Several years ago, I started supplementing with vitamin D (D3, by the way; there is a difference) due to a history of cancer on one side of the family. I wasn't

Several years ago, I started supplementing with vitamin D (D3, by the way; there is a difference) due to a history of cancer on one side of the family. I wasn't expecting to feel anything. Within two days, my mood stabilized significantly. It took me about a week of first noticing this and then thinking about what had changed in my life, to reach the hypothesis that it was the vitamin D. That was when I started noticing and paying attention to reporting and comments regarding this effect. It's significantly more effective than any pharmaceutical or other supplement I've taken with this purpose in mind. And, like the parent comment, I had to discover it and figure it out on my own. If I discontinue the vitamin D, the effect goes away. Except in the summer, if and only if I'm outside and getting plenty of sun exposure. By the way, I think that initial dose was 1000 or 2000 IU, daily. Not an "extreme" dose, compared to some I hear about, but significantly more than the U.S. FDA's recommended daily allowance (RDA). AS I understand it, the FDA's RDA was developed (decades ago) as basically the amount that prevents rickets disease. These days, I take it together with some K2. Supposedly, the K2 helps keep calcium fixed in your bones; higher doses of vitamin D work to mobilize it, both weakening bones and causing calcium deposits where you don't want them. CAUTION: This is what I've heard from some medical professionals, but I can't vouch for it. With vitamin D supplementation, as with most things, moderation and appropriate dosing are probably important. However, my OPINION based upon my experience is that the FDA's RDA is too low.