Although the exact mechanisms aren't known, obesity and diabetes are both associated with higher incidences of Alzheimer's. Ling Li and her colleagues tested whether high sugar consumption in an otherwise normal diet would affect Alzheimer's progression.

They used a genetic mouse model that develops Alzheimer's-like symptoms in adulthood, and over a 25 week period supplemented the regular, balanced diet of half the animals with 10% sugar water. Afterwards, they compared the metabolism, memory skills (by means of various mazes) and brain composition of the regular and sugar-fed mice.

The sugar-fed mice gained about 17% more weight than controls, had higher cholesterol levels, and developed insulin resistance. These mice also had worse learning and memory retention and their brains contained over twice as many amyloid plaque deposits, an anatomical hallmark of Alzheimer's.

Although the researchers cannot be certain if the increased mental impairment resulted specifically from the higher sugar intake or higher calories in general, these results to highlight the potential risk of sugary beverages. They note that the human equivalent of the mouse diet would be roughly 5 cans of soda per day, although since mice have a higher metabolism, it may actually take less sugar intake in humans.