By Michael Smith , MedPage Today Staff Writer – Reviewed by Rubeen K. Israni, M.D., Fellow, Renal-Electrolyte and Hypertension Division, University of Pennsylvania School of Medicine
• Advise patients that this study found an inverse association between asthma and hay fever and all-cancer mortality.
• Note that the study analyzed a very large database of information, collected over 18 years of follow-up, but it is not a randomized trial.
OTTAWA, Aug. 2-Persons who suffer from asthma and hay fever are less likely to die of any kind of cancer, according to a large Canadian study.
Using an enormous database — the 1.2-million-strong Cancer Prevention Study II — epidemiologists have demonstrated that having asthma, hay fever, or both is associated with a lower risk of dying of cancer.
“The study suggests that there may be a protective effect for cancer mortality in those with allergies,” said epidemiologist Michelle Turner, MSc, of the University of Ottawa, whose study appears in the current American Journal of Epidemiology.
Analyzing the records of 1.102 million of the study’s 1.2 million participants, Turner and colleagues found:
• A 12% reduction in risk of dying of all cancers for people with both asthma and hay fever. (The relative risk was 0.88, with a 95% confidence interval of 0.83 to 0.93.)
• An 8% reduction in risk of dying of all cancers for people with just hay fever. (The relative risk was 0.92, with a confidence interval of 0.89 to 0.94.)
The effect appeared to be driven largely by significant inverse associations with lung and colorectal cancer mortality. For instance, for people with both conditions, there was 27% reduction in risk of dying of lung cancer and a 24% reduction in risk of dying of colorectal cancer.
The study also found:
• Hay fever only was associated with a 15% reduction in the risk of pancreatic cancer death.
• Asthma only was associated with a 25% reduction in the risk of leukemia mortality.
On the other hand, a history of asthma alone was also associated with a significantly increased risk of lung cancer mortality. (The relative risk was 1.11, with a 95% confidence interval of 1.02 to 1.20.)
Turner said in an interview it’s not clear why such effects should appear.
“One suggestion is that people with allergies might have better immune surveillance,” she said. Equally, there may be some other unknown difference between people with allergies and the general population, or there may be an undiscovered effect of allergy medication.
“No one really knows the answer,” she said.
Interestingly, among the study participants who had never smoked, most of the associations vanished. Only a slight protective effect for those with both asthma and hay fever — a 9% reduction in risk of all-cancer mortality — remained significant (RR 0.91; 95% CI 0.83-1.00).
That may be due to the relatively small size — 448,610 — of the group who had never smoked, compared to the whole study population, Turner said.
The longitudinal Cancer Prevention Study II, designed and conducted by the American Cancer Society, enrolled about 1.2 million U.S. men and women in 1982. The vital status of participants has been determined every two years since.
Over 18 years of follow-up, there were 81,114 cancer deaths among the participants whose records were analyzed.
The baseline survey listed 25 different medical condition or diseases, including asthma and hay fever, Turner said.
The comprehensive nature of the baseline survey allowed the researchers to control for a large range of possible confounding factors, she said, including co-morbid disease, lifestyle factors, diet, diabetes, body mass index, and family history.
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Primary source: American Journal of Epidemiology. Source reference: Turner, MC et al. Cancer Mortality among US Men and Women with Asthma and Hay Fever. Am J Epidemiol 2005;162:212-221
The above is for general informational purposes only. Always consult your physician regarding specific medical issues and call Hatzalah or your local ambulance service in the event of an emergency.