side effects of too much vitamin c

Vitamin C is a vital nutrient for our body. It acts as an antioxidant and protects cells from the damage caused by free radicals. Our body also needs vitamin C to make collagen, a protein that helps to heal wounds. While we can get the required amount of vitamin C by eating a variety of fruits and vegetables, some of us opt for vitamin C supplements.

Many supplements contain very high doses of vitamin C, which can cause more harm than good. They can lead to diarrhea, nausea, stomach cramps, iron overload, and kidney stones. Read on to find out the correct dosage for vitamin C and the side effects of taking too much vitamin C.

What is vitamin C?

Vitamin C is a water-soluble nutrient that we need for the growth, development, and repair of all body tissues. Also known as ascorbic acid, L-ascorbic acid, and L-ascorbate, vitamin C is involved in many body functions including collagen formation, absorption of iron, helping the immune system to work correctly and maintenance of cartilage, bones, and teeth.

It helps metabolize protein, and its antioxidant activity can help reduce the risk of some cancers. Vitamin C is water-soluble, and the body does not store it. To maintain adequate levels of vitamin C in the body, we need to consume food rich in vitamin C.

How much vitamin C do you need?

According to the National Institutes of Health (NIH), the amount of vitamin C you need each day depends on your age (1) –

Life stage Recommended amount (mg)
Birth to 6 months 40
Infants 7 to 12 months 50
Children 1 to 3 years 15
Children 4 to 8 years 25
Children 9 to 13 years 45
Teens 14 to 18 years (boys) 75
Teens 14 to 18 years (girls) 65
Adults (men) 90
Adults (women) 75
Pregnant teens 80
Pregnant women 85
Breastfeeding teens 115
Breastfeeding women 120

People who smoke need to add 35 mg to the above values to calculate the amount of vitamin C they need daily.

Is it possible to take excessive amounts of vitamin C?

Since vitamin C is water-soluble, people assume that there is no harm in taking large doses. However, there can be many problems in taking high (500 to 1000mg) and very high doses(more than 2000 mg) of vitamin C. Very high doses of vitamin C supplements can cause diarrhea and gastric discomfort. While low dose vitamin C supplements help prevent cataract, high doses can increase the risk.

People who have a history of kidney stone formation, and those who experience iron overload should also exercise caution before using vitamin C supplements (2). If you overload your body with very high doses of vitamin C, it will start to accumulate, leading to symptoms of overdose. It is unnecessary for most people to take vitamin C supplements as you can easily get the recommended amount by eating various fruits and vegetables.

What are the side effects of too much of vitamin C?

1. Digestive distress

The most common complaint of excessive vitamin C intake is diarrhea, nausea, abdominal cramps, and gastrointestinal disturbances. These problems occur due to the osmotic effect of unabsorbed vitamin C in the digestive tract. These effects do not occur by taking food rich in vitamin C; they occur if you take very high doses of vitamin C supplements.

If you take doses higher than 2000 mg in one go, you are most likely to experience digestive distress (3). Some people have also reported that excessive doses of vitamin C lead to acid reflux, though any evidence does not support this. If you experience any of these digestive issues, you should cut back on your dosage or stop taking your supplement altogether.

2. Iron overload

Non-heme iron (derived from plant sources) is not as easily absorbed in the body as heme iron (derived from animal sources). Iron plays a vital role in the absorption of non-heme iron. It binds with the non-heme iron and makes it easier to be absorbed. According to a study by the Institute of Internal Medicine, the Department of Clinical Nutrition, the University of Goteborg, Sweden, iron absorption increased by 67% when they took 100 mg of vitamin C with a meal (4).

Since vitamin C enhances non-heme iron absorption, there is a concern that high vitamin C intakes may cause excess iron absorption. While this not a concern in healthy individuals, in individuals with hereditary hemochromatosis, chronic consumption of high vitamin C doses can increase iron overload. In such cases, iron overload can cause damage to the liver, heart, pancreas, thyroid, and the central nervous system (5).

3. Kidney stones

Oxalate is a bodily waste product that typically exits the body through urine. In some cases, this oxalate may bind with minerals to form crystals that can lead to the formation of kidney stones (6). High vitamin C intake can also increase urinary oxalate, which could lead to the formation of kidney stones (7). During one study, people with a history of oxalate stones were given one gram (group 1) or two grams (group 2) of vitamin C for three days. People with no history of oxalate stones were given a one-gram (group3) dose for three days.

The participants of the study were asked to refrain from consuming food rich in vitamin C during this time. The results showed statistically significant increases in oxalate excretion in all three groups: 61% in group 1, 41% in group 2, and 56% in group 3 (7). According to studies, not only does excessive vitamin C intake increase urinary oxalate, but it can also lead to kidney stone formation (8). There is also a report of acute renal failure in a patient who took extremely high doses of vitamin C. However; these cases are extremely rare (9).

4. Not recommended for diabetics

Too much vitamin C is not suitable for the hearts of people with diabetes. A study researched 2,000 women who have diabetes for nearly 15 years. The researchers found that the women who took heavy doses ( 300 mg a day or more) of vitamin C supplements were twice as likely to die of heart disease or stroke as compared to women who did not take vitamin C supplements.

According to researchers, though this research focused on women, the findings apply to men as well. The researchers suggested that people should bet their antioxidants from food rather than from supplements. The antioxidants in diet are balanced biochemically, while a vitamin pill lacks such a balance. Taking high doses of an antioxidant may perturb the body’s balance of antioxidants and pro-oxidants (10).

5. Drug interactions

Vitamin C supplements can also interact with some medicines that you take. There is evidence to show that vitamin C supplements interact with cancer treatments such as chemotherapy and radiation therapy. If you are taking cancer treatment, check with your doctor before taking vitamin C in high doses. During one study, vitamin C, and other antioxidants like vitamin E, selenium and beta carotene, reduces the heart-protective effects of statin and niacin to control blood cholesterol levels.

Doctors should monitor lipid levels in people taking both statins and antioxidant supplements. High doses of vitamin C supplements can interfere with tests for cholesterol, blood sugar, and for blood in the stool.

Do you need Vitamin C supplements?

It is always better to take your nutrients from food rather than pills. Increase your intake of the following vitamin C rich foods

  • Kakadu plums: 481 milligrams in one plum
  • Acerola cherries: 822 milligrams per 1/2-cup serving
  • Green chili pepper: 109 milligrams in one chili
  • Red pepper(raw): 95 milligrams per 1/2-cup serving
  • Guava(raw): 126 milligrams per one medium fruit
  • Orange juice: 90 milligrams per 3/4-cup serving
  • Orange: 70 milligrams per one medium fruit
  • Kiwi: 64 milligrams per one medium fruit
  • Green pepper(raw): 60 milligrams per 1/2-cup serving
  • Broccoli(cooked): 51 milligrams per 1/2-cup serving
  • Strawberries(sliced): 49 milligrams per 1/2-cup serving
  • Brussel sprouts(cooked): 48 milligrams per 1/2-cup serving
  • Tomato juice: 33 milligrams per 1/2-cup serving
  • Cantaloupe: 29 milligrams per 1/2-cup serving

Final thoughts

Vitamin C is a water-soluble nutrient we need for the growth, development, and repair of all body tissues. It is safe for people when you get it from foods rich in vitamin C like guavas, oranges, cherries, and Brussel sprouts. The recommended intake for vitamin C is 75 mg per day for women and 90 mg per day for men. You can get this amount from your daily diet.

People who take excessive amount (more than 2000 mg per day) vitamin C in the form of supplements can develop side effects. The side effects of vitamin C overdose include digestive distress, iron overload, and kidney stones. It can also harm people with diabetes. Excessive vitamin C can also interact with certain medications. You can avoid these side effects by avoiding vitamin C supplements. Unless prescribed by a doctor, large doses of vitamin C are unnecessary.