...is what scientists had when asked to say what would be a safe amount of alcohol to put by in a week, and they came up with the good-old "21 units of alcohol for men and 14 for women, first introduced in 1987." Ha! In other words, they were just making it up.
Which, of course, all boozers always suspected. Hands up: how many otherwise honest people have consistently lied to their doctor over the years about how much they soak up of a weekend?
It's an aspect of managing our lives which we've given over to people in authority. Any boozer knows when they've drunk too much because the next day they feel like shit and/or their nearest and dearest isn't speaking to them. And if that's happening to you regularly, then you've got a problem. You don't really need a numpty in authority to tell you.