Middle-age spread raises the risk of dementia by up to a third – because being overweight could reduce blood flow to the brain, experts say.
A worldwide study of more than 1.3million people found those with a high body mass index (BMI) in their 50s were much more likely to develop the condition two decades later.
Being overweight is known to be harmful to the cerebrovascular system – the vessels that carry blood to and from the brain.
Researchers suggest the arteries in fatter people do not work as well in supplying oxygenated blood to the brain, harming mental function.
Experts have welcomed the findings of this latest study and said they serve as a wake up call to tackle the growing obesity epidemic – and a warning for complacent overweight middle-aged people.
Someone in the world develops dementia every three seconds. An estimated 50million people worldwide living with dementia, which is set to double every 20 years, reaching 75million in 2030 and 131.5million in 2050.
There are currently 850,000 the UK and 5.4 million in US – and the escalating crisis will place huge pressures on health and social care services.
A large study found those with a high body mass index (BMI) in their 50s were much more likely to develop the condition two decades later (stock image)
The worldwide obesity rate has doubled since 1980, and the US has the highest rates of obesity among high-income countries.
Currently, about one in three American adults are considered obese, and about one in seven children.
More than half of children growing up in the US today could be obese by the time they are middle-aged, worrying research by Harvard University revealed earlier this week.
It also emerged this week that Britain has highest numbers of overweight people in the EU.
Nearly 30 per cent of women and just under 27 per cent of men are overweight, according to the European Society of Cardiology.
Obesity rates in the UK have nearly doubled since the early 1990s.
Today nearly a third of UK children aged two to 15 are overweight or obese.
Experts warn it has become normal to be vastly overweight in both countries.
The latest research, published in the journal Alzheimer’s & Dementia, suggests that maintaining a healthy weight could prevent, or at least delay the devastating disease.
It found that for each five unit increase on your BMI raises the risk by between 16 and 33 per cent. For instance, for a 5ft 7in tall person, five BMI units is 32lbs (14.5kg) – about the difference between overweight and normal weight people, or the obese and overweight.
Study author Professor Mika Kivimaki, from the University College London, said: ‘Obesity is harmful for the cerebrovascular and metabolic systems, increasing the risk of cardiovascular disease and type 2 diabetes.
‘These two conditions, in turn, are related to an increased dementia risk and this is one possible pathway linking obesity to increased dementia risk.’
It contradicts a previous, similarly large-scale study in 2015 that found middle age spread may actually protect against dementia.
But the latest research followed participants for a longer period and found weight loss can occur up to 10 years before the diagnosis – which may have skewed the previous findings.
The 2015 study – carried out by the highly respected London School of Hygiene and Tropical Medicine, London, and a London/Madrid-based clinical research company OXON Epidemiology – examined nearly two million UK adults aged over 40.
It found that overweight and obese people were about 30 per cent less likely to develop dementia 15 years later than people of a healthy weight.
Conversely, underweight people were 34 per cent more likely to develop dementia than those whose weight was normal.
The authors of the latest study, carried out by University College London (UCL), believes he can explain why that research appeared to show being overweight is protective – but the opposite is true.
People with dementia are at a very high risk for weight loss as eating, and drinking, becomes more difficult as the disease progresses.
The UCL team followed participants for so long they found dramatic weight reduction can actually occur up to 10 years before the diagnosis.
This can mask the harm that carrying too many pounds does to the brain, they said.
This research found participants had a higher-than-average body mass index some 20 years before dementia onset – at middle age.
A WAKE UP CALL: EXPERTS’ REACTIONS TO THE FINDINGS
Leading health charities said the latest study should be a wake up call to combat Britain’s obesity epidemic.
Tam Fry, spokesman for the National Obesity Forum, warned that middle-age people are not necessarily worrying about their dementia risk in later life, but should be.
He said: ‘Public health messages, in general, simply extol the virtues of staying in shape, eating well and taking exercise. And, in general, most people pay scant attention to them.
‘But if those messages spelled out fully the morbidities triggered by being obese perhaps they would wake people up to their health danger.
‘Linking dementia to obesity may not remotely cross the mind of a chubby 30 or 40 year old but, as this paper demonstrates, it certainly should. Ignorance is not bliss – in old age it can often be life threatening.’
The findings were also welcomed by the Alzheimer’s Society.
Dr Doug Brown, director of research, said: ‘It is becoming clear the state of our health in midlife could be influencing our risk of developing dementia when we get older.
‘Researchers think this is because some of the underlying factors of dementia begin years, or even decades, before obvious symptoms like memory loss start to show.
‘The effect of obesity on a person’s risk of developing dementia has so far been a matter for debate as studies have been inconclusive.
‘The very long-term nature of this study has helped to tease apart the different influences of BMI across decades.
‘It suggests that having a high BMI in middle-age could increase risk of dementia, but low BMI in later life could be an early sign of the condition.
‘In light of this, we need to know more about the biological reasons for both of these findings, particularly how the early stages of dementia could be linked to weight loss.’