24th February 2017

Vitamin D for a common cold?

Flu and other respiratory infections are a major cause of hospitalisation, morbidity and death among older people. Underlying chronic health conditions make service users both more susceptible and vulnerable to severe disease, and hospitalisation rates during outbreaks can be high. Respiratory infections may also spread rapidly in care homes, resulting in high attack rates due to prolonged close contacts between residents, and between service users and their carers.

New review looks at vitamin D in the prevention of respiratory infections like colds and flu

Now a new review has been published that looks at whether vitamin D could help reduce acute respiratory tract infections, including colds, flubronchitis and pneumonia. The findings of previous studies looking into whether vitamin D can prevent such infections have been inconsistent.  So in order to get a better answer, researchers at Queen Mary University of London pooled together individual data from different studies where vitamin D was compared with a placebo, which together investigated around  11,000 people from different countries, including the US and the UK.

Their published analysis in the British Medical Journal suggested daily or weekly vitamin D supplementation was useful in prevention, with a reported 12% reduction in the proportion of participants experiencing at least one acute respiratory tract infection. Importantly, supplementation was particularly protective for people who had low blood levels of vitamin D.

Scientists clearly recognise that adequate vitamin D status has important skeletal and muscle health benefit.  Low blood vitamin D levels, currently defined as less than 25 nmol/L, increase risk of conditions like osteomalacia, causing bone pain and muscle weakness. While it is also acknowledged that vitamin D contributes to the normal function of the immune system (there is an approved European health claim to this effect), there are still differing views within the scientific community on the strength of evidence for an effect of vitamin D on prevention of colds.

Scientists disagree about the strength of evidence to support the role of vitamin D in prevention of acute respiratory tract infections

Some scientists have argued that because of the mixture of diverse conditions looked at in these studies, ranging from  self-reported colds and flu, ear infections, laboratory-confirmed influenza or radiograph-confirmed pneumonia, It is difficult to know whether a reduction in this mixture of conditions is applicable to the general population and how it should be interpreted clinically. They argue that larger well-designed randomised controlled trials in specific groups with low blood concentrations of vitamin D are needed before any conclusions can be made.

The authors though say that their findings “support the introduction of public health measures such as food fortification to improve vitamin D status in settings where profound vitamin D deficiency is common.”  Again others would disagree. For example, Professor Louis Levy, head of nutrition science at Public Health England (PHE), said: "The evidence on vitamin D and infection is inconsistent, and this study does not provide sufficient evidence to support recommending vitamin D for reducing the risk of respiratory tract infections”.

Around 1 in 5 adults have low vitamin D status

Despite scientific debate over the strength of vitamin D in preventing acute respiratory tract infections, ensuring we have enough vitamin D is important. Yet national surveys show that about 1 in 5 people in the population have low vitamin D levels in the blood. We need to ensure that we have satisfactory vitamin D blood levels throughout the year. Traditionally it was thought that our exposure to sunlight during the summer months would be sufficient to keep our stores topped up over winter, but from national survey data we know that this does not necessarily happen.

The Government, therefore, recommends that everyone aged 5 and over should consider a vitamin D supplement (10 µg per day) from October to March (when we can’t make vitamin D from sun exposure), and has provided stronger supplement advice for particularly vulnerable groups including young children. People with very little or no sunshine exposure are advised to take a daily supplement containing 10 µg vitamin D throughout the year. This includes those who are seldom outdoors such as frail or housebound individuals and those who are confined indoors (e.g. care homes).

Can we get enough vitamin D from food?

The government recommends that everyone aged one year and over has a dietary intake of 10 micrograms per day of vitamin D in order to protect their bone and muscle health. The richest source of vitamin D in our diet is oily fish, but useful amounts are found in eggs, fortified breakfast cereals and fat spreads.

Some countries including the US and Finland have vitamin D fortification policies in place, whereas others, including the UK, permit voluntary fortification. Foods commonly fortified in the UK include spreads, breakfast cereals and yogurts and these make a contribution to our intakes.

Portion sizeVitamin D (µg)
Fish
Salmon red, canned140g15.3
Sardines, canned140g4.6
Mackerel, grilled140g11.9
Tuna, canned140g1.5
Eggs
Boiled50g1.6
2 egg Omelette/scrambled120g3.4
Fortified breakfast cereals30g1.4
Fats
Fat spreads10g0.8
Butter10g0.1

A day’s menu that provides us with our vitamin D requirement of 10 µg could include a fortified breakfast cereal (do check nutrition labels to see if the cereal you are using is fortified), eggs on wholegrain toast with a fat spread, and salmon with potatoes and veg – vitamin-D-licious and nutritious!

However, it is difficult to get all the vitamin D we need from the diet alone. Vitamin D is a hot topic and the debate of its importance in non-musculoskeletal disease is likely to continue. In the meantime, we can always increase our intake of vitamin D by enjoying some oily fish on the menu.

*All information is correct at the time of publishing

Ayela Spiro

Nutrition Science Manager, British Nutrition Foundation

Ayela is a nutrition scientist at the British Nutrition Foundation, where her role involves providing expert advice on nutrition and health issues to a number of key audiences including consumers, health professionals, charities, the media and the food industry. At the heart of her work is the communication of nutrition science that promotes understanding of nutrition and health and contributes to the improved wellbeing of all.

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