Q&A: Can Vitamin C Supplements Boost Your Health Beyond a Balanced Diet?

Takeaway messages

Vitamin C, also known as ascorbic acid, L-ascorbic acid, ascorbate (ionised form of ascorbic acid), dehydroascorbic acid (DHA; oxidised vitamin C) and traditional vitamin C, is water-soluble. The chemical formula of the vitamin is C₆H₈O₆. Vitamin C is an essential vitamin for humans and a few other species because they cannot synthesise it and must obtain it through diet or supplements (1). It is crucial for normal body functioning, growth, and development. Unlike most animals, which can synthesise vitamin C from glucose, humans, primates, guinea pigs, certain fruit-eating bats, and some bird species lack the necessary enzyme to produce it endogenously (1).

Dietary Sources of Vitamin C

Vitamin C is found in various foods beyond citrus fruits, including cantaloupe, strawberries, papayas and mangoes. Fruit juices, such as freshly squeezed orange juice, are significant sources of dietary vitamin C and offer a convenient alternative for enhancing vitamin intake, particularly beneficial for those who struggle to consume sufficient whole fruits. Vegetables like cabbage varieties, dark greens such as green peppers and broccoli, lettuce and tomatoes. Despite their moderate vitamin C content, potatoes significantly contribute to overall intake due to their widespread consumption. A medium-sized potato provides about 20% of the recommended daily intake, making it a key source of vitamin C, though its content decreases as potatoes age.

Table 1: Vitamin C Content in Various Food Sources

Note: These values provide a general guide and can vary slightly depending on the source and preparation method.

Dietary vitamin C is absorbed through the intestines. The effectiveness of vitamin C absorption into the bloodstream is constrained by the sodium-dependent vitamin C transporter (SVCT1), which becomes saturated at high intakes. Because vitamin C is easily destroyed by heat and oxygen, consuming whole raw fruits and some raw or lightly steamed vegetables is recommended (see Table 2 below). There is a moderate correlation between dietary vitamin C intake and plasma vitamin C levels, with the Food Frequency Questionnaire (FFQ) and Dietary Recalls (DR) showing positive correlations highlights that factors like bioavailability, absorption conditions, stress and food processing can influence this relationship (2).

Table 2: Best practices for preserving vitamin C during food preparation and cooking

Daily Vitamin C Requirements

Adult men and women older than 19 years require 90 mg/day and 75 mg/day, respectively, with smokers and passive smokers needing an additional 35 mg/day more than their non-smoking counterparts (3). Consuming five varied servings of fruits and vegetables a day typically provides an adequate amount of vitamin C, making supplementation unnecessary.

Vitamin C Deficiency

Deficiency symptoms include anaemia, atherosclerotic plaques/pinpoint haemorrhages, bone fragility, poor wound healing, bleeding gums and loose teeth, muscle degeneration, rough skin and blotchy bruises. The deficiency disease of vitamin C is called scurvy and only appears when vitamin C intake is less than 1 mg/day (4). The discovery of vitamin C's role in preventing scurvy, particularly through James Lind's 1747 experiment with sailors and citrus fruits, highlighted the critical link between diet and health. This breakthrough led to the British Navy adopting citrus juice to combat scurvy, significantly improving sailors' health. The early 20th-century identification of ascorbic acid (vitamin C) by scientists like Albert Szent-Györgyi, who won a Nobel Prize for this work, spurred nutritional science advancements and public health initiatives promoting balanced diets rich in essential vitamins. This understanding emphasised the broader importance of nutrients in preventing chronic diseases and maintaining overall health, shaping modern dietary guidelines.

Certain individuals might be at risk of vitamin C inadequacy or deficiency. These include:

• Infants fed evaporated or boiled cow’s milk
• Individuals with limited food variety, such as the elderly, those who abuse alcohol or drugs, and food-insecure individuals
• People with medical conditions that limit vitamin C absorption, such as Crohn's disease, ulcerative colitis and certain types of cancer
• Smokers and passive smokers, as smoking increases the body's need for vitamin C (RDA for sex plus 35 mg per day extra)
• People with diets low in fruits and vegetables
• Individuals with chronic illnesses, such as kidney disease requiring haemodialysis
• Those with severe burns or injuries, which increase the body's requirement for vitamin C
• Pregnant women, who require increased vitamin C intake of 85 mg per day
• Breastfeeding women, who need a higher vitamin C intake of 120 mg per day

Functions of Vitamin C in the Body

Unlike B vitamins, vitamin C is not a coenzyme; instead, it acts independently as an antioxidant, donating electrons or hydrogen ions to other substances to inhibit oxidation. Vitamin C is involved in various redox reactions, easily accepting and donating electrons. This antioxidant function protects cells from free radicals, which are highly reactive and unstable molecules produced during normal cellular metabolism. Factors such as intense sunlight, certain drugs and toxic substances like smog and cigarette smoke can increase free radical production. Antioxidants neutralise free radicals by donating electrons, preventing oxidative damage to lipids, DNA and proteins, which can lead to diseases such as cancer.

Vitamin C enhances the absorption of essential minerals like iron, copper and chromium by converting them into more bioavailable forms. Specifically, vitamin C improves the absorption of non-haeme iron from plant-based foods by reducing it to ferrous iron (Fe2+), a more absorbable form. It also counteracts compounds that inhibit iron absorption, such as phytates and tannins. Regular consumption of vitamin C-rich foods with iron-rich meals improves iron status and helps prevent iron deficiency anaemia, particularly in at-risk populations like vegetarians, pregnant women and individuals with chronic illnesses. For example, drinking orange juice with iron-fortified cereal increases the amount of iron absorbed. However, in individuals with conditions that cause excess iron in the body, such as haemochromatosis, high vitamin C intake could be problematic, as it may exacerbate iron overload and lead to tissue damage. Beyond acting as an antioxidant and enhancing mineral absorption, vitamin C plays numerous other crucial roles in the body (see Table 3).

Table 3: Functions of vitamin C in the body

Vitamin C does not directly affect the coagulation cascade—the sequence of reactions that form blood clots—it plays a crucial role in maintaining healthy blood vessels and supporting overall vascular health, which are essential for proper blood coagulation and preventing haemorrhagic conditions. The connection between vitamin C and fibrinogen, the most abundant clotting factor in the blood, is indirectly mediated through its anti-inflammatory effects (5). Many fruits and vegetables that are rich in vitamin C also contain high levels of dietary fibre. Dietary fibre is known for its anti-inflammatory properties, which can enhance gut health and lower blood levels of C-reactive protein, a marker of inflammation. Therefore, the consumption of foods high in both fibre and vitamin C may contribute to reduced inflammation, indirectly influencing blood coagulation positively and impacting blood clot formation.

Upper Limit and Potential Risks of Vitamin C Intake

The Upper Level of Intake (UL) for vitamin C is set at 2000 mg per day for adult (3). Exceeding this amount can lead to adverse effects such as diarrhoea, nausea and abdominal cramps, although high doses are also excreted quickly. Individuals with kidney disorders, iron overload conditions and gastrointestinal conditions are at higher risk for adverse effects from exceeding the UL and should avoid using vitamin C supplements.

Research on Dietary Vitamin C and Health

Research has explored the association of dietary vitamin C with various diseases. Meta-analyses indicate that dietary vitamin C intake is inversely associated with oesophageal cancer (6) and lung cancer (7), but not with ovarian cancer (8) or pancreatic cancer (9). Dietary vitamin C consumption has several benefits related to heart health, with deficiencies linked to a higher risk of mortality from cardiovascular disease (10). In a meta-analysis of 16 prospective studies, the risk of stroke was inversely associated with dietary and circulating vitamin C levels, although supplements showed no clear preventive effect (11). A meta-analysis of 28 observational studies found that higher dietary and circulating (serum and plasma) vitamin C levels were inversely associated with metabolic syndrome, with higher levels linked to a lower risk of the condition (12). A genetic variant in a SVCT1 gene, which can serve as a proxy for lifetime ascorbate concentrations, supports a causal association of vitamin C with age-related cataracts (13).

Vitamin C Supplements: Insights and Research on Health Benefits

Granger and Eck (14) initially argued that supplementation in populations with sufficient vitamin C intake from dietary sources would not provide additional benefits in disease prevention. The effectiveness of vitamin C supplementation, traditionally believed to be limited by the saturation of the SVCT1 transporter at high doses (15), appears to be enhanced through regular high-dose intake (16). Increased dosage has been shown to potentially upregulate the expression of SVCT2, another transporter, which could compensate for SVCT1's limitations, thus improving Vitamin C uptake in skeletal muscle(16). Various forms of vitamin C supplementation, including innovative ones like liposomal vitamin C, are under study to evaluate their efficacy in enhancing delivery directly to cells, thus allowing higher levels of vitamin C to be absorbed without transporter saturation (refer to Table 4 below). This liposomal form is particularly noted for its higher bioavailability, which might enable more effective absorption and utilisation of vitamin C at higher doses. Yet, conclusive scientific evidence confirming the superiority of liposomal vitamin C over traditional forms is still developing, with ongoing research needed to confirm these findings.

Table 4: Vitamin C supplements forms

Notes: To make liposomal vitamin C at home, blend 1 tbsp of sunflower/soya lecithin with 1 cup of water until dissolved. Separately, dissolve 1 tbsp of L-ascorbic acid powder in 1/2 cup of water. Combine both solutions and blend well. Store in the fridge and shake before use. Use within 2 weeks.

The Table 5 provides various benefits including improvements in endothelial function, glucose levels in diabetes, risk factors for stroke and metabolic syndrome, blood pressure reduction, and other health outcomes associated with vitamin C supplementation. Note that the evidence from systematic reviews and meta-analyses, which compile data from multiple studies, generally carries more weight than findings from single studies.

Table 5: Summary of the benefits of vitamin C supplementation

While vitamin C supplementation is generally safe at recommended doses, taking high doses (3,000–10,000 mg) can lead to diarrhoea, increasing discomfort and potentially leading to dehydration. There is also an increased risk of dental erosion when using chewable vitamin C tablets, which could compromise tooth enamel over time (33). While liposomal vitamin C in liquid form offers enhanced absorption, it might also pose a risk of dental erosion due to its acidity. It is recommended to consume it through a straw to minimise direct contact with the teeth and protect enamel. Although rare, there is a concerning possibility of nephrotoxicity—kidney damage—following high-dose vitamin C administration (34, 35). While this severe side effect is unlikely with typical oral supplementation, it underscores the potential risks of exceeding recommended dosages. While severe side effects from typical oral vitamin C supplementation are uncommon, obtaining vitamin C from dietary sources remains safer than supplementation. However, in the case of vitamin C, the benefits of supplementation might outweigh the risks, especially in situations where dietary intake is insufficient and where there is evidence of benefits through supplementation.

Conclusion

Vitamin C is essential for numerous bodily functions, including antioxidant protection, collagen synthesis, immune support and iron absorption. While a balanced diet rich in fruits and vegetables typically provides adequate vitamin C, certain individuals, such as those with limited food variety, certain medical conditions, or increased physiological needs, may benefit from supplementation.

Supplementation can offer specific advantages, such as higher bioavailability in the case of liposomal vitamin C and better gastrointestinal tolerance with buffered or Ester-C forms. For individuals at risk of deficiency or with increased requirements, vitamin C supplements can enhance overall health, improve immune function and prevent conditions like iron deficiency anaemia. The key is to tailor vitamin C intake to individual needs to maximise health benefits and minimise risks associated with supplementation, ensuring an optimal balance for overall well-being.

Reflection Exercise

1. Assess Your Diet: Reflect on your daily fruit and vegetable intake. Are you consuming at least five varied servings of fruits and vegetables each day?
2. Evaluate Your Health Needs: Consider any specific health conditions you have that might increase your need for vitamin C, such as a compromised immune system or chronic illness.
3. Consider Supplementation if you are not at Risk: Based on your dietary intake and health needs, determine if vitamin C supplementation might be beneficial for you. Discuss with a healthcare provider if necessary. If necessary, experiment with traditional vitamin C supplements and liposomal vitamin C (see recipe under Table1).
4. Monitor Your Intake: If you decide to supplement, keep track of your vitamin C intake to ensure it does not exceed the Upper Level of Intake (2000 mg per day for adults) to avoid potential adverse effects.

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