Magnesium, Stress and Fibromyalgia

Fibromyalgia affects an average of 2% of the French population. Data from the literature report that low levels of magnesium could be associated with fibromyalgia. However, no study to date has investigated the effect of oral magnesium administration on stress in fibromyalgia.

This trial therefore aims to evaluate whether magnesium could improve stress and the various disorders that contribute to the complexity of fibromyalgia, including pain, cognition, sleep disorders and quality of life.

This is an interventional, randomized, placebo-controlled, double blind study of the use of magnesium in fibromyalgia. The effect of magnesium on stress measured by DASS-42 over 28 days after taking magnesium / placebo will be studied.

The secondary objectives will evaluate the evolution of the scores of all the tests and questionnaires carried out before taking magnesium or placebo (D0: Visit 2), then at D0 + 28 (visit 3) and D0 + 84 days (visit 4 corresponding to the end-of-study visit).

Secondary parameters are the following :

Impact of fibromyalgia, heart rate variability, pain intensity, cognition, feelings of patients, impression of change, sleep quality, fatigue intensity, social vulnerability, catastrophism, presence of small fiber neuropathy, stress induced by colors, pain induced by thermal stimulation, concentration of magnesium, analysis of microbiota and evaluation of genetic factor.

Blood magnesium and magnesuria will be measured.

Eligibility Criteria:
Inclusion Criteria:

* Patient over the age of 18,
* Patient with fibromyalgia according to the criteria of the 2016 ACR,
* Patient presenting a score on the DASS-42 \> 18 scale,
* Patient free from any initiation of new treatment or diet at the time of inclusion,
* Cooperation and understanding sufficient to comply with the requirements of the study,
* Acceptance to give written consent,
* Affiliation to the French Social Security system,
* Registration or acceptance of registration in the National Register of Volunteers participating in research.

Exclusion Criteria:

* having a contraindication to the administration of magnesium: hypersensitivity to magnesium chloride, or to any of the excipients,
* with a magnesium concentration of \> 1.05 mmol / l,- with severe renal impairment with a creatinine clearance \< 30 ml / min,
* receiving a treatment or dietary supplement containing magnesium at the time of inclusion,
* treated with antibiotics in the three months prior to inclusion,- who has reported gastroenteritis in the two months prior to inclusion,
* physically unfit to place the palms or soles of the feet on the Sudoscan® electrodes,
* having a medical and / or surgical history judged by the investigator or his representative to be incompatible with the test (in particular a disease known to cause small fiber neuropathies: diabetes, Sjögren's disease, vasculitis, sarcoidosis, chronic ethylism ....),
* using anticoagulant therapy or allergy to local anesthetics,- of childbearing age not using an effective contraceptive method, pregnant or breastfeeding woman.
* participating in another clinical trial, or being in the exclusion period, or having received a total amount of benefits exceeding EUR 4500 over the 12 months preceding the start of the trial,
* having cooperation and understanding that does not allow strict compliance with the conditions laid down in the Protocol,
* benefiting from a measure of legal protection (guardianship, guardianship, deprivation of liberty, safeguard of justice),
* not affiliated to the French Social Security system.