While there is inconsistent evidence linking coffee with more or less risk, drinking lots of coffee both raises homocysteine levels and promotes the excretion of protective B vitamins. For example, two cups of coffee raises homocysteine by 11% in 4 hours.
Green tea on the other hand, is associated with a lower risk of cognitive impairment. Ordinary tea drinking is also associated with better cognition. Our advice is to limit coffee to one a day and drink tea, ideally green, instead.