When I was having severe energy and pain issues, my doctor suspected fibro and also low Vitamin D. He said that people with fibro or depression almost always test low on D, but said the jury was out on which was the cause and which was the effect. The lab test showed <0.4 (My guess is that's as sensitive as the lab equipment could detect. Probably should have gone in before I felt at death's door.) My doctor immediately started me on prescription D. 50,000 units once a week for a couple of months and to spend as much time as possible outside. Within about a month my energy levels were getting close to normal.

I'm not sure that a lamp would help much though. I take 5,000 D daily in addition to my lifestyle; I live in San Diego, CA, am outside gardening almost everyday year round and have a very low level of stress, and yet I don't have high levels of D. My last test put me in the lower end of normal range.

I suspect that there is an underlying reason that some people burn through D that hasn't been addressed or studied. I think there might be some merit in studies that look into the causes of low vitamin D and how to retain it as opposed to what to sell people to increase it.