Proudly New Zealand Owned

Immunity from viruses

By Shaun Holt

Not surprisingly, many people are wanting to reduce their chances of suffering from respiratory viruses at the moment.

Having a robust immune system should help with this and our immune systems are definitely assisted by generally living healthily, eating well, exercising, etc. But is it possible to boost your immune system so that it is even more effective at fighting off respiratory viruses?

There are three supplements that have good evidence that they can help reduce the chances of catching respiratory viruses, and of having fewer symptoms and better outcomes if you do catch them. And there is emerging evidence that they may even help to protect against Covid-19.

Vitamin C

Everyone knows that vitamin C can help to prevent and treat the common cold. In a Cochrane review on this subject, 29 placebo-controlled trials involving over 11,000 participants found that regular ingestion of vitamin C had no effect on common cold incidence. However there was a modest but consistent effect in reducing the duration of common cold symptoms. In trials in which participants were exposed to short periods of extreme physical stress (e.g. marathon runners and skiers) vitamin C was more effective and approximately halved the risk of getting a cold. There was no evidence of any additional advantage from taking huge doses and doses used in the studies were around 1,000 mg per day.

Over 200 viruses are known to cause the common cold, particularly rhinoviruses. But around 15-20% of colds are caused by….coronaviruses. While no studies have shown that vitamin C can prevent or treat Covid-19, a recently published paper made the case that there are several good lines of evidence to suggest that it should. In New Zealand and many places overseas, sales of oranges, kiwifruit and other fruits high in vitamin C have surged.


Zinc is increasingly becoming recognised as the most effective supplement for reducing the severity and duration of the common cold and other respiratory viruses. It works in several ways including directly inhibiting virus binding and replication in the nasal mucosa and suppressing inflammation. The Cochrane review on this topic concluded that "zinc (lozenges or syrup) is beneficial in reducing the duration and severity of the common cold in healthy people, when taken within 24 hours of onset of symptoms". Could zinc have a role to play with respect to Covid-19? Researchers increasingly think so. Studies have found that zinc deficiency is associated with more severe Covid-19 symptoms and that adding zinc to other treatments for people suffering from Covid-19 and being treated in hospital lowered the chances of dying.

Vitamin D

It has long been known and accepted that vitamin D supplementation can prevent acute respiratory tract infections, especially in the winter, and many GP’s now prescribe it for this reason. In the absence of a Covid-19 cure or vaccine, scientists are investigating whether vitamin D can reduce the risk of Covid-19 infection or the severity of the disease. Recently published studies suggest that it does. For example, a study found that the risk of Covid-19 infection in people with vitamin D deficiency was nearly double that of people with sufficient levels of the vitamin and another study found that hospitalised Covid-19 patients had higher rates of vitamin D deficiency than a control group of patients who didn't have Covid-19 . As a result, the UK government and others are looking at whether vitamin D should be widely distributed during the pandemic.