The common cold is typically caused by respiratory viruses, which antibiotics cannot treat. Therefore, there is a growing interest in exploring other options and natural remedies to combat the common cold.
One such remedy, vitamin C, is widely known for its antioxidant properties and its role in supporting your immune system. However, the question of whether vitamin C helps with colds remains.
In the United States, the Food and Drug Administration (FDA) does not regulate supplements the way it regulates prescription medications. That means some supplement products may not contain what the label says. When choosing a supplement, look for products independently verified and certified by organizations such as NSF, USP, and ConsumerLab. Consult your healthcare provider, registered dietitian nutritionist (RD or RDN), or pharmacist for further guidance.
Does Vitamin C Help Prevent or Treat Colds?
Vitamin C supplements may help to treat colds. However, it is unclear whether they can prevent colds. Vitamin C deficiency generally decreases immune function and increases your risk of infections.
Based on a group of studies, vitamin C supplementation may have helped prevent the common cold in the following groups of people:
- Don’t get enough vitamin C
- Engaged in extreme physical exertion
- Exposed to significant cold temperatures
Vitamin C levels may decrease during common cold episodes, suggesting that your body uses vitamin C during common cold infections. Furthermore, in clinical study, giving vitamin C during a common cold episode improved the decline of vitamin C levels. This suggests vitamin C may help you recover.
While vitamin C may shorten the duration and intensity of colds, the optimal dosage is unknown. However, clinical research has suggested 1 to 4 grams per day (g/day) of vitamin C for five days demonstrated effectiveness.
However, it’s important to note that the tolerable upper limit (UL) of vitamin C for adults is 2,000 milligrams (mg) per day. For children 1-3 years, the vitamin C UL is 400 mg; for 4-8 years, 650 mg; for 9-13 years, 1,200 mg; and 14-18 years, 1,800 mg. Avoid exceeding this amount unless under the guidance of your or your child’s healthcare provider.
What Is Vitamin C?
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin found in a variety of fruits and vegetables, including citrus fruits, strawberries, bell peppers, and broccoli. Its functions include the following:
- Helps your immune system function properly
- Protects your cells from free radical damage
- Promotes wound healing by helping produce collagen (a type of protein)
- Improves your body’s absorption of iron
A long-term vitamin C deficiency can cause a fatal disease called scurvy, a condition characterized by muscle weakness, swollen and bleeding gums, tooth loss, and anemia.
Vitamin C supplements are usually in the form of ascorbic acid, but also come in other forms, including the following:
- Sodium ascorbate
- Calcium ascorbate
- Other mineral ascorbates
- Ascorbic acid with bioflavonoids (a class of plant-derived antioxidants)
Little evidence indicates which form of vitamin C is better than the other. Your best choice may depend on your individual preferences or needs.
How Much Vitamin C Do I Need?
Several factors can contribute to not getting enough vitamin C, making it difficult for some individuals to meet the recommended dietary levels. These factors include the following:
- Suboptimal dietary habits
- Smoking
- Alcohol misuse and alcohol use disorder
- Substance use disorder
- Various diseases
- Exposure to pollutants, including smoke
- Economic reasons (e.g., limited access to nutritious food)
Excessive physical or psychological stress also increases vitamin C requirements.
Understanding the recommended daily intake, which varies based on age and other factors, is vital to help ensure you get enough vitamin C. The table below lists the average recommended dietary allowances (RDAs) of vitamin C based on different ages.
| Vitamin C Recommendations by Age and Life Stage | |
|---|---|
| Age Group | Milligrams (mg) |
| Adult (men) | 90 |
| Adult (women) | 75 |
| Teens 14-18 years (boys) | 75 |
| Teens 14-18 years (girls) | 65 |
| Children 9-13 years | 45 |
| Children 4-8 years | 25 |
| Children 1-3 years | 15 |
| Infants 7-12 months | 50 |
| Birth to 6 months | 40 |
Individuals Who May Need More Vitamin C
Specific factors and conditions can increase the body’s need for vitamin C. These include lifestyle habits, medical conditions, and specific life stages. Here’s a breakdown of some groups that may require higher vitamin C intake:
- Smokers: Vitamin C levels in smokers are lower than those in non-smokers due to increased oxidative stress caused by tobacco smoke. The recommended vitamin C intake for smokers is 35 mg per day, higher than that of non-smokers.
- People recovering from surgery: Vitamin C levels may drop in people recovering from surgery. Supplementation with vitamin C has decreased oxidative stress and heart muscle damage after heart surgery.
- Critical illness: Due to the significant inflammation and oxidative stress associated with burns, vitamin C requirements increase dramatically in people experiencing burns.
- Pregnant or breastfeeding women: Vitamin C requirements are higher during pregnancy and breastfeeding. The recommended daily intake for pregnant people is 85 mg, and for pregnant teens, 80 mg. For breastfeeding teens, the recommendation is 115 mg, and for breastfeeding people, 120 mg.
In adults, the daily upper limit for vitamin C intake from all sources, including food, beverages, and supplements, is 2,000 mg. Anything above this has the potential to cause adverse effects, particularly after more than five days.
Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian nutritionist (RD or RDN), pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.
Sources of Vitamin C
Since humans cannot produce vitamin C, it must be obtained from diet or supplements. Fruits and vegetables are rich sources of vitamin C, in addition to other vital nutrients.
- Vitamin C from food sources: The best way to obtain vitamin C is through fresh fruits and vegetables. Eating five servings (2.5 cups) of fruits and vegetables a day will provide about 200 to 250 mg of vitamin C.
- Vitamin C supplements: In general, a balanced diet should provide enough vitamin C for most people. However, there are situations where supplementation may be necessary. For example, people with limited access to fresh produce, those with specific health conditions, or people who can’t absorb vitamin C properly from food may benefit from supplements. The latter can be due to celiac disease, pancreatitis, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), bariatric surgery, smoking, specific medication use, and more.
- Medical use of vitamin C: In specific medical conditions, high doses of vitamin C may be needed to achieve an adequate therapeutic effect. For example, a dose of three to four grams per day given by injection into the vein may be necessary to normalize blood vitamin C levels in people with burns or sepsis (a life-threatening bodily response to an infection) or who are critically ill due to trauma. This medical use is typically supervised by healthcare providers.
Natural Sources of Vitamin C
Obtaining vitamin C from food sources is especially beneficial as these foods provide additional helpful nutrients, including vitamins, minerals, and fiber. Natural sources of vitamin C include, but aren’t limited to, the following fruits and vegetables:
| Natural Sources of Vitamin C | |
|---|---|
| Food | Vitamin C (mg) per Serving |
| Raw Red Bell Pepper, 1/2 Cup | 95 mg |
| Orange, 1 Medium | 83 mg |
| Kiwifruit, 1 Medium | 71 mg |
| Raw Green Bell Pepper, 1/2 Cup | 67 mg |
| Strawberries, 1/2 Cup | 50 mg |
| Grapefruit, Half | 46 mg |
| Cooked Broccoli, 1/2 Cup | 35 mg |
| Raw Kale, 1 Cup | 19 mg |
| Diced Cantaloupe, 1 Cup | 17 mg |
| Tomato, 1 Medium | 17 mg |
| Sauerkraut, 1/2 Cup | 11 mg |
Is Vitamin C Safe for Me?
Before adding vitamin C supplements to your routine, it’s essential to understand the potential risks, recommended dosages, and precautions, especially for people with specific health conditions.
High Dosages
While a single vitamin C dose of 5-10 grams taken by mouth has been considered safe, such a high dose is not recommended, particularly long-term.
Allergies
If you obtain vitamin C from supplements and are allergic to certain ingredients, pay close attention to the inactive ingredients contained in the supplements. You may wish to avoid specific vitamin-C-rich fruits and vegetables if you are allergic to them.
Precautions
Use vitamin C cautiously if you have the following conditions:
- Hemochromatosis: This condition causes excess iron build-up in the body. Because vitamin C improves iron absorption, take caution if you have hemochromatosis to prevent iron overload, which can lead to organ damage.
- Kidney stones: Vitamin C increases oxalate levels in the urine, increasing the risk of calcium stone formation. One study showed that taking vitamin C by mouth at a dose higher than one gram per day increases the risk of stone formation.
- Glucose-6-phosphate deficiency (G6PD): Individuals with G6PD deficiency may experience red blood cell destruction from high doses or intravenous vitamin C, especially when doses exceed four grams per day.
- Pregnancy: High vitamin C intake in mothers can cause rebound scurvy in newborns. It’s important to follow recommended guidelines for vitamin C intake during pregnancy.
Always consult with your healthcare provider before starting a supplement, especially if you have, or at risk for, underlying health conditions.
Interactions
Vitamin C may interact with specific treatments or medications, including the following:
- Cancer treatments: Vitamin C’s role in cancer therapy is complex. As an antioxidant, it may either protect tumor cells from treatment or safeguard normal tissues from damage. Intravenous vitamin C is sometimes explored as a potential anti-cancer treatment. Consult your healthcare provider before taking vitamin C or other antioxidants.
- Iron: Vitamin C increases iron uptake, helping your body absorb it better.
- Statins: Vitamin C, along with other antioxidants like vitamin E, selenium, and beta-carotene, may reduce the heart-protective effect of cholesterol-lowering drugs such as statins and niacin. However, the effect of vitamin C alone on the efficacy of cholesterol-lowering drugs is unclear due to the concurrent use of other antioxidants.
- Thyroid medications: Vitamin C increases absorption of levothyroxine, a thyroid hormone treatment.
This is not a complete list of interactions that may occur with vitamin C. Speak to your healthcare provider and pharmacist before starting vitamin C supplementation or adjusting your intake, and let them know what you take. This includes prescription and over-the-counter medications, vitamins, and herbal supplements.
Side Effects
While Vitamin C offers numerous health benefits, it’s essential to be aware of the following potential side effects, particularly when taking high doses:
- Diarrhea
- Nausea
- Stomach cramps
- Bloating
- False negative results in fecal occult blood test
- False high blood sugar levels
- Elevated uric acid, increasing kidney stone risk
- Calcium oxalate formation & kidney stone risk (e.g., in long-term kidney failure, high oxalate, or recurrent stones)
Always consult with your healthcare provider before starting supplementation, especially if you have underlying health conditions or are at risk for kidney stones.
Alternatives for Cold Prevention
In addition to vitamin C, several other measures can help prevent the common cold:
- Maintain adequate hydration: Drinking enough water keeps the mucous membranes wet, reducing the risk of colds and flu. Water also flushes out toxins from the body, helping strengthen the immune system.
- Eat immune-boosting foods: Specific foods and herbs contain bioactive compounds that strengthen the immune system. Citrus fruits, ginger, garlic, onion, elderberry, and turmeric are all rich in these beneficial compounds and may strengthen your immune system.
- Get adequate sleep: Getting enough quality sleep is essential in maintaining a healthy immune system. Adequate sleep duration reduces infectious disease risk.
- Manage stress: Mindfulness meditation decreases inflammatory markers, increases immune system defense, and protects against cell aging.
By incorporating these lifestyle habits—staying hydrated, eating immune-boosting foods, getting sufficient sleep, and managing stress, you can help strengthen your immune system and hopefully reduce the likelihood of catching a cold.
Summary
Known for its immune-boosting property, vitamin C has been shown to shorten the duration of the common cold and reduce the severity of its symptoms. Vitamin C may prevent the common cold only in a particular population group. The use of vitamin C after the onset of the common cold for treatment is unclear.
Though vitamin C is relatively safe, take caution with vitamin C supplements if you have specific medical conditions or undergo cancer treatments. Speak with your healthcare provider if you have further questions.
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