25 January 2008

Smoking may lower allergy risk

Smoking, or exposure to parents' smoking, may lower the risk of allergies developing in young people who are genetically prone to them.

Smoking, or exposure to parents' smoking, may lower the risk of allergies developing in young people who are genetically prone to them, a study suggests.

Researchers speculate that the immune-suppressing effects of smoking, normally a negative, may make allergic reactions less likely. Allergies arise from an immune system overreaction to usually benign substances in the environment, like pollen, cat dander or dust.

No one, however, should view smoking as a way to prevent allergies, the researchers stress in their report, published in the Journal of Allergy & Clinical Immunology.

As for any "take-home message" from the findings, lead researcher Dr Robert J. Hancox told Reuters Health, "If anything, it is that smoking damages the immune system, among many other harmful effects."

"One side effect of this may be that people who smoke may be less likely to develop allergies, but this is a very small benefit compared to the many harmful effects of smoking," said Hancox, of the University of Otago in Dunedin, New Zealand.

The findings are based on a study that followed 946 New Zealanders from birth to the age of 32. The researchers found that among participants whose parents had allergies, those who smoked were less likely to develop allergies by adulthood. The same was true of those whose parents smoked when they were children.

No such protective effect was seen among study participants without a family history of allergies.

Hancox and his colleagues accounted for a number of factors that sway the risk of allergies - such as participants' family income when they were growing up, and whether they were breastfed as infants - and found that the link between smoking and lower allergy risk remained.

The researchers also looked at whether "reverse causation" explained the findings - whether, for instance, children who developed allergies early on were less likely to take up smoking. This was not the case.

There was also no evidence that people who developed allergies as children, then took up smoking, saw their allergies improve.

Avoiding cigarette smoke, whether by not smoking or steering clear of second-hand smoke, has often been recommended as a way to lower allergy risk, Hancox and his colleagues note. This is despite a lack of evidence that the strategy works.

The current findings, the researchers write, suggest that avoiding cigarette smoke is unlikely to prevent allergies. - (Amy Norton/Reuters Health)

SOURCE: Journal of Allergy & Clinical Immunology, January 2008.

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