I guess it depends on your credibility thresholds. I take vitamin D because some studies say it's good for you, none say it's bad, and some people on the inter

I guess it depends on your credibility thresholds. I take vitamin D because some studies say it's good for you, none say it's bad, and some people on the internet report subjective cognitive & mood enhancement. It costs me around $5/year. Sure, it might be doing nothing. But even a subtle cognitive or mood enhancement would easily be worth two orders of magnitude more than that, so I only have to think there's a 1% chance of a tiny effect before it becomes worth it.