• Akiko Shimada, Brian E Cairns, Nynne Vad, Kathrine Ulriksen, Anne Marie Lynge Pedersen, Peter Svensson, and Lene Baad-Hansen.
• Section of Clinical Oral Physiology, Department of Dentistry, Faculty of Health Sciences, Aarhus University, Vennelyst Boulevard 9, Aarhus C 8000, Denmark. akiko.shimada@odontologi.au.dk
• J Headache Pain. 2013 Jan 1;14:2.

BackgroundA single intake of monosodium glutamate (MSG) may cause headache and increased muscle sensitivity. We conducted a double-blinded, placebo-controlled, crossover study to examine the effect of repeated MSG intake on spontaneous pain, mechanical sensitivity of masticatory muscles, side effects, and blood pressure.MethodsFourteen healthy subjects participated in 5 daily sessions for one week of MSG intake (150 mg/kg) or placebo (24 mg/kg NaCl) (randomized, double-blinded). Spontaneous pain, pressure pain thresholds and tolerance levels for the masseter and temporalis muscles, side effects, and blood pressure were evaluated before and 15, 30, and 50 min after MSG intake. Whole saliva samples were taken before and 30 min after MSG intake to assess glutamate concentrations.ResultsHeadache occurred in 8/14 subjects during MSG and 2/14 during placebo (P = 0.041). Salivary glutamate concentrations on Day 5 were elevated significantly (P < 0.05). Pressure pain thresholds in masseter muscle were reduced by MSG on Day 2 and 5 (P < 0.05). Blood pressure was significantly elevated after MSG (P < 0.040).ConclusionIn conclusion, MSG induced mechanical sensitization in masseter muscle and adverse effects such as headache and short-lasting blood pressure elevation for which tolerance did not develop over 5 days of MSG intake.

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