> "morning coffee" could be anything from plain espresso shot to full 600+ calorie starbucks "coffee" but the meta-study-machine will lump them together.
You're inadvertently proving my point, though.
If morning caffeine is correlated with longevity, regardless of the vehicle/extra sugar/etc and controlling for the easy usual circumstances like income, that's pretty useful information!
But if sugar is worse by more than caffeine is good your study is in trouble. Or maybe it works but it is harmful because people who don't like coffee are going to buy the bad sugar drinks trying to get the good coffee down.
It might be useful information for other researchers to try to figure it what is actually going on, but probably not. And it is not at all useful for you and I trying to make sense of what we should eat.
You're inadvertently proving my point, though.
If morning caffeine is correlated with longevity, regardless of the vehicle/extra sugar/etc and controlling for the easy usual circumstances like income, that's pretty useful information!