Written by Mariya Bershad and Laurel Mayer, MD.
Day in and day out, signals from our brain tell us when to eat, doze off, stress out and even feel butterflies. Many of these signals can be attributed to hormones—chemical messengers that travel through the bloodstream and communicate with the rest of the body by interacting with specific receptors.
Hormones influence the way our bodies function, as well as our thoughts, feelings, and actions—however, they are themselves responsive to our behavior and environment. What results is this complex system in which our brain, body, and behavior are constantly interacting.
It is, therefore, no surprise that scientists are interested in studying the role of hormones in a disorder like anorexia nervosa, which itself is characterized by an interplay of physiology, psychology, and behavior. For example, how does a hormonally-mediated signal like hunger work in a person with anorexia nervosa? But first, here’s a review of Hormones 101.
Hormones Involved in Energy, Reproduction, and Growth
Released from: the adrenal gland.
What does it do? Cortisol—which typically acts as part of the response to stress— aids in the metabolism of fat, protein, and carbohydrates. Specifically, it stimulates the formation of glucose (i.e. blood sugar, or readily available energy). Cortisol levels cycle throughout the day, and have been found to have big impacts on memory, sleep, mood, and acid secretion in the stomach and kidneys.
Released from: the lining of the stomach.
What does it do? Ghrelin stimulates appetite, food intake, use of carbohydrates and the release of growth hormone; it also activates pathways that reinforce rewards (e.g. food and some drugs), and inhibits fat utilization and physical activity. Production of ghrelin increases before a meal and then slows down afterward.
Released from: pancreatic beta cells.
What does it do? The net result of insulin release should be a decrease in blood sugar (i.e. glucose) levels when they are elevated, such as when carbohydrates are consumed. When insulin binds to receptors on fat and muscle, it causes glucose transporters to fuse with the cell membranes, allowing for the entry of glucose into these tissues. It also causes glucose to be stored as glycogen in the liver and inhibits the breakdown of fat for energy.
Released from: fat cells (i.e. adipocytes).
What does it do? Leptin, like ghrelin, acts on feeding centers in a brain region called the hypothalamus—but in an inhibitory way, tending to lead to decreases in appetite and food intake. It is also involved in energy expenditure and modulating control of the hormones related to reproduction (discussed below).
While leptin is sometimes referred to as a “satiety hormone,” its primary function seems to be to tell the body whether fat stores are sufficient for growth and reproduction. If fat stores are inadequate (e.g. below a “threshold” that is developmentally and genetically set), we see effects like increased hunger and food consumption, low energy output, and infertility; however, when levels are at or above this threshold, leptin’s actions may be less influential. Therefore, it may actually be more useful in giving cues related to hunger, rather than satiety.
Peptide YY3-36 (PYY)
Released from: cells in the small intestine and colon.
What does it do? In the presence of food, PYY also acts on hypothalamic feeding centers to inhibit hunger and food intake.
Thyroid Hormones (T3 and T4)
Released from: the thyroid gland.
What do they do? T3—the metabolically active thyroid hormone—increases heart rate, ventilation (breathing) rate, and basal metabolic rate. It also influences sympathetic activity (i.e. our fight-or-flight response).
Both male and female sex hormones play a huge role in growth, development and sexual differentiation. Here is how.
Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH)
Released from: the pituitary gland in the brain.
What do they do? In females, LH and FSH levels rise and fall and regulate the menstrual cycle. In addition, LH stimulates the production of testosterone (below) in males.
Released from: the ovaries of females and other neuroendocrine tissues.
What does it do? Estradiol—the primary female sex hormone—stimulates the development of secondary sex characteristics of females and the female reproductive system (e.g. reproductive-organ development, bone-shape changes).
Released from: the testicles of males (primarily), the ovaries of females and other endocrine (i.e. hormone-producing) tissues.
What does it do? Testosterone—the primary male sex hormone—stimulates muscle-mass growth, increases bone density, bone maturation and linear growth. It also promotes the development of secondary sex characteristics of males (e.g. sex-organ development, facial-hair growth, deepening of the voice).
What happens in anorexia nervosa?
Anorexia nervosa significantly impacts both the body and the mind. The low weight state leads to a variety of medical consequences, including bone loss (osteopenia) and the loss of one’s menstrual period (amenorrhea). Many of these symptoms can be explained by the way hormones respond to the signals that we send our body when we restrict food intake for an extended period.
- Amenorrhea: Anorexia nervosa is associated with profound decreases in reproductive hormones (e.g. LH, FSH, and estrogen). The mechanism may be related to leptin levels, which are lower than expected based on height and weight, and seem to send the signal that energy availability is low, and our bodies aren’t ready for reproduction.
- Osteoporosis: Poor bone health is possibly one of the most compelling consequences as people who develop anorexia nervosa at a young age and may never reach peak bone mass. Severe complications, like bone fractures, can occur even as late as 40 years after diagnosis. The combination of low leptin and sex-hormone levels, high cortisol levels and poor nutrition can explain this feature.
- Thyroid levels: It is not uncommon for T3 levels to be low in people with anorexia nervosa. This manifests as bradycardia (slow heart rate) and hypothermia (low body temperature)—features that serve to preserve energy.
- Behavioral/psychological symptoms (e.g., anxiety, hyperactivity, impulsivity): Hormones that activate our fight-or-flight response (i.e. cortisol) are typically elevated in anorexia nervosa. This could have something to do with behavioral features of the illness that promote quick decisions and a high state of alert.
Perhaps the most fundamental question about hormones and anorexia nervosa of interest to researchers is about the impact of physiology in the development of the disorder. Is there a hormonal perturbation that promotes a low-weight state or predisposes one to the illness? Studies have looked at hormones like PYY that may predispose patients to reduce food intake, but in general, there is no evidence to conclude that this is the case. However, the hormonal irregularities experienced by individuals with anorexia nervosa are what one would expect in those who are starved. The question then becomes—what causes individuals with anorexia nervosa to overcome such a strong biological drive to regain lost weight? Whether it has to do with delaying reward, habit formation or differences in taste preference or something else we haven’t thought of yet, is a big focus of research today and is crucial to fully understand the illness.