Dementia and meditation
There is research indicating a possible beneficial effect of meditation practices for brain health, namely enhanced cognition and brain plasticity, and may even help in preventing dementia. Evidence to support such claims come from cognitive, electroencephalogram, and structural neuro-imaging studies.
A 2009 review of the available literature, found out that there seems to be some potential, but also admits that unfortunately it is hard to provide conclusive evidence for this. This is because there are many inconsistencies between different studies, many of which are, furthermore, preliminary in their nature.
It would be wrong also to think of meditation as one single type of practice. Several different types of meditation exist (e.g. transcendental meditation, mindfulness mediation, yoga meditation, just to name a few). For this reason, it is hard to standardise between these similar but different practices.
The authors are, therefore, cautious in saying anything conclusive, since there is no identifiable active ingredient, and since it is hard to establish whether any changes are given solely to the meditation practice or if other factors are in play (e.g. somebody who meditates might also be more prone to healthy living in general, which is known to have beneficial effects), but they recommend further studies and further research.
Nevertheless some doctors are already starting to implement meditation and yoga in novel multimodal dementia management and prevention regimes.
sources: http://onlinelibrary.wiley.com/doi/10.1196/annals.1393.002/full https://www.ncbi.nlm.nih.gov/pubmed/25324467