The most prominent and consistent finding across the literature was the correlation between high glycemia and poor inhibition. This theme is defined as the effect of glycemia on inhibitory performance. More specifically, the findings indicate that hypoglycemia and hyperglycemia have a significant impact on inhibition. For example, (13, p. 14) state that “… these results may suggest that complications of chronic hyperglycaemia, not HbA_1c alone, are related to inhibition difficulties in T1DM.” Therefore, these findings suggest that it is not merely a high level of glycemia that results in difficulties with inhibition, but the complications that arise because of hyperglycemia. Hyperglycemia may result in neuropathy (nerve damage) and microvascular complications, thereby affecting neurons within the brain (47). Broadley et al. (13) found that lower performance related to background retinopathy, a consequence of hyperglycemia, may also have an effect on inhibition, leading to lowered inhibition performance.

Lower inhibition performance was further correlated with hypoglycemia in Broadley et al. (13), Duke et al. (20), Graveling et al. (38), Ohmann et al. (42), Strachan et al. (43), and Rovet and Alvarez (44). These articles indicated that inhibition may be affected by the low blood sugar levels of an individual. For example, Strachan et al. (43) found that individuals who experienced hypoglycemia performed poorly on the Stroop task: “demonstrated that performance on the DS and Stroop Task was poorer in the hypo subjects at all three time points (p < 0.05)”. What was of interest in the study of Rovet and Alvarez (44) was that they found that individuals with a history of seizures due to hypoglycemia were reported to experience lower inhibition. An explanation for such a correlation was not provided and remains open for speculation. Povroznik et al. (48) state that a stroke can lead to reduced blood flow and glucose supply to the brain, resulting in impairments. A stroke can also lead to metabolic stress and the death of brain cells, which may offer an explanation for the long-term effects of stroke in affected individuals (48). Research conducted regarding strokes and inhibition has found that, post stroke, individuals often experience various inhibition difficulties (49–51).

It has, however, become evident that the experience of hypo- or hyperglycemia has an impact on the inhibition performance of an individual living with T1DM. Duke et al. (20), for example, report a significant correlation between glycemia and inhibition, and Rovet and Alvarez (44) specifically highlight that hyperglycemia has a significant effect on the inhibition performance of individuals. These findings substantiate the effect that hypo- and hyperglycemia may have on individuals living with T1DM. Possible explanations for this effect, however, are rarely found in the literature. One possible explanation is the brain’s dependence on a continuous and consistent supply of glucose, which is adversely affected by fluctuations in the supply of glucose caused by hypo- or hyperglycemia (13).

The second subtheme that emerged is that the age at which an individual begins to experience symptoms of T1DM influences their inhibition performance. Luczynski et al. (2019) found that inhibition was lower in adolescents with T1DM than in control group participants, whereas Rovet and Alvarez (44) found lower inhibition only in children. (13, p 16) found that lower inhibition was associated with early-onset diabetes (EOD): “Specifically, preliminary evidence suggests that EOD … may be associated with lower inhibition”. Another example of this subtheme is found in (13, p. 13): “Taken together, this evidence suggests that those with EOD (relative to late-onset diabetes (LOD)) may experience greater inhibition difficulties”. These findings are of importance when considering the neurodevelopmental level of children and adolescents. Inhibition and other executive functions have been found to be located within the prefrontal cortex of the brain (52). The prefrontal cortex, from a developmental perspective, only starts to develop in early childhood to early adolescence until fully developed in early adulthood (53). Thus, children and adolescents are not able to fully utilize the ability to inhibit responses or to exert interference control. Children and adolescents are subsequently more likely to engage in risk-taking behavior (54). Risk-taking behavior in children and adolescents living with T1DM may involve not checking glycemia, missing meals, or forgetting to administer insulin.

The lack of prefrontal cortex development in children and adolescents may offer an explanation as to why early-onset diabetes can have a significant effect on their inhibition performance. One may argue that because inhibition is not yet fully developed, performance will be lower, and despite the developmental evidence that children and adolescents will not have the full capacity to utilize inhibition: when compared to control group participants, inhibition was consistently lower in children and adolescents living with T1DM than in their control group peers.

One of the main subthemes that arose was that individuals living with T1DM were reported to have, in general, lowered inhibition. This theme is, therefore, simply defined as the impact of T1DM on inhibition performance, without reference to specific factors. The findings and discussion of the scientific literature failed to report what specific factor of T1DM led to lowered inhibition performance. The focus of these studies was to determine the relationship between executive functioning and T1DM. Due to inhibition being a subscale on the assessments and measurements used, authors briefly depicted the lowered inhibition scores when compared with control group participants. The results of these studies indicated that individuals with T1DM had lower inhibition scores when compared to control group participants. Despite the ambiguous nature of these results, this finding is an important factor in this critical review, as it points to the fact that aspects of T1DM contribute to lower inhibition. More importantly, it seems that an aspect of T1DM, such as glycemia, does not affect inhibition independently. It is rather multiple factors that are interacting with one another. The general impact further indicates that despite adequate control regarding T1DM, the effects on inhibition are still evident, as other factors also play a vital role (13). These other factors, however, remain unknown and, therefore, require more specific exploration. Foland-Ross et al. (14)Graveling et al. (38), and Łuczyński et al. (41) obtained similar findings, in that a small difference in inhibition was identified in those living with T1DM. Ohmann et al. (42) specifically highlight that a general impairment in inhibition was found in the Stroop Task results of participants living with T1DM.

During the analysis, two studies found that T1DM may have an impact on certain structures or brain regions that are responsible for inhibition. Caruso et al. (19) state that the brain regions that are affected by T1DM are the prefrontal cortex and the limbic system. The reason why these structures are affected, according to Caruso et al. (19), is that these brain regions have an increased density of insulin receptors. Therefore, these brain regions are sensitive to glycemia and, as a result, fluctuating glycemia may have an adverse effect on these regions. 44, p. 807) highlight that the dorsolateral prefrontal and motor cortices are related to the poorer inhibitory function of the individual, as diabetes adversely affects these structures within the brain: “… whereas response inhibition is thought to involve the dorsolateral prefrontal and motor cortices”. The adverse effects of T1DM on the brain in general, but also on the specific regions mentioned above, are corroborated by the findings of Russo et al. (55; Kern et al. (56); Page et al. (57)Mortby et al. (58), and Rosenthal et al. (59). These findings have clinical implications when one considers the fact that inhibition has started to develop in childhood and continues to develop in adolescence. According to Liu et al. (60), the development of inhibition relies on the functional maturation of the frontal lobe; prefrontal cortex changes that occur during development result in the development of inhibition (60). However, the literature indicates that T1DM affects the development of this brain region, thus influencing the development of inhibition. In the case of early-onset diabetes in children, fluctuating glycemia may have an adverse effect not only on the utilization of inhibition but also on the development thereof.

What is of interest to note is that Rovet and Alvarez (44), as briefly mentioned before, found that a history of seizures adversely affects the performance of inhibition. This finding was specific to seizures that were induced by hypoglycemia, “… whereas a history of hypoglycemia-induced seizures was associated with poorer inhibit“ (44, p. 807). This was of specific relevance in children: “… showed that children with a positive seizure history were less likely to inhibit a response before adequately processing information about the second stimulus…” (44, p. 807). As a result, these findings indicate that there is a direct association between the impact of T1DM on neurological development, structure, and function, and inhibition.

The first subtheme can be defined as the difficulty among individuals living with T1DM of inhibiting, stopping, or controlling impulsive behaviors or decisions. During the analysis, it became evident that individuals who live with T1DM often find it difficult to control impulses, as there is a significant correlation with poor control over self-management behaviors, such as control of glycemia. Broadley et al. (13) highlight that one of the functional impairments that occurred in inhibition resulted in poor impulse control and at-risk behavior. These findings are in accordance with the research of (62), who state that lower impulse control may lead individuals to pursue gratification, regardless of goals. Furthermore, impulse control, specifically the management thereof, has often been associated with T1DM, and is most strongly correlated with the ability to control one’s impulses, leading to better health outcomes related to T1DM (20). Considering that inhibition is the ability to override planned or initiated response, it becomes more apparent why it plays such a significant role in controlling impulses in order to facilitate goal-directed behavior. Łuczyński et al. (41) note that inhibition plays an important role in the setting and achievement of goals as it relates to health outcomes. These findings of the relationship between inhibition and impulse control are corroborated by Bari and Robbins (63), (64), and Roberts et al. (65).

The study of Rovet and Alvarez (44) found that hyperglycemia contributes to poor impulse control. Therefore, an individual with poor glycemic control may have difficulty in inhibiting impulses (39). Hanna et al. (40) found that better glycemic control was significantly correlated with impulse control, in which inhibition plays a significant role. Therefore, poor inhibition increases the possibility of impulsive behavior, in turn leading to poor management of T1DM. It is important to become aware of the vicious cycle that arises when considering the effect of T1DM on inhibition and in turn poor inhibition on behavioral management, which ultimately, again, results in hyperglycemia, for example.

The subtheme behavioral control is defined as the ability to inhibit, regulate, control, or perform certain behaviors that may influence T1DM management. Within the findings of this review, the scientific literature indicates that inhibition is strongly correlated with behavior regulation (39). Miller et al. (22) report that behavior regulation was a significant predictor of the quality of self-management behavior. (22, p. 23) conclude by highlighting the importance of moderating behavior: “… thus should be included in the final conditional model investigating how changes in behavioral regulation influence changes in diabetes self-management.” Hanna et al. (40) highlight the importance of behavior with regard to daily routine. Specific behaviors that have been associated with high inhibition and the adequate management of T1DM are seen in Duke et al. (20), who highlight the following: (1) not guessing doses; (2) not leaving home without sufficient goods and supplies; (3) not skipping glycemia checks; (4) good meal planning; and (5) making good choices in accordance with their treatment plan. Poor inhibition may as a result lead to an inability to perform, or a neglect of, the above-mentioned behaviors, in turn resulting in poor management of T1DM. Duke et al. (20) and Hamburger et al (39) support this finding, in that inhibition facilitates behavioral management and is a necessary component of treatment adherence. Treatment and management plan adherence is also a significant factor that has been correlated with behavioral control that is most prominently affected by inhibition.

Related to adherence in T1DM are the findings of Hamburger et al (39), who states that emotional control plays a significant role in the management of diabetes. Łuczyński et al. (41) report that the management of diabetes is influenced by one specific psychosocial factor, i.e., emotional control. Therefore, the ability to manage and control one’s emotions seems to contribute to the ability of an individual living with T1DM to exercise adequate management of the condition.

Inhibition has also been correlated with the ability to control emotions; for example, Caruso et al. (19) found that inhibition was significantly related to the emotional subscales in their study. This is of considerable relevance when one considers that in theme 1 it was reported that the limbic system is affected by fluctuations in glycemia. As a result, T1DM may affect an individual’s ability to utilize inhibition to control emotions, resulting in poor self-management.