows can represent a significant trigger that can set-off a course of other anxiety symptoms. For some people, the anxiety is there more often than not, which leads some to consistently run their glucose high to avoid the risk of lows. This is referred to in the literature as hypoglycaemia phobia and it’s a form of anxiety disorder that is specific to people with diabetes.

The extreme risks: coma, death and brain damage

This is not a pleasant topic to have to breach, but we need to be aware that bad hypos can take lives. A  study  of adults with Type 1, aged between 20 and 49 years, showed that 18% of male and 6% of female deaths happened due to hypoglycaemia.

Severe lows can also lead to longer term brain damage in certain cases, although fortunately the brain is fairly good at recovering from these events in most people. In children below the age of five years, however, the brain may be more vulnerable and, in these cases, severe lows with seizures can be associated with longer term brain damage.

Ending on a high note

Lows are inevitable: they happen as a result of exercise and insulin, factors which people who have diabetes need to thrive. However, the fear and trauma that surrounds this experience is significant for many people. It’s important to remember that bad lows can be avoided, through good planning, awareness and blood-glucose management.

References

 Graveling, A. J., & Frier, B. M. (2009). Hypoglycaemia: an overview. Primary Care Diabetes,

3(3), 131-139.

 Languren, G., Montiel, T., Julio-Amilpas, A., & Massieu, L. (2013). Neuronal damage and cognitive impairment associated with hypoglycemia: an integrated view. Neurochemistry international, 63(4), 331-343.

Laing, S. P., Swerdlow, A. J., Slater, S. D., Botha, J. L., Burden, A. C., Waugh, N. R., … & Keen, H. (1999). The British Diabetic Association Cohort Study, II: cause‐specific mortality in patients with insulin‐treated diabetes mellitus. Diabetic medicine, 16(6), 466-471.

 McNay, E. C., & Cotero, V. E. (2010). Mini-review: impact of recurrent hypoglycemia on cognitive and brain function. Physiology & behavior, 100(3), 234-238.

 McNay, E. (2015). Recurrent hypoglycemia increases anxiety and amygdala norepinephrine release during subsequent hypoglycemia. Frontiers in endocrinology, 6, 175.

 Page, S., Raut, S., & Al-Ahmad, A. (2019). Oxygen-glucose deprivation/reoxygenation-induced barrier disruption at the human blood–brain barrier is partially mediated through the HIF-1 pathway. Neuromolecular medicine, 21, 414-431.