Twenty years ago, my mother was diagnosed with a form of premature dementia. She was 49-years-old but had suffered symptoms for at least five years. The descent from her beautiful, warm and gregarious personality to one that was isolated, silent and suspicious, had been slow and painful. It took so long to diagnose partly because dementia was the very last illness anyone looked for in a woman in her early 40s.
This week, though, a study has shown that the incidence of early onset dementia has risen markedly. Two decades ago, dementia largely occurred in those in their 60s; the "disproportionate increase" measured by scientists recently indicates more frequent occurrences in Western countries, in those aged between 45 and 74, and with more risk to women. They warn of a "silent epidemic", and while there is no single factor identified for its cause, they believe pollution from aeroplanes and cars plays a "major part".
The risk, it should be said, is still relatively small. Among 75-year-olds in the UK, the death rate is 6,862 per million for men; 9,144 per million for women. Age UK recommends regular exercise and quitting smoking. Eating fresh fruit and vegetables is also said to help prevent dementia.
My mother was a smoker, did little in the way of exercise (I remember a brief interest in callisthenics, mainly because it involved only very small movements) but was careful about her food. She was a vegetarian in the 70s when only people who wore togas in public had renounced meat and no one understood the concept. "If I cut up the bacon very small for the salad," said her mother-in-law, "could you eat it then?"
I have now reached the age at which she first started to show signs of the disease - although we didn't recognise them as such - and it astonishes me all over again just how young she was. I'm 41 and still enjoy a night out dancing, wearing the latest fashions and not thinking yet about how much freedom a bus pass will give me. So it was for my mum when she developed strange new habits: counting the flashing light on the top of the Centrepoint tower a certain number of times before she could draw the curtains, or carrying a picture of a toad in her purse because she was obsessed by its texture.
Because we loved her we didn't see these as signs of madness. We either put it down to a late manifestation of eccentricity - a good British trait - or blamed the fact that her own mother had recently died and her husband, my father, had left. If she fell apart at the seams slightly, then it was hardly surprising. My sister was 10, I was 18, and so long as she was recognisably our Mum, we didn't look any further.
It was only when the symptoms became too extreme to ignore - piles of newspapers, rarely bathing, wearing her dressing-gown all day, refusing to see any friends, eating almost nothing but Extra Strong Mints, leaving my sister alone in a cinema on the King's Road and finally setting fire to her bedroom - that she was eventually committed to Guy's Hospital. Even then, it was nearly two more years before she was diagnosed and finally given a place in a care home in Hastings. She died there eight years later.
What will the fallout be for our future generations if this is the end we have to look forward to? Are all our scientific developments, our healthy eating and exercise mantras, our Botox and serums to be thwarted by a rapid spread of early dementia? Are we to require constant care from an even earlier stage? Will we have less of a retirement to look forward to than we thought?
The implications for our children and their children could be overwhelming. And yet, the funding of research into this dismal disease has increased in recent years, as we all, unfortunately, become more familiar with it. There may even be a breakthrough cure in our lifetimes. But most of us can do little more at the moment than cross our fingers.
And if it does happen to you, remember that there is dignity even in dementia. The person you loved may be hard to recognise but they have lived their life and it is still worth celebrating.
My mother's ending was devastating, cruel and early but despite that, she gave me more than dementia could ever take away.