On a related topic, I started taking bacopa monnieri and it improved my memory and mental endurance, anxiety and depression. I gave it to my wife and had the totally opposite effect:

https://en.wikipedia.org/wiki/Bacopa_monnieri

Also I can drink coffee and won't make any effect on my sleep, while my wife gets the boost. I wouldn't be surprised the effects of all those supplements depend on your body chemistry.

They can't differentiate the population, so all these studies will average zero.