Clinical association of vitamin D and serotonin levels among patients with fibromyalgia syndrome.

Fibromyalgia syndrome (FMS) is a chronic disorder associated with severe pain. According to the National Fibromyalgia Association, the prevalence of FMS is between 3% and 6% in the general population, with about 90% of the patients being women. The primary goal of this study was to evaluate the relationship between vitamin D and serotonin levels and FMS severity.