If flow of blood to the brain decreases, drinking two cups of hot cocoa (consuming equivalent chocolate) can improve blood flow 8.3%.
Drinking two cups of hot chocolate a day may help older people keep their brains healthy and their thinking skills sharp, according to a study published in the August 7, 2013, online issue of Neurology®, the medical journal of the American Academy of Neurology
The study involved 60 people with an average age of 73 who did not have dementia. The participants drank two cups of hot cocoa per day for 30 days...
"As different areas of the brain need more energy to complete their tasks, they also need greater blood flow. This relationship, called neurovascular coupling, may play an important role in diseases such as Alzheimer's."
Of the 60 participants, 18 had impaired blood flow at the start of the study. Those people had an 8.3-percent improvement in the blood flow to the working areas of the brain by the end of the study, while there was no improvement for those who started out with regular blood flow. [emphasis mine]