Glycaemic thresholds for hypoglycaemic symptoms, impairment of cognitive function, and release of counterregulatory hormones in subjects with functional hypoglycaemia

Glycaemic thresholds for counterregulatory hormone and symptom responses to hypoglycaemia in people with and without type 1 diabetes: a systematic review

AIM/HYPOTHESIS

The physiological counterregulatory response to hypoglycaemia is reported to be organised hierarchically, with hormone responses usually preceding symptomatic awareness and autonomic responses preceding neuroglycopenic responses. To compare thresholds for activation of these responses more accurately between people with or without type 1 diabetes, we performed a systematic review on stepped hyperinsulinaemic-hypoglycaemic glucose clamps.

METHODS

A literature search in PubMed and EMBASE was conducted. We included articles published between 1980 and 2018 involving hyperinsulinaemic stepped hypoglycaemic glucose clamps among people with or without type 1 diabetes. Key exclusion criteria were as follows: data were previously published; other patient population; a clamp not the primary intervention; and an inadequate clamp description. Glycaemic thresholds for counterregulatory hormone and/or symptom responses to hypoglycaemia were estimated and compared using generalised logrank test for interval-censored data, where the intervals were either extracted directly or calculated from the data provided by the study. A glycaemic threshold was defined as the glucose level at which the response exceeded the 95% CI of the mean baseline measurement or euglycaemic control clamp. Because of the use of interval-censored data, we described thresholds using median and IQR.

RESULTS

A total of 63 articles were included, whereof 37 papers included participants with type 1 diabetes (n=559; 67.4% male sex, aged 32.7±10.2 years, BMI 23.8±1.4 kg/m²) and 51 papers included participants without diabetes (n=733; 72.4% male sex, aged 31.1±9.2 years, BMI 23.6±1.1 kg/m²). Compared with non-diabetic control individuals, in people with type 1 diabetes, the median (IQR) glycaemic thresholds for adrenaline (3.8 [3.2-4.2] vs 3.4 [2.8-3.9 mmol/l]), noradrenaline (3.2 [3.2-3.7] vs 3.0 [2.8-3.1] mmol/l), cortisol (3.5 [3.2-4.2]) vs 2.8 [2.8-3.4] mmol/l) and growth hormone (3.8 [3.3-3.8] vs. 3.2 [3.0-3.3] mmol/l) all occurred at lower glucose levels in people with diabetes than in those without diabetes (all p≤0.01). Similarly, although both autonomic (median [IQR] 3.4 [3.4-3.4] vs 3.0 [2.8-3.4] mmol/l) and neuroglycopenic (median [IQR] 3.4 [2.8-N/A] vs 3.0 [3.0-3.1] mmol/l) symptom responses were elicited at lower glucose levels in people with type 1 diabetes, the thresholds for autonomic and neuroglycopenic symptoms did not differ for each individual subgroup.

CONCLUSIONS/INTERPRETATION

People with type 1 diabetes have glycaemic thresholds for counterregulatory hormone and symptom responses at lower glucose levels than people without diabetes. Autonomic and neuroglycopenic symptoms responses are generated at about similar levels of hypoglycaemia. There was a considerable variation in the methodology of the articles and the high insulin doses in most of the clamps may affect the counterregulatory responses.

FUNDING

This article has received funding from the Innovative Medicines Initiative 2 Joint Undertaking (JU) under grant agreement no. 777460.

REGISTRATION

This systematic review is registered in PROSPERO (CRD42019120083).

Hypoglycemic symptoms in the absence of diabetes: Pilot evidence of clinical hypoglycemia in young women

Aims

Clinical visits of non-diabetic patients reporting hypoglycemic symptoms are common in endocrinology practices, but remain understudied and lack clinical definition and evidence-based recommendations for diagnosis or treatment. Our goal was to pilot test the concordance of hypoglycemic symptoms with low glucose values in young non-diabetic individuals.

Methods

We recruited eight individuals who reported regularly experiencing symptoms consistent with hypoglycemia to wear a blinded Dexcom continuous glucose monitor and report symptoms for seven days. We excluded individuals with diabetes or other known causes of hypoglycemia or similar symptoms.

Results

Participants were all women with an average age of 29 years. 25% were African American and 25% had obesity. All participants experienced glucose values ≤ 70 mg/dL and half (4/8) experienced glucose ≤ 54 mg/dL for at least 15 min or 3 consecutive readings. Average time between last meal and reported symptoms was 4.4 h. Lower glucose values were significantly associated with higher odds of experiencing hypoglycemic symptoms 1.15 (CI: 1.07-1.24) for every -5mg/dL, (p < 0.001) from mixed effects models for repeated measures adjusted for age, race, and body mass index. All participants also reported engaging in potentially obesogenic behaviors in order to avoid symptoms.

Conclusions

Individuals with hypoglycemic symptoms in the absence of diabetes experience clinical hypoglycemia, indicating the need to understand the etiology, behavioral responses, and other health risks that might be associated with this understudied condition.

Cortisol response to individualised graded insulin infusions: a reproducible biomarker for CNS compounds inhibiting HPA activation

AIM

To determine the potential of cortisol secretion, in response to a physiological stressor, as a biomarker for centrally active compounds targeting the hypothalamic-pituitary-adrenocortical (HPA) axis.

METHODS

Cortisol response to hypoglycaemia was measured in 26 healthy males in two stages: firstly to derive an algorithm for individualized, graded insulin infusion rates to achieve defined hypoglycaemic targets over 3 h and secondly to determine the inter- and intra-subject variability of cortisol response to hypoglycaemia over two identical periods by measuring the maximum (t(max) ), time to maximum (C(max) ) response and cortisol area under the response curve (AUC).

RESULTS

Hypoglycaemia induced a consistent cortisol response starting at approximately 1 h, corresponding to blood glucose concentrations of approximately 3.3 mmol l⁻¹, and peaking approximately 3 h after the start of infusion. The inter- and intra-subject coefficients of variation (CVs) of cortisol response were approximately 19 and 19% (AUC), 15 and 19 % (C(max) ) and 10 and 14% (t(max) ), respectively. The intra-subject CVs for the ratio of maximum cortisol response to baseline concentration and rate of initial cortisol response between study days were more variable (32.8% and 59.0%, respectively). The blood glucose-cortisol response model derived from the study was predictive of the individual observed cortisol responses, and estimated a blood glucose EC(50) associated with onset of the cortisol response of 3.3 mmol l⁻¹.

CONCLUSIONS

Gradual hypoglycaemia is an effective, reproducible and well-tolerated method of stimulating a cortisol response and may therefore be useful in assessing the neuroendocrine response to HPA axis inhibitors, such as corticotropin-releasing hormone-1 (CRH-1) antagonists.

Interstitial glucose profile associated with symptoms attributed to hypoglycemia by otherwise healthy women

BACKGROUND

Reports of postprandial symptoms attributed to hypoglycemia by otherwise healthy individuals appear to be relatively common in UK women. Whether these symptoms are related to blood glucose is a contentious issue, which periodic ambulatory blood glucose measurement has failed to resolve.

OBJECTIVE

The authors investigated, using continuous glucose monitoring technology, whether postprandial symptoms are associated with interstitial glucose concentrations (IG) in the hypoglycemic range or with a previous fall in IG.

DESIGN

Thirty healthy nonobese women (age 20-48 y) who reported symptoms attributable to hypoglycemia and 20 nonsymptomatic controls wore a subcutaneous probe in abdominal fat for 4-7 d (median: 5 d) and kept a diet and activity diary during this time.

RESULTS

Twenty women reported postprandial symptoms; 41 episodes were recorded. When symptomatic, IG was < or =3.3 mmol/L in 5% of cases. A significant fall in IG over the preceding 60 min was observed before autonomic symptoms (P < 0.005). The proportion of total energy intake derived from dietary fat in the symptomatic group was higher than that in the controls (P < 0.05). The proportion of total sugars was similar between groups; however, the meal preceding symptoms had a higher percentage of energy derived from total sugars when compared with the individuals' diet over the study period (P < 0.05).

CONCLUSIONS

Most symptoms attributable to hypoglycemia were not associated with an IG concentration in the hypoglycemic range. A previous fall in IG may be implicated in the etiology of autonomic symptoms, with the consumption of meals high in sugars potentially playing a role in symptom initiation.

Macronutrients and mental performance

There is currently intense interest in the effects of macronutrients on psychological states, mental performance, and well-being. A strong theoretical perspective has guided work on carbohydrates and their relation to brain serotoninergic function with concomitant effects on performance. The clearest and most reliable effects have been observed for the beneficial action of glucose on cognitive performance, supported by investigations of hypoglycemia, which is associated with general impairment of cognitive performance. The effects of complex carbohydrates are less distinct and change with time of day; e.g., carbohydrate at breakfast tends to improve morning performance. However, these studies are rarely decisive. Far fewer experiments have been performed on protein and fat, and it is difficult to draw any firm conclusions. Macronutrients are seldom given alone, proportions of protein and fat differ greatly between studies, and comparisons are frequently performed with no food at all. Food intake may mitigate the effects of low doses but not of high doses of alcohol on performance. Effects of macronutrients on cognitive performance may be dependent on their effects on glucose metabolism, metabolic activation, or serotonin. Other factors that modify effects include time of day, circadian rhythms, type of task, habitual diet, and vulnerability of the population.

The supply of glucose to the brain and cognitive functioning

Unlike other organs the energy requirement of the brain is met almost exclusively by aerobic glucose degradation (Siesjo, 1978). The energy requirement of the brain is 20–30% of the whole organism at rest, although its weight is only 2%. The energy stores in the brain are extremely small when compared with the high rate of glucose utilisation: thus the brain is reliant on a continuous glucose supply. Only about 30% of glucose is required for direct energy production; much of the remainder is used for the synthesis of amino acids, peptides, lipids and nucleic acids (Siebert, Gessner & Klasser, 1986). Thus a source of glucose is essential for the synthesis of physiologically active amines such as serotonin, noradrenaline and acetylcholine. Although it is well accepted that hypoglycaemia can result in the disruption of cognitive functioning, this is a rare phenomenon and it has usually been assumed that levels of blood glucose, within the normal range, do not influence intellectual functioning. This assumption is discussed in this paper.

Hypoglycaemia in the adult

Hypoglycaemia is a relatively common cause for referral of patients to the accident and emergency departments of hospitals but most of it is iatrogenic. Occasionally, however, hypoglycaemia is due to any one of up to a hundred different disorders. In some, hypoglycaemia is the cause of intermittent neuroglycopenic symptoms that lead to their referral to medical outpatients for investigation. Only the most important are discussed here. Hyperinsulinism due to abnormal beta-cell function is an uncommon but important cause of spontaneous hypoglycaemia. The diagnosis is suspected from the history of episodes of altered consciousness confirmed by demonstrating raised plasma insulin, C-peptide and proinsulin levels in peripheral blood in the presence of hypoglycaemia. Differentiation of the various causes of endogenous hyperinsulinism before surgery is difficult if not impossible and the low predictive value of most of the localizing techniques that are available makes them an additional and unnecessary cost, producing little clinical benefit. Hypoglycaemia caused by non-islet cell tumours (NICTH) is seemingly rarer than hyperinsulinism from insulinoma and tends to occur in older patients. The clinical features are similar to those of hyperinsulinism but laboratory investigation reveals appropriately depressed plasma insulin, C-peptide and proinsulin levels in the presence of hypoglycaemia. The plasma IGF-II:IGF-I ratio is characteristically high and the concentration of the E-domain of proIGF-II is raised. Autoimmune hypoglycaemia is more common in some countries than others and is most often due to autoantibodies to insulin (AIS). It may also be caused by autoantibodies to the insulin receptor and possibly to autoantibodies that are stimulatory to pancreatic beta-cells. Contrary to popular belief, idiopathic reactive hypoglycaemia is rare and only one of the possible causes of the postprandial syndrome. It is characterized by a low blood glucose concentration in blood collected during a spontaneous symptomatic episode but not at other times. Its cause is unknown. Other causes of hypoglycaemia include endocrinopathies of various kinds; sepsis including malaria; congestive cardiac failure; hepatic and renal insufficiencies; diverse inborn errors of metabolism; and exogenous toxins, of which alcohol is probably the commonest.

Reproducibility of glycaemic thresholds for activation of counterregulatory hormones and hypoglycaemic symptoms in healthy subjects

Nine healthy subjects were studied on two separate occasions, at least two weeks apart, using the glucose clamp technique to produce a gradual hypoglycaemia. Glucose thresholds for neuroendocrine and symptom responses varied up to 1.5 mmol/l between subjects. There was a significant correlation between individual glucose thresholds on day 1 and 2 for adrenaline (p = 0.0008), growth hormone (p = 0.007) and pancreatic polypeptide (p = 0.02), and for autonomic (p = 0.018) and neuroglycopoenic (p = 0.023) symptoms, whereas no significant correlations were found for glucagon and cortisol. The mean intra-individual differences in glucose thresholds between day 1 and 2 were 0.22 mmol/l for the hormones and 0.25 mmol/l for the symptoms. We conclude that healthy subjects differ in hypoglycaemic thresholds, and that the difference reflects individual variation.