Smoke-free regulations and AMI mortality declining: Do babies come from Paris?
This paper from Villalbi and colleagues use a before-after design without control group to analyse deaths due to Acute Myocardial Infarction (AMI) in Spain from 2004-2007 and concludes "the extension of smoke-free regulations in Spain [came into force in January 2006] was associated with a reduction in AMI mortality, especially among the elderly". While we are clearly in favour of this law, their immediate impact on the population coronary health is doubtful, and this paper does not help to raise doubts.
First, coronary deaths have been declining in Spain, as in other developed countries, during the last years. Raw rates for men have changed from 109/100,000 in 2001 to 89 in 2008 (77 to 69 for women). The most important relative change for men was between 2004 and 2003 (before the law implementation). Authors argument that the 2003 heat wave distort the mortality patterns, but previous years maintain a similar pattern than 2003(1). AMI mortality rates in Spain (age-adjusted to European standard population) for 100,000 men were: 2001: 89.5; 2002: 87.5; 2003: 87.9; 2004: 81.2; 2005: 80.0; 2006: 74,6; 2007: 72.7; 2008: 67.8; similar figures for women were: 39.0; 38.8; 38.5; 36.2; 35.3; 31.9; 31.0; 29.2).
Second, the law did not have an additional effect in the prevalence of cigarettes consumption. According to the Spanish National Survey on Drug Use (EDADES, biannual periodicity) the prevalence began to decline years before the smoke-free regulation(2). For adult men: 2001: 51.5%, 2003: 53.0 2005: 47.2%, 2007: 46.0% (for adult women in the same years: 40.5%, 42.6, 37.5%, 37.6%).
Third, while the main effect of the Spanish 2006 law was the smoking ban in workplaces, the paper reports a higher mortality reduction in elderly (retired people who no longer work).
Fourth, in the paper the decline of mortality rates were steeply falling in the first 12 months after the implementation of the law. In contrast, other study that has evaluated the impact of anti-smoke laws in coronary mortality rates reported a modest non significant effect in the short term(3) (1.6% CI95%: -4.0%;7.0%), but larger effects after the first 12 months (18.6% CI95%=13.6%;23.3%).
In the 70s and 80s in Spain the number of storks decreased dramatically, and contemporary, the birth rate fell among the lowest in the world. Policies on these birds were able to recover their number in the 90's. In this period the Spanish birth rate increased again. The association of uncontrolled temporal trends -specially with a very short trend as in this study- should not be interpreted as causal (unless we are willing to accept that babies come from Paris).
Therefore, in the absence of other evidences we should be cautious about establishing causal relationships between the decrease in coronary deaths and one specific policy. As much as we favour that policy, scientific causality has other rules.
1.Instituto de Salud Carlos III. Ministerio de Ciencia e Innovacion. Mortalidad Espana y comunidades autonomas. Available: http://www.isciii.es/htdocs/centros/epidemiologia/anexos/ww9201_cau.htm
2. Ministerio de Sanidad, Politica Social e Igualdad. Encuesta Domiciliaria Sobre Alcohol y Drogas en Espana (EDADES). Available: http://www.pnsd.msc.es/Categoria2/observa/estudios/home.htm
3.Dove MS, Dockery DW, Mittleman MA, Schwartz J, Sullivan EM, Keithly L, et al. The impact of Massachusetts' smoke-free workplace laws on acute myocardial infarction deaths. Am J Public Health. 2010;100:2206-12.
Conflict of Interest: