News · Supplements
Vitamin A, not D, tracked with better lungs in asthma
A Thorax study of 1,165 children and 1,041 adults with asthma found blood vitamin A levels tracked with better lung function, while vitamin D did nothing measurable in children.
Based on a peer-reviewed study in Thorax
- Researchers at Brigham and Women's Hospital analyzed two asthma cohorts, 1,165 children in Costa Rica and 1,041 adults, publishing in Thorax.
- In children, higher vitamin A tracked with better lung volumes, while vitamin D showed no association at all.
- In adults, both vitamins tracked with better lung function on two of the three measures.
- Vitamin D sufficiency corresponded to lower epigenetic aging in adults, a measure of biological rather than calendar age.
- One nuance cuts against a simple reading: in children, higher vitamin A went with a LOWER ratio of forced expiratory volume to forced vital capacity.
- Higher vitamin levels were linked to changes at a gene called IRF5, offering a possible mechanism through DNA methylation.
- This is observational. Nobody was given a supplement, so it cannot show that taking vitamin A helps anyone's lungs.
Vitamin D has had the asthma spotlight for fifteen years, through trials that mostly disappointed. A study in the journal Thorax looked at it alongside a vitamin that gets far less attention, and the less famous one performed better.
Across two asthma cohorts totalling more than 2,000 people, higher vitamin A was associated with better lung function. In children, vitamin D showed no association.
Why look at both together
The rationale is biological rather than fashionable. Vitamins A and D regulate numerous genes through intersecting metabolic pathways, influencing lung development and asthma. They act on overlapping machinery, which is an argument for studying them side by side rather than one at a time.
The researchers aimed to examine the impact of vitamins A and D on lung function, epigenetic aging and regulatory epigenetics in children and adults with asthma. That third element, the molecular layer, is what separates this from another correlation study.
Two cohorts, blood not questionnaires
Two asthma cohorts, a study of 1165 children in Costa Rica and one of 1041 adults were included.
Measurement was unusually thorough. Serum miRNA profiles, blood DNA methylation and plasma or serum vitamin A and D levels were measured, then related to lung function, gene regulation and biological aging.
Using measured blood levels rather than asking what people ate removes one of the largest sources of error in vitamin research.
The split by age and vitamin
In children, higher vitamin A was associated with higher forced expiratory volume and higher forced vital capacity, the two standard measures of how much air the lungs can move. Vitamin D showed nothing.
In adults, both vitamins were positively associated with forced expiratory volume and forced vital capacity. Only vitamin A moved the third measure, the ratio between them.
Vitamin D did earn one distinct result. Vitamin D sufficiency corresponded to lower epigenetic aging in adults, meaning their DNA methylation patterns looked younger than their calendar age would predict.
The complication in the children’s data
Buried in the numbers is a wrinkle that resists a clean headline. In children, higher vitamin A went with a lower ratio of forced expiratory volume to forced vital capacity, even as both individual volumes rose.
That ratio is one of the standard markers of airway obstruction, and a lower one usually reads as worse. Here it fell because total lung capacity rose faster than the volume exhaled in the first second. Bigger lungs, proportionally slower emptying.
Whether that is good, neutral or mildly concerning is not settled by this study, and any account claiming vitamin A simply improves children’s lungs is skipping this.
A mechanism, at least a partial one
The molecular layer gives the findings something most vitamin studies lack. Higher vitamin levels were associated with hypomethylation at a gene called IRF5, corresponding to better lung function and lower aging, and the mediation analysis indicated statistical partial effects through methylation and miRNAs.
IRF5 helps regulate immune responses, which is a sensible place for an asthma signal to appear. “Partial” is doing honest work in that sentence: the molecular route explains some of the association, not all of it.
What it does not license
Nobody took a supplement in this study. It measured what was already circulating, which means people with better-controlled asthma, better diets and more time outdoors will differ in vitamin levels for reasons that have nothing to do with causation.
Vitamin A is also the wrong nutrient to experiment on casually. It accumulates in the liver and is toxic in excess, which is precisely why the trial evidence, rather than the correlation, has to come first.
The authors’ conclusion stays inside the data: vitamin A, but not vitamin D, in children was associated with better lung function and lower epigenetic aging in asthma.
After a decade of vitamin D trials for asthma that underdelivered, the useful takeaway may simply be that the field was looking at the wrong vitamin.
People also ask
Should people with asthma take vitamin A?
Nothing here supports that, and this is general information rather than advice. The study measured vitamin levels already in people's blood; it did not give anyone a supplement. Vitamin A is also fat-soluble and genuinely toxic in excess, causing liver damage and, in pregnancy, birth defects. It is one of the supplements where more is clearly not better. Anyone with asthma should discuss it with their doctor rather than self-prescribing.
Why did the lung ratio go down in children if their lungs were better?
Because the ratio compares two things that grew unevenly. Higher vitamin A in children went with higher forced expiratory volume and higher forced vital capacity, but the second rose more, which mathematically lowers the ratio between them. Larger lungs with proportionally slightly slower emptying is not the same as worse asthma, but it is a real complication in reading the result as straightforwardly good.
What happened with vitamin D?
It split by age. In children, vitamin D showed no association with lung function. In adults it was positively associated with two lung measures, and vitamin D sufficiency corresponded to lower epigenetic aging. Given how heavily vitamin D has been promoted for asthma, a clean null in children is a useful corrective.
What is epigenetic aging?
It estimates biological age from chemical tags on DNA called methylation marks, which change in predictable patterns over a lifetime. Someone whose epigenetic age runs ahead of their calendar age is, by this measure, aging faster. It is a research tool rather than a clinical test, and the clocks disagree with each other more than headlines suggest.
How strong is the evidence?
Moderate. Two independent cohorts totalling over 2,000 people, with blood measurements rather than dietary questionnaires, is better than most vitamin research. But it remains cross-sectional and observational, so it cannot separate cause from consequence: poorly controlled asthma affects diet, activity and sunlight exposure, all of which affect vitamin levels.