The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Avoid if sensitive or allergic to any ingredients present in Vitamin C products.
Side Effects and Warnings
Vitamin C is generally regarded as safe in amounts normally obtained from foods. Vitamin C supplements are also generally regarded as safe in most individuals in recommended amounts, although side effects are rarely reported, including nausea, vomiting, heartburn, abdominal cramps, and headache. Dental erosion may occur from chronically chewing vitamin C tablets.
High doses of vitamin C have been associated with multiple adverse effects. These include kidney stones, severe diarrhea, nausea, and gastritis. Rarely, flushing, faintness, dizziness, and fatigue have been noted. In cases of toxicity due to massive ingestions of vitamin C, forced fluids, and diuresis may be beneficial. In postmenopausal women with diabetes, supplemental vitamin C in doses greater than 300 milligrams daily has been associated with increased risk of heart-related death.
Healthy adults who take chronic large doses of vitamin C may experience low blood levels of vitamin C when they stop taking the high doses and resume normal intake. To avoid this potential complication, people who are taking high doses who wish to reduce their intake should do so gradually rather than acutely. There are rare reports of scurvy due to tolerance or resistance following cessation after long-term high-dose use, such as in infants born to mothers taking extra vitamin C throughout their pregnancy.
Vitamin C in high doses appears to interfere with the blood-thinning effects of anticoagulants such as warfarin by lowering prothrombin time (PT). Caution is advised in patients with bleeding disorders or those taking drugs that affect bleeding. Dosing adjustments may be necessary.
Vitamin C may affect blood sugar levels. Caution is advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
Use cautiously in patients with cancer, glucose-6-phosphate dehydrogenase deficiency, anemia and related conditions, kidney stones, or sickle cell disease, or after angioplasty. Use cautiously in patients taking antibiotics, anticancer agents, HIV medications, barbiturates, estrogens, fluphenazine, or iron supplements. Use parenteral (injected) vitamin C cautiously, as it may cause dizziness, faintness, or injection site discomfort, and in high doses, it may lead to renal insufficiency (kidney function problems).
Avoid in patients with known allergies or hypersensitivities to any ingredients in Vitamin C products. Avoid high doses of vitamin C in people with conditions aggravated by acid loading, such as cirrhosis, gout, renal tubular acidosis, or paroxysmal nocturnal hemoglobinuria. Avoid high doses of vitamin C in patients with kidney failure or in those taking agents that may damage the kidneys, due to an increased risk of kidney failure.
Pregnancy and Breastfeeding
Vitamin C intake from food is generally considered safe during pregnancy. It is not clear if vitamin C supplementation in amounts exceeding Dietary Reference Intake recommendations is safe or beneficial during pregnancy. There are rare reports of scurvy due to tolerance or resistance in infants born to mothers taking extra vitamin C throughout the pregnancy. The data are too few to say if vitamin C supplementation alone or combined with other supplements is beneficial during pregnancy. Preterm birth may increase with vitamin C supplementation.
Vitamin C is present in breast milk. Vitamin C intake from food is generally considered safe in breastfeeding mothers. Limited research suggests that vitamin C in breast milk may reduce the risk of developing childhood allergies. It is not clear if vitamin C supplementation in amounts exceeding Dietary Reference Intake recommendations is safe or beneficial during breastfeeding.