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Too much vitamin C can cause severe insomnia


Moderator Resource
Southern California
I learned the hard way recently that too much vitamin C can cause severe insomnia. The insomnia which hit me seemed rather sudden onset (though in hindsight it may have come on gradually), and was different than my usual ME/CFS difficulty sleeping. I'd sleep or, rather, dose lightly from 9:30 to 11:00, and then be wide awake until 5:00 a.m. or later with no sleep in sight. It was a bit scary and took a bit of detective work to sort it out.

The culprit ended up being the (homemade) liposomal vitamin C I'd been taking for several weeks. Apparently I finally hit bowel tolerance (though did not connect that with the insomnia for over a week).

I could find scant information on-line, no studies, but just a few references to insomnia and too much vitamin C, and also one person's description of the insomnia which sounded like my experience: Too much vitamin C: Is it harmful? - Mayo Clinic
What Happened When I Took Too Much Vitamin C (spoonuniversity.com)

And the proof was in the pudding - when I stopped the vitamin C, I started sleeping again. It was a bit scary for several days until I figured this out!