Most people with insulin dependent diabetes have experienced the slipping, sliding loss of control and reason. A few units of insulin too many – an accidental overdose – can trigger a hypoglycemic episode.
These experiences vary from person to person. In the case of Mike Hoskins, who lives with Type 1 diabetes, it can get pretty bad. Aliens invade. Conspiracy theories march through his mind. His wife wakes up at the middle of the night at risk of physical violence, because once his levels sink below 40, Mike bites, hits, and scratches. When he turns violent, they have a plan of action.
“My wife, she’s smaller than I am. So we have a standing rule when I get uncooperative or even violent, she’ll call the paramedics.”
Fortunately, this hasn’t happened in a few years, because Mike uses a continuous glucose monitor to alert him of dangerous lows.
Hallucinations and aggressive violence are not part of everyone’s reaction to a dangerously low blood sugar. I, for example, tend to fall mute and still, paralyzed by confusion. Anyone who has experienced severe hypoglycemia knows the powerful effects of the condition.
But is severe hypoglycemia the only cause of aggressive behavior related to diabetes? Several recent scientific studies have examined aggressive behavior and propose more facets to the relationship between blood sugar, exertion of self-control, and aggression. Some research even suggests that due to problems metabolizing glucose, people with diabetes are more prone to aggressive behavior and violent crime, including murder, rape, and robbery.
Self-Control: A Finite Resource
The most recent study of the relationship between blood sugar and aggression, published earlier this year, “Low glucose relates to greater aggression in married couples,” received a flurry of media attention, in part because the study authors included the trendy word “hangry” in their findings. The team of researchers wrote in the Proceedings of the National Academy of Sciences that individuals, with or without diabetes, are more prone to aggressive behavior when their blood sugar levels are lower than usual.
The study, which I’ll refer to as “Low glucose relates to aggression,” cites to a growing body of research that attributes aggressive behavior to low self-control in its explanation of why the connection between blood sugar levels and aggressive behavior might exist. Previous studies have shown that the exertion of self-control requires energy from glucose and that each person’s reserve of the required energy is limited in the short term.
As stated in the study, “Self-control requires a lot of brain food in the form of glucose.” The implication is that once you use self-control to modify your behavior, you will be less able to use self-control until your store of energy – your “brain food” – has been replenished.
The researchers conclude that “the healthy metabolism of glucose may contribute to more peaceful homes by providing couples a boost to their self-control energy.” Finally, they suggest that intimate partner violence can be reduced through ensuring healthy metabolism of glucose.
Diabetes, Self-Control, Aggression, and Violent Crime
The researchers point out that the study does not take into account the effects of diseases that interfere with glucose metabolism, such as diabetes, and suggest that future work may consider the possibility that diabetes could contribute to intimate partner violence.
In support of this hypothesis, the researchers reference a study published in 2011 in the journal Aggressive Behavior, “Sweetened Blood Cools Hot Tempers: Physiological Self-Control and Aggression” that observes a propensity toward violent crime among people with diabetes. This finding was based on the positive correlation that exists in U.S. states between violent crime and diabetes. The correlation held true even when controlled for income, meaning that the phenomenon cannot be attributed entirely to socioeconomic status.
It is important to note that “Sweetened Blood” does not present direct evidence that diabetes in any way causes violent crime. It only shows that U.S. states with high rates of diabetes also have high rates of violent crime and that poverty is not the direct cause. It also does not mention or consider the possibility that other conditions relatively common among people with diabetes, such as depression, may be related to the positive correlation between rates of diabetes and violent crimes.
As part of “Sweetened Blood,” the researchers also show a relationship between diabetic status (defined in the study by the severity of symptoms) and aggressive behavior. In a laboratory setting, people with more severe diabetic symptoms tend to exhibit more aggressive behavior. The researchers attribute this finding to decreased self-control, based on the premise that “glucose is brain food for self-control” and that diabetes interferes with glucose metabolism.
The Brain’s Glucose Transporters and Diabetes
Indeed, there are absolutely times when people with diabetes cannot control their behavior due to low blood sugar and may be consequently prone to aggression. Insulin-induced hypoglycemia, as described above in Mike’s scenario, occurs when a person injects too much insulin, which plunges blood sugars to dangerously low levels. In this situation, there is no glucose available, and the brain, requiring glucose to function, enters a crisis mode.
However, the authors of “Sweetened Blood” do not attribute their findings to insulin-induced hypoglycemia, nor was this condition a contributing factor in the laboratory experiments. Instead, they state that impaired glucose metabolism in diabetes causes insufficient glucose to be available to the brain. I will argue that this claim is flawed and undermines the validity of their findings.
The researchers state the following in the study’s abstract:
“… problems with the use of glucose (e.g. hypoglycemia, diabetes) have been linked to numerous signs of poor self-control, including eating fatty and sugary substances over a long period of time … Self-control is also impaired by inadequate levels of brain glycogen … a metabolite that provides energy for sustained effortful exertion. Thus, low glucose and problems metabolizing glucose into glycogen reduce self-control [my emphasis].”
In fact, regardless of whether low self-control contributes to consuming an unhealthy diet, diabetes does not deprive the brain of glucose. To the contrary, most diabetics are full of syrupy-sweet blood, and the brain has ready access to this glucose.
This is because while diabetes does lead to problems metabolizing glucose, only certain glucose transporters in the body are affected. For example, while insulin (which all Type 1 and some Type 2 diabetics lack) is needed to bring glucose into muscle, liver, and fat cells, glucose transporters in the brain do not depend on insulin and therefore should be influenced neither by impaired insulin secretion (among Type 1 diabetics) nor impaired insulin signaling (among Type 2 diabetics).
For this reason, for an individual with diabetes experiencing chronically high blood sugar, deprivation of glucose to the brain is unlikely – less likely, in fact, than among the general population – except in the case of an overdose of medication, leading to the insulin-induced hypoglycemia described above.
In their discussion of the “Sweetened Blood,” the researchers write the following.
“As expected, diabetic status was positively correlated with aggressiveness … [g]lucose is brain food for self-control, and people who have difficulty metabolizing glucose also have difficulty controlling their aggressive impulses.”
This reasoning does not align with the process by which the brain obtains glucose as described above. Given that the brain glucose transporters are not insulin dependent, they should have no trouble transporting sufficient glucose from the blood stream to the brain.
Hypoglycemia-induced violence and other erratic behavior is a real concern among people with diabetes and the people in their lives. It is important to have glucose on hand at all times for such emergencies, and a set plan for when to call an ambulance. Just ask Mike Hoskins or his wife.
If an aspect of living with diabetes aside from insulin-induced hypoglycemia makes a person more likely to commit violent crimes, it would be important to identify this phenomenon and develop strategies to manage it. But contrary to the suggestions of recent articles in the media and peer-reviewed scientific literature, evidence supporting the notion that impaired glucose metabolism leads to violent crime among diabetics does not currently exist.