People who develop type 2 diabetes before they turn 60 could double their risk of developing dementia in old age, a study has claimed.
French scientists found that dementia at age 70 was twice as likely if someone had been diagnosed with diabetes 10 years earlier.
The risk was also increased for people who got the illness, which affects more than 4.8million people in the UK and 34.2m in the US, in their 60s.
Type 2 diabetes, which often goes hand-in-hand with obesity, is largely preventable and can even be reversible for some patients.
The study by the Université de Paris suggested years of irregular insulin and glucose sugar levels in the brain can contribute to dementia developing.
And there is already a known link between diabetes and vascular dementia, a fairly common type of the illness accounting for around one in six cases. This is because it damages vessels supplying blood to the brain, blocking the flow of oxygen.
It said ‘younger age at onset of diabetes was significantly associated with higher risk of subsequent dementia’.
Experts said that too much or too little glucose being transported to the brain in the blood stream could cause damage to blood vessels and nerves that may later raise the risk of dementia developing (stock image)
Type 2 diabetes is one of the biggest medical challenges faced by the NHS in Britain, with millions of people requiring treatment for the condition, costing around £10billion per year.
An 800-calories-per-day diet plan has been adopted by the NHS for some patients after a trial last year showed it could put them into remission.
One of the reasons the common condition is so devastating is it can make people’s overall health decline faster – research has linked it to a higher risk of heart disease, stroke and kidney failure, for example.
The Paris study suggests there is a link between the condition and dementia, which is the UK’s number one cause of death.
There are almost a million people living with dementia across Britain, most of them with Alzheimer’s disease, and its causes are hard to pin down.
The study looked at medical records from 10,095 people spanning over an average of 32 years each in the UK, from 1985 to 2019.
If people had been diagnosed with type 2 diabetes by a doctor, had been prescribed medication for the illness or had it marked on a hospital record, they were counted as diagnosed.
For someone with no diabetes at age 70, the baseline risk of having dementia was calculated to be 8.9 per 1,000 person-years.
This meant that, for every 1,000 people in the study, researchers would expect 8.9 of them to have dementia in any given year.
For people diagnosed with diabetes at age 59 or younger, the rate was increased to 18.3 – double the risk.
If they got diagnosed between 60 and 64 the risk was 49 per cent higher than if they didn’t have diabetes, with a rate of 13 per 1,000 person-years.
Every extra five years that somebody lived with diabetes before they turned 70 raised their dementia risk by 24 per cent, the study claimed.
Researchers led by Dr Archana Sing-Manoux said: ‘The precise mechanisms underlying the association between type 2 diabetes and dementia remain unclear.
‘Further, studies do not always show a consistent association between diabetes and hallmarks of Alzheimer disease.’
They suggest one possible reason for the link is that less insulin gets into the brain – diabetics do not produce enough of the hormone – meaning that it is less able to use glucose sugar for energy.
The brain uses glucose to power its normal nerve functions and ability to maintain healthy cells, and a lack of it could cause damage to the organ.
The researchers said the opposite could also be true, that too much glucose is absorbed by the brain when people have high blood sugar.
Glucose is known to be toxic in large amounts and it can damage nerves – this is why diabetic people’s feet can go numb – and also blood vessels.
Damage to the brain’s nerves or blood supply could increase the risk of damage that could lead to dementia.
Studies have already found that vascular dementia – a type caused by blocked blood flow to the brain – can be accelerated by diabetes for this reason.
And even low-level brain damage caused in younger age, known as mild cognitive impairment, is known to both be contributed to by diabetes and also to lead to dementia in older age.
The study was published in the Journal of the American Medical Association (JAMA).