High-dose vitamin D 'doesn't prevent colds and flu in kids'

Pregnancy and child

"Vitamin D will not protect your child from a cold: myth-busting study says 'more isn't always better' to help toddlers stay healthy," says the Mail Online. The story is based on a study that looked at…

"Vitamin D will not protect your child from a cold: myth-busting study says 'more isn't always better' to help toddlers stay healthy," says the Mail Online.

The story is based on a study that looked at whether giving healthy young children high doses of vitamin D in the winter protects them from colds and flu better than the standard recommended lower dose.

It found children taking the high dose were just as likely to get ill as children taking the standard dose – both groups got an average of about one case of cold or flu during the winter.

There was a reduction in flu cases with the high dose, but flu cases were uncommon and therefore the reduction was small (four fewer infections per 100 children over the winter season).

Current UK advice is that children aged one to four years old should be given a daily supplement containing 10 micrograms (mcg) of vitamin D – the same as the standard dose in this study.

Giving children the higher dose used in the study (50mcg) seems unlikely to offer much benefit for winter colds and flu if they're generally healthy.

Where did the story come from?

The study was carried out by a large group of researchers at various centres in Canada who were part of the TARGet Kids! Collaboration. This group is studying the health of Canadian children and the impact of early health in later life.

It was funded by the Canadian Institutes of Health Research Institutes of Human Development, Child and Youth Health and Nutrition, Metabolism and Diabetes, and the Thrasher Research Fund.

The vitamin D used in the study was provided for free by the manufacturer Ddrops.

The study was published in the peer-reviewed Journal of the American Medical Association (JAMA).

The Mail Online provides good coverage of this story, making it clear that the study isn't challenging the usefulness of the recommended vitamin D dosage, but saying more isn't better for colds.

What kind of research was this?

This randomised controlled trial (RCT) compared the effect of high- and standard-dose vitamin D on the risk of children catching a cold or flu in winter.

Observational studies have suggested that people with low vitamin D levels are at greater risk of getting viral infections affecting their upper airways – essentially colds or the flu.

Young children in the US and the UK are advised to take a daily dose of around 10mcg (400 international units, IU) of vitamin D.

The researchers wanted to see if taking five times as much (50mcg or 2,000 IU) during the winter might be even better for preventing colds and flu.

We get most of our vitamin D from sunlight and some food sources, such as eggs and oily fish like tuna.

Winter is when our vitamin D levels tend to be lower because there's less sunshine, and is also when we tend to get more upper airway infections. It's plausible that giving more vitamin D might be helpful at this time of year.

Assigning children to receive either the standard or high dose of vitamin D at random makes sure the groups are as similar as possible before the study starts.

This means that any difference between the groups in how many times they got ill would be directly caused by what vitamin D dose they were taking.

What did the research involve?

The researchers enrolled 703 healthy children aged between one and five years old.

They randomly assigned the children to receive either 10mcg or 50mcg of vitamin D by mouth each day during winter. They then compared how often the children got colds or flu over this time.

The children were all from Toronto in Canada and were recruited at "well-child visits" to paediatric or family medicine practices between September and November 2015.

Children with any chronic illnesses (other than asthma) and those born prematurely weren't eligible to take part. The vitamin D3 given to both groups was given as a drop a day of identical-looking and tasting liquid.

Parents and children didn't know what dose they were taking. The parents were told not to give their children any other supplements containing vitamin D during the study.

The children took the drops for between four and eight months.

Whenever the children got symptoms of a cold, their parents filled in a checklist to record what symptoms they had.

Parents were also trained to take a swab of the inside of their child's nose and send it to the lab. The researchers then tested the swab for viruses.

The main outcome the researchers were interested in was how often the children got colds or flu that could be confirmed as being viral infections by laboratory tests.

The researchers also compared how often the parents reported their child as having a cold or the flu.

Children went to the clinic to have blood samples taken to measure vitamin D levels at the four and eight-month mark.

Almost all (99.4%) of the children who started the study remained in it until the end and could be included in the analyses.

What were the basic results?

At the end of the study, children in the high-dose group had higher levels of vitamin D in their blood than those taking the low dose.

The parents didn't report noticing that their children had any side effects from taking the vitamin D drops.

But high-dose vitamin D didn't reduce the number of colds and flu the children got over the winter.

On average there were:

  • 1.97 cases in the high-dose group and 1.91 cases in the standard-dose group of parent-reported cases of cold and flu
  • 1.05 cases in the high-dose group and 1.03 in the standard-dose group of laboratory-confirmed cases of cold and flu

The differences between the groups were very small and not large enough to be statistically significant.

The higher dose of vitamin D did halve the risk of flu compared with the standard dose (incidence rate ratio [iRR] 0.50, 95% confidence interval [CI] 0.28 to 0.89).

But there were very few cases of flu – only 16 in the 349 children in the high-dose group and 31 in the 354 children in the low-dose group – so the difference of four fewer cases per 100 children (CI 1-8 fewer cases per 100 children) over the winter season wasn't considered to be an important reduction.

How did the researchers interpret the results?

The researchers concluded that giving 50mcg of vitamin D a day to healthy young children in the winter didn't reduce the number of upper airway infections overall compared with the standard dose of 10mcg a day.

They said: "These findings do not support the routine use of high-dose vitamin D supplementation in children for the prevention of viral upper respiratory tract infections." 


This study found giving a high dose of vitamin D to healthy children in the winter doesn't reduce their overall risk of upper airway infections compared with the standard recommended dose.

This well-designed study used several measures to ensure the results were robust. For example, researchers:

  • used randomisation to split the children into groups
  • blinded parents as to which treatment the child was receiving to make sure this knowledge couldn't affect their perception of their child's health
  • used laboratory tests to confirm that the child did have a viral infection

There was a reduction in flu with high-dose vitamin D, but the number of cases was very small, so this finding needs to be treated cautiously. The researchers have called for this to be looked at in further studies to see if this finding can be confirmed.

But there are some other important points to bear in mind. The study only included healthy children – it can't rule out possible benefits for children with chronic conditions or in specific subgroups, such as children who have asthma or particularly low vitamin D levels.

And researchers only looked at upper airway infections, so the study doesn't tell us about other outcomes that may be affected by vitamin D.

On balance, this study suggests that if your child is generally healthy, they aren't likely to get much extra cold and flu protection from taking more than the recommended dose of vitamin D in winter.

Flu is normally more serious than a cold – the NHS offers a free flu vaccine to children of certain ages and with certain conditions to reduce this risk. Check if your child is eligible for the children's flu vaccine.

Article Metadata Date Published: Tue, 15 Aug 2017
Author: Zana Technologies GmbH
NHS Choices