Does extra fat around your belly raise the risk of dementia?

More than a quarter of adults in the UK have obesity, which often involves gaining weight around the belly (abdomen) and arms, particularly as people get older.

But does carrying extra weight in these areas also increase the risk of diseases that damage the brain and nerves (neurodegenerative) like dementia, including Alzheimer’s disease, and Parkinson’s disease?

In July, several UK newspapers ran stories claiming this was the case. According to the reports, having a high level of fat around the belly increases the chance of being diagnosed with any kind of dementia, Alzheimer’s or Parkinson’s disease by 13 per cent, compared to having low levels of fat around the waist.

And having more fat around the arms raises this risk by 18 per cent, compared to having low levels of arm fat.

They also reported that people with high muscle strength are 26 per cent less likely to develop neurodegenerative diseases than those with low levels of strength.

The reports were based on new research in the journal Neurology that used data from almost 413,000 people in the UK Biobank database – none of them had a neurodegenerative disease at the start of the study.

The researchers from China measured participants’ bodies to see how much fat, muscle and bone they had in different areas. Muscle strength was assessed by measuring their grip strength.

Participants were put into groups depending on whether they had a large amount of fat on their belly, arms or legs in relation their overall body fat. 

The researchers then looked at people in each of these groups – belly, arms and legs – to see whether those with high, moderate of low amounts of fat in these specific body areas were the most likely to develop any type of dementia, Alzheimer’s or Parkinson’s disease.

After an average of 9 years, 8,224 of the participants developed a neurodegenerative disease. This included 6,076 people with any type of dementia, 2,933 with Alzheimer’s disease and 2,427 with Parkinson’s disease.

The researchers found high amounts of fat around the belly or arms was linked to a higher risk of these diseases. In contrast, those with a high amount of fat on their legs, or high muscle strength, or high bone density, had a lower risk of developing them.

It is already known that having too much body fat increases the risk of developing heart and circulatory diseases.

With more analysis of the data, the researchers found that in many cases there was a link between having a heart and circulatory disease and developing these brain-damaging conditions.

For example, 35 per cent of those with a high amount of belly fat, who developed a neurodegenerative disease, also had a heart or circulatory disease, and for those with a high amount of arm fat this was 14 per cent.

How good was the research?

The research was published in a journal with a very good reputation, and has been ‘peer-reviewed’, meaning other experts in the field assessed the work and found it to be trustworthy.

The main strength of the study was the size of the population it looked at. By looking at data from almost 413,000 people, the researchers could spot subtle trends that may not have been seen in a study with fewer people.

The size means it is much more likely the findings are reliable. There is little chance the results would be different if the same study was done with 400,000 different British people.

The researchers also accounted for many other factors that could have influenced someone’s risk of developing dementia, Alzheimer’s or Parkinson’s disease. This included biological sex, fruit and vegetable intake, smoking, drinking, medical history, and socioeconomic factors.

This helped ensure the findings were linked to a person’s body fat levels and that these other factors did not influence the results.

However, the study only looked at people in the UK, so the results may be true in Britain and other countries with similar populations, but we cannot assume they are true worldwide.

Another limit of the study is that it only observed what happened: the researchers made body measurements and counted who got a neurodegenerative disease.

This means the results can only show us that fat around the belly and arms is linked to a higher risk of these diseases, not that one causes the other.

How good was the media coverage?

The research was covered in several media outlets, including the Daily Mail, The Times, the Daily Express, The Independent and The Telegraph. Each paper gave a pretty balanced account of the research and its results.

The headline in The Times: “Arms and belly: the danger areas where fat is linked to Alzheimer’s” was an accurate representation of the study.

The coverage in every paper also accurately used the statistics that belly and arm fat are linked to a 13 per cent and 18 per cent higher risk, respectively.

However, some of the headlines could have given the reader the impression that fat in these areas directly caused these diseases. For example, The Telegraph’s headline “Having fat arms ‘heightens risk of Alzheimer’s by nearly one fifth’”.

It is important to bear in mind that observational studies like this can only say that the fat is connected to a heightened risk. Further research is needed to confirm whether it does directly cause dementia, Alzheimer’s or Parkinson’s disease.

The BHF verdict

The link between obesity and neurodegenerative diseases like Alzheimer’s and Parkinson’s disease is long-established.

It is thought to be because obesity increases the risk of heart and circulatory diseases, which in turn can raise the risk of damage to the brain and nervous system.

This research is further evidence of this link, and interestingly pinpoints 2 possible danger areas: the belly and the arms.

However, no matter where people carry excess fat, it can lead to an increased risk of a variety of heart health problems, including coronary heart disease, heart attacks, strokes and vascular dementia.

• Find out more about research into diets that may help reduce dementia risk. 

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