Reacción a "Reactions: exposure to urban green spaces is associated with slower epigenetic ageing "

This is an interesting study on the relationship between exposure to greenness within a 5-km radius over 20 years (measured by satellite imagery that detects greenness using infrared), and ageing by studying changes in gene expression associated with ageing. Overall, the results show that greater exposure to greenness is associated with less ageing. Furthermore, they find that this association is more pronounced among women, white people and people from more deprived neighbourhoods, which has implications for the design of public policies to reduce health inequalities. As the study was conducted in different regions of the United States, the results may not be extrapolated to the Spanish context, for example, as urban design has a different history and evolution. 

The value of the study is that the researchers have followed up the same people over a time interval of twenty years, which makes it possible to control for some of the design problems in epidemiological studies without follow-up. However, of the more than 5,000 participants who started the study, [the researchers] only analyse 924 people for whom they have complete information on the study variables after 20 years of follow-up. These people may have different characteristics from the rest of the people not included in the analysis. Another problem with the research is that it does not study the types of green spaces to which people have been exposed and their quality, which could explain some of the differences found between social groups who might make different use of these spaces, despite considering themselves exposed because they are located around their homes. Finally, although the study of genetic changes is interesting, the results are more difficult to interpret in comparison with other studies that analyse quality of life, diseases or mortality.