GC and myalgic encephalomeyelitis/chronic fatigue syndrome: It has recently been shown that there is a need to assess all of the vitamin D metabolites.35 It may be more appropriate to measure the amount of serum-free and bioavailable 25(OH)D as a predictor of vitamin D status than serum total 25(OH)D, while controlling for vitamin D binding protein phenotype.36 Future studies assessing these aspects of vitamin D metabolism in patients with CFS/ME are warranted.