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Vitamin C Side Effects & How to Prevent Adverse Reactions

Vitamin C side effects - Dr. Axe

Many studies have found that people who eat diets high vitamin C foods have better protection against diseases like cancer, vision loss and obesity, along with other positive vitamin C side effects. Also known as ascorbic acid, this water-soluble vitamin acts as an antioxidant. It helps reduce free radical damage and inflammation that can lead to many health problems.

Vitamin C is obtained from eating lots of different fruits and vegetables — such as citrus fruits like oranges, kiwi, berries and leafy greens — plus many people get additional vitamin C from supplements. Your body can't make its own vitamin C, and it's important to get an ongoing supply from your diet, since it is flushed out of your body regularly via urine. But can too much vitamin C have side effects?

While it doesn't happen very often, high doses of vitamin C taken in supplement form can cause "vitamin C toxicity," which is characterized by a number of adverse reactions. Potential negative vitamin C side effects can include digestive issues like diarrhea, nausea or abdominal cramps, along with insomnia, excess iron absorption and possibly kidney stones.

Positive Vitamin C Side Effects

If you don't get or absorb enough vitamin C from your diet, then there's good reason to supplement, considering how many vitamin C benefits there are. For example, vitamin C has the ability to:

  • Help slow the effects of aging by protecting against free radical damage/oxidative stress
  • Support the immune system and help fight infections and allergies
  • Counteract the negative effects of sun damage, cigarette smoke, air pollution and other environmental stressors
  • Lower the risk of certain types of cancers and also cardiovascular disease
  • Help to form collagen and maintain connective tissue, including the skin, bones, joints and blood vessels
  • Support eye health/vision and may reduce the risk for cataracts
  • Help with absorption of iron, thereby preventing issues like fatigue

Given that vitamin C in high doses can potentially cause side effects, is it a good idea to take extra vitamin C? Certain people can benefit from getting higher amounts of vitamin C compared to the general population. While it is an essential nutrient for everybody, those with the following conditions can especially benefit from a vitamin C-rich diet and/or supplements:

  • Anyone who smokes or is around secondhand smoke
  • People whose diets lack vegetables and fruits
  • Anyone with a medical condition that leads to severe malabsorption
  • Those with cancer
  • Anyone who abuses drugs and/or alcohol
  • Those living in poverty who may be undernourished

Negative Vitamin C Side Effects

The recommended daily allowance of vitamin C (RDA) for adults is between 75 to 90 milligrams (mg) per day depending on someone's age, while the safe upper limit is 2,000 milligrams a day, according according to the National Institutes of Health (NIH). This means that a general recommendation is to take no more than 2,000 milligrams per day of vitamin C, especially for weeks or months on end. Pregnant women need about 85 milligrams per day of vitamin C, while breastfeeding women require about 120 mg/day.

Is 1,000 mg of vitamin C too much? While the NIH recommends no more than 2,000 mg/day, according to the Linus Pauling Institute, "There is no reliable scientific evidence that doses of vitamin C up to 10 g/day (10,000 milligrams) in adults are toxic or detrimental to health." That said, you can only absorb so much vitamin C at one time, which means smaller doses are both safer and more effective.

If too much of this vitamin accumulates in the body, vitamin C side effects can possibly include:

  • Digestive issues like diarrhea, nausea or abdominal cramps
  • Heartburn
  • Headaches
  • Insomnia/sleeplessness
  • Skin flushing and redness
  • Accumulation of iron, which can damage tissue and cause problems with the kidneys
  • In rare instances, development kidney stones, increased oxidative stress and excess iron absorption

While eating foods that supply vitamin C is not dangerous and won't cause an overdose, taking vitamin C supplements in very high doses may be problematic. Usually vitamin C overdose treatment isn't necessary because the body can excrete vitamin C in the urine pretty quickly — however sometimes overdose/toxicity can lead to complications if it persists. Some people taking high vitamin C doses can develop problems due to iron accumulation, the urine becoming too acidic and the antioxidant balance in the body being disturbed.

Drug Interactions

Certain people are more likely to experience vitamin C side effects due to taking medications that may interact with vitamin C or if they have a health condition that affects absorption of this vitamin. In supplement form, especially in high doses, vitamin C can interact with a number of drugs. To be safe, vitamin C shouldn't be taken without supervision from a doctor if you take any of these drugs:

  • Certain cancer treatments (potentially chemotherapy)
  • Hormone replacement therapy/birth control pills containing estrogen
  • Aspirin
  • Statins/drugs used to control cholesterol levels
  • Niacin
  • Aluminum
  • Blood-thinning drugs, such as warfarin (Coumadin)
  • Antipsychotic drugs (like luphenazine or Prolixin)
  • The antiretroviral drug called Crixivan

How to Prevent Adverse Side Effects

The ideal way to prevent vitamin C side effects, while still getting the vitamin C your body needs, is to eat a variety of vitamin C-rich foods each day. Some of the foods richest in vitamin C include:

  • citrus fruits like oranges and grapefruit
  • leafy green vegetables
  • currants
  • red peppers
  • melon
  • berries
  • kiwi
  • tomatoes
  • guava
  • mango
  • broccoli and cauliflower
  • Brussels sprouts
  • peas
  • potatoes

What's the optimal vitamin C dosage per day?

As mentioned above, it's recommended that adults get between 75 to 90 milligrams per day of vitamin C. However, daily intake of vitamin C upward of 1,000 mg/day (in divided doses) may be more beneficial for certain people or during times of illness. Men need a bit more vitamin C than women do, while teens and children need between 40 to 65 mg/day.

Can you take vitamin C capsules daily?

Yes, just be sure to take a dose that is within the safe/recommended range. As long as you're not taking very high doses, if you take too much vitamin C (more than your body can use) you will urinate the extra amount out, typically within hours, but sometimes within several days.

How much vitamin C can the body absorb at one time?

In order to actually absorb vitamin C and prevent it from being lost in the urine, it's best to take smaller doses spread out throughout the day.

Taking between 200 and 500 milligrams per day of vitamin C seems to be plenty to experience health benefits, since much higher doses are unlikely to be absorbed and utilized when taken long term. In some cases, such as if you're feeling sick or have a health condition that means you could benefit from extra vitamin C, taking 1,000 milligrams may be beneficial. If you've been low in vitamin C for a while, you will be able to absorb and use more as your levels increase.

What's the best time to take vitamin C? Can you take vitamin C at night?

Vitamin C is found in most multivitamins, so if you already take a multivitamin supplement at certain time of day, then there's no reason to change what you're doing. Vitamin C is best absorbed when taken with a meal, so ideally have it with a meal or just after.

Risks and Precautions

To sum things up, there usually isn't much concern when it come to vitamin C side effects, considering that vitamin C is not stored in the body and excess amounts are excreted. In general, overdosing on water-soluble vitamins is not easy to do, but it is still important not to exceed the safe upper limit of 2,000 milligrams a day.

Because certain studies have found a link between taking vitamin C supplements and kidney stones, if you have a history of kidney stones, you should consider consulting with your doctor before starting supplementation. When it doubt, simply try increasing your intake of vitamin C foods and drinks to meet your daily needs instead of taking high doses of supplements.

Read Next: Vitamin C Deficiency Symptoms & How to Overcome Them