There is no cure, no treatment for dementia.

According to the World Health Organization, dementia affects around 50 million people. There are 10 million new cases every year. In Hong Kong, more than 10 per cent of the over-70s suffer from it.

Calvin Cheng Pak-wing, a clinical assistant professor of psychiatry at the University of Hong Kong, says there is a strong link between depression and dementia – and that many studies suggest depression is a significant risk factor for developing dementia.

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Dr Andrew Sommerlad, a consultant old-age psychiatrist at University College London, says it’s a tricky connection.

“It’s likely that being depressed creates an additional cognitive burden on the brain, so when – if – a person begins to develop the brain changes that cause dementia, one person may only suffer relatively mild cognitive challenges while those who have battled with depression have greater competition for brain activity.”

He speaks about the concept of “cognitive reserve”. The burden of depression is thought to diminish that reserve and magnify whatever else may be placing a burden on cognition. Dementia is never about just one thing, he says.

Dementia and depression both have roots in vascular damage which may – certainly in the case of dementia – develop long before any symptoms appear. By its nature, depression presents with additional risk factors for dementia: my mother went for months existing on an unhealthy diet of tea and biscuits, not taking any exercise and withdrawing from the world entirely.

Sommerlad says socialising is key – think of the brain power required to engage in the dynamics of a conversation. My mother went for months without having one.

Lead author Jessica Gong says the study “found hysterectomy, and especially hysterectomy without simultaneous removal of the ovaries or with a previous ovary removal, was associated with a greater risk of dementia”. The removal of the uterus triggers changes in hormone production which may be harmful to cognition, also.

“Some studies have revealed a neuroprotective effect of oestrogens on memory and cognition, by reducing the extent of injury to the brain,” Gong says, and as women age, their oestrogen levels drop.

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In 2021, The Centre for Innovation in Brain Science at the University of Arizona published a study that suggested a positive link between hormone therapy and reduced risk of Alzheimer’s disease (the most common cause of dementia), but noted that the “magnitude of risk reduction varied depending on the compositions of that therapy, route of administration, and duration of therapy”.

The terrifying statistics on dementia inspire fear in us, especially those of us with a close family member who suffers. But Professor Craig Ritchie, Director of Brain Health Scotland, says there are reasons to be hopeful. There is strong evidence that lifestyle changes could delay the onset of dementia to 95 or even 100, he says.

My mother is well educated, her heart is sound, she has never battled with hypertension and she never smoked or drank to reckless excess. Certainly her depression presents as a risk, possibly her early hysterectomy does, but her laissez-faire (non-intervention) attitude to exercise might have also predisposed her to cognitive decline.

Dr Paddy Dempsey, lead author of a recent study conducted by the UK’s University of Leicester on the effects of brisk walking on ageing says “moderate-to-vigorous intensity physical activity has been well studied for its ability to acutely improve cognitive performance and stimulate molecular mechanisms that enhance learning and memory”.

His study examined the link between walking pace and telomere length. Telomeres are the “caps” at the end of chromosomes which help protect DNA in much the same way as the plastic tip at the end of your shoelaces keeps them from unravelling.

The team found that walking fast was associated with longer telomeres and estimated that a lifetime of brisk walking could lead to the equivalent of 16 years’ younger biological age by midlife.

Shorter telomere length has been associated with the development of dementia and cognitive impairment. “It is a complex picture and the mechanisms are unclear. It is also unclear whether short telomeres are a cause, consequence or both for cognitive impairment,” Dempsey added.

How fast is fast walking, though? The UK’s National Health Service deems a brisk walk as striding out at the rate of “about three miles (4.8 kilometres) an hour” and helpfully elaborates: “You can tell you’re walking briskly if you can talk but cannot sing.”

Dempsey, though, says he advocates “any movement (even ambling)” as being important for improved health because the evidence shows that any activity is beneficial – so every step counts, but brisk ones may count a bit more.

Does it matter how late in life one embarks on a brisk walking programme, I ask, as I try to work out whether what I undertake daily with the dog is a “brisk walk” or an “amble”.

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“Previous research suggests that while being more physically active earlier in life is beneficial for overall health and disease risk (including dementia), it is never too late to start and gain some health benefits. The relative benefits in older age can be quite meaningful and substantial.”

A long time ago, I used to fear I might succumb to my mother’s life-stealing, debilitating depressions. I worried because of the proposed genetic links. I worried especially because my maternal grandmother suffered, too.

As a consequence, I consciously lived my life differently to Mum: I sought out occupation, company, swam hard, walked most days. I kept busy and I kept moving.

Could understanding her illness, her triggers, protect me?, I asked a psychiatrist. Could forewarned be forearmed?

Definitely, she said.

I was never complacent about my mother’s mental illness. I was respectful of it, fearful of it. And I managed to avoid it. I don’t know if I’ll avoid her dementia, but if I adopt the same approach as I did to her depression, perhaps I’ll stand a chance.