ACAAI 2011: Vitamin D and Asthma, Part 2

There are conflicting data regarding whether vitamin D (vit D) deficiency is a risk factor for asthma. Observational studies have linked low vit D status with impaired lung capacity, increased airway hyperresponsiveness (AHR), corticosteroid unresponsiveness, relatively poor asthma control, and higher rates of asthma-related hospitalization.

The following studies that suggest that vit D deficiency is a risk factor for asthma:

• The National Health and Nutrition Examination Survey (NHANES) III had two findings supporting an association for vit D deficiency as a risk factor for asthma. First, there was a strong relationship in adults between low serum levels of 25(OH)D and reduced lung function in a cross-sectional analysis of approximately 25,000 subjects. Also, more upper respiratory tract infections (URIs) were noted with lower 25(OH)D levels, regardless of season of year; this association was even stronger in subjects with asthma.
• A RCT involving over 300 Japanese school children provided additional evidence for an association between vit D deficiency and asthma. Children who received vit D daily (1,200 IU) for 4 months had 42% fewer influenza B infections (p = 0.04). Also, children with a history of asthma who took vit D had a 6-fold reduction in asthma attacks.
• Sutherland and colleagues examined 54 adult asthmatics and found that low vit D levels were associated with increased production of proinflammatory protein in blood. Adults with higher vit D levels had better lung function measures, improved AHR, and better response to corticosteroid in vitro.

These studies suggest vit D may not be as beneficial as initially believed:

• A 3-month RCT of vit D supplementation in adults showed no difference in URI severity or incidence. Dr. Foggs noted that the mean 25(OH)D levels in the treatment arm were low (35 ng/mL). It was unclear from this study what level of supplemental vit D is adequate for optimal immune function.
• In a study from Finland, children who received vit D supplements in the 1st year of life had a higher risk of developing asthma, atopy, & AR in adulthood.
• A UK study noted high maternal plasma 25(OH)D levels during late pregnancy were associated with higher risk of eczema in children at 9 months of age.
• Lastly, a Swedish study showed higher intake of vit D in 1st year of life was associated an increased risk of developing atopic dermatitis by age 6.

Dr. Foggs noted there are several gaps in our knowledge of vit D, including:

• Do low vit D levels contribute to increasing asthma severity?
• Do low vit D levels make steroids less effective?
• Does vit D directly affect corticosteroid activity?
• Does vit D supplementation help reverse corticosteroid resistance?

(Dr. Foggs was also elected vice president of the College at this meeting. Congratulations.)

Click here to read part 1 of Dr. Foggs's discussion on vitamin D and asthma.