From Reuters Health Information
NEW YORK (Reuters Health) Mar 02 - The prevalence of peanut and tree nut allergy is increasing in US children, according to data reported this week at the annual meeting of the American Academy of Allergy, Asthma and Immunology in New Orleans.
Dr. Hugh A. Sampson of Mount Sinai School of Medicine in New York and colleagues determined the prevalence of peanut, tree nut and sesame allergy in 2008 and compared the results (for peanut and tree nuts) to similar surveys conducted in 1997 and 2002.
The same methodology was used in all three time periods -- a nationwide, cross-sectional random-digit telephone survey. A total of 5,300 households (13,534 individuals) were surveyed.
The investigators report that the prevalence of peanut and/or tree nut allergy in children younger than age 18 years was 2.1% in 2008, up from 1.2% in 2002 and 0.6% in 1997.
The prevalence of peanut allergy in children rose from 0.4% in 1997 to 0.8% in 2002 and 1.4% in 2008. There was a similar increase in the prevalence of tree nut allergy -- from 0.2% in 1997 to 0.5% in 2002, and 1.1% in 2008.
The change in peanut and tree nut allergy prevalence in US children seen from 1997 to 2002 "is the most solid data that we have that nut allergy really did go up in that five-year period," Dr. Robert A. Wood, of Johns Hopkins University School of Medicine in Baltimore, Maryland, who was not involved in the study, said at a gathering of reporters Monday.
He acknowledged that random-digit dialing surveys "may overestimate prevalence because some people may think they have an allergy when they don't, but because the methodology was the same, we can be pretty confident that the increase that was seen in an 11-year period from 0.4 to 1.4 (in children) has to be real. It's hard to imagine that it is not."
In 2008, sesame allergy was reported by 0.1% of those surveyed. Sesame allergy was not asked about in the two earlier surveys.
Dr. Wood said there are "at least a dozen" theories as to why nut allergies are increasing in children.
The hygiene theory -- which postulates that reduced microbial exposure because of improved sanitation and cleaner lifestyles leaves a young child's immune system unchallenged and therefore at greater risk for allergies -- is perhaps the "most intriguing" one, he noted, "and probably makes sense when you look at an underdeveloped country versus a developed country."
Rates of allergy are much higher in developed countries, and if a country becomes more developed its inhabitants seem to develop more allergies, he said. "But when you look at certain populations, there are huge holes in the hygiene theory that can't explain everything. For example, in developed countries, we see lots of allergies in urban, inner city populations where exposures are high," Dr. Wood pointed out.
Two other theories revolve around nutritional issues. One involves vitamin D and charges that a higher rate of vitamin D deficiency has predisposed people to allergy. "The way that might make sense is we do believe that there is much more vitamin D deficiency over the last 10 to 20 years," Dr. Wood said, and in epidemiological studies there is an association between vitamin D deficiency and higher rates of allergy. Whether there is a cause-and-effect link is still being determined.
Another nutritional theory says that having too much folate can predispose to allergy. This, too, has been shown in a couple of epidemiological studies, Dr. Wood explained, and the theory makes some sense from a timing standpoint, given that in the 1980s, there was an influx of folate into the diet of pregnant women via folate supplementation at the time that allergies seemed to be rising.
These are just a few of the theories, and there are many others, Dr. Wood noted, adding: "I think it's clear that none of them explain the whole thing, even remotely."