Vitamin C (ascorbic acid) is probably the most famous vitamin in the world, commonly associated with citrus fruits and cold prevention. The reality is more complex and far more interesting: the richest food sources aren't oranges, its functions go well beyond immunity, and its role against colds is much more nuanced than health marketing suggests.

Vitamin C functions: far more than immunity

Vitamin C is an essential cofactor for collagen synthesis: without it, proline and lysine cannot be hydroxylated and collagen cannot form properly. Scurvy, the disease caused by vitamin C deficiency, manifests as deterioration of collagen tissues (bleeding gums, wounds that won't heal, brittle bones). It's the most powerful water-soluble antioxidant in plasma: it protects LDL, cell membranes, and DNA from oxidation. It increases the absorption of non-heme iron: a glass of lemon juice or a kiwi with a plate of legumes increases plant-based iron absorption by 30-80%. It's essential for the synthesis of carnitine (fatty acid transport in mitochondria) and certain neurotransmitters (noradrenaline, serotonin).

Food sources: the surprising ranking

Raw red bell pepper is the richest source of vitamin C among common foods: 190 mg per 100g, nearly three times more than oranges (50 mg). Yellow bell pepper: 184 mg. Black currants: 181 mg. Fresh chili peppers: 144 mg. Fresh parsley: 133 mg. Kiwi: 93 mg per 100g (one serving covers 100% of daily requirements). Raw broccoli: 89 mg. Strawberries: 59 mg. Orange: 50 mg. Lemon: 53 mg.

Cooking destroys vitamin C: it's sensitive to heat and oxidation. Broccoli boiled in water loses 50-75% of its vitamin C. Steamed broccoli loses 20-30%. Microwave cooking preserves more (shorter cooking times). To maximize vitamin C, eat fruit and vegetables raw as much as possible, or cook them briefly at moderate temperatures.

Actual daily requirements: how much you need

Italian dietary guidelines recommend 105 mg per day for adults (85 mg for non-pregnant women, 105 for men). During pregnancy, requirements increase to 100 mg, and during breastfeeding to 130 mg. Smokers need about 35 mg more per day because smoking increases vitamin C catabolism. The maximum tolerable dose (UL) is 2,000 mg per day: beyond this, gastrointestinal disturbances (osmotic diarrhea) can occur. Vitamin C toxicity is very low: excess is eliminated in urine.

Vitamin C and colds: the real evidence

The most recent Cochrane meta-analysis (2013, updated 2023, 29 trials, over 11,000 participants) concludes: regular vitamin C supplementation (200 mg per day or more) does not reduce the incidence of common colds in the general population. It reduces symptom duration by about 14% in adults and 8% in children. It significantly reduces incidence in people exposed to intense physical stress (athletes, military personnel in cold environments: -50%). So: vitamin C doesn't prevent colds if you're already well-nourished, but it slightly shortens symptoms if you take it regularly. There's no point taking it once you're already sick: the benefit comes from continuous preventive intake.

Supplementation: when it makes sense

For most people eating a diet rich in fresh fruits and vegetables, vitamin C supplementation adds no measurable benefits. The body saturates its absorption capacity around 200 mg per day: higher doses are eliminated in urine. Supplementation makes sense for: smokers (increased requirements), people with low fruit and vegetable consumption, high-volume training athletes, elderly people with poor diets, people under prolonged stress. Liposomal vitamin C has slightly higher bioavailability than standard supplements, but doesn't necessarily justify the much higher price for most uses.

How to maximize vitamin C from food

Eat raw bell pepper: sliced into strips as a snack or in salads, raw bell pepper retains all its vitamin C. Cooked, it loses up to 60%. Kiwi for breakfast instead of orange juice: almost twice the vitamin C, more fiber, less sugar. Fresh parsley on everything: a tablespoon of fresh chopped parsley on pasta, soup, or meat adds 15-20 mg of vitamin C. Steam vegetables or cook them briefly: this preserves vitamin C. Store fruit at room temperature (not in the fridge for too long): cold slows degradation, but oxidation continues once cut.

Vitamin C for iron absorption: the winning combination

If you eat legumes, spinach, or whole grains as iron sources: always add a vitamin C source to the same meal. No need to calculate doses: just squeeze half a lemon over your lentil plate, add some parsley to your vegetable soup, or have a kiwi as fruit after a grain-based meal. This increases non-heme iron absorption by 30-80%. For those following a vegetarian or vegan diet, this combination is essential to prevent iron-deficiency anemia.

How to tell if your diet is rich in vitamin C

Count how many times a day you eat raw fruit or vegetables. If the answer is zero or once, you're probably below your requirements. No need to count milligrams: a kiwi, a bell pepper, a serving of strawberries, a nice salad with parsley easily covers the 105 mg daily requirement. Two or three servings of fresh fruit and vegetables a day are almost always enough for a healthy adult.