Too much belly fat is a warning sign of an unhealthy brain, new research from over 5,000 people concludes.

The more belly fat people had, the worse their brain function was, as measured by tests of memory, language and their general mental faculties.

Belly fat is assessed by measuring the waist and the hips and then dividing one by the other to get a ratio.

Belly fat may be particularly bad for the brain due to increased secretion of inflammatory markers.

Inflammatory proteins - too many of which are bad for the body - frequently increase before people get dementia.

The study was carried out in Ireland where half the population over 50 is centrally obese.

Less than one-quarter of older people have a BMI (body mass index) in the normal range.

In the US, around 57% of people are centrally obese - having a waist larger than 40 inches.

Dr Conal Cunningham, who led the study, said:
"While we have known for some time that obesity is associated with negative health consequences, our study adds to emerging evidence suggesting that obesity and where we deposit our excess weight could influence our brain health.

This has significant public health implications."
The conclusions come from 5,186 people over 60 who were given tests of their cognitive function.

The research suggests that belly fat is a better index of cognitive health than BMI.

Although this study was carried out in older people, other research has suggested a link between obesity and cognitive decline.

The study's authors write:
"In adults aged 19-65 years, cross-sectional studies suggest that the overweight perform worse on tests of semantic memory, visuospatial ability and executive function compared with normal-weight participants.

Prospective studies have observed lower cognitive scores and greater cognitive decline in obese v. normal-weight participants, with fastest decline in those with both obesity and metabolic abnormality."
The study was published in the British Journal of Nutrition (Ntlholang et al., 2018).