Association of Membrane Polyunsaturated Fatty Acid Content and Intracellular Magnesium Concentration With Mental and Physical Symptoms in Fibromyalgia and SLE: a Case-control Study

Background:

Fibromyalgia is a common, chronic pai n disorder that is recognized by the American College of Rheumatology as a distinct clinical entity (1). In addition to the core feature of long-term, body-wide "soft tissue" pain, patients often report co-morbid mental and physical symptoms, including exercise intolerance, un-refreshing sleep, depressed mood and anxiety (2). Much remains to be learned from the disorder's pathophysiology, but evidence exists of inter-related perturbations involving the nervous, endocrine and immune systems (2,3). For instance, depressive and anxiety symptoms are common and frequently severe, even in community studies of FM (4). Fibromyalgia patients exhibit an increase in pro-inflammatory cytokines, which may contribute to pain and emotional distress (5,6). Although nutrients such as polyunsaturated omega-3 fatty acids and magnesium attenuate hypersensitivity to pain, little is known about the impact of nutrition on the development and persistence of fibromyalgia (7).

Polyunsaturated omega-3 fatty acids (ω3 PUFAs) are essential nutrients that are not sufficiently consumed by many individuals. The brain accrues long-chain ω3 PUFAs -particularly DHA- and a sufficient supply of ω3 PUFAs is necessary for CNS development and function (8). The accessibility of circulating PUFAs renders them suitable for assessment of PUFA status in epidemiologic studies. Indeed, studies indicate that the incidence of Major Depression (MD) is inversely related to the consumption of fish (which are rich in ω3-PUFAs) and to the concentration of ω3 PUFAs in the plasma or Red Blood Cell (RBC) membranes. RBC ω3 PUFA content is negatively correlated to the degree of depression in different settings. In several studies, the ω6 to ω3 ratio was elevated (ω6 PUFAs are pro-inflammatory, compared to ω3) (9-14). ω3 PUFAs are also inversely associated with anxiety and neuroticism (15,16) but apparently not with somatization (12).

Supplementation of fish oil alleviates joint pain in patients with auto-immune disease (17). Inhibition of pro-inflammatory cytokines (which induce both pain and depression-like symptoms) by ω3 PUFAs may underlie the benefit conferred by fish oil consumption (18). Interestingly, RBC ω3 PUFA content is lower in patients with Systemic Lupus Erythematosus (SLE, refs 19,20) and chronic fatigue syndrome (CFS, ref 21), compared to healthy controls. SLE and CFS are considered to be auto-immune and functional disorders, respectively, but both share characteristics of fibromyalgia: a higher incidence in women, increased depressive co-morbidity and the frequent presence of fibromyalgia-like symptoms (22,23). However, the ω3 PUFA status of fibromyalgia patients has not been assessed.

Magnesium is an essential nutrient and plays a regulatory role in neural transmission. It appears to counter the development of hyperalgesia by inhibition of the NMDA-receptor (24,25). Intracellular magnesium concentration reflects magnesium intake, distribution and secretion, and varies widely between individuals. It is not known whether magnesium concentration is associated with pain in humans.