Key points from article :
Dementia risk 38% higher for 50 year-olds with 130mmHg systolic pressure.
Length of time people had high blood pressure for was important.
Risk not seen in older people, perhaps because damage already done.
High blood pressure can cause bleeding and damage to the brain.
Based on 8,639 people tracked in 30-year Whitehall II study.
The study was published in European Heart Journal.