If you’ve grown up with a glass of orange juice or serving of grapefruit as a permanent fixture at the brekkie table, you know how important vitamin C is. Water-soluble vitamin C, also known as ascorbic acid, keeps your cells healthy and is responsible for the growth and repair of tissues throughout the body. You also need vitamin C to keep skin supple, aid iron absorption, heal wounds, and form that all-important scar tissue. It also helps keep your bones, teeth, cartilage, and blood vessels in good working condition. While there’s no denying the benefits of vitamin C and how integral it is to our bodies, can you still have too much of vitamin c? If yes, what happens to your body when you do?
Vitamin C cannot be made by our bodies and must be sourced from our diet, and if necessary, from supplements. A water-soluble vitamin, it is not stored in the body and any excess amount is eliminated. So, the good news is its toxicity is very low and even high intakes are not linked to serious or fatal implications.1 That being said, excessive intake is associated with some side effects. Here’s what you should look out for:
Many of the side effects associated with excessive vitamin C supplementation have been seen in isolated cases or lab studies. In some cases, they have also been invalidated by other studies. But the bottom line is still that there are some potential risks you should be aware of, especially if you have pre-existing health conditions.
1. Gastrointestinal Disturbances
The most common side effects of taking too much vitamin C are stomach cramps, diarrhea, and nausea, all of which happen when the vitamin is not absorbed efficiently by the gastrointestinal system. The amount of vitamin C that can trigger these problems have been found to vary from person to person. While some reported problems after taking supplements of over 3 gm per day, others faced these only at 10 gm per day. Most mild to moderate cases tend to resolve when the supplements are temporarily stopped or the dosage reduced.2 3
2. Kidney Stones
When vitamin C is metabolized in the body, compounds called oxalate are produced which are normally excreted in urine. High levels of oxalate can combine with calcium in the bloodstream and raise your risk of kidney stones. Some studies implicate excessive supplemental vitamin C with a higher risk of kidney stones. In one prospective study among subjects aged 40–75 years, vitamin C intake from supplemental sources and foods were recorded every four years. At the 14-year follow-up mark, it was noted that those who took more than 1000 mg of vitamin C per day showed a 41% higher risk of kidney stones than those who took less than 90 mg every day.4 However, there have been conflicting results in other studies that did not find the same association. To be safe, however, people who are prone to kidney stones or have other renal problems should steer clear of high dose vitamin C supplementation.5 6
3. Iron Overload
[pullquote]Taking too much vitamin C has also been associated with lowered high-altitude resistance, wearing away of tooth enamel, and allergic reactions. As a matter of caution, if you do suffer from any of these side effects, discuss supplements you are taking with your physician.7[/pullquote]
Vitamin C promotes the absorption of non-heme iron and thus helps prevent iron deficiency anemia. Non-heme iron is iron sourced from plant-based foods and is also found in meat to some extent. Heme iron is rarely found in plant foods. A high intake of vitamin C could enhance iron absorption in people who already have high iron stores and can possibly lead to iron toxicity. By and large, this does not have an impact on healthy people. However, people who suffer from hereditary hemochromatosis, a rare disease where the body absorbs dangerously large quantities of iron, may face tissue damage if they consume high doses of vitamin C over long periods.8 9
4. Possibility Of Cardiovascular Disease
Vitamin C is well known for its antioxidant properties that protect the body from diseases. But can one have too much of a good thing? Possibly, under some conditions. One study showed that high doses of vitamin C supplements can trigger cardiovascular disease in individuals who already have other underlying health conditions – consuming over 300 mg per day of vitamin C supplements was associated with cardiovascular disease among postmenopausal women with diabetes. However, this was observed only in a single study and is not established firmly yet.10
5. Possibility Of Genetic Damage
While vitamin C is well-known for its antioxidant properties, some evidence point to its pro-oxidant tendencies in certain circumstances – one of them being higher dosages. In one study where healthy subjects were administered supplemental vitamin C every day for 6 weeks, oxidative damage was reported at a dosage of 500 mg per day. Researchers speculate that as a pro-oxidant, vitamin C supplements can alter and damage DNA and even lead to diseases like cancer. This effect was not seen in dosages less than 500 mg and may be restricted to excessive supplemental use rather than intake via natural foods. However, these claims have been disputed in other studies and will need further extensive study before it can be confirmed.11 12 13
6. Interference With Blood Thinning Drugs And Blood Tests
According to some research, vitamin C may react adversely with certain drugs. High dose supplements of vitamin C may block the functioning of blood thinners or anticoagulants, necessitating an increased dosage for the drug to stay effective. While there is no conclusive evidence to support this yet, experts still recommend that individuals taking blood thinners take no more than 1 gm of vitamin C a day and have their blood clotting mechanism regularly monitored.
Excess vitamin C may also interfere with the reading of certain lab tests such as those for serum bilirubin and serum creatinine, leading to incorrect results. It may also distort blood sugar tests. If you are slated for any medical tests, do inform your physician about the vitamin supplements you are taking.14 15
Stick To Recommended Intake
So how much vitamin C can you take safely? The recommended intake for adult males is 90 mg a day, while the level suggested for adult females is 75 mg. However, if a woman is pregnant she will need 85 mg every day, and if she is nursing, that requirement rises to 120 mg daily. Pregnant women, nursing mothers, smokers, burn victims, and those recovering from surgery may need more vitamin C as prescribed by their doctor. The Food and Nutrition Board (FNB) of the US Institute of Medicine has set the tolerable upper intake level (UL) of vitamin C to 2000 mg (2 gm). This indicates the maximum amount you can take daily without any adverse effects on your health. But even this level of intake should be under the guidance of a physician.16
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