Research suggests that cynics are three times more likely to develop dementia

Committed sceptic Rhodri Marsden decides to get happy

Enthusiasm curbed: irritable types such as Larry David are apparently not helping themselves (Charles Fern)

As I was having lunch earlier, a nearby television screen was showing the end of Hans Christian Andersen, the 1952 film starring Danny Kaye. As he trilled the chorus of "Thumbelina" to a crowd of delighted children in period costume, I pushed a slab of Red Leicester into my face and regarded the unfolding action with a grimace, as if I were watching scenes broadcast from a rat-infested sewer.

"This," I thought to myself, "does not reflect the harsh realities of life." I imagined furious off-set arguments between the cast and crew over sound and lighting in order to align the film more closely with my cynical worldview. And then I stopped myself. I'd just read that mental state has a close link to physical health, and, by failing to appreciate the infectious enthusiasm of Danny Kaye, I realised that I might actually be doing myself some damage. I checked my cheerfulness, and found it wanting. "Thumbelina dance, Thumbelina sing," continued the tune. I forced an unconvincing half-smile, reminiscent of Gordon Brown on the campaign trail.

There's been a recent surge in the popularity of mindfulness (formerly "meditation") to help us to take a more nuanced, self-aware view of our negative thoughts and consequently promote mental and physical well-being. But research at the University of Eastern Finland has just uncovered a more startling finding: that cynical, grumpy people are three times more likely to develop dementia than those who have a sunnier outlook.

The figures, taken from a sample of 1,500 people over an eight-year period and adjusted for other factors such as high blood pressure, make for alarming reading for those of us who regularly question the motives of friends and have precious little faith in strangers. I'd always thought grumpiness and pessimism to be useful strategies that allowed me to experience pleasure when things turned out to be merely bad rather than dreadful, while simultaneously alienating the kind of indiscriminately upbeat Pollyannas whom I find pretty exhausting in any case. But no. My health might be suffering. Maybe it's time for a rethink.

Thing is, it's hard to rewire your brain in this fashion, and it's particularly hard these days. We seem to have become conditioned as a species to believe that things are bad and getting worse, even when it's manifestly obvious that this is not the case – the country's plummeting crime figures being an obvious example. We've just come out of a period of political campaigning that's been characterised by cynicism, covered cynically by the media and has inspired cynicism in the electorate, a never-ending feedback loop of dissatisfaction that leads to a corrosive belief that everything is screwed and an impotent feeling that nothing can be done.

Neither of these things is true, but a corrosive misery inevitably takes hold, and we bombard each other with bad news in some kind of warped competition to see who can generate the most misery by teatime. It's toxic – and no wonder it leads us to answer the kind of questions posed by the Finnish study ("Is it safer to trust nobody?" "Would most people lie to get ahead?") in the affirmative.

A representative from the Alzheimer's Society was quoted yesterday as saying that the sample size of this study was too small to draw any real conclusions as regards dementia, but regardless of any empirical data, we should all be aware of the abrasive effects of anxiety, stress and melancholia. Yes, cynicism can be useful, occasional grumpiness is inevitable, but doubting the benevolent intentions of the film Hans Christian Andersen? This does us no favours whatsoever.