A person's risk of developing dementia could be linked to being anxious and shy, research suggests.
Over a period of six years, 506 older people were monitored and their personalities and lifestyles assessed. Out of these, 144 people developed Alzheimer's disease or another form of dementia.
The chances of developing the disease appeared to be linked to people who get stressed easily and are socially isolated.
The researchers asked the volunteers a series of questions designed to see how extrovert, emotionally stable, calm, or negative and anxious they were.
People's lifestyles were then evaluated through a questionnaire which asked about participation in leisure or organisational activities, and volunteers' social networks.
The journal Neurology carried the findings, which showed that even if people were not socially active, but were calm and relaxed, they were 50% less likely to develop dementia than those who were easily stressed and isolated.
Outgoing people also had a 50% lower chance of developing the disease when they were calm rather than stressed.
Study leader Dr Hui-Xin Wang, of the Karolinska Institute in Stockholm, Sweden, said: "In the past, studies have shown that chronic distress can affect parts of the brain, such as the hippocampus, possibly leading to dementia, but our findings suggest that having a calm and outgoing personality in combination with a socially active lifestyle may decrease the risk of developing dementia even further.