Hormones are chemical messengers which travel in the bloodstream. They are involved in several biological processes, apoptosis (cell death), homeostasis (maintaining equilibrium in biological systems), and stress. Hormones can be classified into different forms such as eicosanoids, proteins, and steroids, and are secreted by the endocrine glands in response to biochemical signals and reactions. Hormones can be classified into different types, such as eicosanoids, proteins, peptides, and steroids. They are secreted by endocrine glands in response to specific biochemical signals and stimuli.
The endocrine glands, namely, the thyroid gland, pancreas, testes, and ovaries, are responsible for the synthesis, storage, release, and metabolism of the hormones they produce. More specifically, these hormones are critical to development and behaviour and are involved in the sleep-wake cycle, mood fluctuations, menstruation, secondary sexual development, and stress responses.
Disturbances in normal hormone levels can lead to hormonal imbalances, which may cause a range of symptoms and, over time, contribute to chronic health conditions. Common examples include hormonal acne, obesity, and, in severe cases, infertility. Therefore, understanding and identifying potential risk factors is crucial in preventing or managing these issues.
The main differences in the hormones produced in the biological male and female human body are a result of distinct reproductive functions and secondary sexual characteristics. Testosterone, produced in the testes, is responsible for sperm production, which is further governed by other hormones such as the luteinizing hormone (LH) and the follicle-stimulating hormone (FSH).1 Testosterone production also drives hair growth, libido, bone density, and muscle mass.
In someone assigned female at birth, AFAB, estrogen and progesterone are the primary sex hormones. They are synthesised in the ovaries and are involved in the development of female secondary sexual characteristics, menstruation, pregnancy, and menopause.1 Additionally, small amounts of testosterone are produced in the ovaries and adrenal glands.
Most of these changes are first observed during puberty and can have significant impacts on further development. For instance, a hormonal imbalance in estrogen and progesterone levels can lead to a delayed menarche1 (the first period). Accordingly, imbalances in males can cause gynaecomastia and hypogonadism, and potentially, infertility.1 Gynaecomastia is when a person assigned male at birth, AMAB, develops larger breasts than usual, and hypogonadism is when the testes do not produce enough testosterone.
Fluctuations in sex hormones govern pregnancy-related changes. Estrogen and progesterone steadily increase throughout pregnancy and can initiate neo-angiogenesis.2 The initiation of neo-angiogenesis drives placenta formation and eventually prepares the body for lactation.2 Any harmful fluctuations in hormone levels can cause miscarriage, preeclampsia, and gestational diabetes.
Estrogen and testosterone have been documented to decrease with age. Decreases in estrogen levels are commonly associated with menopause, and those with testosterone are associated with reduced muscle mass and bone strength.3 Menopause is initiated at around 50-51 years of age and can also be influenced by other factors such as genetics and the onset of menstruation.4 It is also associated with physiological changes like dryness, hot flashes, brain fog, and mood disturbances.
The decrease in testosterone, on the other hand, is typically gradual and is clinically termed andropause.4 It is important to note that andropause can be selective and does not occur in every male.4 While sperm production may still go on, sperm quality can decline and, in some cases, also occur alongside late-onset hypogonadism.4
An individual's diet significantly influences endocrine and reproductive health. Diets high in unhealthy fats, sugar, and sodium but low in micronutrients can trigger hormonal acne by increasing sebum production, leading to inflammation and scarring.5 Poor nutrition can also disrupt the gut microbiome, impair oocyte quality, and affect menstrual function.6
The association between physical activity and hormonal signalling can be studied using the hormonal exercise response model (HERM), which monitors the effect of exercise on the sex hormones and cortisol.7 According to the HERM, exercise triggers the release of cortisol from the pituitary gland and regulates other endocrine functions. While the amount of cortisol is subject to different factors, it is important to note that excessive training can increase cortisol release and prompt muscle breakdown and inhibit muscle growth.7
The growth hormone and insulin-like growth factor-1 are responsible for driving protein synthesis and muscle mass.7 In addition, overtraining and undereating can cause menstrual disorders and reduced bone density in women.7
Sleep, stress, and hormones have long since exhibited strong interactions with each other. Hormones like melatonin and cortisol regulate the sleep-wake cycle.8 High levels of stress can lead to the activation of the hypothalamic-pituitary-adrenal axis (HPA) that can further exacerbate sleep disorders like insomnia and sleep apnea.8 High cortisol levels have been reported in patients with disordered sleep.8
Sleep deprivation also has negative effects on the hunger hormones leptin (which prevents hunger) and ghrelin (which promotes hunger). A study reported a 28% increase in ghrelin and an 18% decrease in leptin in men with restricted sleep.8 These participants also had an increased appetite for fatty and sugary foods.
As mentioned above, the effects of high stress and poor sleep can negatively impact hormone modulation and, consequently, an individual’s well-being. The downstream effects can occur in the form of impaired metabolism and appetite regulation and increases in HPA axis activation, cortisol release, and ghrelin levels, which significantly increase the risk of diabetes and obesity.8 Sleep disorders like narcolepsy are linked to obesity due to the presence of binge eating, fat deposits, and insulin resistance.8
PCOS is one of the most common endocrine abnormalities occurring in people AFAB of reproductive age. Patients with PCOS can experience painful or irregular menstruation, acne, and hair overgrowth. Most hormones, such as insulin, ghrelin, LH, FSH, and estrogen, are highly prone to abnormal fluctuations as a result of PCOS pathology.9 These variations also make the individual more susceptible to diabetes, obesity, and infertility.9 Patients with PCOS also exhibit higher amounts of testosterone and lower amounts of progesterone compared to people AFAB without PCOS.10
Thyroid disorders are also commonly observed to occur alongside PCOS, with approximately 28% of the population with PCOS reporting thyroid abnormalities.10 Thyroid disorders may occur as a result of excessive (hyperthyroidism) or low (hypothyroidism) production of the T3 and T4 thyroid hormones. The former can lead to Graves’ disease, while the latter can cause autoimmune disorders. The most common form of hypothyroidism is Hashimoto’s thyroiditis (HT) and is characterised by the presence of anti-thyroid antibodies. Patients AFAB with hypothyroidism frequently report menstrual irregularities and fertility issues. They also report higher rates of miscarriage (~53%) than those without HT, and couples with fertility issues often exhibit anti-thyroid antibodies in their bloodstream.10
Breast cancer is the most frequently occurring cancer in people AFAB worldwide, and is characterised by the presence of cancerous cells in the breast tissue. It is influenced by a myriad of factors, including, but not limited to, genetics, fitness levels, and age.
Hormonal imbalances have also been studied due to the role of estrogen and progesterone in the development of female secondary sexual characteristics and driving reproductive maturation.11 Estrogen and progesterone imbalances can activate the specific receptors in breast tissue and lead to uncontrolled cell proliferation.11 As mentioned earlier, estrogen also promotes neoangiogenesis, thereby initiating new vascular connections and inhibiting apoptosis.11
