Hong Kong – When a sore throat or runny nose strikes, many people instinctively reach for a vitamin C supplement or a glass of orange juice. Yet health experts caution that this last-minute rush may do little to fight off an infection. The key, they argue, lies in consistent, daily consumption of the nutrient long before symptoms appear.
Vitamin C is essential for immune function, collagen production, wound healing, and the absorption of iron and calcium. Since the human body cannot synthesise it, all supplies must come from diet or supplements. But can it actually prevent or treat a cold? And how much is enough?
The Science Behind Vitamin C and Immunity
A wealth of research has examined the link between vitamin C and respiratory infections. According to Dr. Bruce Bistrian, clinical nutrition director at Harvard-affiliated Beth Israel Deaconess Medical Center, taking vitamin C only after catching a cold yields “very limited” results. To truly bolster the immune system, he explains, people need to maintain adequate daily levels year-round.
A 2013 study involving over 11,000 participants found that individuals who engage in extreme physical activity—such as marathon runners, skiers, and soldiers—reduced their risk of catching a cold by half when taking more than 200 mg of vitamin C daily. For the general adult population, the same dose lessened cold symptoms by 8%, while children experienced a 14% reduction, shortening illness duration by roughly one day.
Recommended Intake: How Much Is Enough?
Official dietary guidelines recommend 90 mg per day for adult men and 75 mg for adult women. However, some studies suggest that consuming significantly higher amounts may offer additional protection. The catch: the body cannot absorb more than about 400 mg at once; excess vitamin C is simply excreted in urine.
The Hong Kong Consumer Council has warned that certain supplements on the market contain doses far exceeding safe limits. Two tested samples recommended up to 2,000 mg per day, the maximum tolerable upper intake for adults. One product, a popular effervescent tablet, provided 1,000 mg per serving—ten times the adult requirement—while advising use for children as young as eight, exposing them to 40 times their recommended amount.
Consuming over 2,000 mg daily can lead to nausea, diarrhoea, abdominal cramps, and, in some cases, interfere with blood glucose tests or contribute to kidney stones. Dr. Bistrian strongly recommends obtaining vitamin C from whole foods, which provide additional nutrients and fibre. The Consumer Council agrees: a balanced diet with two servings of fruit each day, combined with regular sleep and exercise, is more effective than relying on supplements.
Surprising Sources: Which Foods Pack the Most Vitamin C?
Many people assume oranges are the top source, but they rank only 11th among vitamin-C-rich foods. Here are the top contenders:
- Yellow bell peppers take first place: 100 grams contain 183.5 mg of vitamin C—3.4 times that of an orange.
- Golden kiwifruit comes second with 161.3 mg per 100 grams, nearly double the content of green kiwifruit.
- Green kiwifruit (third) offers 154% of the daily value per 100 grams. Eating the skin adds fibre and extra vitamin E.
- Broccoli (fourth) provides 148% of the daily value per 100 grams and helps protect skin from UV damage.
- Red bell peppers (fifth) deliver 142% of daily needs per 100 grams.
- Other notable entries include persimmons, strawberries, green peppers, lemons, and chestnuts.
Chestnuts are unique in that their starch coating protects vitamin C from being destroyed during cooking.
A Broader Perspective: Food First, Supplements Second
The prevailing message from nutrition experts is clear: consistent dietary habits trump crisis-driven supplementation. While vitamin C cannot cure a cold, adequate daily intake supports overall immunity and may reduce symptom severity. The safest, most effective strategy is to incorporate a variety of colourful fruits and vegetables into every meal. For those considering supplements, moderation is crucial—and professional guidance is advised before exceeding standard doses.
As Hong Kongers brace for seasonal sniffles, the takeaway is simple: eat your bell peppers, kiwis, and broccoli long before the cough begins, and let food be your first line of defence.