Abstract
Nutrition significantly impacts health and well-being. A proper diet is crucial for maintaining bodily homeostasis. Modern lifestyle changes, characterized by increased food processing, diminish the nutritional value of available products. This necessitates technological interventions like fortification and dietary supplements to complement nutrient intake. Environmental factors such as physical activity induce adaptive changes in the endocrine system. Cortisol, a corticosteroid, plays a diverse role depending on its concentration. It mobilizes the body to combat stress by stabilizing glucose levels, promoting tissue regeneration, and inhibiting inflammation. However, chronic stress from work, personal issues, or intense training can lead to sustained, elevated cortisol levels, contributing to metabolic disorders like insulin resistance, high blood pressure, impaired bone regeneration, collagen synthesis abnormalities, and calcium deficiency. Dietary supplementation is widely practiced by individuals of all ages, particularly those who are physically active, to regulate steroid hormone homeostasis. Optimizing diet is essential for overall well-being, health, and success.
Introduction
Cortisol (hydrocortisone) is the predominant glucocorticoid hormone in the human body. It acts on various physiological processes, preparing the body for physical and mental stress. It influences protein, carbohydrate, and fat metabolism and regulates water and electrolyte balance, blood pressure, body temperature, bone mineralization, and immune response. Additionally, it affects mood, behavior, appetite, and pain perception.
Cortisol mobilizes the body to cope with stress by influencing various organs and systems. It regulates nutrient utilization by increasing gluconeogenesis and lipolysis in adipose tissue. It also enhances protein synthesis in the liver while reducing it in muscles and skin cells. Furthermore, it promotes water and sodium retention, controls adrenaline production in the adrenal medulla, inhibits inflammation, and affects the psyche, potentially inducing euphoria or depression.
This article aims to present current scientific perspectives on the role of dietary components and nutrition in cortisol production in physically active individuals.
Dietary Components and Cortisol Metabolism
A well-composed diet provides essential nutrients from plant and animal sources. Cholesterol, a fat-like substance found in animal fats and synthesized in the body, is crucial. Endogenous cholesterol synthesis starts with the condensation of three acetyl CoA molecules, with subsequent reactions dependent on enzymes and vitamin B3. This process leads to cortisol production (Fig. 1), which is released into the bloodstream.
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Fig. 1 Endogenous synthesis and metabolism of cortisol. Figure 1 shows the synthesis and metabolism of cortisol including the effect of B vitamins (B3 and B5).
Cortisol metabolism primarily occurs in the liver, where reductases convert it to tetrahydrometabolites (THMs) for urinary excretion. Before reaching target cell receptors, cortisol can be deactivated to cortisone by microsomal 11β-hydroxysteroid dehydrogenase.
Factors Regulating Cortisol Production and Secretion
Cortisol secretion is governed by circadian rhythms, external stimuli, and feedback regulation. The hypothalamus releases corticotropin-releasing hormone (CRH) and vasopressin (ADH) in response to circadian and stress factors. These hormones stimulate the anterior pituitary gland to produce adrenocorticotropic hormone (ACTH). ACTH influences StAR protein expression, facilitating cholesterol transport across the mitochondrial membrane for cortisol formation in the adrenal cortex.
Cortisol is transported in biologically inactive forms bound to transcortin (90 %) and albumin (7 %). In target cells, it affects DNA transcription and can also influence bodily functions through non-genomic mechanisms. The body's response to cortisol depends on its concentration and receptor concentration, influenced by development stage, cell cycle timing, and endocrine disorders.
Functions of Cortisol in the Human Body
Endocrine functions are influenced by environmental factors, including diet and physical activity. Cortisol plays a crucial role in maintaining appropriate blood glucose levels. It activates hepatic glycogen stores, reduces glucose oxidation, stimulates lipolysis, and intensifies gluconeogenesis from amino acids. Persistently high cortisol levels can lead to insulin resistance, dyslipidemia, hypertension, and obesity. Mobilizing glucose reserves is vital during rapid stress situations like endurance training.
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Cortisol also affects appetite. Studies have shown that cortisol amplifies startle responsiveness to high-glycemic-index food images. Ghrelin, a hormone that stimulates hunger, increases cortisol, ACTH, and growth hormone levels but does not affect leptin.
In physiological concentrations, cortisol stimulates collagen synthesis. However, elevated levels due to mental stress or intense physical exertion can disrupt osteoblast structure and the concentrations of chemicals involved in bone remodeling, leading to impaired bone mineralization and inhibited collagen synthesis. Excess cortisol impairs active calcium ion transport across cell membranes and reduces its absorption in the gastrointestinal tract, leading to calciuria.
Cortisol enhances tissue sensitivity in blood vessels and the heart to noradrenaline, vasopressin, and angiotensin II, increasing blood pressure. It also affects water and electrolyte balance by increasing water and sodium retention. Cortisol also aids in thermal regulation to prevent overheating.
Cortisol has anti-inflammatory and immunosuppressive effects on the immune system by reducing pro-inflammatory cytokine secretion, decreasing white blood cell migration to inflammation sites, and inducing cell apoptosis. This stimulates the body's defensive responses to injuries, including those during training and sports.
Cortisol influences neuronal plasticity and neurodegenerative processes by acting on neurons and glial cells in the central nervous system. It also modifies mood, behavior, and pain perception, which is particularly important for athletes during competitions.
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While cortisol prepares athletes for increased effort, its excess can lead to catabolic reactions, negatively affecting the body. As a catabolic hormone, cortisol exists in dynamic equilibrium with anabolic hormones. High cortisol levels inhibit testosterone synthesis, contributing to hormonal imbalances. The cortisol/testosterone (C/T) ratio indicates athlete exhaustion and overtraining.
The Impact of Training and Competitions on Cortisol Levels
Studies show a relationship between perceived stress and endocrine system changes in athletes, marked by increased cortisol and adrenaline levels and a less pronounced increase in testosterone. Cortisol and testosterone levels can assess pre-start stress. Athletes with higher motivation and a focus on success tend to have higher hormone levels and achieve better results.
Long-lasting endurance efforts, especially in low temperatures and high altitudes, result in increased cortisol levels. Emotional factors associated with competition and extreme burden and psychological exhaustion also affect cortisol levels. Mental depletion can limit pituitary gland and sympathetic nervous system activity.
The increase in cortisol levels after exercise depends on the athlete's fitness level, the discipline, and the volume and quality of training. Cooling the body with cold water after training can lower post-training cortisol levels compared to a control group.
Effect of Nutritional Components on Blood Cortisol Levels
Nutrition, dietary nutrients, and physical activity significantly impact bodily functions, including endocrine system balance. A balanced diet with optional supplementation is crucial for high physical and mental capacity. Elderly individuals, athletes, and those with heavy workloads often use nutritional supplements to increase efficiency, durability, and accelerate healing.
These groups are particularly susceptible to abnormal hormone secretion, metabolism, and transport, including cortisol. Sustained high cortisol levels are detrimental, highlighting the need to enrich daily diets with supplements that can help stabilize hormones.
Stressful situations often increase cravings for sweet and fatty foods due to their rewarding nature. Food consumption induces an increase in cortisol levels, more pronounced in men than in women. Research on the influence of macronutrients on cortisol concentration yields unclear results.
Carbohydrate content and type significantly affect the endocrine system of active individuals. Cortisol levels increase in response to hypoglycemia. Therefore, athletes should replenish carbohydrates before, during, and after training. Supplementation with 7 % sugar solutions during endurance training can lower post-exercise cortisol concentration, while liquids containing up to 1.5 % carbohydrate or 8 % maltodextrin solutions do not affect cortisol levels.
The impact of around-training protein or branched-chain amino acid (BCAA) supplementation and their combination with carbohydrates remains unclear and requires further research. Tryptophan supplementation may reduce exercise-induced cortisol increases. Around-training administration of glutamine and arginine does not alter cortisol concentration.
Phospholipids like phosphatidylserine and phosphatidic acid may affect cortisol levels. Supplementation with their complex at 400 mg/day for 6 weeks reduced exercise-induced cortisol secretion, but a 200 mg dose did not. Natural sources of phosphatidylserine include egg yolks, and serine is abundant in protein-rich products. Serine, an endogenous amino acid, can be synthesized from other amino acids, underscoring the importance of adequate protein intake for athletes.
Gamma-aminobutyric acid (GABA) affects cortisol hormonal control by reducing corticotropin-releasing hormone (CRH) secretion, which triggers a cascade of hormonal changes leading to cortisol secretion. Natural sources of GABA include fermented milk products, brown rice sprouts, barley, and beans. Dietary supplements containing GABA are available, but natural sources are preferred due to potential side effects associated with chemically prepared GABA.
Trace elements like lithium, vitamin B6, vitamin B12, and folic acid accelerate GABAergic system activity. Taurine, an amino acid, can stimulate the GABA receptor. GABA is produced from glutamine in the presence of endogenous vitamin B6.
Fig. 2 Effect of food nutrients on concentration of γ-aminobutyric acid (GABA) and associated with its level of cortisol.
Yoga, a philosophical system from India involving exercises, meditation, and breath work, has been shown to increase GABA concentration in the brain.
Dietary Supplements
The influence of ascorbic acid on cortisol levels has been extensively studied. In vitro research shows no influence of vitamin C on ACTH-induced cortisol synthesis. However, taking 3000 mg of vitamin C per day may lead to faster cortisol recovery after acute psychological stress, but it doesn't decrease overall concentration.
Many manufacturers of cortisol blockers claim their products promote weight loss by reducing cortisol levels. Cortisol release is triggered by stress, and some evidence links this hormone to weight gain.
Cortisol Inhibitors for Weight Loss
Claims that cortisol blockers or inhibitors aid weight loss are based on evidence suggesting that increased stress levels can lead to weight gain. A study in the journal Obesity found that long-term exposure to elevated cortisol levels is associated with higher body weight and obesity.
However, there is little to no evidence that cortisol inhibitors contribute to weight loss. The Federal Trade Commission (FTC) has cited manufacturers of cortisol blockers for making false claims about their effectiveness. For example, the FTC filed a complaint against the manufacturers of CortiSlim and CortiStress in 2004, requiring them to refund customers for false claims.
For weight loss, the Centers for Disease Control and Prevention (CDC) recommends regular exercise, balanced eating, and limiting calorie consumption. Before using cortisol blockers, carefully examine the manufacturer's claims, as they are often exaggerated.
Natural Stress and Weight Management
Natural steps can help manage both weight and stress:
- Get enough sleep: Adequate sleep positively affects stress levels and weight management.
- Get regular, moderate exercise: Exercise geared to relieve stress.
- Eat a balanced diet: A well-rounded diet supports overall health.
To reduce cortisol levels naturally:
- Practice relaxing: Incorporate relaxation techniques into your daily routine.
- Schedule time to have fun: Enjoyable activities can alleviate stress.
- Maintain healthy relationships: Social connections provide support.
- Take care of a pet: Pet ownership can reduce stress and improve well-being.
Specific foods may help reduce cortisol levels:
- Dark chocolate: Research suggests it can lower cortisol levels.
- Green and black teas: Some studies indicate they can reduce cortisol.
- Bananas and pears: Research suggests they can lower cortisol levels.
- Water: Staying hydrated can reduce physical stress on the body.
- Prebiotics and probiotics: Some studies show they can reduce cortisol levels, but more research is needed.
Before starting any new diet or exercise program, consult a doctor. The relationship between weight and cortisol is complex. Cortisol blockers can help reduce high levels in people with disorders affecting the adrenal glands.
Cortisol Blockers and Their Claims
Cortisol, known as the stress hormone, affects several bodily functions. It helps the body function under stress. Cortisol levels fluctuate throughout the day, but consistently high levels may indicate an underlying issue. Cortisol blockers can help decrease cortisol levels in people with high cortisol-level disorders who may not be able to have surgery, such as in Cushing syndrome.
Companies market some cortisol blockers as dietary supplements that can help build muscle, lose weight, and feel less hungry. To evaluate these claims, understanding cortisol's role is crucial.
When you feel fear or danger, the hypothalamus activates the fight-or-flight response. The adrenal glands release cortisol and adrenaline. Cortisol streamlines the body's workload to focus on the immediate threat. Adrenaline increases heart rate, blood pressure, and energy.
Cortisol has several effects on the body:
- Acts on the pancreas to decrease insulin, raising blood sugar levels.
- Drives circulating glucose to the brain, improving alertness.
- Enhances the body’s ability to repair tissue.
Cortisol levels naturally fluctuate, peaking in the morning and decreasing at night. Children tend to have less cortisol than adults.
High cortisol levels can result from:
- Pituitary gland conditions or tumors.
- Adrenal gland tumors or conditions.
- Certain medications, including oral contraceptives and corticosteroids.
Consistently high cortisol levels can cause Cushing syndrome, or hypercortisolism. Treatment may include a cortisol blocker.
Symptoms of Cushing syndrome include:
- Flushed face.
- High blood pressure.
- Skin changes.
- Rapid weight gain in the face, abdomen, and chest.
High cortisol levels can indirectly cause weight gain. Chronic stress, which elevates cortisol levels, can increase food cravings and has been linked to weight gain and obesity. Higher cortisol levels, chronic stress, and insulin may be associated with greater future weight gain.
Despite claims that cortisol blockers can assist in weight loss, the government has intervened. In 2004, the FTC filed suit against marketers of CortiSlim and CortiStress for making unsubstantiated claims.
Before taking dietary supplements that claim to aid weight loss, consult a doctor. Lifestyle changes are more effective than short-term diets for weight loss, including:
- Regular exercise.
- Eating a variety of fruits and vegetables.
- Choosing whole grains over refined grains.
- Avoiding highly processed foods.
- Avoiding sugary drinks.
Blood, urine, or saliva tests can determine cortisol levels. Multiple tests at different times of the day may be recommended, as cortisol levels fluctuate. If concerned, consult a doctor about getting a cortisol test. From there, a doctor can help support effective measures toward balancing your hormones and losing weight.
Research does not clearly link cortisol levels and weight loss. The FDA has taken action against companies selling products that claim to support weight loss by lowering cortisol levels. Consistently high cortisol levels can indicate an underlying medical condition.