BV123,
I'm neither a doctor nor a healthcare professional. But your description of your nightcap very much brings to mind a very close relative of mine. Before I describe our situation, I would like to make it clear I'm not saying you are like the person I'm talking about. I'm just writing this as it sounds like someone has possibly made a comment to you which has made you think about the quantity of your nightcap, and they possibly had a good reason for mentioning it.
The person I am talking about has a nightcap that isn't excessive by any standards, but when it kicks in, there is no question about the negative effect it has on their behaviour. Is it affecting their health? Probably not. Is it shortening their life? Who knows for sure. And if they're happy, who are we to judge. They do not drink and drive and they live alone.
The downside to the drinking is that we will not phone them after 5.30pm as conversations are pointless, often descending into unpleasantness. Staying with them becomes quite uncomfortable as the time comes for the nightcap. It can turn quite nasty, and we would rather not be in their company. If we are like that, what effect is it having on this person's friends? If you were invited for supper with someone you know drinks in a way that is detrimental to their behaviour, chances are you'd turn that invitation down.
As I say, this is a very close member of our family. We have tried to address the drinking, but it is somewhat of a taboo subject. And we go back to "if its not harming anyone, is it really that wrong?"
I don't know if this is any help to you, just my thoughts on how it affects others and how our situation is from our perspective.