Being overweight 'can cut risk of dementia'
10 April 2015 Last updated at 16:20 BST
Being overweight cuts the risk of dementia, according to the largest and most precise investigation into the relationship.
The researchers admit they were surprised by the findings, which run contrary to current health advice.
The analysis of nearly two million British people, in the Lancet Diabetes & Endocrinology, showed underweight people had the highest risk.
Sophie Hutchinson reports.