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In children and adults, vitamin D3 supplements reduce acute respiratory tract infections

Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017 Feb 15;356:i6583.

Review question

In children and adults, do vitamin D supplements reduce risk for acute respiratory tract infections (ARTIs)?


ARTIs include the common cold, bronchitis, and pneumonia. Some studies have found that people with low vitamin D levels have an increased risk for ARTIs. People may have low vitamin D levels when they don’t have regular exposure to sunlight or don’t get enough vitamin D in the foods they eat. This review looks at whether vitamin D supplements can reduce your risk for getting an ARTI.

How the review was done

The researchers did a systematic review of studies available up to December 2015. They found 25 randomized controlled trials (RCTs) with 11,321 people (about 50% girls or women). Most people were younger than 16 years of age, 28% were between 16 and 65 years of age, and 11% (about 1,200 people) were older than 65 years of age.

The key features of the RCTs were:

  • some people were healthy and some had respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD);
  • oral vitamin D3 in a variety of doses (most commonly 20 to 50 µg daily) was used for supplementation;
  • vitamin D3 supplements were compared with placebo; and
  • trials lasted for 7 weeks to 1.5 years.

What the researchers found

The evidence for the effect of vitamin D3 supplements on ARTIs was of high quality (high confidence in results).

Compared with placebo, vitamin D3 supplements:

  • reduced ARTIs, and results were similar in all age groups;
  • reduced ARTIs more in people with low vitamin D blood levels than in those with normal vitamin D blood levels;
  • did not affect risk for other clinical outcomes including death or ARTI-related hospitalizations or emergency department visits; and
  • did not increase serious adverse events.


In children and adults, vitamin D3 supplements reduce acute respiratory tract infections.

Note: Vitamin D3 supplements are not safe for everyone. Ask your doctor if taking vitamin D3 supplements is a good idea for you.

Oral vitamin D3 supplements vs placebo in children and adults*


Number of trials and people

Rate of events with vitamin D3 supplements*

Rate of events with placebo

Absolute effect of vitamin D3 supplements


25 trials (10,933 people)



About 3 fewer people out of 100 had an ARTI (from as few as 1 person to as many as 5 people)†

ARTI-related hospitalization or emergency department visit

11 trials (7,872 people)



No difference in effect‡


25 trials (11,224 people)



No difference in effect‡

Serious adverse events

25 trials (11,224 people)



No difference in effect‡

ARTI = acute respiratory tract infection.

*The event rate in the vitamin D3 supplements group was weighted. This means it may be a little different than you would expect if you just divided number of people who had an event with the number of people who were treated.

†Evidence was of high quality (high confidence in results).

‡Although the rates for the 2 groups look a little different, the differences were not statistically significant. This means that the differences could simply be due to chance rather than due to the different treatments.


A harmless, inactive, and simulated treatment.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.

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