Thanks for that. These studies discuss polypharmacy and the effect of inappropriate medication in the elderly. There is no association with the number of medications, but the type of medication used in the elderly. Cognitive impairment is mentioned, but I cannot find anywhere anything to support your assertion that more three medications is correlated with dementia. It's not a correlation, it's an association. In other words, demented people tend to be on a lot of tablets as a result of their condition, not as a cause as your use of words suggest. Correlation and association are different things, so it might be an idea to delete that sentence from your post in case folk get worried by it. And the one before it.
If that prompted you to decline medication because you were on more than three, then you can relax. If you ever, heaven forbid, get demented you might be on more, but you won't care then 🙂