Geography seems to play a role in a person’s risk of developing dementia

The paper is co-authored by the CDP’s Dr Tom Russ and researchers from the Alzheimer Scotland Dementia Research Centre at the University of Edinburgh. The research was supported by Alzheimer Scotland. The authors found evidence that environmental risk factors seem to play a role in a person’s risk of developing dementia.

The researchers have previously found that dementia risk may be higher in the north compared to the south in Scotland and in Sweden. While we don’t know why this is the case, it is likely to relate, at least in part, to environmental risk factors. The authors suggest that most of this variation is likely to result from unshared environmental factors that have their effect in adolescence or later life. Tom and his colleagues were interested to see whether the reverse pattern would therefore be found in the southern hemisphere – with higher risk of dementia the further from the equator you are.

The authors calculated mortality ratios for dementia-related deaths for different regions in Italy, New Zealand and Chile and found that in line with their previous findings in Sweden and in Scotland, dementia mortality was higher in northern than southern Italy. In New Zealand, they found the reverse pattern – with higher risk the further from the equator you are – at least in women. That would add support to the idea of sunlight potentially being important. However, in Chile there was a more complex pattern without a clear north-south difference. In fact, one of the highest risk areas was the Santiago Metropolitan Region so this leads to question which other environmental risk factors may affect dementia rates – perhaps pollution?

Tom Russ describes the publication's findings

Tom concludes that where we live seems to affect our risk of developing dementia. As it is becoming increasingly clear that geography plays a key role in dementia risk, although patterns vary in men and women, we need to find out why men and women are at different risk in the same environment and more globally, what the unshared environmental factors are that may cause dementia later in life. The next step is to do a lot more work to confirm the importance of specific environmental factors with the ultimate aim of preventing or delaying the onset of dementia.

Full text can be found at http://www.ncbi.nlm.nih.gov/pubmed/27536986

Russ, T., Murianni, L., Icaza, G., Slachevsky, A., Starr, J. (2016). Geographical Variation in Dementia Mortality in Italy, New Zealand, and Chile: The Impact of Latitude, Vitamin D, and Air Pollution. Dementia and Geriatric Cognitive Disorders. 42(1-2), 31-41