Interesting thread!
Your GP is quite wrong though GypsyRoseLee... she doesn't understand natural selection nor genetics!
The distinction should be made between life expectancy and life-span. There is a stuff written about this which you can google! CLKD is right. I wouldn't use the word "designed" as that implies a higher power at work (!) but as BrightLight said it's all about evolution and natural selection.
Our life-span is the average age a woman can live to - without other intervening factors like disease etc. As far as I remember from what I read a while back, our potential life-span has not changed much (if at all) over the same time period that our life expectancy has changed a great deal. The GP is is right about survival and death (life-expectancy). However it doesn't alter the fact that women have evolved (genetically) to have a period of time in post-menopause. The grandmother hypothesis is one explanation for why this is so.
We are absolutely not genetically engineered to die at 40 (life-span)! That is absolute rubbish! What she is meaning which is true that because our life-expectancy has inreased dramatically due to modern medicine we do now on average live to our allotted life-span which (itself may be increasing) - which means yes maybe a third of our life or more in menopause.
It is most definitely a natural process - but that doesn't mean we should suffer because of it! The main problem with any changes that happen after reproductive age is that natural selection cannnot operate (by which I mean that any genes which confer some sort of advantage due not prefentially survive to the next generation). One thing is certain that we are not genetically programmed to die as soon as we have finished reproducing. As well as the grandmother hypothesis you could argue that because of the dependence of human infants on their mothers for survival, more children will survivie to the next generation (and pass on their genes) if their mothers stay alive long enough to be able to rear them to maturity and independence. Using that argument I would expect in the very long (evolutionary) term (thousands of years?) that there should be less of a difference between menopause and death - say 15 or 16 years or up to 18. The fact that there is a disparity is because medicine etc is artificially increasing our life expectancy so that natural selection maybe will not operate in quite the same way. Anyway, of course, the evolution of menopause and reproduction and lifespan does not operate in isolation so other factors affecting our survival, and other aspects of ageing etc come into play.
Oh that was a bit of a ramble...
The main point aside from all that (that GypsyRosLee's GP was making) - our bodies do suffer and deteriorate from lack of oestrogen and I agree that it is bizarre to expect us to live 30-40 years without it ( due to our increased life-expectancy). As for hypothyroidism - many people who are given thyroxine will not have the condition anywehere near severe enough to die from it - under general NHS principles it is given when TSH falls outside the "normal" range (I'm not talking here about people who have no thryoid hormone production at all just as some people have no insulin). However it does improve quality of life enormously for those who take it, in the same way that oestrogen does.
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Hurdity x