Summary - Taking particular supplements may produce a blood glucose reading that is erroneously higher than the actual glucose concentration due to the non-specificity of the various tests. False high readings can be misdiagnosed as high glucose levels, a result that can have dangerous repercussions. Prescription of medication that reduces actual blood glucose levels in people with false high readings can result in hypoglycemia and death. If you are having a blood glucose test and are taking supplements that can increase the concentration of reducing agents in your blood (e.g. Vitamin C, N-acetylcysteine, glutathione, Vitamin U), be sure to mention it to your medical practitioner.
Quantifying blood sugar levels is a standard medical procedure that is commonly used to diagnose diabetes. There are many different tests used to quantify glucose. The tests typically use an enzyme to catalyze the oxidation of glucose. This reaction usually involves a cofactor that is reduced during the process. A third molecule reacts with the reduced cofactor to produce a colored product which can be readily measured and the concentration of glucose deduced.
If you have looked at your lab results, you may have seen a note that taking supplements such as Vitamin C, N-acetylcysteine or glutathione may affect blood glucose test results. These chemicals are reducing agents and act as antioxidants in your body. In their reduced form, these chemicals have a similar reactivity to that of the reduced cofactor in the reaction coupled with glucose oxidation. Consequently, when moderate amounts of these supplements show up in the blood, they will also react with the indicator to produce a color. Grzych et al (2021) showed that even modest amounts of these supplements in the blood can lead to a false positive result for diabetes based on seven commonly used glucose test kits.
If your medical practitioner is unaware you are taking these or similar supplements, they may mistakenly think you have elevated blood glucose and prescribe medication to decrease your sugar levels. Such measures are very dangerous in people with normal blood glucose levels as medication that stimulates the removal of glucose will result in hypoglycemia (low blood glucose). Accidental death has unfortunately occurred from this very problem. When your medical practitioner asks whether you are taking supplements, it is certainly in your best interest to list everything you take so they may interpret lab results in a fuller context.
Vitamin U is not a reducing agent, so it will not directly react with the indicator. However, Vitamin U is metabolized into compounds that are reducing agents, such as S-adenosylmethionine (SAM), homocysteine, cysteine and glutathione. Therefore, if you are getting a blood glucose test and are taking Vitamin U, it would be wise to tell your medical practitioner about this supplement.