Key messages
• The children of women given high doses of vitamin D during pregnancy are less likely to develop wheeze (a whistling sound heard on exhalation, due to lower airway swelling, inflammation, or constriction) than children whose mothers did not take vitamin D in pregnancy.
• Vitamin D treatment in early childhood may have little effect on preventing asthma or wheeze, though we are uncertain of these results.
• We are very uncertain about the evidence for any unwanted effects of vitamin D treatment in pregnant or breastfeeding women or young children.
Background
Asthma is a common childhood condition that affects the lungs. Children with asthma experience recurrent attacks of breathlessness, wheezing, and coughing due to inflammation, mucous production, and narrowing of the airways. Atopic dermatitis (a chronic inflammatory skin disease), sensitisation to allergens, and recurrent respiratory tract infections may contribute to the development of asthma. Vitamin D is an essential nutrient that affects the immune system. Previous studies have connected low vitamin D status to an increased risk of allergic disease.
What did we want to find out?
We wanted to find out if vitamin D treatment in early life helps prevent: (a) childhood asthma, wheeze, or both; and (b) risk factors for childhood asthma, including atopic dermatitis, airway infections, sensitisation to allergens, and airway inflammation.
We also wanted to find out if vitamin D treatment was associated with any unwanted effects.
What did we do?
We searched for studies exploring any of the following comparisons:
• any vitamin D versus placebo (an inactive 'dummy' medicine) or no treatment in pregnant or breastfeeding women;
• any vitamin D versus placebo/no treatment in young children;
• higher-dose vitamin D with lower/standard dose (400 international units/day or less) vitamin D in pregnant or breastfeeding women,
• higher-dose vitamin D with lower/standard dose (400 international units/day or less) vitamin D in young children.
Our outcomes of interest were childhood asthma, wheeze, atopic dermatitis, airway infections, allergic sensitisation, and airway inflammation.
We compared and summarised the results of the studies and rated our confidence in the evidence, based on factors such as study methods and the number of people in the study.
What did we find?
We found 18 studies involving a total of 10,611 pregnant women, infants, mother/infant pairs, and children up to age five. Four studies compared any vitamin D with placebo/no treatment in pregnant women, five studies compared any vitamin D with placebo/no treatment in young children, four studies compared higher versus lower doses of vitamin D in pregnant women, and seven studies compared higher versus lower doses of vitamin D in young children. Studies were conducted around the world; most were done in higher-income countries. The largest study included 3046 participants; the smallest included 50. The duration of vitamin D treatment ranged from 28 days to two years, with most studies treating for six months or less.
Main results
Any vitamin D treatment in pregnancy may help prevent childhood asthma (1 study, 236 participants), and higher-dose vitamin D treatment in pregnancy likely helps prevent childhood wheeze (3 studies, 1439 participants).
Vitamin D treatment in early childhood, regardless of dose and comparison, may have little effect on asthma or wheeze, though we are uncertain of these results. High-dose vitamin D treatment in early childhood may help prevent airway infections (6 studies, 2385 participants).
Vitamin D treatment in pregnancy or early childhood, regardless of dose and comparison, may have little to no effect on atopic dermatitis, sensitisation to allergens, and markers of airway inflammation.
We are uncertain whether vitamin D treatment in pregnancy or early childhood has any unwanted effects because the studies reported limited information about unwanted effects.
What are the limitations of the evidence?
For interventions in pregnancy, we are moderately confident in the effects of high-dose vitamin D on wheeze and asthma. We are less confident in the effects of any vitamin D on asthma because the evidence is based on results from one small study. However, these findings are limited to prenatal vitamin D treatment in the second and third trimesters; the effects of vitamin D treatment starting around the time a woman becomes pregnant or in the first trimester are unclear.
For interventions in young children, we have low confidence in our findings for the effects of vitamin D, regardless of dose, on any outcome evaluated.
We have little confidence in the findings for unwanted effects because the evidence is based on a few cases and there were not enough studies evaluating most unwanted effects.
How current is this evidence?
The evidence is current to October 2023.