It makes me think of all those reports that claim that having a single glass of wine per day makes you healthier.
It's probably the case that people who have just one glass of wine are drinking socially, and therefore have friends, and having friends is an indicator of having status and health. The alcohol itself is poison but one glass is more than offset by otherwise living a good life.
Oh they studied this! It's because if you're the kind of person who can afford a glass of wine every day, you're also the kind of person who can afford health care. In USA at least.
Here's the best source I can find right now:
> The study authors write that βthe observed cardiac benefits of alcohol have been hypothesized to be the product of residual confounding because of favorable lifestyle, socioeconomic, and behavioral factors that tend to coincide with modest alcohol intake.β
You just don't see a lot of sedentary people with poor nutrition who have a high muscle mass index.