As an exception, for the utility (or else quality of life) parameters (with and without dementia), we used a relative standard error of 5% to restrict the cases where people attach higher utility to having dementia than not to having it, which is hardly realistic. Vitamins were assumed not to have negative impact on health and therefore, incremental QALYs can theoretically never become negative in our analysis. However, we allowed in cremental QALYs to take negative values to incorporate extreme, close to unrealistic, cases in which treated patients would value the disutility of taking vitamins every day during the gained dementia-free years higher than having dementia in the same period. Moreover, the model assumed that people would receive B-vitamin treatment until dementia onset or death.