While risk of dementia due to hyperinsulinemia has been shown previously,1,3 the present study is the first to replicate the observation of an adverse association between low fasting insulin values and dementia, which was described in a cohort of elderly men followed up over 5 years.5 Our results generalize this finding to women while enhancing the evidence for a causal association because the 34-year follow-up, with a minimum of 20 years in sensitivity analyses, decreased the probability of reverse causation for dementia. This evidence concerns the gene INS and hyperinsulinism.