To the Editor Kessing et al1 effectively demonstrate an association between lithium concentration in regional water in Denmark and the prevalence of dementia. However, in Denmark, there is a notable geographic variation in lithium concentration, which may act as a confounder.2 A higher concentration of lithium is present in the south of Denmark compared with the north.2 Latitude has been found to correlate with dementia risk. Significantly, decreasing latitude, namely a more southern residence, is associated with a lower risk of dementia.3-5 This has been demonstrated globally and notably in Scandinavian countries.3,5 The mechanism is not entirely clear; however, vitamin D, photo-generated through ultraviolet light, has been implicated.3,4 Hence, a number of potential confounders, including latitude of residence, need to be excluded before an incontrovertible link between lithium and dementia can be established.
Uzoigwe CE, Franco LCS, Conde IG. Lithium and Dementia. JAMA Psychiatry. 2018;75(3):301. doi:10.1001/jamapsychiatry.2017.4190
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