Vitamin C is a water-soluble substance and therefore it does not accumulate in the body. This explains the absence of any data on vitamin C toxicity. Vitamin C itself has lower toxicity and only minor adverse effects, such as diarrhea, nausea and other digestive disturbances.
These disorders are osmotic withdrawal of water from the intestinal contents by the unabsorbed vitamin C in the gastrointestinal tract. Other physiological disorganizations include metabolic acidosis and altered levels of clotting factors such as prothrombin for the high level of vitamin C.
Vitamin C metabolism produces oxalate as a product. Some research suggests that vitamin C supplements may increase urinary concentrations of oxalate. It may make double the risk of kidney stones from calcium oxalate.
Several drugs reduce levels of vitamin C, such as birth control pills. Those contain estrogen, barbiturates, and tetracyclines. Vitamin C also increases estrogen levels.
Regular intake of aspirin over a certain frequency, such as 1000 mg every 6 hours, increases urinary excretion of vitamin C. It reduces your blood levels. Vitamin C causes higher serum levels of aspirin and other NSAIDs.
Vitamin C can inhibit the action of warfarin. The dosage of warfarin thus requires to be monitored for prothrombin time. It can also reduce the cardioprotective action of cholesterol-lowering drugs such as simvastatin and niacin. The evidence is far from clear. Some large judgments indicate that it does not affect the positive effects of these drugs.
It has been suggested that the use of vitamin C during chemotherapy of the cancer cell could decrease the effectiveness of the treatment by protecting the tumor cells from destruction. Another study, however, indicates that vitamin C exerts a possible protective effect on normal cells against damage induced by radiotherapy or chemotherapy.
It has also been suggested that high doses of vitamin C could lead to oxidative damage contributing to the production of the free radical. But this has not been shown experimentally.
Tests such as serum bilirubin, serum creatinine and the guaiac test for the presence of hidden blood depend on the presence of reducing substances. Vitamin C levels may interfere with its interpretation.
Vitamin C and cardiovascular disease
A single study showed that vitamin C supplementation appeared to increase the mortality of cardiovascular disease in postmenopausal diabetic women. But this has never been confirmed.
Vitamin C and mineral cushioning
Vitamin C can theoretically cause excessive iron cushioning. This is likely to be significant only in those who have hereditary hemochromatosis and consume high doses of vitamin C.
When taken together with aluminium antacids, vitamin C reinforces the dumping of aluminium and therefore the risks of side effects.
Megadoses of vitamin C in pregnancy can cause scurvy of rebound in the child due to the sudden drop in levels. It causes a relative deficiency of the vitamin in the baby’s blood after birth. Above vitamin C 1000 of magnesium should be avoided in pregnancy unless on medical advice.
Doubtful harmful effects
Other doubtful effects, which have been increased over the years, but never proven to exist, include:
- Reduction in vitamin b12 and serum copper levels
- Erosion of tooth enamel
- Vitamin C allergy
Prevention of the harmful effects of vitamin C
Higher FNB-established levels are age-specific and are thought to prevent side effects. Precautions to prevent adverse reactions include:
- Adequate fluid intake to counteract the diuretic effect of vitamin C supplements
- Avoid vitamin C supplementation if you have hemochromatosis, sickle cell anemia, G6PD, or thalassemia.
- Medical advice you seek before starting vitamin C supplementation, in case of kidney disease or during chemotherapy.
- Stopping nicotine use if you plan to take vitamin C supplementation.
- stopping vitamin C supplements just before or after angioplasty