Upward Trend: What’s to account for the increased prevalence of allergic rhinitis?

In the third study, ozone exposure resulted in epithelial disruption and increased permeability, inflammatory cell influx and proliferative and secretory responses in the nasal epithelium (J Toxicol Environ Health B Crit Rev. 2003;6(5):521-568). The effects “…had a priming effect on the late-phase response to allergen challenge, providing new insights into the pathophysiology of respiratory allergic diseases,” the authors concluded.

More people are moving from rural, agricultural settings, which traditionally have had lower rates of allergies, to more urban settings, which have higher levels of air polllution.
—Matthew Ryan, MD

Location, Location, Location

The International Study of Asthma and Allergy in Childhood (ISAAC) has demonstrated a large variation in the prevalence of asthma and rhinitis symptoms in children around the world (Lancet. 1998;351(9111):1225-1232). In particular, the study finds that countries with a very low prevalence of asthma (<5 percent), such as Indonesia, Albania, Romania, Georgia and Greece, also have low prevalence of rhinitis. On the other hand, countries with a high prevalence of asthma (>30 percent), such as Australia, New Zealand and the United Kingdom, have a higher prevalence of rhinitis (15 percent to 20 percent). In countries where the prevalence of allergy and rhinitis is high, “we have seen either a reduction in increase of allergic rhinitis, a plateau in incidence, or a slight reduction in recent years,” Dr. Ryan noted.

The interplay between geography and genetics was the focus of a study of 200,682 men and women (ages 20 to 44 years) seen in 57 centers in Europe, North America, North Africa, India, Australia and New Zealand. Latitude was used as a proxy for ultraviolet exposure (vitamin D), as well as climatic differences responsible for different pollen seasons.

The median prevalence of allergic rhinitis was 22 percent, the authors reported (PLoS Med. 2005;2(10):e294). There was, however, substantial variation across geographic areas. For example, the disorder was far more common the further patients were from the equator. But when the investigators restricted their analysis to Europe, geographical latitude was not a significant factor.

“One intriguing possibility,” wrote lead author Matthias Wjst, “is that a risk factor within language borders might be even more relevant than geographical latitude alone in determining the distribution of allergic diseases—reflecting genetic influences or cultural differences in raising children.”