Hormones: definition, tasks and the most important hormones at a glance

Hormones, those tiny biochemical messengers produced in our bodies, have an enormous influence on our daily lives. They affect almost every aspect of our well-being. Whether we eat, sleep, exercise, or simply relax, hormones are always active in the background, regulating our basic biological functions. Read on to learn more about what hormones are, why they are important, and what they do.

Table of Contents

• What are hormones?
• How can hormones be classified?
• Where are hormones produced?
• What is the function of hormones?
• An overview of the most important hormones
• Summary

What are hormones?

Hormones are chemical messengers produced and released by specialized cells and glands in our body. Their primary function is to facilitate and regulate communication between different parts of the body. Think of hormones as keys that send a specific message to a cell, which acts as a lock. Once the key fits the lock, the message is transmitted, and the cell responds accordingly.

These hormonal messengers are part of the so-called endocrine system, which plays a central role in regulating most bodily functions. The endocrine system is a complex network of glands and organs responsible for producing, storing, and releasing hormones. This network includes the pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries, and testes, among others. Hormones control numerous processes in our body. They affect our mood, metabolism, growth, development, and reproduction. They also help regulate body temperature, heart rate, bone density, and much more. They are vital because they help us respond to changes in our environment and maintain our internal balance, known as homeostasis.

Hormonal imbalances can be triggered by a variety of factors and can have significant impacts on our health (Britannica, 2023).

How can hormones be classified?

Hormones can be categorized based on several aspects, including:

• Chemical structure: Hormones can be classified by their chemical composition. The main groups are peptide hormones (e.g., insulin), steroid hormones (e.g., cortisol), amino acid derivatives (e.g., thyroxine), and fatty acid derivatives (e.g., prostaglandins).

• Site of production: Hormones can be grouped by the gland or tissue where they are produced. Examples include thyroid hormones produced in the thyroid gland and adrenal hormones produced in the adrenal glands. If you want to check your thyroid function, you should buy a thyroid test.

• Target function: Hormones can also be classified according to their main function. These include hormones that regulate metabolism (e.g., insulin), hormones that control growth (e.g., growth hormones), and hormones that regulate reproduction (e.g., sex hormones).

• Release and mechanism of action: Hormones can be categorized by how and when they are released and how they act. Some are constantly released in small amounts, while others are released in response to specific signals.

• Effect on the body: Some hormones have systemic effects on the entire body, while others have targeted effects on specific organs or tissues.

It is important to note that many hormones fall into more than one of these categories due to their complex structures and functions (Nussey & Whitehead, 2001).

Where are hormones produced?

Hormones are produced in endocrine glands that are distributed throughout the body. Each gland has a specific role and produces certain hormones. Some of the main endocrine glands include:

• The pituitary gland sits at the center of the skull, at the base of the brain. Though only the size of a pea, it is incredibly powerful and is often called the "master gland." It controls many other glands in the endocrine system by producing and releasing its own hormones. These hormones travel through the bloodstream and signal other glands to release their specific hormones.

• The thyroid gland is a small gland located at the front of the lower neck. It produces the hormones triiodothyronine (T3) and thyroxine (T4), which are responsible for regulating metabolism, body temperature, and heart rate.

• The adrenal glands are small, pyramid-shaped glands located on top of each kidney. They produce a variety of hormones, including cortisol, adrenaline, and aldosterone.

• The pancreas, located behind the stomach, produces both digestive enzymes and important hormones such as insulin and glucagon. Insulin and glucagon work together to keep blood sugar levels stable.

• The sex glands, which include the ovaries in women and the testes in men, are responsible for producing sex hormones. The ovaries produce estrogen and progesterone, while the testes play an important role in producing testosterone.

Source: Endocrine Society, 2023

What is the function of hormones?

Each hormone has a specific function in the body and acts on specific cells or tissues. They are the body’s regulators, ensuring everything runs smoothly. Here is a summary of some of the most important functions of hormones:

• Regulation of metabolism

• Control of growth and development

• Regulation of the immune system

• Regulation of fluid and electrolyte balance

• Regulation of reproduction

• Control of body temperature

• Regulation of mood and emotions

• Control of the sleep-wake cycle

These are just some of the many vital functions that hormones perform in our bodies. An imbalance in any of these hormones can therefore lead to a wide range of health issues (NCI, 2023). 

An overview of the most important hormones

Sex hormones

Sex hormones are a group of steroid hormones that play an important role in sexual development and reproduction. The two most common are estrogen and testosterone.

Estrogen

Estrogen is the primary female sex hormone, produced mainly in the ovaries but also released by fat tissue. There are different forms of estrogen, including estradiol, estrone, and estriol. Of these, estradiol is the most active and is mainly produced during a woman's reproductive years. Key functions of estrogen in women include:

• Regulates female reproductive physiology: Estrogen plays a key role in regulating the menstrual cycle, menopause, and potential pregnancy.

• Influences bone health: Estrogen helps maintain bone health and can reduce the risk of osteoporosis.

• Supports the development of secondary sex characteristics: In girls, estrogen contributes to the development of secondary sexual characteristics such as breast growth.

• Affects mood: Changes in estrogen levels can affect mood and are often associated with premenstrual and menopausal mood swings.

However, estrogen is not exclusive to women; it is also produced in smaller amounts in men and plays a role in regulating libido and sperm production. An estrogen imbalance can lead to symptoms such as irregular menstrual cycles, mood swings, and hot flashes in women. In men, it can lead to weight gain, decreased muscle mass, and sexual dysfunction (Endocrine Society, 2022). 

Testosterone

Testosterone is the primary male sex hormone, produced mainly in the testes. Major functions of testosterone in men include:

• Supports the development of secondary sex characteristics: In boys, testosterone is responsible for the development of features such as muscle mass, deep voice, and facial hair.

• Promotes sperm production: Testosterone plays a key role in sperm production and the maintenance of male fertility.

• Affects sexual behavior and libido: Testosterone helps regulate sexual behavior and libido.

Testosterone is not exclusive to men; it is also produced in small amounts in women. A testosterone imbalance can lead to fatigue, loss of muscle mass, increased body fat, sleep disturbances, and sexual problems in men. In women, excess testosterone can cause irregular menstrual cycles, acne, hair loss, and voice changes (Nassar & Leslie, 2023). 

Hormones are essential for the smooth functioning of the body. A hormone test for women from Homed-IQ can be a useful method to determine the current hormone status. This test measures six key hormones that influence female fertility, menopause, and overall health, including estradiol and testosterone. The hormone test for women can be conveniently performed at home and helps detect hormonal imbalances that may lead to a variety of symptoms and conditions. The blood test for athletes from Homed-IQ measures important parameters for overall fitness, including testosterone levels, giving athletes insights into their body and helping optimize training results.

Cortisol – “stress hormone”

Cortisol, often called the “stress hormone,” is a highly important steroid hormone produced in the adrenal cortex. This essential hormone greatly affects how our body responds to stress and is far more than just a simple messenger. The main functions of cortisol include:

• Stress response: Cortisol prepares the body for a “fight or flight” response by mobilizing energy reserves and increasing heart rate and blood pressure.

• Metabolism regulation: Cortisol plays a central role in metabolism by helping to produce glucose (sugar) for energy and process fats, proteins, and carbohydrates.

• Immune system regulation: With its anti-inflammatory properties, cortisol helps regulate the immune system and reduce inflammatory responses.

• Blood pressure regulation: Cortisol helps regulate blood pressure and supports cardiovascular health.

• Sleep-wake rhythm: Cortisol levels fluctuate throughout the day and help regulate our sleep-wake cycle.

However, chronically elevated cortisol levels—often a result of prolonged stress—can lead to a range of health issues, including sleep disorders, weight gain, depression, memory problems, and an increased risk of cardiovascular disease. This is why it’s important to manage stress effectively and maintain a healthy lifestyle to keep cortisol levels balanced and support overall health (Thau, 2022).

Oxytocin – “cuddle hormone”

Oxytocin is a peptide hormone and neurotransmitter often referred to as the “cuddle hormone” or “bonding hormone.” It is produced in the hypothalamus and released by the pituitary gland. Oxytocin plays a key role in a variety of social and physiological functions. The main functions of oxytocin include:

• Labor and childbirth: Oxytocin is released during childbirth and helps to stimulate contractions.

• Milk release: It supports milk production and flow in breastfeeding mothers.

• Bonding behavior: It promotes bonding between mothers and their newborns and also plays a role in social bonding and romantic relationships.

• Stress relief and relaxation: Oxytocin has a calming effect and can help lower blood pressure and reduce stress.

A deficiency in oxytocin can be caused by factors such as stress, certain medical conditions, or lack of social contact and may lead to complications such as social anxiety, depression, or difficulties forming bonds (Cleveland Clinic, 2022).

Melatonin – “sleep hormone”

Melatonin, also known as the “sleep hormone,” is produced by the pineal gland in the brain. The main functions of melatonin are:

• Regulation of the sleep-wake cycle: Melatonin is the hormone that prepares your body for sleep.

• Antioxidant properties: Melatonin acts as an antioxidant and can help protect cells from damage.

• Immune system support: It also has immunoregulatory properties and can strengthen the immune system.

The production and release of melatonin are closely linked to the light-dark cycle of the environment. In darkness, the body increases melatonin production, making us sleepy, while in daylight, production decreases. Disruptions such as nighttime light exposure, shift work, or jet lag can interfere with this natural rhythm, leading to sleep problems, mood swings, or even chronic health issues (Mayo Clinic, 2021). 

Insulin

Insulin, an essential peptide hormone, is produced in the pancreas. It plays a key role in controlling and regulating blood sugar levels. When we eat, blood sugar levels rise, triggering the release of insulin. Insulin acts like a key that opens the doors of body cells, allowing glucose to move from the bloodstream into the cells. There, glucose is either used immediately for energy or stored for later use. The main functions of insulin include:

• Blood sugar regulation: Insulin facilitates the uptake of glucose into body cells for use as an energy source.
• Glucose storage: In the case of excess glucose, insulin helps store it in the liver and muscle cells.
• Control of fat and protein synthesis: Insulin plays a crucial role in the production of fats and proteins.

A lack of insulin—when the body does not produce enough insulin—or insulin resistance—when the cells do not respond adequately to insulin—can lead to significant health issues, particularly diabetes. In both cases, this results in elevated blood sugar levels. There are two main types of diabetes: Type 1 diabetes, characterized by insulin deficiency, and Type 2 diabetes, which involves insulin resistance. To manage blood sugar levels effectively, medications, a balanced diet, and regular physical activity may be required (CDC, 2022).

Serotonin – “happiness hormone”

Serotonin, often referred to as the “happiness hormone,” is an important neurotransmitter and hormone that plays a central role in a variety of bodily functions. It is mainly produced in the brain and digestive tract, with around 90% of the body’s serotonin found in the gut. Key functions of serotonin include:

• Mood regulation: Serotonin is associated with enhanced well-being and happiness.

• Sleep-wake cycle control: Serotonin helps regulate the sleep-wake cycle and circadian rhythm.

• Appetite regulation: Serotonin influences appetite and food intake.

• Blood clotting: Serotonin is released by platelets and contributes to blood clotting by narrowing blood vessels.

A serotonin imbalance can be caused by factors such as stress, diet, lack of physical activity, and genetic predisposition and is associated with sleep disorders and mood disorders such as depression (Cleveland Clinic, 2022).

Thyroid hormones

Thyroid hormones, particularly thyroxine (T4) and triiodothyronine (T3), are essential regulators of metabolism. They are produced in the thyroid gland, a small butterfly-shaped gland at the front of the neck. To regulate the production of T3 and T4, the pituitary gland releases thyroid-stimulating hormone (TSH), which stimulates the thyroid to produce and release T3 and T4.

Key functions include:

• Metabolism regulation: Thyroid hormones influence almost all metabolic processes in the body. They determine how the body uses energy and affect the metabolic rate, i.e., how fast or slow our cells work.
• Growth and development: In children, thyroid hormones are essential for normal growth and development, particularly brain and nervous system development.

• Heart function: They help regulate heart rate and affect how efficiently the heart pumps blood (cardiac output).

• Body temperature: They help regulate body heat and influence how the body responds to temperature changes.

• Bone maturation: Thyroid hormones are crucial for normal bone growth and development.

An imbalance in the production of these hormones can lead to health issues such as hypothyroidism ( meaning an underactive thyroid) or hyperthyroidism (overactive thyroid) (Cleveland Clinic, 2022).

Summary

Hormones are essential messengers that fulfill a wide range of functions in our bodies—from regulating metabolism and mood to controlling growth and reproduction. An imbalance in hormone levels can lead to a variety of health problems, which is why it’s important to monitor your hormone levels through healthy lifestyle habits and, if needed, medical tests.