The dementia epidemic: is it really stabilising?

The Lancet Neurology published an article last week on dementia prevalence in Western Europe. Surprisingly, in spite of an ageing population, the data suggests that the prevalence of dementia is stabilising rather than continuing to increase.

The paper presented findings from five European studies that measured changes in dementia prevalence over time. The headline finding is that in the UK-based study, the prevalence of dementia in those aged 65 or over fell from 8.3% in the 1990s to 6.5% in the same age group 20 years later. The authors of the review paper suggest that this fall in dementia prevalence could be due to improvements in general public health and better management of risk factors for dementia.

While this is potentially very encouraging, the results need to be interpreted with some caution. Most of the studies done outside the UK found that rates of dementia had remained stable. The only studies that found a reduction in the prevalence of dementia were the UK study and the Spanish study, which looked at people over the age of 65.

Those over 65 in 1990 would have been born before the Second World War and those surveyed 20 years later in the UK would have been a post-war cohort. The post-war group had access to better education, living conditions and general health than those born before the war – and this could have impacted on their cognitive health and given them protection against dementia. So the fall in prevalence could be purely due to a birth cohort effect, the reasons for which are not fully understood.

The authors also point out that the incidence and mortality of cardiovascular disease in most high-income countries has decreased since the 1980s and there has been a general focus on improving health through reducing smoking, drinking and modifying cardiovascular risk factors. Risk factors for heart disease like high blood pressure, diabetes, smoking and physical inactivity are also major risk factors for dementia. As the management of chronic medical conditions improves and the population starts to lead a generally more healthy life, the risk of dementia could well decrease.

The problem with this is that although our management of chronic conditions like diabetes and hypertension has improved, these conditions are now becoming more common. If the prevalence of diabetes increases as expected, the prevalence of dementia will show a corresponding jump. We should also remember that age is still one of the biggest risk factors for dementia so as we live longer we can expect to see greater numbers of people with dementia. Hopefully, improving care of people living with chronic conditions means that there may not be the explosion in numbers that was previously predicted - but dementia will remain a serious social and healthcare concern for the foreseeable future.

The causes of dementia are complex and it is important to explore risk factors that could be modified to give a lower risk of dementia. The results from the Lancet paper are encouraging as they suggest that improving the general health of the population might lead to a corresponding drop in the risk of dementia. But the increasing rates of obesity and diabetes mean that it is quite possible the prevalence of dementia over the next 20 years will actually increase. Dementia remains a potentially devastating illness which receives much less funding than research into heart disease and cancer, despite costing the UK economy more in social and healthcare costs. There is still an urgent need to do more for both prevention and cure.

Dr Naaheed Mukadam is a Clinical Training Fellow at the Division of Psychiatry, Faculty of Brain Sciences, UCL