The ovaries are the main source of oestrogen and progesterone throughout our reproductive years. When ovarian function is at its peak, these hormones follow a steady monthly rhythm. From around age 35, ovarian activity naturally begins to decline, which means hormone production gradually decreases and becomes less predictable. This shift is the starting point of the perimenopausal transition. It can influence much more than our menstrual cycle.

The endocrine system is the body’s hormone communication network. It includes organs such as the thyroid, pancreas and adrenal glands, which release hormones that help regulate metabolism, blood sugar, energy, stress responses and many other essential functions. The brain helps coordinate these hormonal signals through the hypothalamus and pituitary gland.

The brain and ovaries work together to regulate our sex hormones. The hypothalamus and pituitary act like the body’s central coordinators, sending signals to the ovaries to help regulate the production of oestrogen, progesterone and other reproductive hormones. As ovarian function changes during perimenopause, this communication changes too.

The adrenal glands are best known for helping us respond to stress, but they also contribute to our overall hormone balance. They produce hormones such as cortisol and DHEA, which can influence stress resilience and the wider sex-hormone environment. The stress system and reproductive system are closely connected, so ongoing stress can affect reproductive hormone signalling and reduce the body’s capacity to maintain overall hormone balance.

The nervous system is our body’s communication and control network. It connects the brain with every part of the body, helping us respond to what is happening both inside and around us. It also plays an important role in regulating sleep, mood, stress, appetite, energy and body temperature. During perimenopause and menopause transition, changing hormones can influence how the nervous system responds to stress and how strongly we experience these changes.

The liver is a key part of our metabolic system and plays an important role in balancing hormones. It helps process and metabolise hormones after they have done their job, including oestrogen and other steroid hormones. The liver also produces cholesterol, an important building block for steroid hormone production. Through this two-way communication, the liver and reproductive system are closely connected. As ovarian hormone production changes during perimenopause, how the body processes and manages these hormones also becomes increasingly important.

The gut is more than a system for digesting food. It is an important part of hormone clearance, communication and whole-body health. After the liver processes hormones, their metabolites can be sent into the gut for elimination. But this isn't necessarily the end of the story. Certain gut microorganisms can modify some of these metabolites, potentially converting them back into forms that can be reabsorbed and become biologically active again. This downstream process helps fine-tune how much hormone is ultimately available to the body.

The gut also constantly communicates with other systems through the gut–brain and gut–liver axes. This means gut health can influence, and be influenced by, processes involving the brain, liver, metabolism, immune function and more. Supporting a healthy gut is therefore foundational to the wider ecosystem.