What is an adequate sample size depends entirely on the effect size.

Yep. I wouldn't eat a mushroom that killed someone, sample size being 1

I've also had anecdotal experience in agreement with this. There have been many studies on this but most of them have a similar small sample size. Wonder why it hasn't been conducted with a larger sample size yet, or maybe it has but didn't find anything so it's not being posted on HN ¯\_(ツ)_/¯