I have read no books on Vitamin D and only a couple asthma-related articles on its benefits. My lungs were in severe pain and I had been looking for anything that could help, so I tried it. WOW. HUGE difference. Turns out D is extremely important and being deficient can impair and damage many things. It has helped with focus, agility, and I feel MUCH better. It has really help with my depression and lack of focus, which were very serious issues (I was unable to work.. seriously).

Try it for yourself and judge. Not the puny 400IU a day. Take 10,000IU a day for a week (it's not toxic) and see if you feel better.

I have hypothyroid and this perpetuates D deficiency.. I desperately needed it. But most people need more Vitamin D, and its effects are widespread and largely unknown. You can do your own research, but please don't tell me its toxic because of the FDA. Try for yourself and pay attention to your body. Just know 400IU is worthless.