Lots of information on the NHS website is out of date because they haven't embraced new research. One prime example is their advice to people at risk of diabetes: several diabetes charities and experts have criticised NHS dietary advice which is outdated now re. fat in diet as opposed to limiting carbs.
This would surely mean that women not taking HRT would be protected past the date of their menopause too, from their natural oestregen?
You don't have any after the menopause (or only the minutest amount - hence osteoporosis occurs post menopause.)
In terms of research yes, here is a link which I hope is helpful.
www.thebonejournal.com/article/S8756-3282(03)00479-4/abstract
Post menopause, women lose up to 5% of their bone each year rapidly for 5 years then the loss slows down a little.
It used to be thought that the rate of bone loss after using HRT was the same- a rapid fall. The link shows otherwise.
The other point is that for someone who has osteopenia and uses HRT for maybe 5 years, her bones are going to be better for some time compared to if she'd not used it. It can keep someone in the osteopenia range rather than the full osteoporosis range for longer and give them a window to build bone through exercise and diet at the same time.
There are also some consultants who prescribe tiny doses of estrogen 0.25mgs - to prevent osteoporosis as shown in this paper by Panay.
nickpanay.com/Papers%20pdf/Low%20Dose%20HRT%206th%20IMS%20Workshop.pdf
He says that there is even no need with ultra low doses for progestogens (which are shown to possibly increase breast cancer.)
if you are one of the very, very few women who have special risks, then you must do what your consultant advises. For women who do not have special risks this is what consultant Dr Currie shows on her website.
menopausematters.co.uk/balance.php