« Update on Diet and Asthma »

Low vegetable intake is associated with allergic asthma and moderate-to-severe airway hyperresponsiveness

Asthma has increased in prevalence in recent decades1, and now affects approximately 14% of youth worldwide2. Over a similar period, there has been a shift from a traditional or prudent diet, to a western diet. Individual nutrients , and foods4,5 are often studied as exposures for asthma outcomes, thereby potentially resulting in different conclusions than if diet quality was the exposure4. Asthma has many phenotypes. Consideration is warranted to two phenotypes: allergic asthma and non-allergic asthma, as atopy (described below) may infl uence diet and asthma7.

A study of diet quality and asthma in youth

The study was conducted to determine if diet quality is crosssectionally associated with asthma amongst youth. Data were collected from youth enrolled in a nested case-control study of the 1995 Manitoba, Canada Birth Cohort Study of Allergy, Genes and the Environment (SAGE)8. From responses to a food frequency questionnaire (FFQ) based on the FFQ used in the Nurses’ Health Study9, and adapted to suit the study, diet quality scores were created based on the Youth Healthy Eating Index (YHEI)10. The YHEI includes both a total diet score and component scores, based on recommendations from the United States’ Department of Agriculture’s Dietary Guidelines for Americans11 and which are similar to those from Canada’s Food Guide to Healthy Eating12. Youths’ scores were classified as either low or high, with a cut-off at the median.

In the study, 26.2% of youth had asthma, according to pediatric allergists’ assessments. Youth were skin prick tested to common allergens to determine atopy status. Youth with asthma were classifi ed as having either allergic asthma (asthma + atopy, n=107) or non-allergic asthma (asthma, no atopy, n=38).

Airway hyperresponsiveness (AHR) was also considered, which is informative in the presence of asthma-like symptoms but the absence of obvious airway obstruction13. AHR was classifi ed as mild, or moderate/severe, and compared to non-AHR. Of youth assessed, 44.3% were non-AHR, 23.5% had mild AHR and 32.2% had moderate/severe AHR.

Diet quality is relatively poor

FFQ were completed by 476/489 youth (mean age 12.6 ± 0.5 years). The median diet score was 33.5/85, which is suggestive of relatively poor diet quality. Component scores for whole grains, vegetables, fruit, dairy, snack foods and fried foods were around the 50th percentile. Component scores for multivitamin use and fish were very low.

Diet quality is not statistically signifi cantly associated with asthma, but high vegetable intake protects against allergic asthma

Diet quality and asthma were not statistically signifi cantly associated. With consideration to asthma phenotypes, the results showed that high vegetable intake was associated with ~50% reduced odds of allergic asthma (p<0.02). No such associations were found for total diet quality, or other components and allergic asthma, or between diet quality and non-allergic asthma.

Diet quality is not statistically signifi cantly associated with AHR, but high vegetable intake protects against moderate/severe AHR

Similar to the results for diet quality and asthma phenotypes, only high vegetable intake was protective against moderate/severe asthma, again by ~50% (p<0.02). No associations were found between diet quality and mild AHR.

Clinical Implications and Conclusions

Although vegetable intake was associated with reduced odds of allergic asthma and moderate-to-severe AHR, it is too soon to advise patients that high vegetable intake protects against these conditions. Like other youth14, youth in the study had relatively poor diet quality. High vegetable intake should be encouraged as it is associated with many other health benefits.

Based on: Protudjer JL, Sevenhuysen GP, Ramsey CD, Kozyrskyj AL, Becker AB. Low vegetable intake is associated with allergic asthma and moderate-to-severe airway hyperresponsiveness. Pediatr Pulmonol. 2012 Dec;47(12):1159-69.

  1. Douwes J, et al. Importance of allergy in asthma: an epidemiologic perspective. Curr
    Allergy Asthma Rep. 2011 Oct;11(5):434-44.
    2. Lai CK, et al. Global variation in the prevalence and severity of asthma symptoms: phase
    three of the International Study of Asthma and Allergic in Childhood (ISAAC). Thorax. 2009
    3. Popkin BM, et al.. The nutrition transition: worldwide obesity dynamics and their
    determinants. Int J Obes Relat Metab Disord. 2004 Nov;28:S2-S9.
    4. Allan K, Devereux G. Diet and asthma: nutrition implications from prevention to
    treatment. J Am Diet Assoc. 2011 Feb;111(2):258-68.
    5. Nurmatov U, et al.. Nutrients and foods for the primary prevention of asthma and allergy:
    systematic review and meta-analysis. J Allergy Clin Immunol. 2011 Mar;127(3):724-33.
    6. Mertz W. Food nutrients. J Am Diet Assoc. 1994; 84:769-70.
    7. Chatzi L, et al. Diet, wheeze, and atopy in school children in Menorca, Spain. Pediatr
    Allergy Immunol. 2007 Sep;18:480-5.
    8. Kozyrskyj AL, et al.. A novel design to investigate the early-life origins of asthma in
    children (SAGE study). Allergy. 2009 Aug;64:1185-93.
    9. Willett W. Nutritional epidemiology. New York: Oxford University Press;1990.
    10. Feskanich D, Rockett HR, Colditz GA. Modifying the healthy eating index to assess diet
    quality in children and adolescents. J Am Diet Assoc. 2004 Sep;104:1375-83.
    11. United States Department of Agriculture. My Pyramid. 2005. Available on-line at www.
    12. Health Canada. Eating well with Canada’s Food Guide. 2007. Available on-line at www.
    13. O’Byrne PM, Inman MD. Airway hyperresponsiveness. Chest. 2003Mar;123:411S-416S.
    14. Hiza HA, et al.. Diet quality of Americans differs by age, sex, race/ethnicity, income, and
    education level. J Acad Nutr Diet. 2013 Feb;113(2):297-306.
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