Menopause is the point when the ovaries stop working, after which there is no further ovulation, periods, or production of three key hormones – oestrogen, progesterone and testosterone - and women can no longer spontaneously become pregnant.
Women’s experiences throughout perimenopause and post-menopause are highly variable. Such as the age of spontaneous menopause and the type and intensity of symptoms experienced. So, is menopause a major stage in ageing for animals?
Interestingly almost all other animals retain the ability to reproduce throughout their lifespan. Other than humans, only female toothed whales (beluga, short-finned pilot, killer whales and narwhals) are known to go through menopause.
So why are humans almost unique in experiencing menopause? This is not yet fully understood, but – in evolutionary terms – there must be a reason why female humans have developed to stop reproducing, then continue to live afterwards.
One theory is the ‘grandmother hypothesis’, which suggests that older non-reproductive females benefit the group e.g. they can concentrate on seeking food and caring for the babies of younger mothers, and cannot produce any young that would be direct competition to descendants.
Also, there are benefits to the individual - including the transition of cyclical hormone patterns to a stable pattern, ceasing of periods and the pain and bleeding that goes with them, and no concerns of pregnancy.
In humans, the ovaries are dormant in early life until puberty, similar to the testes. However, unlike the testes, the ovaries are the fastest ageing tissue of all - ageing at up to five times the rate of other tissue. This is obviously significant, although we don’t yet know why. Much research is being done on this, to understand what is happening at a cellular level and why it is the case.
It could be that menopause confers biological benefits we haven’t yet identified. However, it’s also possible that evolution has made the reason for menopause irrelevant, and it now fails to give us any positive effects. It could be a hangover from our ancestors, which human evolution has not caught up with biologically to push menopause to later in life, or even stop it.
And, if that’s the case, perhaps we could speed up the process and delay menopause through medical intervention – or even prevent it altogether?
There are biologically negative effects of menopause linked to the reduction in hormones - low levels of oestrogen in particular. In females, it’s known to have significant negative impact on longer term health, impacting bone, brain, cardiovascular and immune function, which in turn can lead to a multitude of chronic conditions.
Women have a longer lifespan than men, but health is not maintained throughout the entire lifespan. The leading causes of death in females in the UK are Alzheimer’s disease and other dementias and cardiovascular disease.
But this negative effect is lessened in women who go through a late menopause, defined as being after 55 years. They are found to have improved bone, brain and heart health, and increased longevity in comparison to those who go through menopause earlier.
This suggests that delaying menopause could have significant beneficial impact on long-term health.However, studies show that women with a long exposure to natural oestrogen (i.e. women who go through puberty at an early age and/or have a late onset menopause) do have a higher risk of breast, uterine and ovarian cancers, which are associated with oestrogen. So, prolonged exposure to oestrogen in these circumstances is not without risk and there appears a fine balance is needed.
Even if delaying menopause was considered a good idea, how exactly would you do it?
First, we must understand what triggers menopause. Research by Jennifer Garrison, an associate professor based at the Buck Institute for Research on Aging and the Global Consortium of Reproductive Longevity and Equality, suggests that menopause is initiated by signals from the brain, in particular the hypothalamus. They are exploring these complex signals, which involve neuropeptides sent from the brain to the ovaries, which may start the ‘switching off’ process that leads to menopause.
Currently, many of the physical neural circuits in the brain are mapped. However, the complex communication in these pathways needs to be made clearer. What, when and where are these messages and what regulates them?
If this is understood, there is the potential to delay or switch off this signalling pathway - enabling the ovaries to continue to function. In this way, there would be no decline in hormone levels - thereby delaying and possibly preventing the adverse outcome on various organs in females and the ageing process.
There is an increasing body of work across basic science and biotechnology on the brain-ovary pathway and the ovarian endocrine function which operates separate to a purely reproductive one. This work is looking at addressing hormonal dysfunction such as in polycystic ovary syndrome, endometriosis and infertility. But its learnings will significantly help our overall understanding of ovarian function, menopause and ageing.
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