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Too early to tell if vitamin D has a role in reducing the common cold

Community pharmacists are repeatedly asked for recommendations to reduce the risk of catching a cold. The advertising of novel products such as nasal sprays, gargles, face masks and a plethora of potential protective botanical products can cause confusion about what really might be useful and appropriate.

A recent publication in The BMJ[1] (2017;356:i6583) summarised a meta-analysis of randomised, double-blind, placebo- controlled trials of any form of vitamin D supplementation. This vitamin contributes to immunological and mucosal protection and is insufficient or deficient in many British citizens. The strength of this study was its analysis of individual participant data of just under 11,000 trial participants. A protective effect in those participants receiving daily or weekly vitamin D supplements was identified, although overall vitamin D did not influence the proportion of participants experiencing at least one upper respiratory tract infection.

This vitamin D study, widely reported in the media, would suggest a change in advice given to patients. But perhaps caution is a wiser strategy because there are many factors that contribute to the common cold.

Virologists tell us of seasonal and dynamic patterns of seven families of common cold viruses moving through populations. Paediatricians identify nurseries, play groups, towels and shared toys as points from which viruses and common bacterial pathogens spread. Vaccinologists emphasise the importance of an annual influenza vaccine. Those measuring air quality have detected strong associations between rates of upper respiratory tract infection and air quality. Allergy specialists are concerned about airborne allergens and reducing the exposure of atopic individuals to these so as to reduce secondary infections. Nutritionists will point to the significant roles played by micronutrients including vitamins A and C and zinc in maintaining robust immunological and mucosal defences. These varied messages are delivered by specialists working from limited platforms. Within specialist areas there will be different advice for infants, children, pregnant women or the elderly. We do not have what we could use practically — sound contemporary data taking into account all the variables relevant to our customer, patients, or communities.

In this study, we do not have a specific breakdown of the age groups, the air quality, vitamins A, C, folate or zinc status, let alone participants’ smoking history, allergic backgrounds or whether or not they regularly contracted colds. The practicality of this study to those on the frontline, particularly in pharmacies, therefore remains unclear.

In light of these doubts, we should all, instead, support the national vitamin D advice published in 2016[2] and recognise that the common cold will remain a challenge.

Colin Michie

Paediatrician

London

Citation: Clinical Pharmacist DOI: 10.1211/CP.2017.20202561

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