One in 14 people over the age of 65 have dementia with the condition affecting roughly one in six people over the age of 80. There's no certain way to prevent all types of dementia, as researchers are still investigating how the condition develops. However, there's good evidence that certain lifestyle habits can increase your risk of developing dementia when you're older with a new study pinpointing the three main factors which could be increasing your risk. The study found people whose scores on dementia risk tests indicated a less brain-healthy lifestyle, which included smoking, high blood pressure and a poor diet.