Colds, flu and complementary medicines
As irritating and unwelcome as cold and flu symptoms may be, they are mostly benign. However these illnesses can last for several days and are a major cause of work absences. This can leave many of us reaching for readily available products that claim to help speed up our recovery and get us back to normal.
Two out of three Australians regularly use natural healthcare products, otherwise known as complementary and alternative medicines. But what is known about the effectiveness of complementary approaches for colds and flu?
What does the science say?
For colds, complementary products with some good quality evidence to support their use are oral zinc, vitamin C for people under severe physical stress, and probiotics. Some echinacea products may be useful but the evidence overall is mixed because preparations vary greatly.
For flu, the evidence is not conclusive.
Researchers have looked at the effectiveness of vitamin C as a continuous daily supplement or as therapy following onset of symptoms. Overall, there is no evidence that vitamin C has any effect on the common cold if taken once symptoms have started.
However, when taken continuously at doses of 0.25 to 2 g/day, vitamin C can slightly shorten the duration of colds, with a greater benefit in children than in adults. Regular supplementation also halved the number of colds in participants undergoing heavy physical stress.
Most colds are caused by a type of virus called rhinovirus, which multiplies in the nasal passages and throat. Zinc may work by stopping the virus from adhering to the nasal membranes and replicating.
A recent review of the evidence found that zinc acetate lozenges in doses of 80–92 mg/day may be useful to shorten the duration of illness if started within 24 hours of developing cold symptoms, but won’t affect symptom severity.
Echinacea has been shown to stimulate the immune system (eg, increasing numbers of circulating white blood cells and other immune cells such as monocytes and neutrophils). However, the mechanism of action is currently unknown and the benefit of stimulating a broad immune response rather than a targeted one (such as with most drug treatments) is yet to be determined.
Studies that focus on echinacea to prevent or treat colds have had mixed results that are difficult to interpret, because different species, different parts of the plant and different doses have been studied.
Despite these factors, assessment of the research has concluded that some echinacea products might be useful in the prevention and treatment of the common cold, but large studies are needed to determine which species and dosage are most useful.
Probiotics have demonstrated effectiveness in a range of disorders related to inflammation and infections, and may even be helpful to treat colds and flu.
A recent British study found probiotics – the Bifidobacterium bifidum strain, in particular – reduced the reported number of sick days among students taking it.
The wide array of probiotic species and dosing strengths used in research trials makes it difficult to draw broad conclusions, so more information is needed before recommendations can be made. But overall, probiotics may be of some use in reducing the risk of contracting a cold, shortening the duration of symptoms, and reducing the number of sick days.
Points to consider:
- Tell your health care provider about any complementary medicines you use. All medicines, including herbal and natural medicines, can cause side effects and may interact with other medicines. The benefits and risks of herbal and natural medicines may not have been tested.
- Complementary medicines should never be used as a substitute for flu vaccination.
- People with questions about their medicines (prescription, over-the-counter or complementary) or seeking general information about side effects can call NPS Medicines Line on 1300 633 424
Last Reviewed: 31/10/2019
Norman Swan Medical Communications
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