The website http://www.patientslikeme.com/ has lots of information about what people take for various chronic problems
There is a huge discussion section for each problem and treatment

The following are some vitamin D examples - Go to their web site to get LOTS of user comments

It is the # 1 supplement across ALL problems

Here is what patients use it for - and what they what kind of benefits they experience

Here is the use of vitamin D for fatigue