Health Benefits of Vitamin C Supplements (9 min.)

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Quick Summary

• Vitamin C does not prevent colds, but daily supplementation may reduce their length and severity†.
• Regular intake supports immune health, antioxidant protection, wound healing, and collagen formation†.
• Vitamin C enhances non-heme iron absorption and may support heart and brain health†.
• New research explores roles in gut health, cognitive function, and immune response, though more studies are needed†.
• The RDA is 75 mg/day for women and 90 mg/day for men, with a UL of 2,000 mg/day. Smokers need an extra 35 mg/day.
• Many fruits and vegetables contain vitamin C, and Cooper Complete supplements offer additional support†.

Many people reach for vitamin C supplements at the first signs of a cold. However, research has not shown significant benefits when vitamin C is taken after symptoms begin. On the other hand, taking vitamin C regularly may help reduce the frequency and duration of colds and other minor respiratory issues†.

COVID-19 heightened the awareness of supplementation and immune health, and nutrients like vitamin D, zinc, and vitamin C continue to be widely studied for their roles in supporting a healthy immune response†.

While the body cannot make vitamin C on its own, this essential nutrient plays a key role in protecting cells from oxidative stress and supporting immune system function†. Vitamin C also enhances iron absorption†, and may help maintain healthy cholesterol levels and cardiovascular function†.

Table of Contents

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• Vitamin C and Immune Health†
• Research on Vitamin C for Cold Prevention†
• Research on Vitamin C for Cold Treatment†
• Vitamin C Health Benefits†
• Emerging Research on Vitamin C†
• Vitamin C Deficiency
• Food Sources of Vitamin C
• Vitamin C Daily Intake Recommendations
• How Much Vitamin C Is Too Much?
• Vitamin C Frequently Asked Questions
• Summary

Vitamin C and Immune Health†

Vitamin C may not prevent illness outright, but it is essential to immune health and may help reduce the severity or duration of respiratory illnesses like the common cold†.

In a review of 29 clinical trials involving more than 11,000 participants, researchers examined the effects of daily vitamin C on cold prevention and treatment†.

Research on Vitamin C for Cold Prevention†

For the general population, routine vitamin C supplementation did not significantly reduce the risk of developing colds. However, in a subset of studies involving individuals under intense physical stress, such as marathon runners, skiers, and soldiers in cold climates, daily vitamin C supplementation cut cold incidence by roughly 50%†.

While more research is needed, these findings suggest that vitamin C may offer protective benefits in extreme conditions†. This aligns with Kenneth H. Cooper, MD, MPH‘s early work with athletes, which showed increased nutritional needs in individuals with high levels of physical activity.

Cooper Complete® Natural Vitamin C includes bioflavonoids and provides antioxidant support for immune system function†. As an antioxidant, vitamin C helps neutralize free radicals—unstable molecules that can damage healthy cells†.

Research on Vitamin C for Cold Treatment†

Despite popular belief, high doses of vitamin C taken at the onset of a cold have not shown consistent benefits in clinical trials. Studies indicate that starting vitamin C supplementation after symptoms have appeared truly does not noticeably shorten the cold duration or severity†.

Plainly stated, “The trials in which vitamin C was introduced at the onset of colds as therapy did not show any benefit.” Unfortunately, reactive supplementation does not seem to reduce the symptoms or the duration of the cold.

A large meta-analysis published in PLOS Medicine looked at 55 studies on vitamin C and the common cold. To qualify for inclusion in the meta-analysis, the trials used doses of 200 mg per day or more of vitamin C, with some studies going as high as 1,000 mg (1 gram) daily.

While the researchers found that taking vitamin C after symptoms began didn’t reduce the severity or duration of the colds, regular daily supplementation was associated with a modest but measurable benefit. On average, cold duration was reduced 8% in adults and 14% in children. These findings suggest that while vitamin C may not be effective as a treatment once a cold starts, consistent daily use could help shorten the duration of illness when it does occur.

Vitamin C Health Benefits†

Vitamin C supports many functions in the body and must be replenished daily because it is water-soluble and not stored long-term. Key benefits include:

• Collagen formation – Vital for building and maintaining healthy skin, cartilage, bones, and blood vessels. Collagen also supports skin elasticity and joint function†
• Wound healing – Helps the body repair tissue by supporting new cell growth and strengthening connective tissue†
• Tooth and gum maintenance – Maintains gum integrity and helps prevent gum bleeding by supporting collagen in gum tissue†
• Iron absorption – Enhances absorption of non-heme iron from plant foods, helping prevent iron deficiency and supporting red blood cell production†
• Antioxidant support – Helps protect cells from oxidative stress by neutralizing free radicals, supporting immune and cellular health†
• Heart health – May help support healthy cholesterol levels and blood vessel function, with research linking higher intake to reduced cardiovascular risk†

These roles make vitamin C essential for daily maintenance, especially for individuals who may have increased nutrient needs or limited dietary intake.

(Bonus: Learn about the two types of iron, and how iron benefits the body†.)

Emerging Research on Vitamin C

While vitamin C’s benefits for immune health, collagen production, and antioxidant production are well known, new research continues with the goal of uncovering potential roles for this essential nutrient. Much of this emerging research comes from observational studies and pilot trials. While these findings are promising, it’s important to remember that observational studies can suggest associations, but cannot prove cause and effect, and pilot studies are small by design and not strong enough to support definitive conclusions. A pilot study will either eliminate an idea or have encouraging enough results that researchers move forward with a larger trial. Recent findings include:

• Enhanced immune support – Certain forms of vitamin C, like calcium ascorbate, may help immune response by increasing vitamin C levels in white blood cells†
• Cognitive health – Higher vitamin C intake has been linked to better mental performance in older adults, suggesting potential brain health benefits†
• Gut microbiome support – Preliminary studies indicate vitamin C may promote beneficial gut bacteria and help maintain a strong intestinal lining†

Vitamin C Deficiency

A diet low in fruits and vegetables may lead to inadequate vitamin C intake. Individuals who smoke or have certain health conditions, such as hyperthyroidism, are at a greater risk. Common symptoms of vitamin C deficiency include bleeding gums, bruising easily and slow wound healing.

Food Sources of Vitamin C

Because the body cannot make vitamin C, it depends on food or supplements. Many fruits and vegetables provide ample vitamin C, it’s not just citrus. Some excellent sources include:

Fruits

• ¾ cup grapefruit juice: 248 mg
• 1/2 medium cantaloupe: 100 mg
• 1 cup sliced strawberries: 98 mg
• 1 small papaya: 94 mg
• 1 large kiwi: 84 mg
• 1 cup passionfruit: 71 mg
• 1 medium orange: 70 mg
• 1 cup mango: 60 mg
• 1 cup tangerines: 52 mg
• 1 plantain: 50 mg
• 1/2 cup orange juice: 41 mg

Vegetables

• 1 cup sliced bell pepper: 74 mg
• 1 cup cooked chopped broccoli: 74 mg
• 1 cup of cauliflower: 56 mg
• 1 cup cooked kale: 53 mg
• 1/2 cup Brussels sprouts: 48 mg
• 1 cup of asparagus: 45 mg
• 1 cup tomato juice: 44 mg
• 1 cup peas: 32 mg
• 1 medium sweet potato: 22 mg
• 1 cup onion: 12 mg
• 1 cup carrots: 7 mg

Vitamin C Daily Intake Recommendations

The Recommended Dietary Allowance (RDA) for vitamin C:

• 75 mg per day for adult women
• 90 mg per day for adult men
• 85 mg for pregnant women
• 120 mg for lactating women

The RDA table specifies that tobacco users should add 35 mg per day. As vitamin C is water-soluble, any excess vitamin C is excreted in urine.

Research reported in the American Journal of Clinical Nutrition found that increasing intake from 200 to 2,500 mg only slightly raised blood levels, due to limited absorption and increased elimination.

Vitamin C in Cooper Complete Supplements

Several Cooper Complete formulations contain vitamin C. The chart below shows the amount of vitamin C found across the Cooper Complete line.

Vitamin C in Cooper Complete Supplements
Cooper Complete Supplement	Amount Per Serving
Natural Vitamin C	850 mg
Basic One Multivitamin	150 mg
Original Multivitamin	500 mg
Collagen Complex	100 mg
Dermatologic Health	350 mg
Quercetin Complex	300 mg
Berberine Complex	10 mg
Eye Health	350 mg

How Much Vitamin C Is Too Much?

The upper intake level (UL) for vitamin C is 2,000 mg per day. High doses may cause:

• • Upset stomach, nausea, or diarrhea

• Increased risk of kidney stones
• Tooth enamel damage (especially with chewables or gummies)
• False blood glucose readings in home tests

Vitamin C can also interact with medications such as antacids and acetaminophen, so it’s important to talk with your physician or health care provider before starting a new supplement routine.

Vitamin C Frequently Asked Questions

Q: Is natural vitamin C better than synthetic vitamin C?
A: Chemically, natural and synthetic vitamin C (ascorbic acid) are identical in structure and absorbed the same by the body. The difference is that natural sources, such as oranges and other citrus fruits or rose hips, also provide bioflavonoids and plant compounds that may offer added antioxidant support†. Rose hips are a popular botanical source of vitamin C in supplements, but their vitamin C content is relatively low, so products often combine rose hips with ascorbic acid to deliver a meaningful dose†.

Q: Are rose hips, a natural form of vitamin C available in supplements, better than synthetic vitamin C?
A: Chemically, synthetic vitamin C (ascorbic acid) is identical to natural vitamin C in molecular structure and has the same bioavailability, so the body absorbs and uses natural and synthetic vitamin C the same way. Rose hips are a natural plant source of vitamin C.

Q: Can taking vitamin C prevent colds?
A: For most people, vitamin C does not prevent colds. However, daily use may slightly reduce the severity and duration of colds, and it may be more effective for people under extreme physical stress, such as marathon runners†.

Q: What’s the best time of day to take vitamin C?
A: Because vitamin C is water-soluble, it does not need food, so it can be taken with or without food. We recommend taking vitamin C with food as this reduces the chance of stomach upset.

Q: How much vitamin C should I take daily?
A: The Recommended Daily Allowance (RDA) is 75 mg for adult women and 90 mg for adult men. Tobacco users should add 35 mg per day. The tolerable upper intake level (UL) for adults is 2,000 mg per day.

Q: Are there side effects of taking too much vitamin C?
A: Although the body eliminates vitamin C that isn’t needed, too much vitamin C can cause gastrointestinal distress such as diarrhea, nausea, or stomach upset. High levels of vitamin C can also increase the risk of kidney stones in some people. It’s important to talk with your physician or health care provider before starting high-level vitamin C supplementation.

Summary

While not a cure-all, vitamin C supports a healthy immune system and, when consistently taken, may help reduce the frequency and duration of minor respiratory illnesses and support overall nutritional needs†.

Cooper Clinic recommends focusing on a diet rich in fruits and vegetables first, with supplementation to bridge nutritional gaps as needed.

As a reminder, your physician or health care provider understands your health profile best, so it’s important to talk to them about which supplements are best for you.

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About the Author: Jill Turner is the President of Cooper Complete® Nutritional Supplements, where she oversees product development and customer experience. She enjoys writing about vitamins, supplements, and preventive health to help consumers make informed, science-backed decisions.

Cooper Complete August 15, 2025