"Let me live, love, and say it well in good sentences."

Photographs of my mother, hers, me cradling my newborn son against me (“Look! Four generations,” we’d laughed that day). Mum carefully considers this little group, standing smiling on the back step of a home bathed in September sunshine: “There’s my mum!” she said.

Then, pointing at me: “Who’s she?”

Mum’s depressions started in her thirties. How much of a role did they play in the dementia that revealed itself in her seventies? There are several compelling hypotheses that suggest one drives the other.

A study published this week suggests that statins might be the latest to join the arsenal against Alzheimer’s. It’s a tablet millions of people pop daily, my husband among them. My mother, who died of dementia, also took statins — but only after having had a stroke in her seventies. Is it possible that had she taken them earlier in her life, she would have been spared from the development of this cruel disease?

The author enlists her investigative journalism skills to understand her mother’s illness and, later, to learn how she might save herself from the same neurodegenerative fate.

Dementia may feel like a wrecking ball, but it’s not simply absent one day and fully present the next. No, it settles in, makes itself at home and lingers in the shadows for 10, 15, or even 20 years.

I watched my mother draw a clock while she was in a brain rehabilitation centre after her stroke. Until then, I did not know how common a test it was, how often it was used – or why.

The clock drawing test – or CDT – is used regularly to assess several mental processes. Over the past two decades, it has become a key tool in early screening for cognitive impairment – especially dementia.

You might expect it to be simple: drawing a clock that shows the time, say, at six o’clock: a circle, numbers, a big hand, a little hand.

It was not hard to imagine how I might have fared in my mother’s shoes. I would have battled to pick up a mug of tea and navigate it to my mouth without spilling. Experiencing the same effect as headphones playing senseless sounds in my ears, I would not have been able to focus or think straight.

And then I remembered that into my mother’s confusing, frustrating world and through the non-stop hiss and rasp of unwelcome sounds and disembodied voices, there was I – her carer – insisting it was time for a shower or that she must finish her juice or go to the loo.

Did my words get through to her? Or did they just add to the upsetting noises in her head?

Breakfast was once eaten enthusiastically. Mum declared everything delicious, especially the marmalade she ate every day, but professed never to have eaten in her life. Near the end breakfast was a miserable exercise in spoon-feeding. Using the telly as distraction I might force another mouthful in.

Dementia, I discovered, isn’t just common — the UK’s biggest killer for a second year running — and it’s about more than lost memories. It stole Mum’s bearings so she couldn’t orientate herself (“Where am I?”), her family (“Who are you?”), her mobility (“What do I do with my feet?” when I urged her to walk) and, in the end, it stole her.