Type 2 diabetes, essential hypertension, obesity, and hyperlipidemia are the major components of the metabolic syndrome. Understanding the psychophysiologic basis of the metabolic syndrome is important since its prevalence has been increasing dramatically over the last decade. In the past, type 2 diabetes was diagnosed almost exclusively in persons in their 40s or older. Health care providers are now reporting emergence of type 2 diabetes and the metabolic syndrome in individuals in their 30s and even their late 20s.1,2
This article outlines the psychophysiologic bases for components of the metabolic syndrome and reviews the application of biofeedback and other psychophysiologic interventions on the two components for which such interventions have been most studied—diabetes and essential hypertension.
ETIOLOGY OF METABOLIC SYNDROME: THE INTERSECTION OF BIOLOGY, LIFESTYLE, STRESS
The disorders that constitute the metabolic syndrome share several etiologic factors. First, genetic predisposition increases the risk for diabetes, hypertension, hyperlipidemia, and obesity.3,4 Second, patients’ own behaviors—their choice of activity or inactivity, their food preferences, and their appetite—lead to gradual loss of control over body weight, blood glucose, blood pressure, and lipid levels. Third, chronic stress and its coincident psychological burden contribute to the etiology of various components of the metabolic syndrome.5 As life events accumulate and individuals lose their ability to cope, the stress response system maintains a higher than optimal level of activation.5–8
Chronic stress affects multiple organ systems, including the two master systems—nervous and endocrine. The biologic effects of stress include disordered breathing, increased activation of the renin-angiotension system, vascular constriction, tachycardia, decreased heart rate variability, inflammation, and sleep disruption.9 The mechanisms involved in acute stress responses are purpose-driven and adaptive. In contrast, chronically activated stress response systems involving increased sympathetic activity, decreased parasympathetic activity, and release of stress hormones have serious deleterious effects.10 Psychobiologic systems fail to adapt, delay recovery, or become exhausted.11
Role of psychological factors
As summarized in a review by Goldbacher and Matthews, 12 psychological factors have been related to increased risk for the metabolic syndrome. Depression has probably been most studied in the settings of cardiovascular disease and diabetes, whereas the psychological states of anger, hostility, and anxiety have been identified as salient etiologic factors in hypertension. In particular, depressed mood has been linked to decreased heart rate variability during the stress response.13 Anxiety affects blood pressure and blood glucose in normal individuals as part of the adaptive stress response, and the effects of anxiety are exacerbated in persons with the metabolic syndrome.14
Importance of sleep
Sleep disruption is often ignored in discussions of the mind-body interface in hypertension and diabetes. However, Knutson and Van Cauter15 suggested that sleep quality and sleep length have important effects on leptin levels and risk for diabetes. Very short sleepers have stronger appetites, as a result of lower leptin concentrations, and are much more likely to be obese compared with long sleepers (≥ 10 hours). This indicates that sleep length and quality affect metabolism. With regard to hypertension, a very important reduction of blood pressure occurs during the night, and a lack of nighttime blood pressure “dipping” is one of the markers for sustained blood pressure elevation.16
Factors overlap and begin to affect self-care
In addition to the effects of stress on mood and anxiety, repeated necessary demands for adaptation have marked effects on self-care behavior. Patients who suffer from anxiety are less efficient in managing their time and may be distracted from monitoring blood glucose and blood pressure. Anxious people often turn to the use of high-calorie comfort foods to soothe themselves during stressful times. Alcohol may be chosen as a means of reducing worry and tension. Depressed people lack the energy needed to maintain medical regimens and tend to be poor adherents to treatment recommendations. They also may choose comfort foods and addictive substances instead of nutritious, high-quality food and drink.17
Both anxiety and depression affect sleep routines and efficiency. Anxious people have trouble getting to sleep and may wake up often during the night, while depressed individuals frequently wake up early and cannot get back to sleep. Additionally, psychological distress influences social behaviors. Overt depressive and anxious symptoms tend not to foster social interactions with family and friends. Lack of social support and a scarcity of personal resources eventually contribute to the risk for diabetes and hypertension.18,19
In short, the metabolic syndrome is most likely to emerge when there is a combination of genetic factors, chronic stress, negative emotion, and unhealthy habits. The application of psychophysiologic interventions to diabetes and hypertension is based on our understanding of the etiology of these disorders, particularly the roles of psychological distress and behavior on blood glucose and blood pressure.
BIOFEEDBACK IN TYPE 2 DIABETES
Diabetes is characterized by elevated blood glucose and resistance of cell membranes to insulin, such that glucose is impeded from crossing from the blood into the cells. Standard treatment consists of oral antihyperglycemic agents, exogenous insulin, diet, and exercise.20 Type 2 diabetes may be the most behaviorally demanding of all chronic illnesses because patients must take an active role in daily management. Typical requirements are to measure blood glucose and take oral medicine, perhaps along with insulin, as well as to exercise, monitor diet, and adjust calories depending on activity level.
Therapy goals and a sampling of evidence
The goal of psychophysiologic therapy is not to replace standard treatment with relaxation training or biofeedback but rather to use biofeedback-assisted relaxation therapy to improve control of blood glucose. For example, McGinnis and colleagues compared the effects of 10 sessions of biofeedback (both surface electromyography and thermal feedback) and relaxation therapy versus three sessions of education in a sample of 30 patients with type 2 diabetes.21 No medicines were changed unless medically necessary. Patients kept daily logs of blood glucose, and had their hemoglobin A1c measured before and after treatment. Significant between-group differences in hemoglobin A1c and average blood glucose emerged in favor of the biofeedback group.21 However, patients with high scores on the Beck Depression Inventory22 (indicating more severe depressive symptoms) tended to drop out of the study or did not do as well as patients who were not symptomatic.
Another application of biofeedback in type 2 diabetes has been demonstrated by Rice and Schindler23 and Fiero et al.24 These investigators showed that patients with peripheral neuropathy, a common long-term complication of diabetes, were able to warm their hands and feet with the use of thermal biofeedback. Increased peripheral blood flow mediated the decrease in neuropathic pain.
Possible mechanisms of biofeedback in diabetes
Several explanations can be suggested to account for the results of biofeedback on blood glucose levels. Forehead muscle tension feedback (surface electromyography) helps patients to reduce facial tension and relax skeletal muscles, while increased finger temperature is an indicator of general relaxation. In the patients who completed the above study by McGinnis et al,21 both depression and anxiety scores decreased, which suggests a psychological mechanism for blood glucose reduction. Patients also reported improved sleep duration and quality with the use of relaxation therapy at bedtime.