Vitamin c and immunity

You may have noticed the vitamin C section of the supplement aisle looking bare these days or seen the claims on social media that vitamin C can help with COVID-19.

While physicians and researchers are studying the effects of high dose intravenous (IV) vitamin C on the new coronavirus, no supplement, including vitamin C, can prevent or treat COVID-19.

This article reviews what vitamin C is, how it affects immunity, how it’s being tried for COVID-19 treatment in a hospital setting, and whether taking an oral supplement is beneficial.

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What is vitamin C?

Vitamin C is an essential nutrient with several roles in your body. It’s a potent antioxidant, meaning it can neutralize unstable compounds in your body called free radicals and help prevent or reverse cellular damage caused by these compounds (1 ✓Source✓).

It’s also involved in a number of biochemical processes, many of which are related to immune health (1 ✓Trusted Source).

The Daily Value (DV) for vitamin C is 90 mg per day, but breastfeeding women need an extra 30 mg and people who smoke need an extra 35 mg per day (2 ✓).

It’s pretty easy to meet your vitamin C needs through your diet as long as you eat a variety of fruits and vegetables. For example, a single medium orange provides 77% of the DV, and 1 cup (160 grams) of cooked broccoli provides 112% of the DV (3 ✓Trusted Source, 4 ✓Trusted Source).

How does it affect immunity?

Vitamin C affects your immune health in several ways. Its antioxidant activity can decrease inflammation, which may help improve your immune function (5 ✓TrustedSource).

Vitamin C also keeps your skin healthy by boosting collagen production, helping the skin serve as a functional barrier to keep harmful compounds from entering your body. Vitamin C in the skin can also promote wound healing (1Trusted Source).

The vitamin also boosts the activity of phagocytes, immune cells that can “swallow” harmful bacteria and other particles (1Trusted Source).

In addition, it promotes the growth and spread of lymphocytes, a type of immune cell that increases your circulating antibodies, proteins that can attack foreign or harmful substances in your blood (1Trusted Source).

In studies of its effectiveness against viruses that cause the common cold, vitamin C doesn’t appear to make you any less likely to get a cold — but it may help you get over a cold faster and make the symptoms less severe (6Trusted Source).

There’s also some evidence from animal research and case studies in humans that high dose or IV vitamin C can reduce lung inflammation in severe respiratory illnesses caused by H1N1 (“swine flu”) or other viruses (7Trusted Source, 8Trusted Source, 9Trusted Source).

However, these doses were far above the DV, and there’s not enough research to support the use of high dose vitamin C for lung inflammation at this time. You shouldn’t take high doses of vitamin C supplements — even orally — because they can cause side effects like diarrhea (2).

Dosing

The following doses have been studied in scientific research:

BY MOUTH:

General: The daily recommended dietary allowances (RDAs) are: 90 mg for men and 75 mg for women; Pregnancy and Lactation: age 18 or younger, 115 mg; ages 19 to 50 years 120 mg. People who use tobacco should take an additional 35 mg per day. Do not take more than the following amounts of vitamin C: 1800 mg per day for adolescents and pregnant and breast-feeding women 14 to 18 years, and 2000 mg per day for adults and pregnant and lactating women.

For vitamin C deficiency: 100-250 mg once or twice daily for several days for scurvy.

For an eye disease that leads to vision loss in older adults (age-related macular degeneration or AMD): 500 mg of vitamin C, 400 IU of vitamin E, and 15 mg of beta-carotene, with or without 80 mg of zinc, per day for up to 10 years.

For irregular heartbeat (atrial fibrillation): 1-2 grams of vitamin C per day for 1-3 days before heart surgery followed by 1-2 grams in two divided doses daily for 4-5 days after heart surgery has been used.

For emptying the colon before a colonoscopy: 2 liters of solution containing polyethylene glycol and vitamin C is used the evening prior to colonoscopy or as a split-dose taken on the evening prior to and the morning of colonoscopy. The most commonly studied product for this indication is MoviPrep (Norgine BV).

For treating the common cold: 1-3 grams daily.

For preventing limb pain that usually occurs after an injury (complex regional pain syndrome): 500 mg of vitamin C each day for 50 days starting right after the injury.

For airway infections caused by exercise: 600 mg to 1 gram of vitamin C per day for 3-8 weeks before heavy exercise has been used.

For swelling (inflammation) of the stomach (gastritis): 1200 mg of vitamin C daily along with omeprazole has been used.

For a condition in which red blood cells are broken down faster than they are made (hemolytic anemia): 200-300 mg of vitamin C three times per week for 3-6 months has been used.

For high cholesterol: 500 mg vitamin C each day for at least 4 weeks.

For high blood pressure: 500 mg of vitamin C per day along with blood pressure-lowering medication has been used.

For treating the reduced benefit of nitrate therapy that happens when nitrates are used all day (nitrate tolerance): 3-6 grams of vitamin C daily has been used.

For osteoarthritis: 1 gram of vitamin C in the form of calcium ascorbate daily for 2 weeks has been used.

For reducing pain after surgery: 2 grams of vitamin C one hour prior to anesthesia has been used.

For preventing sunburn: 2 grams of vitamin C along with 1000 IU vitamin E taken before sun exposure has been used.

APPLIED TO THE SKIN:

For skin redness caused by injury or irritation (erythema): A formulation containing 10% vitamin C, 2% zinc sulfate, and 0.5% tyrosine applied daily for 8 weeks has been used.

For skin wrinkles from sun damage: Most topical vitamin C products are applied daily. Studies have used creams containing 3% to 10% vitamin C. Don't apply vitamin C preparations to the eye or eyelids. Also avoid contact with hair or clothes. It can cause discoloration.

BY IV:

For irregular heartbeat (atrial fibrillation): 2 grams of vitamin C once or twice in the day before heart surgery followed by 1-2 grams daily for 4-5 days after heart surgery has been used.

For reducing pain after surgery: 3 grams of vitamin C during the first 30 minutes of surgery has been used.

CHILDREN

BY MOUTH:

General: The daily recommended dietary allowances (RDAs) are: Infants 0 to 12 months, human milk content (older recommendations specified 30-35 mg); Children 1 to 3 years, 15 mg; Children 4 to 8 years, 25 mg; Children 9 to 13 years, 45 mg; Adolescents 14 to 18 years, 75 mg for boys and 65 mg for girls; Pregnancy and Lactation: age 18 or younger, 115 mg. Do not take more than the following amounts of vitamin C: 400 mg per day for children ages 1 to 3 years, 650 mg per day for children 4 to 8 years, 1200 mg per day for children 9 to 13 years, and 1800 mg per day for adolescents and pregnant and breast-feeding women 14 to 18 years.

For an inherited disorder marked by the body's inability to properly break down the amino acid tyrosine (tyrosinemia): 100 mg of vitamin C has been used in premature infants on high protein diets.

BY IV:

For an inherited disorder marked by the body's inability to properly break down the amino acid tyrosine (tyrosinemia): 100 mg of vitamin C has been used in premature infants on high protein diets.

AS A SHOT:

For an inherited disorder marked by the body's inability to properly break down the amino acid tyrosine (tyrosinemia): 100 mg of vitamin C has been used in premature infants on high protein diets.

Side Effects & Safety

When taken by mouth: Vitamin C is LIKELY SAFE for most people when taken by mouth in recommended doses. In some people, vitamin C might cause nausea, vomiting, heartburn, stomach cramps, headache, and other side effects. The chance of getting these side effects increases the more vitamin C you take. Amounts higher than 2000 mg daily are POSSIBLY UNSAFE and may cause a lot of side effects. These may include kidney stones and severe diarrhea. In people who have had a kidney stone, amounts greater than 1000 mg daily greatly increase the risk of kidney stone recurrence.

When applied to the skin: Vitamin C is LIKELY SAFE for most people when applied to the skin.

When given by IV: Vitamin C is LIKELY SAFE for most people when given by IV by a health care provider.

When given as a shot: Vitamin C is LIKELY SAFE for most people when given as a shot into the muscle by a health care provider.

Special Precautions & Warnings:

Pregnancy and breast-feeding: Vitamin C is LIKELY SAFE for pregnant or breast-feeding women when taken by mouth in amounts no greater than 2000 mg daily for women over 19 years-old, and 1800 mg daily for women 14 to 18 years-old, or when given intravenously (by IV) or intramuscularly and appropriately. Taking too much vitamin C during pregnancy can cause problems for the newborn baby. Vitamin C is POSSIBLY UNSAFE when taken by mouth in excessive amounts.

Infants and children: Vitamin C is LIKELY SAFE when taken by mouth appropriately. Vitamin C is POSSIBLY UNSAFE when taken by mouth in amounts higher than 400 mg daily for children 1 to 3 years, 650 mg daily for children 4 to 8 years, 1200 mg daily for children 9 to 13 years, and 1800 mg daily for adolescents 14 to 18 years.

Alcoholism: Alcohol intake can cause the body to excrete vitamin C in the urine. People who regularly use alcohol, especially those who have other illnesses, often have vitamin C deficiency. These people might need to be treated for a longer time than normal to restore vitamin C levels to normal.

Alzheimer disease: Taking vitamin C along with vitamin E and alpha-lipoic acid might worsen mental function in people with Alzheimer disease.

Angioplasty, a heart procedure: Avoid taking supplements containing vitamin C or other antioxidant vitamins (beta-carotene, vitamin E) immediately before and following angioplasty without the supervision of a health care professional. These vitamins seem to interfere with proper healing.

Weight loss surgery: Weight loss surgery can cause the body to absorb more oxalate from food. This can increase the amount of oxalate in the urine. Too much oxalate in the urine can cause problems such as kidney stones. Vitamin C can also increase the amount of oxalate in the urine. Taking large amounts vitamin C after weight loss surgery might increase the risk of having too much oxalate in the urine.

Cancer: Cancerous cells collect high concentrations of vitamin C. Until more is known, only use high doses of vitamin C under the direction of your oncologist.

Kidney disease: Vitamin C can increase the amount of oxalate in the urine. Too much oxalate in the urine can increase the risk of kidney failure in people with kidney disease.

Diabetes: Vitamin C might raise blood sugar. In older women with diabetes, vitamin C in amounts greater than 300 mg per day increases the risk of death from heart disease. Do not take vitamin C in doses greater than those found in basic multivitamins.

A metabolic deficiency called "glucose-6-phosphate dehydrogenase" (G6PD) deficiency: Large amounts of vitamin C can cause red blood cells to break in people with this condition. Avoid excessive amounts of vitamin C.

Blood-iron disorders, including conditions called "thalassemia" and "hemochromatosis": Vitamin C can increase iron absorption, which might make these conditions worse. Avoid large amounts of vitamin C.

Kidney stones, or a history of kidney stones: Large amounts of vitamin C can increase the chance of getting kidney stones. Do not take vitamin C in amounts greater than those found in basic multivitamins.

Heart attack: Vitamin C levels are reduced during a heart attack. However, low vitamin C has not been linked to an increased risk for heart attack.

Kidney transplant rejection: Long-term use of vitamin C in high doses before a kidney transplant may increase the risk of transplant rejection or delay how long it takes until the transplanted kidney works.

Schizophrenia: Taking vitamin C along with vitamin E might worsen psychosis in some people with schizophrenia when taken with antipsychotic drugs.

Smoking and chewing tobacco: Smoking and chewing tobacco lowers vitamin C levels. Vitamin C intake in the diet should be increased in people who smoke or chew tobacco.