Margo - I think it may be the The Framingham Study. This page talks about it here:
If you put the words: "higher risk of developing Alzheimer’s Disease TSH thyroid' into Google you will get lots of links to more information.
From a personal non medical point of view, I think there is a bigger picture than just the TSH levels - how many of the people in any of these studies have been looked at holistically? You only need to browse pages on this forum to see how many deficiencies co-exist (or are they the cause) with thyroid disease. There are many pages that link alzheimers with vitamin deficiencies.
I am so lucky that I don't have the extra worry about keeping TSH low to reduce the return of cancer risks - but gut istinct tells me I would want to keep it low and make sure all the usual vitamins we talk about on here are optimal.
As for family history - stories like the posters here sets me off on one!
So many of us seem to have similar experiences with relatives who had years of ill health ending in a tragic demise. My mother is just one who was labelled a hypochondriac and never got to the bottom of her illnesses and eventually died with stomach cancer. I obtained her medical records and found test results which clearly show she had pernicious anaemia amongst other things. Never diagnosed or treated. We know that B12 deficiency brings increased risk of stomach cancer. Need I say more? Her life was a misery which affected every member of the family and still does.
They didn't have access to information on sites and forum like we do now. GPs kept generations of people in the dark with no access to information and were treated like gods who could do no harm. Their secrecy protected them from ever being challenged. You can't challenge what you don't know.
Access to information is changing all that. The medical profession can't handle it and that's why you read so many posts of GPs that chastise or laugh at their patients for using the internet.
Three people on this little page: nobodysdriving, margo and numberone1, who all have similar stories to tell of family tragedy and it makes my heart ache. We see there are links don’t we?
It's a shame the medics don't spend more time on Google and listen to what their patients are telling them - it might make up for the lack of training and help them put the pieces of the jigsaw together like we have to do for them.