Teens at the top of Israel's socioeconomic ladder are 34 percent more likely to suffer from asthma than those at the bottom, according to new research by the Israel Defense Forces' medical corp.
A study of 159,243 17-year-old candidates for induction showed that 8.5 percent of both boys and girls suffered from asthma.
However, when socioeconomic status was factored in, it was found that 9 percent of the teens in the upper one-fifth of the population had asthma, while in the lower one-fifth, the figure was 3.7 percent.
The figures applied to both severe and slight cases of asthma.
In Tel Aviv, the gap was much bigger: 13.7 percent in the top 20th percentile as opposed to 3.4 percent of the bottom 20th percentile had asthma.
Among families with numerous children, usually among the poorer segments of the population, the frequency of asthma was also found to be lower. In families with up to two children, 8.7 percent were found to have asthma, while in families with nine or more children, the percentage was 1.9 percent.
Similar studies in Boston and Chicago found that asthma risk was greater in poorer families than in wealthier ones, while a New Zealand study found no link at all.
Asthma in lower income groups has been explained by smoking, exposure to air pollution and obesity, all of which are more common among the poor than the rich.
Therefore the IDF study, which was headed by Dr. Alon Perel, sought explanations for their opposite results. They concluded that diet among the rich may not be ruled out as a risk factor.
A 2009 study found that a Mediterranean diet helps prevent asthma; Israel's poorer families may consume more of such a diet - rich in fruits and vegetables, olive oil and chicken - than the wealthy.
Living conditions among wealthier Israelis could encourage the development of asthma, the authors of the study say.
In such families, wall-to-wall carpets and pets are more common, both of which raise the risk of asthma and other allergies.
The findings also indicate that too sterile an environment from a young age, typical of wealthier families, can contribute to asthma.
Such children have fewer siblings and tend to receive better medical care. Consequently they suffer from less infections and also from less protection of their immune systems, the study says.
The study also found that asthma was lower among immigrant teens from Ethiopia (3.5 percent ) and higher among teens from the former Soviet Union (7 percent ).
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