Disadvantages of Vitamin C

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Vitamin C is a naturally occurring, water-soluble vitamin found in many different types of fruits and vegetables, and can also be taken as a nutritional supplement for its potential health benefits, such as its antioxidant properties. Despite its potential health benefits, vitamin C has some disadvantages as well, such as the risk for developing side effects when ingesting large doses of the nutrient. As with all nutritional supplements and vitamins, consult your physician before taking vitamin C supplements to make sure it is safe for you.

Gastrointestinal Distress

Large doses of vitamin C, or ascorbic acid, taken at one time might cause gastrointestinal distress, especially if you consume it on an empty stomach, according to the book, "Nutrition for Health, Fitness and Sport." Symptoms of gastrointestinal distress include upset stomach, nausea, indigestion, stomach cramps, headaches, fatigue, diarrhea and vomiting. These effects are usually mild and are related to the acidity of vitamin C, which can be minimized when taken with food or when combined with an alkaline base, such as calcium ascorbate, to help neutralize the acidity.


Hemochromatosis is a condition that involves excess iron in your body, which can have toxic effects. According to the National Heart, Lung and Blood Institute, a high intake of vitamin C can make the symptoms of hemochromatosis worse because vitamin C helps your body absorb more iron from foods and supplements. Hemochromatosis can poison your organs and cause organ failure, damaging your heart, liver and pancreas.


Vitamin C supplementation can affect the production of certain sex hormones, such as progesterone, especially during the early stages of pregnancy in women, according to the book, "New Encyclopedia of Vitamins, Minerals, Supplements and Herbs." Progesterone is important in the gestation process during pregnancy, and its release can be inhibited due to high concentrations of vitamin C circulating in your bloodstream. Low progesterone levels during pregnancy can increase the risk of the fetus developing birth defects.

Negative Effect on Performance

Vitamin C supplementation might have a negative effect on athletic performance. In a 2008 study published by the "American Journal of Clinical Nutrition," vitamin C supplementation decreased endurance capacity in athletes. The researchers say the adverse effects might be related to vitamin C's capacity to reduce the exercise-induced expression of key factors that are involved in the formation of new muscle cells, thereby preventing some of the natural cellular adaptations to exercise.

Kidney Stones

Excess vitamin C intake increases the risk of kidney stones, according to a report from Harvard Medical School, and men are particularly at risk. When some break down vitamin C in the body, it converts into oxalate, which can promote the formation of kidney stones. You should avoid high doses of vitamin C, and stay closer to the recommended intake of 75 milligrams per day for women, and 90 milligrams per day for men.