Cereals regarded as healthy may actually raise your risk of dementia — and it's not because of the sugar. A study published in the journal General Psychiatry found a link between a vitamin in brands such as Cheerios and Shreddies and cognitive decline, which can be a precursor for dementia. Thiamine, or vitamin B1, is also found naturally in whole grains, legumes, liver and salmon, and not getting enough of it has also been linked to health issues. But researchers say for the first time they've discovered a J-shaped curve that indicates consuming too much also has negative consequences.