This paper came up on my news feed today: https://www.jabfm.org/content/jabfp/33/6/842.full.pdf
According to the research, daily intake of glucosamine/chondroitin supplements for at least a year is associated with a 39% reduction in all-cause mortality.
This is a cohort study, not a randomized trial, so the evidence is not conclusive. Individuals taking supplements were self-selected. Perhaps there is another factor not controlled for in the paper. The researchers are calling for a more thorough study.
However a 39% reduction appears to be a pretty large effect. And glucosamine/condroitin supplements are fairly inexpensive and available over-the-counter, and seem likely to be relatively harmless even if the effect is illusory. Maybe the kind of person who takes this kind of bet comes out ahead, even if they're wrong sometimes.
I'm not looking for mere social permission or a gut-feel answer here. I want to understand your reasoning. How should a rationalist reason about this? Do we plug numbers into a Bayesian net? Should I take the bet and start supplementing daily? Is the effect too small to bother with? Should I wait for more evidence?