Several years ago, my father, Trevor, was diagnosed with vascular dementia, which is, like Alzheimer's, a type of dementia. Vascular dementia is characterised by a stepped decline in both cognitive and physical capacities - in other words, everything seems fine for a while, and out of the blue, you get a sudden deterioration, which then stabilises for a while, before the next sudden drop. This sequence of decline has very much what my family have seen in my father over the last few years.

When he was younger, my father lived for golf, loved sport, spoke several languages, was gregarious and outgoing. The difference now is stark: he cannot walk without support; his memory is inconsistent, his ability to hold a conversation, fraying. My father, a globetrotting businessman, now occupies a world that has largely shrunk to the dimensions of his bedroom. Things so small they had never been noticed are now much harder - remembering to swallow his mouthful of tea once he has taken a sip can no longer be assumed.

I want to raise money and awareness for the Alzheimer's Society, to help donate to support care interventions, diagnostic tools and further research. Raising money by running the longest distance I have ever run in my life seemed to me to be the most appropriate way of doing this: to raise money, I am running, something my father can no longer do. I remember in the late 80s and early 90s, I would laugh at my father's jogging, that was more trotting-not-much-faster-than-walking. It isn't quite so funny now. I may not have his ridiculous jogging accoutrements - exaggerated blown-out cheeks; squeezing hand-grips; tight, white shorts; a towel around his neck, tucked into the V of his jumper, like some sort of ham pugilist - but I'm rubbish at running, stagger about sweatily, and am trotting myself now not much faster than he. And now that I have bought a head torch, I am beginning the accoutrement trend. But now that he can't, I will run for him, and you donating all you can to a really worthwhile cause would be hugely appreciated.