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.

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.

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.
Study author Professor Mika Kivimaki, from the University College London

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 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. 


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