People who are obese and have other metabolic abnormalities such as diabetes can experience a faster decline in their cognitive abilities, according to a study published today in Neurology, the medical journal of the American Academy of Neurology.

French and UK researchers found that people who were obese and had high blood pressure and other risk factors called metabolic abnormalities could increase their risk of developing dementia.

Scientists led by the French medical research institution INSERM examined the cognitive function, body mass index and conditions such as diabetes and blood pressure of 6,401 adults with an average age of 50 at the start of the study over a 10-year period.

They defined metabolic abnormalities as having two or more of various risk factors including high blood pressure or taking medication for it; low HDL or “good” cholesterol; high blood sugar or taking diabetes medication; and high triglycerides (a type of fat found in the blood) or taking medication to lower cholesterol.

The participants took tests on memory and other cognitive skills three times over the next 10 years.

A total of 31% of the participants had two or more metabolic abnormalities. From the group, 9% were obese and 38% were overweight.

Of the 582 obese people, 60% met the criteria for metabolic abnormality. The metabolically normal obese individuals also experienced more rapid decline.

Over the 10 years of the study, people who were both obese and metabolically abnormal experienced a 22.5% faster decline on their cognitive test scores than those who were of normal weight without metabolic abnormalities.

Study author Dr Archana Singh-Manoux, of INSERM and University College London, said: “More research is needed to look at the effects of genetic factors and also to take into account how long people have been obese and how long they have had these metabolic risk factors and also to look at cognitive test scores spanning adulthood to give us a better understanding of the link between obesity and cognitive function, such as thinking, reasoning and memory.”

Dr Singh-Manoux said the study also provided evidence against the concept of “metabolically healthy obesity” that has suggested that obese people without metabolic risk factors do not show negative cardiac and cognitive results compared to obese people with metabolic risk factors.

A spokesperson for the Alzheimer’s Society said: “We all know that piling on the pounds is bad for your physical health, but this robust study suggests that it is bad for the head as well as the heart. These results back up existing evidence that obesity in mid-life increases the risk of developing dementia, as well as adding to our understanding of the relationship between dementia and our metabolism.”

DOI:10.1212/WNL.0b013e3182661f63