If you use the Freestyle Libre CGM this article is for you! Learn the connection between the Freestyle Libre CGM sensor and vitamin C.
Freestyle Libre and Vitamin C – False Readings
To get the most accurate CGM readings there are a few things you need to know about… like compression lows, proximity to your insulin injections, and more.
And if you have the Freestyle Libre CGM then you can add vitamin C to that list.
Since Libre’s inception, Vitamin C has played a critical role in its accuracy. Even tho Abbott continues to come out with new models, their sensor chemistry has not changed.
On their indications & important safety information page they state,
“Taking ascorbic acid (vitamin C) supplements while wearing the sensor may falsely raise sensor glucose reading. Taking more than 500 mg of ascorbic acid per day may affect the sensor readings which could cause you to miss a severe low glucose event.”
Abbott, Freestyle Libre
What does 500 mg a day look like?
- 4 glasses of orange juice
- 11 oranges
- 2.5 cups of red bell pepper
- 3.5 kiwis
- 6 cups of strawberries
- 3.5 cups of broccoli
Unless you’re chasing lows all day with OJ, or pounding strawberry smoothies, it’s pretty hard to hit 500mg of vitamin C a day via whole foods.
What you do need to watch out for is supplements.
Supplements that contain over 500mg include:
- Airborne® (1,000 mg)
- Emergen-C® (1,000 mg)
- and many other Vitamin C supplements
Can I Still Use My CGM When Taking Vitamin C Supplements?
Yes! However, I wouldn’t bolus off the CGM results since they would be inaccurate. I would stick to finger sticks for the day(s) that you’re taking heavy dose supplements of Vitamin C.
Personally, I haven’t seen that the effects last past a few hours of taking high dose vitamin C, and the readings for me were never too far off, but you should definitely try it out yourself.
Will Abbot Change Their Sensor Chemistry?
Abbot is working on eliminating this issue because it is one of the reasons the FDA did not approve them to be an iCGM authorized for automated dosing systems.
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Very good to know! I’ve been using freestlye for years and had no idea about this. and i’m fairly certain i’ve taken airborne during that time too hahah – Oops!
Hahaha! I’ve taken high dose vitamin C without knowing this connection too.
this reminds me of dexcom with tylenol, same issue. Thank you for this. I’ve been using libre for over a year now and love it.
Yes!
wow, that is good to know. Thank you.
you’re welcome!
I am recently diagnosed, use diet and exercise instead of medicine… I go a little overboard… I wear the Libre 14 day and test regularly with both Accu Chek and One Touch… I take 1000mg of C daily, and i have not seen it affect the Libre’s accuracy… and i compare it to meter readings often
That’s awesome you’re seeing so much accuracy!
I took Apple cider vinegar in a shot glass. An hour later I put in my new CGM and it went bizzerk with below chart readings waking me up several times at night.. it was horrible. It is reading 20 below my normal level. Has this happened to anyone? I am reading that it raises it instead of falsely lowering.
Anyone have an idea of roughly what percentage the readings would overstated after taking a dose of 1000mg Vitamic C?
The freestyle libre 2 does come with a warning when starting up a new sensor, that high level of intake of vitamin C will cause you to miss a low glucose event because of false high readings.
Was this warning also available for the freestyle libre 1?
I incurred awkward situations as I was taking 5000 mg of Vitamin C during Covid…per theory from Nobel Prize winner Linus Pauling that high level of Vitamin C intake would help you fight viruses.
I have seen that on the Libre 3 start up screen as well. it is not on the libre 1 startup screen, but it is on the fine print (folded paper)… which nobody reads LOL. I have taken super high doses of vitamin C as well (for colds/flus/etc) and never personally experienced false readings.
How can you know if you are getting a false reading?
How can you know if you are getting a false reading?
Do a finger prick. The finger prick will be accurate. And if your CGM is far off from that finger prick number then you know the CGM is giving you a false reading.
I take 1000 mg vitamin C daily and use Dexcom G8 , my last two A1C readings were 0.4 points lower than Dexcom values. Dexcom claims that high doses of vitamin C doesn’t affect the readings!
I’ll switch to Libre 3+
What if you take 400mg in the morning, then take another 400mg later in the day. Vitamin c is reported to clear your system every x (4) hours. Why wouldn’t that work?