As of December 2015, there is not enough evidence to substantiate coconut oil as a treatment or preventative against the effects of dementia or Alzheimer's disease, according to the Alzheimer's Society. For this reason, doctors cannot recommend a specific dosage.
There is a clinical trial in process, however, and those conducting it expect results in 2017. Alzheimer's disease is linked to changes in insulin, responsible for metabolizing sugar, in the brain, according to the Alzheimer's Society. This may cause the brain to "starve," and coconut oil may potentially be an alternative source of energy.
There is also evidence that coconut oil causes an increase in a protein called acetylcholinesterase, notes the Alzheimer's Society. Increased levels of this protein are associated with Alzheimer's, which suggests that coconut oil is counterproductive as a treatment for the disease.