Vitamin C from Natural Sources

Vitamin C: More Than a Cold Remedy

Vitamin C (ascorbic acid) is an essential micronutrient that the human body cannot produce on its own. It is involved in over 300 enzymatic reactions and fulfils a wide range of functions that extend far beyond immune support.

Key functions at a glance:

• Immune system: Vitamin C may support the production and function of white blood cells. A Cochrane Review by Hemilä and Chalker (2013) analysed 29 studies involving over 11,000 participants. The finding: regular vitamin C intake was associated with an 8% reduction in cold duration in adults. The frequency of colds was not significantly affected in the general population. However, in individuals under high physical stress (e.g. marathon runners), a reduction in risk of approximately 50% was observed.
• Collagen synthesis: Vitamin C is a necessary co-factor for the enzymes that synthesise collagen. Collagen is the most abundant protein in the human body and is essential for skin, bones, joints and blood vessels.
• Iron absorption: Vitamin C may enhance the absorption of non-haem iron (from plant sources) in the gut. It reduces ferric iron ions to ferrous ions, which are more readily absorbed.
• Antioxidant protection: As a potent antioxidant, vitamin C can neutralise free radicals and regenerate other antioxidants such as vitamin E.

Natural Vitamin C Sources Compared

Not all vitamin C sources are created equal. The concentration varies enormously between different foods:

Source	Vitamin C per 100 g	Notable features
Camu-camu	2,000-3,000 mg	Highest known vitamin C content, rich in polyphenols
Acerola	1,600-1,700 mg	Very high content, good bioavailability
Rosehip	400-500 mg	Also rich in carotenoids
Sea buckthorn	200-900 mg	High variability depending on variety
Red bell pepper	140 mg	Everyday source, readily available
Kiwi	90-95 mg	Also rich in vitamin K and potassium
Orange	50 mg	Best known but not the richest source

So-called superfruits such as camu-camu and acerola deliver not only significantly more vitamin C per unit of weight. They also contain a wide range of accompanying phytochemicals that may act synergistically.

Natural vs. Synthetic: The Role of Bioflavonoids

Synthetic ascorbic acid is chemically identical to the vitamin C found in foods. Yet there are relevant differences. Natural sources always contain a full spectrum of accompanying plant compounds, particularly bioflavonoids. These function as co-factors and may modulate the effects of vitamin C.

Langley (2015) examined the differences between whole food complexes and isolated synthetic vitamins. The study showed that vitamins in their natural food context are embedded with enzymes, co-enzymes, minerals and bioflavonoids. This matrix may influence absorption and utilisation in the body.

Key bioflavonoids found in natural vitamin C sources include:

• Hesperidin and rutin: Found in citrus fruits and rosehips. Studies suggest they may support vascular health.
• Quercetin: Present in many fruits and berries. Associated with antioxidant and inflammation-modulating properties.
• Anthocyanins: Abundant in camu-camu and other darkly pigmented fruits.

Bioavailability: Whole Foods vs. Isolated Ascorbic Acid

Bioavailability describes how much of an ingested nutrient actually reaches the body and can be utilised. Carr and Maggini (2017) investigated the relationship between vitamin C and immune function in a comprehensive review. They found that vitamin C from food sources may be better integrated into cellular processes due to the simultaneous presence of other micronutrients and phytochemicals.

Relevant factors for bioavailability:

• Synergistic effects: Polyphenols from fruits may slow the oxidative degradation of vitamin C in the digestive tract. This extends the absorption window and may improve overall uptake.
• Matrix effect: In whole foods, vitamin C is embedded in cellular structures that allow gradual release during digestion.
• Transport proteins: Certain plant compounds may influence the expression of vitamin C transport proteins (SVCT1 and SVCT2) in the intestinal mucosa.

At moderate doses (up to approximately 200 mg), the absorption rate of isolated ascorbic acid and natural vitamin C is comparable. At higher doses, the absorption rate of isolated ascorbic acid drops significantly. The body can only absorb a limited amount at one time. Unabsorbed ascorbic acid is excreted via the gut.

Recommended Intake and Supplementation

The Swiss Society for Nutrition (SGE) recommends a daily intake of 95-110 mg vitamin C for adults. The European Food Safety Authority (EFSA) does not set a defined tolerable upper limit, as vitamin C is water-soluble and excess amounts are excreted. In practice, amounts up to 2,000 mg per day are considered safe. Higher doses, however, may cause digestive discomfort.

When might supplementation make sense?

• Smokers: Vitamin C requirements are approximately 35 mg per day higher in smokers.
• High physical stress: Intense training increases oxidative stress and therefore vitamin C consumption.
• Restricted diets: Those who eat little fruit and vegetables often fail to meet the recommended intake.
• Chronic stress: Prolonged stress may increase requirements, as the adrenal glands need vitamin C for cortisol production.

Conclusion

Vitamin C is an essential nutrient with diverse functions. Research suggests that natural sources may offer advantages over synthetic ascorbic acid. Not because of the ascorbic acid itself, but because of the accompanying plant compounds that act as co-factors. Camu-camu, acerola and rosehip are among the richest natural vitamin C sources and simultaneously provide a broad spectrum of bioflavonoids and polyphenols. A balanced diet with varied fruits and vegetables remains the best strategy for meeting vitamin C requirements.

---

Sources:

• Hemilä H, Chalker E (2013). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews, (1), CD000980.
• Carr AC, Maggini S (2017). Vitamin C and Immune Function. Nutrients, 9(11), 1211.
• Langley P (2015). Why a pomegranate? Whole food versus synthetic supplements. BMJ, 351, h3997.