What is asthma?
Asthma is a lifelong lung disease that makes it difficult to breathe. There are tubes or airways, which carry air to and from the lungs to the mouth and nose. If an individual has asthma, these airways can become swollen, clogged with mucus and constricted by surrounding muscles.
When symptoms worsen and become more intense, this is called an asthma attack. Asthma attacks can be so severe that a person would need emergency care. Individuals can have an asthma attack if they are exposed to things like allergens, smoke, extreme air temperatures and air pollution, or if they become sick or get an infection.
Asthma is treated using inhalers and/or oral medication. These help relax the muscles that surround the airways, or reduce airway swelling. Two common medicines are inhaled steroids and β-agonists. There are also other kinds of asthma medications.
If you have asthma, it’s important to try and avoid coming into contact with the things that trigger attacks, such as allergens and smoke. Most of the time, you manage asthma yourself, taking inhalers and medication regularly and avoiding things that trigger your attack to help keep your condition under control.
How common is asthma?
Three hundred million people have asthma worldwide. In the United States, 1 out of every 10 people will have asthma at some point in their life. Most of the time, doctors diagnose asthma in children before they turn six years of age. Around half of all people with asthma will have an asthma attack every year.
What are the symptoms of asthma?
People with asthma may experience chest tightness, wheezing and a long-lasting cough. They cannot get their breath.
The main symptoms of asthma include: 
- Chest tightness
- Long-lasting cough
- Difficulty breathing
When an individual has an asthma attack, one may experience the above symptoms with an increased level of severity. 
Symptoms of severe asthma attacks may include:
- Little to no improvement after use of medication
- Bluish fingers and lips
- Exhaustion and confusion
It’s important to prepare a treatment plan with a doctor to manage future asthma attacks. Doctors often setup a set of rules to follow depending on the severity of the asthma attack.
What causes asthma?
Doctors and scientists don’t fully understand the etiology of asthma. The number of people diagnosed with asthma has increased exponentially since the 1960s. Doctors and scientists think this is a result of a change in diet, behavior and environment. Some think that not getting enough sun exposure and vitamin D may be one cause of asthma, but we don’t know yet if this is the case.
What is the link between vitamin D and asthma?
One theory is that vitamin D helps reduce inflammation in the airways caused by asthma.
Vitamin D is a nutrient that the body produces when the skin is exposed to the sun. Supplementation and sun exposure is essential for the body to receive adequate vitamin D. Doctors and scientists believe there is a link between vitamin D and asthma, because individuals are more likely to get asthma if they live in a city, are obese or African American. These people are also more likely to be vitamin D deficient.
If an individual has asthma, their airways swell, clog with mucus and tighten because they become inflamed. Inflammation is the body’s response to an injury, infection or irritation. Doctors and scientists are interested in vitamin D, because it reduces inflammation. So, in theory, it may make the airways healthier by building better airways in early childhood, improving day-to-day symptoms and decreasing the risk for an asthma attack.
Doctors and scientists are also interested in vitamin D, because it makes the immune system smarter by helping the body produce defenses to fight off infections. A smarter immune system may reduce inflammation and the likelihood of developing an infection along with an asthma attack.
Scientists are looking into whether vitamin D supplementation during pregnancy reduces the chance of the infant developing asthma. They are also researching whether vitamin D sufficient children have a reduced risk of developing asthma.
In addition, researchers are investigating the potential role of vitamin D in the prevention and treatment of asthma. They also want to know if getting enough vitamin D can reduce the likelihood of asthma attacks.
A study in Canada involving people between the ages of 13 to 69 years found that those with vitamin D levels below 20 ng/mL (50 nmol/L) were 50% more likely to have asthma than those with levels between 20 and 30 ng/ml. Those with low levels were also twice as likely to have had asthma at one point in their life.
What is the link between sunlight and asthma?
Since solar UVB is the primary source of vitamin D, it is expected that people receiving more sunlight would have a reduced risk of asthma. In addition, there may be other effects of sunlight in reducing the risk.
Several studies have found that people who spend more time in the sun have lower rates of asthma. A study in the United States found that higher latitude, lower sunlight in winter and lower temperatures were linked to higher rates of asthma.
A study in Spain found that children between the ages of 6-7 years had a 6% reduced risk of asthma for each 100 hours spent in the sun per year. However, those between 13-14 years of age only experienced a 1% reduced risk under the same conditions.
A study involving 6-7 year old children from 10 European countries and 13-14 year old children from 13 European countries in the fall and winter found that the highest associations with asthma were low temperature, low sunshine and rainfall.
A study in Turkey found that children with asthma had much lower vitamin D levels and spent less time in the sun than age-matched children.
Can getting enough vitamin D during pregnancy and early childhood prevent asthma in children?
Several research studies have looked at how much vitamin D mothers get during pregnancy and whether or not their children develop asthma later in life.
Two studies measured the amount of vitamin D in women’s blood during pregnancy:
- One study found that there was no link between vitamin D levels in the mother during pregnancy and the chances of the child developing asthma. Another study found that if a mother had high vitamin D levels in her blood, her child was more likely to develop asthma.
- Neither study found a link between the amount of vitamin D in the cord blood at birth and the likelihood of the child later getting asthma.
One study looked at how much vitamin D pregnant mothers got from their diet and then the chances of their child getting asthma.
- This study found that mothers who received the most vitamin D from their diet during pregnancy had children who were less likely to develop asthma.
A study in the United Kingdom found that taking vitamin D during pregnancy reduced the risk of asthma at age 10 years by about 10 to 15%.
Given these mixed findings, it isn’t known whether there is a link between the amount of vitamin D a woman gets during her pregnancy and the chances of her child getting asthma.
There is no research about whether getting enough vitamin D during early childhood, up to the age of 6, can lower the chances of a child developing asthma later in life. However, there is some research underway looking at this.
Can getting enough vitamin D help improve how well asthma medication works?
Budesonide is a medicine that you inhale or use as a nasal spray and it’s sometimes prescribed for people with asthma. In the United States, it is marketed under the names Rhinocort or Pulmicort.
In one study on children with asthma scientists gave all the children budesonide. Then, they gave half the children a dummy pill and the other half 500 IU of vitamin D every day. After 6 months, the children who took vitamin D had fewer asthma attacks than those who took a dummy pill.
Therefore, there is some evidence that vitamin D might help increase the efficacy of budesonide. However, the study was small, so scientists can’t say if vitamin D helps for certain.
A study in India evaluating children with moderate to severe bronchial asthma found that taking 60,000 IU of vitamin D3 per month significantly improved pulmonary function tests (peak expiratory flow rate) and reduced the requirement of steroids, emergency visits and number of asthma exacerbations.
A vitamin D supplement randomized controlled trial of adults with baseline vitamin D level of 19 ng/mL treated with 100,000 IU once followed by 4,000 IU/d for 28 weeks did not reduce the rate of first treatment failure or exacerbation in adults with persistent asthma and vitamin D insufficiency .
Can getting enough vitamin D prevent asthma attacks or make them less severe?
There have been some studies that have looked at whether vitamin D can reduce the severity and frequency of asthma attacks in children.
In one study, scientists gave one half of a group of Japanese school children (aged 6-15) 1,200 IU of vitamin D/day and the other half a dummy pill every day. Scientists mainly wanted to know if vitamin D could prevent the flu (it did), but they also wanted to know if vitamin D reduced the number of asthma attacks. The children that took the vitamin D supplement had fewer asthma attacks than the children that took the dummy pill.
A review found that giving children 500 to 2000 IU/day reduced asthma exacerbations by 60%. So vitamin D may help childhood asthma.
We know that, in adults with asthma, 4,000 IU/day for 28 weeks only slightly reduced the amount of inhaled corticosteroids needed but did not prevent asthma exacerbation. This does not mean adults with asthma should refrain from taking vitamin D; it only means the vitamin D will not help the asthma.
Key points from research
- At this time, it isn’t known if receiving adequate vitamin D from sun exposure, or taking supplements when pregnant, can affect the chances of the child developing asthma. Research also doesn’t show whether maintaining sufficient vitamin D levels during childhood affects the risk of developing asthma later in life.
- A couple of small studies have found that vitamin D supplementation reduced the risk of asthma attacks in children.
- A large well-designed and well-executed study in adults showed vitamin D does not help adult asthma.
What does this mean for me?
There is some evidence that supports adequate vitamin D levels may help reduce the number of asthma attacks for children.
If you’re pregnant or have a young baby, there is currently some evidence that more vitamin D, through either supplementation or sunshine, will reduce the risk of your child getting asthma. However, taking a vitamin D supplement is helpful for other reasons and important for your baby’s development.
If your child takes a budesonide, like Rhinocort or Pulmicort, there is some evidence that taking a daily vitamin D supplement may be helpful in reducing the number of asthma attacks your child has.
Research also shows that getting enough vitamin D may be able to reduce the number of asthma attacks for children between the ages of 6-15 years old, whether or not they are taking a budesonide.
If you or your child has asthma and want to take vitamin D, it’s unlikely to harm you or make your symptoms worse. However, you may not see any improvement in your symptoms either.
You should not take vitamin D in the place of other medications for your condition. Talk to your doctor about taking vitamin D or any other supplement.
How much vitamin D to take?
The Vitamin D Council recommends that healthy children take 1,000 IU of vitamin D a day for every 25 lbs of their weight, rounded up. So for example, if your child weighs 35lbs, he or she should take 1,400 IU of vitamin D/day. This amount is higher than the amount that has been used in research studies of children with asthma. So it isn’t known if this amount is helpful for children with asthma; though, it is unlikely to do any harm.
For adults, the Vitamin D Council recommends taking 5,000 IU of vitamin D a day. This amount hasn’t been tested on adults with asthma, though the federal government says taking up to 10,000 IU of vitamin D a day is unlikely to do any harm.
For pregnant mothers, the Vitamin D Council recommends 6,000 IU of vitamin D a day. How this affects the risk of your child developing asthma later in life isn’t known but that amount of vitamin D appears to reduce pregnancy complications. 
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This page was last updated November 2015.