The researchers conducting the HUNT Study are aware that the possible reasons behind any association between headache and the likelihood of going on to develop dementia are at present unknown. They examined the association between headache and dementia, via a large population-based study in Norway over decades, and appear to have discovered an association between non-migrainous headache and the probability of developing dementia later. Conversely, individuals unaffected by dementia appear to have been less likely to report non-migrainous headache previously.
Stræte Røttereng, AK. Bosnes, O. [and] Stordal, E. [et al] (2015). Headache as a predictor for dementia: the HUNT Study. The Journal of Headache and Pain. 2015, Vol.16, 89. (Click here to view the PubMed abstract).