Researchers can even see the physical consequences of 'repetitive negative thinking' (RNT), as they call it, with 'half-empty' thinkers developing more harmful proteins in the brain that are linked to Alzheimer's.
If that's you, start meditating or doing mindfulness practices—becoming aware of your thoughts and surroundings—say researchers from University College London. Negative thinking is "an underlying reason" why some people suffer from dementia or Alzheimer's, says researcher Natalie Marchant.
But it has to be a long-term, chronic view of the world. The occasional set-back when we suddenly have negative thoughts and feelings won't cause any long-lasting damage to our cognitive abilities.
The researchers tracked the mental health of 292 people over the age of 55 for two years. The way they ruminated about the past and worried about the future was an important measure of their RNT score.
Those with high RNT scores suffered greater cognitive decline over a four-year period, including greater memory loss, and brain scans also revealed they had higher deposits of tau and amyloid proteins which are seen in dementia and Alzheimer's patients.
RNT is a new risk factor, the researchers say, and so it's important people who regularly have negative thoughts should counteract them by taking up meditation or mindfulness.
As they say, our thoughts do matter and can even change us physically.