Relationship between patients' month of birth and the prevalence of chronic diseases

Patients' month of birth can reflect exposure to certain factors during pregnancy and the first few months of life, which could influence the onset of chronic diseases during adulthood. The aim of this study is to evaluate the association between a patient's month of birth and the presence of chronic diseases in the Spanish population, by analysing the National Health Survey for the year 2006.

We measured the association between 27 common chronic diseases and the month of birth, estimating the odds ratios and confidence intervals at 95%, using multivariate logistical models and adjusting the results for month of birth and potentially confounding variables.

The sample population was made up of a total of 29,478 individuals, representing approximately 44.7 million Spanish residents on 1 January 2007. Significant associations were found between the month of birth and several chronic diseases. There is a gender-differentiated risk pattern of developing chronic diseases according to the month of birth, with more significant associations and of greater magnitude being detected among men compared to women.

The associations detected might reflect early exposure to environmental factors in the uterus and during the first few months of life. More specific studies are required to gain a more in-depth understanding of these associations.