While vitamin C is an essential nutrient, too much vitamin C can be harmful. If you're getting vitamin C from foods, your chances of overdosing are slim, but it is possible take in too much of the vitamin if you're using supplements. While a vitamin C overdose is rarely toxic, it can cause some uncomfortable side effects.
Initially, you might notice stomach aches and cramps, diarrhea and nausea. Vitamin C can also interfere with your body's insulin response, causing spikes; decreased urine and urinary tract infections are common. Very high doses can even cause severe back pain, due to its effect on the kidneys.
If you take high levels of vitamin C for a long period of time, you can see other symptoms. For example, because vitamin C can be broken down into uric acid, it can increase levels of the acid in urine, which may raise risk of kidney stones. You can also experience jaundice, when your skin develops a yellowish discoloration. Another skin effect is itchy skin.
Also, if a mother has a consistent vitamin C overdose during pregnancy, the baby can experience scurvy due to vitamin C withdrawal after it has been born. The baby may have a lack of appetite, irritability, weight loss, dry rough skin and wounds that won't heal.
Too much vitamin C can also cause you to have too much iron in your body. Vitamin C can cause you to absorb more iron from plant foods and high supplemental doses of the nutrient can exacerbate this effect. Alternately, it can cause deficiencies in B12, zinc and copper.
Vitamin C is a water-soluble vitamin perhaps best known for its role in immune-system health: it protects you from infection, helps heal wounds and cuts and assists in red blood cell formation and repair.