Progesterone: The Forgotten Hormone

Oestrogen gets almost all the attention in conversations about women's hormonal health. The evidence suggests that's a mistake — and that progesterone's role extends well beyond pregnancy, into bone density, cardiovascular health, sleep, and healthy ageing.

Ask most women what oestrogen does, and they'll have an answer. Ask about progesterone, and the conversation usually stalls at "something to do with pregnancy." That gap in public understanding isn't accidental — it reflects decades of research and marketing attention flowing almost entirely toward oestrogen, while progesterone's independent roles have gone largely unexamined.

A February 2026 review from researchers at the University of British Columbia's Centre for Menstrual Cycle and Ovulation Research makes a compelling case that this imbalance has real consequences. The dominant model of women's healthy ageing treats menopause, and its associated drop in oestrogen and progesterone, as the starting point of hormonal risk. The review argues that many of the disease risks attributed to menopause actually take root much earlier, during the menstruating years — and that progesterone, not oestrogen, may be the more important protective factor.

A regular cycle isn't proof of ovulation

This is the detail that tends to surprise people most: a menstrual cycle can arrive on time, every time, and still not involve normal ovulation. Researchers call this a subclinical ovulatory disturbance — a cycle of predictable length where the luteal phase (the second half, after ovulation, when progesterone is produced) is either too short or absent altogether.

These disturbances are thought to occur in more than a quarter of cycles among otherwise healthy women, and they're typically an adaptive response to physiological, nutritional, or emotional stress — the body's way of down-regulating fertility when conditions seem unfavourable. Because cycle length and bleeding pattern look normal, the disturbance is invisible without specific hormone testing, which isn't part of routine care.

What progesterone actually does

Progesterone's best-known job is preparing and maintaining the uterine lining for a potential pregnancy. But its receptors are found throughout the body — in bone, blood vessels, and the brain — and research increasingly points to independent roles in each of those systems.

Bone formation, not just bone protection

Oestrogen's role in bone is often described as protective, but what it actually does is slow the rate at which old bone is broken down. Progesterone works differently: it directly stimulates osteoblasts, the cells responsible for building new bone. In a prospective study of healthy, normally-cycling women, those with more short luteal phases or anovulatory cycles lost significantly more spinal bone density over a year than women with consistently normal ovulation — even though their cycles were otherwise indistinguishable.

A cardiovascular signal that's easy to miss

A large Netherlands cohort study followed over 11,000 women in their 40s and later compared those who went on to have heart attacks or need coronary surgery with matched controls. Oestrogen levels didn't differ meaningfully between the two groups. Ovulation status did: women who later had cardiac events had a notably higher rate of anovulatory cycles years earlier. Separately, primate research has linked socially-stressed, ovulation-disrupted females to coronary artery changes similar to those seen in males on the same high-fat diet — while their normally-ovulating counterparts stayed protected.

Sleep and the perimenopause transition

Progesterone appears to have a calming effect on the nervous system, partly through its metabolite allopregnanolone, which interacts with the brain's GABA system. In a randomised controlled trial of 189 perimenopausal women with problematic night sweats, oral progesterone significantly improved sleep quality and reduced night sweat intensity and frequency. Notably, when progesterone was stopped, symptoms didn't rebound the way they typically do after stopping oestrogen therapy — they eased off gradually instead.

The caveats worth knowing

None of this is a case for progesterone as a cure-all, and the research itself is careful to say so. The Women's Health Initiative trials — still the largest randomised evidence available — found that neither oestrogen alone nor oestrogen with a progestin improved overall mortality, a result that held up even after 18 years of follow-up. Much of the confusion in this area also comes down to terminology: synthetic progestins (like medroxyprogesterone acetate, used in many HRT preparations and in the WHI trials) are not the same molecule as bioidentical progesterone, and the two are frequently — and misleadingly — used interchangeably in both research and everyday conversation.

There are also real gaps in the evidence. Progesterone's effects on cognition, ischaemic stroke risk, and endogenous (as opposed to therapeutic) progesterone during the natural cycle are all areas where researchers say the data is too thin to draw firm conclusions. Anyone considering hormone therapy of any kind — combined, oestrogen-only, or progesterone-only — should work through the decision with a GP or menopause specialist rather than a blog post, since individual risk factors change the calculation considerably.

Why this matters day to day

Understanding progesterone's role isn't just academic. For women tracking their cycles, it reframes what "normal" ovulation actually requires — adequate energy intake, manageable stress, and a luteal phase of sufficient length, not just a period that arrives on schedule. For women approaching perimenopause, it explains why symptoms like disrupted sleep and night sweats can appear well before periods become irregular, since progesterone often declines before oestrogen does. And for anyone weighing up hormone therapy options, it's a reason to ask specifically about progesterone rather than assuming oestrogen is the whole conversation.

Supporting the body's hormonal foundations — through sleep, nutrient status, and stress load — remains the groundwork that any hormone, endogenous or prescribed, depends on. It's the same clinical logic behind formulating HER Revive: not as a replacement for medical care, but as nutritional support for the systems progesterone and oestrogen both rely on.

HER Revive

Formulated to support women's hormonal and vitality needs across life stages, from GMP-certified UK manufacturing.

View HER Revive →

The takeaway

Progesterone has spent decades in oestrogen's shadow, treated as a side character in the story of women's hormonal health rather than a lead. The emerging evidence — on bone, on the heart, on sleep and the nervous system — suggests that framing needs to change. A regular cycle looks reassuring on a calendar, but it doesn't tell the whole hormonal story. Where questions remain, they're worth raising directly with a GP or menopause specialist, particularly around perimenopause, when progesterone's decline often starts before anything else feels obviously different.

This article is for general information and does not constitute medical advice. Speak to your GP or a menopause specialist about any symptoms or before starting hormone therapy.