In this study of FM/chronic fatigue syndrome, patients who were good responders were found to be using a higher and more frequent doses of vitamin B12 for a longer period [17]
Doubt they will even ask about multivitamin/B complex/fortified food intake, all potentially affecting accuracy of even serum
Update (2023)
Cognitive difficulties: Often referred to as "fibro fog," this impairs the ability to focus, pay attention, and concentrate on mental tasks
Not only are they safe, but also like soya, flaxseeds may, in fact, be beneficial to those with breast cancer and who are on tamoxifen, with studies suggesting that its consumption may reduce the risk, growth and recurrence of breast cancer 36, 37, 38,39, 40