Kivimaki M, et al. - Researchers examined the body mass index (BMI)-dementia association using raw unpublished data from over 1.3 million adults from Europe, the United States, and Asia. The relationship between BMI and dementia was likely to be attributable to 2 different processes: A harmful effect of higher BMI, which was observable in long follow-up, and a reverse-causation effect that made a higher BMI to appear as protective, when the follow-up was short.