If your eyebrow is twitching and you aren't sure why, magnesium deficiency is one possible explanation. This deficiency is rare, however, even if your diet is low in this important nutrient, according to the University of Maryland Medical Center. If the twitching persists, see your doctor for a diagnosis.
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Magnesium and Muscles
When your body lacks sufficient magnesium or other electrolytes, such as salt and potassium, ion balance in the muscles or nerves may be disrupted, causing spasms. Magnesium deficiency may occur with medical conditions such as excess vomiting or diarrhea, irritable bowel syndrome, ulcerative colitis, diabetes or hyperthyroidism, according to UMMC. Other possible causes include heavy sweating or high intake of coffee or alcohol.