Jo, I had never read/heard anything like this either...

Dr. Bernstein, 2007 update of Diabetes Solution, pg 65:

"Dietary vitamin C is important to good health. In doses above 500 mg/day, however, vitamin C supplements can destroy the enzymes on blood sugar test strips and can also raise blood sugars. Finally, in levels higher than about 400 mg/day, vitamin C becomes an oxidant rather than an antioxidant and can cause neuropathies. If you are already taking supplemental Vitamin C, I urge you to taper it off or lower your dose to no more than 250 mg daily. Only use the timed-release form."

Dr. Bernstein also says that more than his recommended amount of Vit C will falsely lower A1c readings.

Jo, my concern is that I have taken 4000 mg daily for many years!

I'm still looking for causes for my ISFPN.