The importance of research on the association between socioeconomic conditions and asthma.

After your excellent issue on asthma (1), you will be aware that the prevalence of asthma has increased in several countries, especially in affluent Western countries and Latin America. In our opinion, studies of the relationship between asthma and socioeconomic differentials provide an opportunity to advance our knowledge of what causes asthma and may even lead to the possibility of preventing it. The speed of this increase suggests an environmental rather than genetic source. It has been hypothesized that this increase was a consequence of better living conditions and hence less exposure to infection, the so-called hygiene hypothesis. This hypothesis is supported by the high rates of asthma in affluent countries and a greater prevalence of atopic diseases in populations with higher socioeconomic status (SES). However, there is increasing evidence of a greater frequency of asthma in populations of lower SES in affluent societies, such as African Americans in the United States (2, 3) and subpopulations in Europe (4, 5), as well as in some Latin American countries where societies are characterized by a marked inequality in wealth, with large pockets of poverty. We believe there is a need for further studies on SES and asthma and that some major methodologic aspects must be addressed to find the right answer; we list them below and propose guidelines for research. First, we must establish how and why the direction of the association with SES has changed over time, as has been observed in some places. For example, surveys in Sweden showed that the population of lower SES had lower prevalence of asthma in earlier cohorts, but later cohorts had the highest rates, a reversal of the effect with successive generations (6). In a study in Germany, higher prevalence of asthma was found in previous generations with high SES but not in recent ones (7). Second, we need to assess the effect of SES at the collective as well as at the individual level. SES at the individual level is more closely related to factors such as genetic makeup, family resources, living standards, occupation, education, diet, and indoor environment. At the collective level, it may be related to, for example, community resources and outdoor environmental exposures. There is some evidence that SES at the collective level is associated with asthma morbidity; for instance, a study in the United States showed increased prevalence of asthma in children exposed to community violence (8). This evidence is particularly important in Latin America, where violence has become a major cause of morbidity and mortality (9). In addition, determination at the collective level can be seen as reLa Revista Panamericana de Salud Pública/Pan American Journal of Public Health se complace en publicar cartas de los lectores dirigidas a estimular el diálogo sobre los diversos aspectos de la salud pública en las Américas, así como a esclarecer, discutir o comentar de manera constructiva las ideas expuestas en la revista. Las cartas deben estar firmadas por el autor y especificar su afiliación profesional y dirección postal o electrónica. Cuando se trate de comentarios sobre un artículo que requieran contestación del autor, se procurará conseguir esa respuesta con el fin de publicar ambas cartas. La redacción se reserva el derecho de editar las cartas recibidas y resumirlas para mayor claridad.