She arrived to find him layered in heavy jumpers on a sweltering hot day. Worried he might forget to drink and become dehydrated, she tried to help him out of the layers into a cooler shirt.

That's when he began to touch her "suggestively", first on her arm, then elsewhere. "I could teach you a few tricks . . . I was a bit of a lad in my day," he told his stunned daughter.

"He was flirting with me – I was gobsmacked," Hore recalls.

But as awkward and embarrassing as the situation was, it's just one example of the kind of assault on character that dementia can have. Stories abound: formerly placid people who become aggressive, even violent, kicking and hitting. Some refuse to take showers day after day until they are rank.

They might become much more disinhibited and use inappropriate language, or become incontinent.

Some put their safety at risk, leaving the house with the stove on, poke forks into toasters, drive erratically or wander away.

This week the Australian Institute of Health and Welfare released a report highlighting the social and economic burdens that dementia creates – and predicting the number of people living with dementia will skyrocket from 175,000 at last count in 2003 to 465,000 by 2031 as the population continues to age.

In 2003 health and welfare payments attributed to dementia totalled $1.4 billion, and the number of new cases of dementia grew by 37,000 that year.

But in fact those may be conservative estimates. Advocacy group Alzheimer's Australia puts the figures even higher.

The toll on the healthcare system already has been substantial: people with dementia used 1.4 million hospital patient days and 24.7 million residential aged care bed-days in 2003.

Dementia is a broad term that describes any of more than 70 conditions that impair memory, perception and thinking.

While it's "not a natural part of ageing", according to the report, dementia does affect older people disproportionately – and the older you get, the higher your risk. Twenty-four per cent of people aged 85 and over, and half of all centenarians have some form of dementia, and the likelihood of having it doubles every five years after you hit 65.

Alzheimer's disease is the most common form of dementia, accounting for about 60 per cent of all cases.

The average healthy person loses about 1 per cent of their brain cells every year, but that number climbs to 5 per cent in people with dementia.

As brain cells shrink or disappear, abnormal material builds up as "tangles" in the centre of the brain cells, and "plaques" outside the brain cells.

They disrupt messages within the brain, damaging connections between brain cells, which eventually die. The result is that information cannot be recalled. As Alzheimer's disease runs its course on each area of the brain, certain abilities are lost and personalities can change dramatically, says David Ames, professor of psychiatry and old age at the University of Melbourne.

Witnessing that sort of metamorphosis in someone you love can have a devastating impact, he says, and it's one reason why carers are among the hardest hit by the disease.

Spouses make up the majority of carers, Ames says.

This can make the personality changes and other hallmarks of the disease such as not recognising people you've known for years or misidentifying them, particularly difficult.

"You'll have a couple who's been married 40 years and they'll be lying in bed and the wife will turn to the husband and say 'Who are you?'. It's easy to become overwhelmed and overcome – it puts lots of strain on the relationship," he says. "Carers experience very high rates of anxiety and depression and other stress-related symptoms – two to five times higher than what we see in the background populations. They do it because they want to, and because they love the person they're caring for, but it can cause a lot of grief and take great strength."

Forty-six per cent of carers reported at least one negative effect linked to looking after a dementia patient – including feelings of anger or resentment, developing a stress-related illness themselves, or feeling weary, worried or depressed, the AIHW report found. More than half (61 per cent) said their caring role had made them lose touch with friends or left them less time for their own relationships.

Research shows that carers who are given intensive education in the early stages – such as information about what to expect, what the symptoms are and where to get help – experience lower levels of stress, Ames says.

As yet dementia has no cure, though more than 100 trials for drugs are in progress in Australia, including some that could have a preventative function.

In the meantime, Alzheimer's Australia has launched a campaign called "Mind your Mind" to encourage people, particularly those in their 40s and 50s, to alter their lifestyle in an effort to reduce their risk of developing the disease.

In 2004 the group published a report it commissioned from Access Economics that showed the benefits even a small delay in onset could have on the healthcare system: it estimated that if the age of onset of dementia were delayed by just five months, the cumulative savings between 2005 and 2020 would be $1.3 billion.

Increasing evidence shows that keeping your mind active and staying socially engaged could go some way toward achieving that.

A metanalysis of 29,000 people across 22 research studies found that people with a history of complex mental activity were 46 per cent less likely to develop dementia than those who had less active minds. The research was published in the journal Psychological Medicine (2005;35:1-14).

Playing games or just keeping your mind exercised through hobbies or continuing education can all have a protective effect, says professor Michael Woodward, who heads the Memory Centre at the Austin Hospital in Melbourne and developed the content for Mind Your Mind.

"It doesn't have to be specifically crosswords or sudoku, but certain mental activities are better than others," Woodward says. Sitting in front of the TV is not as effective as engaging in social events, card games or board games, or physical activity such as walking, dancing or even knitting.

The more mentally demanding the activities are, the better. The reason is that the more your brain is stimulated, the greater connections form between the neurons in your brain.

"What that does is it creates more reserve, so you have more protection from the damage that amyloid (a plaque deposited in your brain that is found in patients with Alzheimer's disease) does – there's a greater buffer," Woodward says.

Surveys by Alzheimer's Australia have found most people know that their genes and getting older increase their chance of getting the disease, but much of the public is unaware that lifestyle factors are associated with increased risk, says Lynette Moore, executive director of Alzheimer's Australia Victoria, which is managing the Mind Your Mind campaign.

Having cardiovascular disease increases your risk of dementia, and not surprisingly the risk factors for both seem to overlap.

"High cholesterol and high blood pressure in mid-age does increase people's risk of dementia in their 70s and 80s," Moore says. "If you're carrying a particular gene you're more likely to get it, but even adjusting for that, lifestyle factors do make a contribution. There are no guarantees but it's worth a go to adopt a healthy lifestyle – that way you have the best chance possible."

To do that, experts recommend many of the same things that help prevent cardiovascular disease: get at least 30 minutes' of physical activity a day, eat a balanced diet that's low in saturated fat and rich in fruits and vegetables, don't smoke, limit the amount of alcohol you drink.

Research is still in progress, but there is also some evidence that diets that are high in antioxidants, as well as some vitamins and minerals such as folate and vitamin B12, may also provide some protection, Woodward says.

A healthy diet and exercise also reduces your chances of developing high blood pressure, type 2 diabetes and obesity, which are all other risk factors for dementia. Injury to your head also increases your risk so taking precautions such as protective gear when you play sport is also important.

Still, there are no hard and fast rules. The evidence shows that at a population level people with certain risk factors are more likely to have dementia, but at an individual level you could have several of the risk factors but never develop dementia. And the opposite is also true.

"Unfortunately the biggest risk factor for dementia is something we can't address: getting older," Ames says.

www.alzheimers.org.au