Are you reaching for orange juice or vitamin C supplements when you feel a cold coming on? This practice became popular thanks to Linus Pauling, a two-time Nobel laureate who advocated for high daily doses of vitamin C (equivalent to that found in 12 to 24 oranges) to prevent colds and chronic diseases starting in the 1970s.
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin. This means it dissolves in water and travels throughout the body, but isn’t stored effectively. Therefore, daily intake through food or supplements is essential. Long before its scientific identification in 1932, the importance of citrus fruits in preventing scurvy was understood. Scurvy was a deadly disease that affected millions of sailors between the 16th and 19th centuries. [1]
Vitamin C is crucial for immune function, wound healing, and acts as a potent antioxidant, neutralizing harmful free radicals in the body. It’s also vital for the production of collagen, a structural protein found extensively throughout the body, including in the nervous, immune, skeletal, and circulatory systems. Furthermore, vitamin C aids in the synthesis of various hormones and neurotransmitters essential for brain and nerve function. [2]
While high-dose vitamin C supplementation is common, understanding the optimal amount needed for health and whether excessive intake could be harmful is important.
Recommended Daily Vitamin C Intake
- Recommended Dietary Allowance (RDA): For adults aged 19 and older, the RDA is 90 mg per day for men and 75 mg per day for women. During pregnancy, the recommendation increases to 85 mg daily, and for breastfeeding women, it’s 120 mg daily. Smokers need an additional 35 mg per day due to the vitamin C depleting effects of smoking.
- Tolerable Upper Intake Level (UL): The UL represents the maximum daily intake unlikely to cause adverse health effects. For vitamin C, the UL is 2000 mg per day. Exceeding this amount may lead to gastrointestinal issues like stomach upset and diarrhea. Higher doses above the UL are sometimes used in specific clinical settings under medical supervision, such as in controlled clinical trials. [2]
Vitamin C Absorption and High Doses
The body’s capacity to absorb vitamin C in the intestines is limited. Studies indicate that vitamin C absorption significantly decreases to less than 50% when intakes exceed 1000 mg. In generally healthy individuals, very high doses of vitamin C are not typically toxic because once the body tissues are saturated, absorption decreases, and excess vitamin C is excreted in the urine. However, negative effects are possible with daily intakes above 3000 mg. These can include diarrhea, increased risk of kidney stones particularly in those with pre-existing kidney conditions or a history of kidney stones, elevated uric acid levels (a gout risk factor), and increased iron absorption potentially leading to iron overload in individuals with hemochromatosis, a genetic condition causing excessive iron accumulation. [2] Vitamin C absorption is similar whether it comes from food or supplements. In some medical contexts, vitamin C is administered intravenously (directly into a vein) to achieve higher blood levels. This is generally restricted to medically supervised settings, such as to improve quality of life for cancer patients or in research studies. While clinical trials haven’t shown negative side effects from high-dose intravenous vitamin C, it should only be given under strict medical supervision and avoided in people with kidney disease, hemochromatosis, and glucose 6-phosphate dehydrogenase deficiency. Vitamin C is involved in numerous metabolic processes, and meeting the RDA or slightly exceeding it may offer protection against certain diseases. However, no proven health benefits have been found in healthy, well-nourished people taking very large amounts of vitamin C. Research in cell studies suggests that in very high concentrations, vitamin C can reverse its role and act as a pro-oxidant, potentially causing tissue damage instead of providing antioxidant benefits. [2, 3] The effects of extremely high doses of vitamin C, far exceeding the RDA, in humans are not fully understood and could increase the risk of kidney stones and digestive upset.
Vitamin C and Its Impact on Health
Vitamin C’s antioxidant properties are of significant interest, as research has demonstrated its ability to neutralize free radicals, which can damage cells if present in excess. Vitamin C also supports the immune system by enhancing the activity of white blood cells. But does this translate to protection from specific diseases?
Chronic Diseases: While some large-scale observational studies following groups of people over time have suggested a protective association between higher vitamin C intake (from both food and supplements) and reduced risk of cardiovascular disease and certain cancers, other studies have not confirmed these findings. Randomized controlled trials, considered the gold standard in research, have not shown that vitamin C supplements offer a preventive benefit against cardiovascular disease or cancer. The overall inconsistent data prevents establishing recommendations for vitamin C intake above the RDA specifically for these conditions. [2]
Age-Related Vision Diseases: It’s been proposed that vitamin C might protect against eye conditions like cataracts and macular degeneration. However, studies using vitamin C supplements in humans haven’t shown consistent benefits. There does appear to be a strong link between high daily consumption of fruits and vegetables and a decreased risk of cataracts. [4]
The Common Cold: Despite being a popular remedy, vitamin C’s effectiveness in combating the common cold is not well-supported by evidence. Reviews of multiple studies indicate that high doses (greater than 500 mg daily) of supplemental vitamin C do not significantly prevent the common cold but may offer a modest benefit in reducing the duration and severity of cold symptoms in some populations. [2] Small studies suggest that the amount of vitamin C in a typical multivitamin taken at the onset of a cold might lessen symptoms. However, for most people, there’s no evidence that high doses make a difference or prevent colds. [5]
Gout: The Physicians’ Health Study II, a large randomized, placebo-controlled trial involving over 14,000 male physicians, found a slightly lower risk of developing gout in men who took 500 mg vitamin C supplements daily for up to 10 years. [6] Other short-term studies have found that vitamin C may lower blood uric acid levels, a substance that can contribute to gout if levels are too high.
Food Sources of Vitamin C
Fruits and vegetables are the richest sources of vitamin C. To increase your vitamin C intake naturally, incorporate these foods into your diet:
- Citrus Fruits: Oranges, lemons, grapefruit, limes
- Bell Peppers: Especially red and yellow bell peppers
- Berries: Strawberries, kiwi, raspberries, blueberries
- Tomatoes
- Cruciferous Vegetables: Broccoli, Brussels sprouts, cabbage, cauliflower
- White Potatoes
Signs of Vitamin C Deficiency
Vitamin C deficiency is uncommon in developed countries but can occur with diets very low in vitamin C (less than 10 mg daily for a month or more). Risk factors for deficiency include limited fruit and vegetable intake, smoking or prolonged exposure to secondhand smoke, and alcohol or drug abuse. The most common signs of severe deficiency include:
- Scurvy: The hallmark disease of severe vitamin C deficiency, characterized by symptoms resulting from collagen loss and weakened connective tissues:
- Skin discoloration due to bleeding and bruising from fragile blood vessels
- Swollen or bleeding gums, and eventual tooth loss
- Hair loss
- Delayed wound healing
- Fatigue and Malaise
- Iron-Deficiency Anemia due to reduced absorption of non-heme iron.
Interesting Facts About Vitamin C
- Vitamin C enhances the absorption of non-heme iron, the type of iron found in plant-based foods like leafy greens. Drinking a small glass of 100% fruit juice or including a vitamin-C-rich food with meals can significantly improve iron absorption.
- Vitamin C is sensitive to heat and light. High-heat cooking or prolonged cooking times can degrade vitamin C. Being water-soluble, it can also leach into cooking water and be lost if the liquid is discarded. Quick cooking methods or using minimal water, like stir-frying or blanching, help preserve vitamin C content. Consuming foods raw at their peak ripeness provides the highest vitamin C levels.
- Vitamin C serums and creams are popular in skincare because normal skin contains high concentrations of vitamin C, which promotes collagen production and protects against UV damage. However, research indicates that topical vitamin C may have limited benefits, as only a small amount can penetrate the skin’s surface, and it won’t provide additional benefits if you already obtain sufficient vitamin C through diet or supplements. [7]
Related Articles
Vitamins and Minerals
References
Last reviewed March 2023
Terms of Use
The contents of this website are for educational purposes and are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The Nutrition Source does not recommend or endorse any products.
