Debunking 4 vitamin-C myths

Do you reach for vitamin C effervescent tablets as soon as you catch a cold, hoping to recover faster? A doctor debunks 4 common myths, warning that excessive intake not only fails to shorten the illness but may also cause diarrhoea and nausea.

ENT doctor Dr. Hu Hao-chun posted on his Facebook page that many people immediately take vitamin C when they have a cold—a belief deeply rooted in households. High-dose effervescent tablets and capsules fly off pharmacy shelves. But this "cold remedy" image is actually built on a misunderstanding that has persisted for over half a century. He breaks down 4 common myths about vitamin C:

1. Vitamin C Does Not Prevent Colds

The idea that vitamin C prevents colds originated from a book by Nobel laureate Linus Pauling in the 1970s. It caused a sensation at the time, but large-scale clinical studies over the following decades repeatedly debunked it. A 2013 meta-analysis of over 10,000 participants concluded that for the general public, daily vitamin C supplementation does not reduce the incidence of colds. In other words, taking an extra tablet today won't make you less likely to catch a cold.

2. It Has a Minor Effect, But Not Much

Rushing to take vitamin C only after cold symptoms appear has almost no significant effect on shortening the illness or reducing symptoms. The same meta-analysis found that for people who already regularly supplement vitamin C, the illness duration was shortened by an average of only about 8%—roughly half a day. It seems to help a little, but only if you've been taking it consistently beforehand.

3. Excess Vitamin C Can Be Harmful

Although vitamin C is water-soluble and excess is theoretically excreted in urine, exceeding 2,000mg daily can cause gastrointestinal symptoms like diarrhoea, nausea, and abdominal cramps.

4. Long-Term Excess May Increase Kidney Stone Risk

Long-term excessive intake also increases the risk of calcium oxalate kidney stones, especially for those with existing kidney issues or a history of stones. Before taking supplements, always check your total daily intake—don't assume more is always better.

Hu emphasises that getting vitamin C from natural foods is the best approach. They contain sufficient amounts. He particularly recommends guava—one guava already exceeds the daily recommended vitamin C intake, offering a natural and delicious way to meet your needs.

What's the Difference Between the Flu and a Cold?

According to the Hong Kong Department of Health:

• Common Cold: A viral upper respiratory infection with symptoms like runny nose and mild cough.

• Seasonal Influenza (Flu): An acute respiratory illness caused by influenza viruses, usually peaking in Hong Kong from January to April and July to August.

Sources: ENT Doctor Dr. Hu Haochun, Department of Health (Hong Kong)

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