One of the most devastating things about a diagnosis of dementia – and there are many to choose from – is the sense of isolation it causes.

There is the isolation that sufferers feel, trapped in a dark, confused world, and the isolation and loneliness that their carers often experience.

And, for the wider circle of family and friends, there is the sense of isolation that comes with losing the person they once knew.

My mother has been in the cruel grip of dementia for more than a decade and I still catch my breath when I realise how much I miss her. It can come when I least expect it, hitting me like a punch in the stomach.

Caring for someone who is fading in front of you is mentally and physically isolating. And what makes this even worse is when people you regarded as friends are notable by their absence.

My mum was very sociable, belonged to various groups and societies, and had lots of friends. I was reminded of this recently while sorting through some old things of hers, when I came across some birthday cards she’d kept. Several of them were from friends, and the lovely messages they’d written showed how much she’d meant to them.

That was before she became ill. I could count the number of those friends who have bothered to visit her over recent years on one hand. In fact, I could count them on one finger.

Occasionally I’ve come across one or two of her old friends; they’d ask how she was and promise to visit her. But they never did, not even those from her church whose Christian values didn’t seem to include visiting a friend in need.

With the exception of one treasured friend, no-one called to sit with her, to lift her spirits with a familiar voice or to give my dad a break. That has been one of the most upsetting things of all.

In a study by the Alzheimer’s Society, a third of people with dementia had lost friends after a diagnosis. The charity is now calling on comissioners to ensure appropriate support services are available, as part of its drive for dementia-friendly communities.

When someone close to you has dementia, it’s important to help them try and retain their sense of identity and self-worth. Friends can play a vital role in this, so long as they can cope with the stigma of dementia.

It’s a stigma the Alzheimer’s Society is trying to break, by building dementia-friendly communities to help the growing numbers of people affected by the condition. One day that could be you – and only then will you know who your real friends are.