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New Study Suggests That Vitamin D Supplements May Reduce Asthma Severity

Adding vitamin D supplements to standard medication could reduce the severity of asthma attacks for individuals with the respiratory condition, suggests a new review.

Researchers found that people with asthma who took vitamin D supplements alongside their usual medication were 50 percent less likely to visit the emergency department or require hospital admission as a result of an asthma attack. What is more, the researchers found that vitamin D supplementation was linked to a reduction in the need for steroid injections or tablets following an asthma attack. Lead researcher Prof. Adrian Martineau, from Queen Mary University of London (QMUL) in the United Kingdom, and colleagues recently reported their findings in The Lancet Respiratory Medicine. Asthma is one of the biggest health burdens across the globe, affecting approximately 300 million children and adults. Although there is currently no cure for asthma, there are medications that can help patients to manage the condition and reduce their risk of an asthma attack; But these medications are not always effective. As such, researchers are searching for ways to further reduce asthma severity. Could vitamin D supplements be one such strategy? 

Can Vitamin D Help Reduce Asthma Severity?

Respiratory infections, such as the common cold or the flu, are known to trigger symptoms of asthma - including airway inflammation, which can bring on an asthma attack. Some studies have suggested that vitamin D may help to lower the risk of respiratory infection-induced asthma attacks by boosting the immune system. To gain a better understanding of this association, Prof. Martineau and colleagues conducted a review of seven randomised controlled trials that looked at the effects of vitamin D supplementation on asthma severity.


The review included a total of 955 subjects with asthma, all of whom were receiving standard treatment for the condition. It was found that vitamin D supplementation reduced the need for asthma-related emergency department visits and hospital admissions by 50 percent when compared with a placebo, with the rate of such events falling from 6 percent to 3 percent. Also, among adults who did experience an asthma attack, vitamin D supplementation reduced the need for treatment with steroid tablets or injections by 30 percent, from 0.43 events per person per year to 0.30 events per person per year.


From a subgroup analysis, the researchers found that patients whose vitamin D levels were low at study baseline experienced the greatest benefit from vitamin D supplementation; their need for treatment with steroid tablets or injections fell by 55 percent. Still, they note that the small number of participants in each subgroup makes it difficult to confirm whether or not initial vitamin D levels influence the effect of supplementation on asthma severity. Importantly, it was also found that vitamin D supplementation was safe for participants at the doses used, and there were no differences in adverse effects between subjects who took vitamin D and those who took a placebo. Overall, the researchers believe that their findings indicate that vitamin D supplementation may be an effective way to help reduce asthma severity. "Vitamin D is safe to take and relatively inexpensive," adds Prof. Martineau, "so supplementation represents a potentially cost-effective strategy to reduce this problem." First study author Dr. David Joliffe, also of QMUL, notes that because the majority of study subjects were adults with mild to moderate asthma, they are currently unable to generalize the findings to children or individuals with more severe asthma. "Further clinical trials are ongoing internationally," adds Dr. Joliffe, "and we hope to include data from them in a future analysis to determine whether the promise of today's results is confirmed in an even larger and more diverse group of patients. 

What Is Vitamin D?

According to NHS Choices Vitamin D helps to regulate the amount of calcium and phosphate in the body. These nutrients are needed to keep bones, teeth and muscles healthy. A lack of vitamin D can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia in adults.

What Are Good Sources Of Vitamin D?

From about late March/early April to the end of September, most people should be able to get all the vitamin D they need from sunlight. The body creates vitamin D from direct sunlight on the skin when outdoors. But between October and early March we don't get enough vitamin D from sunlight. Vitamin D is also found in a small number of foods. Sources include:

  • Oily fish – such as salmon, sardines, herring, mackerel and fresh tuna
  • Red meat
  • Liver
  • Egg yolks
  • Fortified foods – such as most fat spreads and some breakfast cereals

Another source of vitamin D is dietary supplements. In the UK, cows' milk is generally not a good source of vitamin D because it isn't fortified, as it is in some other countries.

How Much Vitamin D Do I Need?

Babies up to the age of one year need 8.5-10mcg of vitamin D a day. Children from the age of one year and adults need 10mcg of vitamin D a day. This includes pregnant and breastfeeding women, and people at risk of vitamin D deficiency. From about late March/early April to the end of September, the majority of people should be able to get all the vitamin D they need from sunlight on their skin.

Should I Take Vitamin D Tablets?

For Infants And Young Children

The UK's Department of Health recommends that:

  • Breastfed babies from birth to one year of age should be given a daily supplement containing 8.5-10mcg of vitamin D to make sure they get enough
  • Formula-fed babies shouldn't be given a vitamin D supplement until they're having less than 500ml (about a pint) of infant formula a day, as infant formula is fortified with vitamin D
  • Children aged 1-4 years old should be given a daily supplement containing 10mcg of vitamin D


You can buy vitamin D supplements or vitamin drops containing vitamin D (for under fives) at most pharmacies and supermarkets. Women and children who qualify for the Healthy Start scheme can get free supplements containing the recommended amounts of vitamin D. See the Healthy Start website for more information.

For Adults And Children Over 5 Years Old

The UK's Department of Health recommends that:During the autumn and winter, you need to get vitamin D from your diet because the sun isn't strong enough for the body to make vitamin D. But since it's difficult for people to get enough vitamin D from food alone, everyone (including pregnant and breastfeeding women) should consider taking a daily supplement containing 10mcg of vitamin D during the autumn and winter. Between late March/early April to the end of September, most people can get all the vitamin D they need through sunlight on their skin and from a balanced diet. You may choose not to take a vitamin D supplement during these months.

People At Risk Of Vitamin D Deficiency

The UK's Department of Health recommends that: Some people won't get enough vitamin D from sunlight because they have very little or no sunshine exposure. The Department of Health recommends that you take a daily supplement containing 10mcg of vitamin D throughout the year if you:

  • Aren't often outdoors – for example, if you're frail or housebound
  • Are in an institution like a care home
  • Usually wear clothes that cover up most of your skin when outdoors.

People with dark skin from African, African-Caribbean and south Asian backgrounds may also not get enough vitamin D from sunlight. They should consider taking a daily supplement containing 10mcg of vitamin D throughout the year.

What Happens If I Take Too Much Vitamin D?

Taking too many vitamin D supplements over a long period of time can cause too much calcium to build up in the body (hypercalcaemia). This can weaken the bones and damage the kidneys and the heart. If you choose to take vitamin D supplements, 10mcg a day will be enough for most people. Don't take more than 100mcg of vitamin D a day as it could be harmful. This applies to adults, including pregnant and breastfeeding women and the elderly, and children aged 11-17 years. Children aged 1-10 years shouldn't have more than 50mcg a day. Infants under 12 months shouldn't have more than 25mcg a day. Some people have medical conditions that mean they may not be able to safely take as much. If in doubt, you should consult your doctor. If your doctor has recommended you take a different amount of vitamin D, you should follow their advice. Your body doesn't make too much vitamin D from sun exposure, but always remember to cover up or protect your skin if you're out in the sun for long periods to reduce the risk of skin damage and skin cancer.