Dementia rates falling since leaded petrol ban
Dementia rates are decreasing and will continue to fall across Europe and North America because of the ban on lead in petrol, scientists have suggested.
Because of an expanding and ageing population, the total number of people with dementia has been rising, but a study from Harvard claimed that the dementia rate – the proportion of people who develop the disease – is falling by up to 15 per cent per decade.
A new study suggests that high dementia rates may have been caused by exposure to lead from car exhaust fumes, and that the gradual switch to unleaded petrol in the 1970s and 1980s, and the ban on lead in petrol 20 years ago is bringing down the rates of dementia.
Researchers from the University of Toronto described a form of dementia called limbic-predominant age-related TDP-43 encephalopathy (Late), which is similar to Alzheimer’s disease. Their paper, published in the
states: ‘‘Before leaded gasoline was phased out during the 1970s and 1980s, average blood lead levels were 15 times what they are today. Thus, each successive birth cohort entering old age has had less cumulative life exposure to lead. Lifetime exposure can be tracked in the tibia bone, where the half-life of lead is many decades. We hypothesise that lead plays a role in the development of Late.’’
The researchers said that other studies had linked lead exposure to cognitive decline and that excessive exposure could increase the brain’s age by up to six years. Lead is a neurotoxin that can cross the barrier between the blood and the brain, causing ‘‘neuronal cell death’’, the paper states.
Petrol infused with lead was introduced in the 1920s when it was found to reduce ‘‘knocking’’, where pockets of air explode in the wrong place in the engine. In the early 1970s there was 0.84g of lead per litre of petrol. This had fallen to 0.4g by 1986, when the law changed to limit levels to 0.15g per litre.
magazine warned in 1989: ‘‘Lead is an extremely nasty pollutant – it can cause brain damage, particularly in children.’’
One estimate has placed the halflife of lead in the body – the period over which it halves in potency – at 49 years. Compared with those born between 1965 and 1982, those born before 1925 have five times more lead in their bones, those born between 1926 and 1935 have four times more and those born between 1936 and 1945 have three times more, the paper explains. A 2016 study estimated that the dementia rate in England and Wales decreased by 20 per cent in the 20 years between the early 1990s and early 2010s. The researchers described their theory as ‘‘speculative’’, adding that other environmental factors, such as the reduction in smoking, could also affect the development of the disease. ZhiDi Deng, who co-wrote the article, said: ‘‘If lifetime lead exposure is found to be a major contributor to dementia, we can expect continued improvements in the incidence of dementia.’’