Norwegian study: People aged 60 to 90 are less likely to develop dementia than before
Nevertheless, the total number of people living with dementia is on the rise.
Society must be prepared to provide care to an increased number of people living with dementia in the future. In 2022, researchers warned that the number of people with dementia in the world could triple by 2050.
Both life expectancy and the population have increased. With a greater number of elderly in the population, it’s reasonable to expect more people to develop dementia.
But it’s not just the number of elderly that determines how many people will live with dementia in Norway in the future.
It’s also a question of what proportion of 70- or 80-year-olds actually develop dementia, a statistic that is called incidence.
A new Norwegian study now shows that 60- to 90-year-olds are developing dementia less often today than they did 20 years ago.
Very good news
The study is the first of its kind in Norway.
“From the age of 60, and actually all the way up to the oldest age group, the incidence has decreased in each age group,” Bente Johnsen says. “This is very good news for the future.”
Johnsen is a medical doctor and research fellow at the University Hospital of Northern Norway HF and UiT The Arctic University of Norway. The study is part of her PhD and has been published in the journal Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring.
The number of people with dementia in Norway has been unclear.
One estimate suggested there were 70,000 to 80,000 people with dementia, which was later revised to between 80,000 and 104,000, according to an article from Faktisk.no (link in Norwegian).
Incidence and prevalence
- Incidence tells us how many people are diagnosed with a certain disease in a given period of time.
- Prevalence tells us how many people have a disease at a given time.
- Example: HIV has a fairly low incidence today. Few people develop the disease. The prevalence is nevertheless quite high, because once you have the disease, you live with it for the rest of your life. As a consequence, many people have the disease at the same time.
(Source: Great Norwegian Encyclopedia)
These figures were based on studies in other Western countries and transferred to Norway.
“We didn't know how many people in Norway had dementia,” Johnsen says.
In 2021, a large study based on the Trøndelag Health Study (HUNT) was published. This calculated that approximately 101,000 Norwegians have dementia, based on Norwegian figures.
That was 25 per cent more than had previously been assumed.
“It was quite a lot more than in comparable countries,” Johnsen says.
The researchers also estimated that the incidence would double by 2050 and quadruple by 2100.
At the same time, Johnsen looked at figures from a similar population survey called the Tromsø Study.
Johnsen’s new study, based on the Tromsø Study, suggests the number of elderly people with dementia will increase in the future, but perhaps not as much as expected.
Johnsen and her colleagues investigated something called age-specific dementia. This is a measure of how common it is to get dementia in an age group now, compared to before.
The study shows that there has been an improvement.
“There are fewer 70-year-olds who get dementia now than there were 20 years ago,” Johnsen says.
The improvement applies to all age groups between 60 and 99 years.
There was no change for the 50 to 59 age group. This was somewhat expected, since few people get dementia this young, Johnsen explains.
"People believe that younger people might have a slightly different cause for developing dementia. It could be related to genetics," she says.
Important to have Norwegian numbers
Geir Selbæk is Professor II at the University of Oslo and head of research at the Norwegian National Centre for Ageing and Health. He has looked at the new study.
“It is very important to have Norwegian figures for this area,” he wrote in an email to sciencenorway.no.
“A number of international studies have shown that the incidence of dementia is on the way down, at least in the Western world. Nevertheless, the number of people with dementia is increasing significantly because there are more elderly people in society. This study confirms that findings from other countries also apply to Norway,” he wrote.
Diagnoses within 20 years
The Tromsø Study is a large health survey that has been ongoing in Tromsø since 1974. It is based at UiT the Arctic University of Norway.
A total of 45,000 people have participated in the survey over the years. The data has been used to investigate everything from involuntary childlessness, to diabetes, pain tolerance, and celiac disease.
In the new study, Johnsen and her colleagues looked at how many of the participants were diagnosed with dementia between 2000 and 2019.
A total of 44,214 participants in the Tromsø survey were included, of whom 2,049 received a diagnosis of dementia.
The study showed, for example, that in the 60 to 69 age group, people had a 61 per cent lower risk of developing dementia today compared to 20 years ago.
Johnsen adds that this applies at the population level, but not for the individual.
Same trend in international studies
Several international studies show a similar tendency. The researchers list several examples in their study.
The Framingham Heart Study in the USA found a 20 per cent decrease in dementia incidence per decade between 1977 and 2008. This applied to people over 60.
A study from Sweden found a 30 per cent decrease between 1987 and 2004 for people over 75.
The reason why there is a lot of dementia in Norway is not that people get dementia more often than before.
“There is something else that is the reason why we have high prevalence figures. It is probably because we live longer,” Johnsen says.
The study suggests that the number of dementia cases in the future may be slightly reduced. However, the researchers have not calculated this yet.
Several possible reasons
The researchers have not yet addressed the possible reasons for the improvement.
Johnsen points to a summary of risk factors for dementia from The Lancet's dementia commission. 12 risk factors have been identified that can be addressed.
These factors include low education, poor hearing, smoking, and social isolation, according to the Norwegian National Centre for Ageing and Health (link in Norwegian).
“The risk factors found in the Tromsø Study are improving,” Johnsen says.
This may help explain why dementia is not as common as before.
Not certain this trend will continue
Geir Selbæk wrote in an email to sciencenorway.no that the decrease in incidence seen in the last 20 years is most likely due to the fact that today’s elderly are more well educated and have better cardiovascular health.
“If this development continues, the projection figures should probably be adjusted downwards,” he writes.
However, there is no guarantee that the trend will continue, he points out.
“More sedentary lifestyles, more obesity, and earlier onset of diseases such as type 2 diabetes can cause the incidence to increase again. This underlines the importance of working purposefully with preventive measures, not only for the elderly, but equally for middle-aged people,” he writes.
Regarding the study itself, Selbæk says that there are some limitations in how the information on dementia diagnosis is obtained, but that the method is otherwise good.
“There is reason to believe that what they have found is correct. It remains uncertain how strong the effect is,” he writes.
Translated by Nancy Bazilchuk
Johnsen et al. Incidence of dementia over a period of 20 years in a Norwegian population, Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring, vol. 15, 2023. DOI: 10.1002/dad2.12479