Does vitamin D cut lung infection risk in older adults?

NHS: "Why you should take vitamin D as you get older: High doses reduce the risk of respiratory illnesses by 40%," the Mail Online reports. Researchers in Colorado investigated whether a high dose of vitamin D in older adults living in long term care facilities could reduce their risk of acute respiratory (lung) infections, such as pneumonia.

Pneumonia is of particular concern in older people who are especially frail or have a pre-existing chronic health condition.
More than 100 older adults were included in the trial. Participants were randomly assigned to receive either a high or standard dose vitamin D supplement for a period of 12 months.
At the end of the 12-month period researchers found 40% fewer respiratory infections in those receiving the high dose – but this was mainly due to a reduction in simple upper respiratory infections like coughs and colds, rather than more serious infections such as pneumonia.
When it came to side effects, the researchers found that the high dose group had a higher number of falls, though no increase in the number of fractures. But there was no difference in the rate of other side effects linked with high doses of vitamin D, such as high blood calcium.
Due to the small number of participants, the study did not have the "statistical power" to reliably detect differences in respiratory infections or, importantly, in safety outcomes; so any result could have been due to chance.
Further research in a larger randomised trial is needed to prove any benefit and to check high dose vitamin D doesn't cause harms in this group.

Where did the story come from?

The study was carried out by researchers from a number of institutions including the University of Colorado, the Colorado School of Public Health and the Eastern Colorado Department of Veterans Affairs.
Funding for the study was provided by the Beeson Career Development Award, National Institute on Aging Grant, National Center for Advancing Translational Sciences Colorado Clinical and Translational Science Awards Grant, and the American Geriatrics Society Jahnigen Career Development Scholars Award.
The study was published in the peer-reviewed Journal of the American Geriatric Society.
The study has been reported reasonably accurately in the Mail Online, but the research's limitations were not discussed.

What kind of research was this?

This was a randomised controlled trial which aimed to assess whether high dose supplementation with vitamin D for 12 months would prevent acute respiratory infections in older adults in long term care.
Older adults are at higher risk of vitamin D deficiency and observational studies have provided some evidence of an association between deficiency and acute respiratory infection.
This trial was double blind which means patients and investigators were unaware which group they were assigned to for the whole 12 month period, limiting the risk of bias.
With this type of study it is most likely that the effect seen is due to the intervention rather than any confounding variables.

What did the research involve?

The researchers included 107 older adults (60 years and above) from 25 long term care facilities in Colorado. They excluded people with cancer, terminal illness or other conditions where they couldn't take too much vitamin D.
Participants were randomly assigned to one of two groups:

• high dose – equivalent to 3,000-4,000 international units (IU) per day (75mcg-100mcg per day)
• standard dose – equivalent to 400-1,000 IU per day (10mcg-25mcg)

If the participant was taking vitamin D as part of their usual care then this continued in addition to the study drug, but the doses where balanced out to ensure the person was receiving their allocated study dose. For example, if people allocated to the standard dose group were already taking this amount, they just took an extra placebo.
The main outcome of interest was the number of acute respiratory incidents (ARI) during the 12 month follow up period. These incidents were split into upper respiratory (common colds, sinusitis, sore throats and ear infection) and lower (acute bronchitis, influenza, pneumonia) requiring medical attention.
The researchers also looked at secondary outcomes which included severity of ARIs as measured according to emergency department visits or hospitalisation for ARIs, time to first ARI, and incidence of other infections.

What were the basic results?

Participants in the high-dose group had significantly fewer acute respiratory incidents, 0.67 per person per year versus 1.11 per person per year in the standard dose group. This equates to a 40% lower risk of ARIs in the high dose group (Incidence rate ratio (IRR) = 0.60, 95% confidence interval (CI) = 0.38 to 0.94).
When splitting up by type of infection, upper ARIs were less common in the high dose group, but there were no differences in incidence of lower ARI. There was also no difference in urinary tract infection, or other infections or hospitalisation for ARI.
Falls were more common in the high dose group (IRR = 2.33, 95% CI = 1.49 to 3.63), however this did not result in more fractures. There was no difference in the rate of other side effects associated with too much vitamin D, including high blood calcium or kidney stones.

How did the researchers interpret the results?

The researchers conclude: "Monthly high-dose vitamin D3 supplementation reduced the incidence of ARI in older long-term care residents but was associated with a higher rate of falls without an increase in fractures."

Conclusion

This randomised controlled trial assessed high dose supplementation with vitamin D for a period of 12 months as a way of preventing acute respiratory infections in older adults in long term care.
This study was well designed and reduced risk of bias where possible. However, there are some important limitations which affect the reliability of the findings:

• The study has a small sample size and the authors state they did not manage to reach their target recruitment level; this means the study did not have the statistical power required for certainty in the findings.
• There were some differences in the characteristics of the participants at the start of the study, including differences in body mass index, smoking status, heart disease and respiratory diseases. Ideally, differences of these types should be minimised in a randomised study. But they were present in this case – possibly as a result of the small sample size – and may have affected findings.
• The study only included participants who are in long term care and this may not be representative of the effect in all older adults, including those with serious illnesses or contraindications to taking high doses of vitamin D.

The study did appear to find that supplementation reduced the chance of respiratory events – though this seemed only due to a reduction in upper respiratory infections such as coughs and colds rather than more serious infections.
It didn't find the increased dose of vitamin D caused high calcium levels in the blood which can affect the kidneys and weaken bones. However, it was associated with a higher risk of falls which needs further investigation.
As this was a small trial, further research would be needed to prove any benefit and ensure that high dose vitamin D in this group doesn't cause side effects.
From the age of one, throughout life, people need 10 micrograms of vitamin D per day. This can be obtained through dietary sources (e.g. red meat and fortified cereals) and exposure to natural daylight.
However, some people may not be able to get enough through these sources, including elderly adults who may have a poorer diet and get less sunlight exposure.
They may need supplements of 10 micrograms per day. The current level of evidence does not support taking any higher dose than this.
Read more advice about vitamin D.

Analysis by Bazian. Edited by NHS Choices. Follow NHS Choices on Twitter. Join the Healthy Evidence forum.