LAUSR

Too often, we read about declining stroke incidence and mortality over the years (Feigin et al. 2016). Yet, this supposedly good news is only part of the whole story. The total number of stroke survivors and the quality of life after the accident are missing from the news. Moreover, global figures do not reveal other more frightening trends like stroke hitting people at a younger age and sex differences. The message of awareness campaigns is partly wiped off. Last, not the least, figures by country need to be read in the light of factors like age, socio-economic status, urban/rural and geographic location. As clearly shown in the paper of Guo et al. (2019), there is a correlation between temperature/climate variable and the occurrence of stroke. The last point is of interest because it is the way that many studies present their results: by country. It is surely important to know the stroke incidence at a national level, but it can become even more important to know the incidence at a regional level. This is true especially when it comes to large countries like China, India, Australia, Chile, Argentina, the USA and Russia. These countries extend on a huge part of the land. They spread over many parallels, including very cold and very hot provinces with different diets too. It has been noted that some national stroke incidence data are not matched by regional/local data. A study on the geographic patterns in cardiovascular disease incidence reported a higher risk of stroke in the Southeast than in the Northeast US (Rich et al. 2007). A huge difference in stroke prevalence, incidence and mortality was found in Hunan Province compared with China’s national data (He et al. 2018). Probably, it is time to take another step in the Study of the Global Burden of Disease and to add a new classification based on latitude. It would be interesting to see a world map with different colours depending on the regional incidence of stroke. It could happen that stroke incidence in Texas is closer to the incidence in Mexico than to the incidence in Massachusetts. The same way that Hong Kong’s figures could be more similar to Hanoi’s figures and very different from Urumqi’s figures. This would highlight the impact of latitude and diet on the occurrence of cardiovascular accidents. Different methodologies require a new way of looking at the problem based on a different hypothesis. Our world has been reshaped by globalisation with all its collateral effects. Borders decided after World War I and World War II as integral parts of the Peace Treaties have lost most of their significance. Research needs to take this into account when reading data. Human’s adaptability to climate is well known, and the interplay between genetics and human climate adaptability is now investigated in deeper details. People living at high altitude, like the Andes and the Himalaya, are more resistant to hypoxia and thus more protected from cardiovascular diseases. Less known are the interactions between the environment and gene-expression, also known as epigenetics. DNA methylation has been found to be a stronger risk factor for stroke than chronological age (Hannum et al. 2013). Not least, epigenetics is also involved in stroke recovery (Kassis et al. 2017). And epigenetics does not oblige national borders.