In regards to CFS and vitamin D you must maintain a serum vitamin D level of between 50-80 ng/ml, 25 OH D.
If your doctor has indicated a sufficiency level of 30 ng/ml, 25 OH D, he/she needs to look at the new research, NOW!
The higher serum levels make al lthe difference in the world.
Do your own research at sites dedicated to D research. DO NOT accept repeated, parroted standards as they were based on a derth of research.
50-80 ng/ml, 25 OH D, is the natural healthy range of humans in sunny places. 30 ng/ml, 25 OH D, is associated with numerous chronic conditions and early onset diseases, including CFS.
It can do no harm to raise serum vitamin D to healthy levels. Should someone say otherwise do your own research and find a new health care professional.
There is no excuse to suffer continuously with CFS. Rsise your serum vitamin D and see the difference a few 1000 i.u. / day can make!