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    Low Vitamin D Linked to Severe Asthma

    Study Does Not Show Causal Relationship Between Vitamin D Deficiency and Severe Asthma
    By Caroline Wilbert
    WebMD Health News
    Reviewed by Louise Chang, MD

    April 23, 2009 -- Low levels of vitamin D may be linked to severity of asthma in children, according to a new study.

    The study, published in the American Journal of Respiratory and Critical Care Medicine, examined the blood levels of vitamin D in children with asthma. Lower levels of vitamin D were associated with more severe asthma.

    Participants included 616 children with asthma in Costa Rica between the ages of 6 and 14. Of the participants, 175 had insufficient levels of vitamin D.

    John Brehm, MD, from Brigham and Women's Hospital, and colleagues found that low vitamin D levels were associated with more asthma hospitalizations in the previous year, more airway hyperactivity in lung function tests, more use of anti-inflammatory asthma medications like inhaled steroids in the previous year, and higher blood levels of allergy markers.

    People primarily get vitamin D through their skin, which makes it from sunlight exposure. Also, some foods and supplements are sources of vitamin D. The authors note that because vitamin D deficiency can also be seen in warmer climates with abundant sun exposure, other factors likely also play a role.

    The study doesn't establish a cause-effect relationship, but the researchers note that vitamin D may influence asthma in different ways, such as its effect on the immune system and muscle cells of the airways.

    Further studies to address the potential benefits of increasing vitamin D supplements for asthma patients may raise important issues, according to an accompanying editorial written by Graham Devereux, MD, of the department of environmental and occupational medicine at the University of Aberdeen.

    "Ideally, any intervention study should address the issue of dose; however, studies supplementing with doses above those currently recommended, although scientifically justifiable, will raise ethical and regulatory concerns,” Devereux writes.

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