Abstract
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.
Highlights
A single intake of monosodium glutamate (MSG) may cause headache and increased muscle sensitivity
Healthy young men who consumed a single dose of 150 mg/kg MSG had a significant increase in headache and craniofacial muscle sensitivity as well as an elevated systolic blood pressure [13], suggesting that MSG consumption may trigger more types of craniofacial pain than just headaches
There is evidence that glutamate concentrations are elevated in painful regions of masticatory muscles of myofascial Temporomandibular Disorders (TMD) patients compared to healthy controls [16]
Summary
A single intake of monosodium glutamate (MSG) may cause headache and increased muscle sensitivity. Healthy young men who consumed a single dose of 150 mg/kg MSG had a significant increase in headache and craniofacial muscle sensitivity as well as an elevated systolic blood pressure [13], suggesting that MSG consumption may trigger more types of craniofacial pain than just headaches. The resulting elevation of interstitial glutamate concentration sensitizes muscle nociceptors to mechanical stimuli [15]; an effect which could underlie reports of craniofacial muscle pain sensitivity in healthy young men given MSG [13]. There is evidence that glutamate concentrations are elevated in painful regions of masticatory muscles of myofascial TMD patients compared to healthy controls [16]
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