Vitamin C Interactions/Interference

by James Sloane

Pharmaceutical drugs often react with foods and supplements, including vitamin C. And as we have seen, excessive vitamin C intake can interact with some nutritional compounds. Sometimes these interactions are beneficial, such as increasing the absorption of minerals. And sometimes it leads to problems such as iron overload or copper and B12 deficiencies.

Another area that is often overlooked is the interference of laboratory tests by excessive intake of vitamin C. For example, excessive vitamin C intake may lead to false high or low bilirubin levels, depending on the assay test being used. Lactate dehydrogenase, cholesterol, and triglyceride levels will read erroneously low. Aspartate aminotransferase levels may read erroneously high. The National Institute of Health (NIH) reported on a case in which a woman with unexplained anemia was taking 2,000mg of vitamin C daily. When tested for occult blood in the stool, repeated tests showed negative results. The woman discontinued taking the vitamin C for 4 days, and when retested stool samples tested positive for blood. It was also found that taking 750mg of vitamin C daily can interfere with detecting blood in the urine.

Vitamin C interferes with several glucose tests, including tests diabetics use at home. Urinary glucose test strips will test false positive with as little as 2,000mg of vitamin C daily. Home test strips can show normal blood glucose readings, even when glucose levels are elevated, also at 2g of vitamin c daily. Laboratory glucose tests may show erroneously low glucose levels with excessive vitamin C intake.

To decrease the risk of false laboratory readings it is recommended that all supplements be stopped at least 48 hours before having any lab work done.

Below is a link from the NIH and a portion of the article that discusses the interactions of vitamin c with drugs and supplements, and interference with laboratory tests.

http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-vitaminc.html

Interactions with Drugs

Acetaminophen (Tylenol): Vitamin C may increase adverse effects associated with acetaminophen.

Antacids: Vitamin C may increase adverse effects associated with aluminum- containing antacids such as aluminum hydroxide (Maalox, Gaviscon).

Aspirin: Vitamin C may increase blood levels and adverse effects of aspirin, whereas aspirin may decrease blood levels of vitamin C.

Barbiturates: The effects of vitamin C may be decreased by barbiturates including phenobarbital (Luminal, Donnatal), pentobarbital (Nembutal), or secobarbital (Seconal).

Fluphenazine (Permitil, Prolixin): Vitamin C supplementation may decrease levels of the drug fluphenazine in the body.

HIV medications (protease inhibitors): Concomitant administration of high doses of vitamin C can reduce steady-state indinavir plasma concentrations.

Levodopa (Dopar, Larodopa): There is limited case report evidence that high dose vitamin C may reduce side effects of levodopa therapy such as nausea or malcoordination.

Nicotine: Nicotine products such as cigarettes, cigars, chewing tobacco, or nicotine patches may decrease the effects of vitamin C. Oral contraceptives/estrogens: Oral estrogens may decrease the effects of vitamin C in the body. When taken together, vitamin C may increase blood levels of ethinyl estradiol.

Tetracyclines: The effects of vitamin C may be decreased by tetracycline antibiotics such as doxycycline (Vibramycin), minocycline (Minocin), or tetracycline (Sumycin).