Is Dementia Linked to Abnormal Magnesium?
Where the study had its limits
The limitations of this study were that the total body magnesium could not be measured, and the magnesium level in the blood was measured only once. This can cause errors in the tests since the blood magnesium level is susceptible to changes due to the intake of different forms of food. Since the level of serum magnesium was in the normal range, it was difficult to study the effect of either hypermagnesemia or hypomagnesemia on dementia. The researchers later stated that they expect the levels to be higher than the effects they observed.
https://draxe.com/magnesium-deficient-top-10-magnesium-rich-foods-must-eating/
http://www.who.int/mediacentre/factsheets/fs362/en/