Dear Doctor: I love ham sandwiches -- and have one almost every day. I also have asthma, and just read that processed meats can increase the risk of asthma. How can this be?
Dear Reader: Meats have been cured -- that is, preserved and flavored -- since ancient times, largely through salting or smoking. Potassium nitrate and sodium nitrite salts were used to some degree in the Middle Ages, though the practice was not widespread. In the United States, these salts have been used to cure meat since 1925, and are highly effective in decreasing the incidence of bacterial disease. However, ingested nitrates and nitrites can form nitrosamines, which are carcinogenic.
Now comes a study, published last year in the journal Thorax, concluding that cured meats like ham increase the risk of asthma. The study enrolled 971 male and female participants from five cities in France. The enrollees -- not all of whom had asthma -- filled out a 118-item food-frequency questionnaire. Cured items included ham, sausage and dried sausage. Exposure was categorized as less than 1 serving a week; 1 to 3 servings per week; or greater than 4 servings per week. Participants reported the severity of their asthma over a 12-month period and scored this from 0 to 5, with 5 being waking up from sleep with an asthma attack.
At the beginning of the study, those who consumed more than 4 servings of cured meat per week were more likely to be men, were slightly more likely to smoke, were slightly more obese and had slightly lower educational levels. Those who ate more than 4 servings per week of cured meat were also more likely to be asthmatic and have more severe asthma at the beginning of the study.
After seven years, the participants filled out another survey regarding their level of asthma. Among those who ate less than 1 serving of cured meat per week, 14 percent reported increased asthma symptoms; among those who ate more than 4 servings of cured meat per week, 22 percent reported increased asthma symptoms. Noting that increased weight is also a factor for worsening asthma symptoms, the researchers adjusted for weight, smoking and educational levels -- and still found a correlation between worsening asthma and cured meat.
Oddly enough, two U.S studies have found that people newly diagnosed with chronic obstructive pulmonary disease were more likely to eat cured meats four to six times per week, but they did not find an increase in asthma risk. The cured meats here also included hot dogs and bacon.
As for why eating cured meat might worsen asthma, theoretically, nitrites can cause oxidative stress within the lungs and lead to more inflammation within the body, which can worsen asthma. While nitrates and nitrites may worsen asthma, I am not certain that they create asthma.
In addition, these studies did not separate meats cured by nitrites or nitrates and those cured by other means.
The take-home message: Stay away from meats cured with sodium nitrite or potassium nitrate. Not only are cured meats associated with greater obesity and increased asthma, meats cured with nitrites and nitrates increase the risk of cancer. If you don't have asthma and you don't smoke cigarettes, cured meats without nitrites and nitrates should be safe, but still, it's better to limit them. When you're shopping for smoked meats, make a close read of the food labels part of your pre-purchase routine.
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