End of September 2011 till August 2012 I had chronic mid to lower back-pain with no apparent cause, and which prevented me from sleeping for three consecutive months, including severely limiting my mobility. Ten visits to a chiropractor didn't help much, and an MRI scan didn't reveal anything, until I discovered that supplementation with D3 can totally resolve the problem, which it did within several short weeks. There have been other benefits as well but too numerous to mention here. A high dose is vital, such as 20-30,000 ius per day.