Anybody have a CGM hack for taking vitamin c?

I’m having an issue with my Freestyle Libre. If I take any vitamin c my CGM suddenly says that I’m in the 200’s but a finger stick says I’m fine. I’d really like to be able to keep taking my vitamin c because I can feel the health benefits of doing so, but I’d also like to be able to rely on my CGM’s numbers. Anybody else have this problem? Suggestions? I know there is a warning on BG meters and CGMs about vitamin c but I never noticed any difference with finger sticks whether I was taking vitamin c or not.

This does not appear to be a universal problem.

For example, the Contour Next test strips make specific mention of this not being an issue for that particular BG meter/strip system:

Automatic compensation for many common interfering substances (such as acetaminophen and vitamin C)

The FreeStyle Libre system however has the following note which indicate this is a problem on their system:

Taking ascorbic acid (vitamin C) while wearing the Sensor may falsely raise Sensor glucose readings. Taking salicylic acid (used in some pain relievers such as aspirin and some skin care products) may slightly lower Sensor glucose readings. The level of inaccuracy depends on the amount of the interfering substance active in the body.


I had concerns about this too, so I called Abbott and asked about this interference. I’m taking a pill for an unrelated medical need that contains 250 mg of vitamin C. Abbott said this should be no problem and I’m not seeing any effect on my Freestyle readouts. I’m into my second sensor with the Libre — so far, so good. Perhaps at a higher dose level things start to go wonky?

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Sounds like an opportunity for a test/experiment…

Most folks don’t need supplements.

I do take higher doses. I tried taking just 1 pill (1000 mg) last night and it didn’t seem to adversely effect my readings. So maybe I need to just space out my doses throughout the day to mitigate this issue.

Does anyone know if Vitamin E or Calcium Citrate impact the freestyle?

I doubt that it would because vitamin c is the only vitamin singled out in the information pamphlet that comes with the Libre and none of my other supplements have given me wonky readings yet.

@Firenza - Just curious. What Vit C dosage did you take when you noticed the higher readings?

5000 mg

Do you think you will suffer some illness if you stop taking supplements?

I start to experience mild symptoms of scurvy (joint pain, nails breaking,etc.) if I don’t take supplemental vitamin c and I am on a diet that doesn’t include a lot of natural vitamin c which would be more effective in smaller doses because vitamins from food are better absorbed by our bodies.

Interesting, and sorry for your problem.

It’s an easy fix, so no big deal.

Have you tried eating more foods that have higher Vitamin C content? I take iron pills, but I don’t absorb the iron very well unless I take Vitamin C with it. I only take 500 mg and fortunately I haven’t had any issues with the Libre because of it.

I can’t eat a lot of the foods that are high in vitamin c, oranges for instance (I have unpleasant reactions when I eat them) and I don’t like bell peppers.

I’ve been taking my vitamin c in smaller doses throughout the day instead of all at once and that seems to prevent my Libre numbers from being affected.

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That is making it work for you.