Study examines possible link between diet and dementia

UK researchers examining a possible link between diet and dementia have suggested eating processed meat could be associated with a higher risk of developing the disease.

However they and other scientists cautioned that the results of the study required further research and that a definitive link between processed meat and dementia cannot be drawn.

Researchers at the University of Leeds looked at data from nearly 500,000 people comparing their consumption of processed meats with the chances members of the group would go on to develop dementia.

Meat consumption has previously been associated with dementia risk, but this is believed to be the first large-scale study of participants over time to examine a link between specific meat types and amounts, and the risk of developing the disease.

Professor Kevin McConway, emeritus professor of applied statistics at the Open University, said any claim that eating processed meat could cause an increase in dementia risk would go “well beyond a reasonable interpretation of what the researchers found”.

He said: “The problem is that the study is observational. The researchers didn’t make people eat different amounts of processed meat – they simply recorded what they said they ate, followed them up for some time, recorded when any of them got a diagnosis of dementia, and looked whether the chance of getting a dementia diagnosis varied according to how much meat they said they ate.

“The findings are interesting, but they don’t establish anything for certain.”

The findings, from the university’s Nutritional Epidemiology Group, are published in the American Journal of Clinical Nutrition. 

Professor Janet Cade, who oversaw the research, said: “Anything we can do to explore potential risk factors for dementia may help us to reduce rates of this debilitating condition. 

“This analysis is a first step towards understanding whether what we eat could influence that risk.”

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The team studied data provided by UK Biobank, a database containing in-depth genetic and health information from 493,888 British participants aged 40-69, to investigate associations between consuming different types of meat and the risk of developing dementia. 

Data collected by the UK Biobank between 2006 and 2010 included how often participants consumed different kinds of meat, with six options from never to once or more daily.

The study did not specifically assess the impact of a vegetarian or vegan diet on dementia risk, but it included data from people who said they did not eat red meat.

Among the participants, there were 2,896 cases of dementia over an average of eight years of follow up, with a higher proportion of cases among people who were older, more economically deprived, less educated, more likely to smoke, less physically active, more likely to have stroke history and family dementia history, and more likely to be carriers of a gene which is highly associated with dementia. 

Those who consumed higher amounts of processed meat were also more likely to be male, less educated, smokers and overweight or obese.

Prof McConway said: “As the researchers reported, those who ate more processed meat were more likely (for instance) to be smokers, to be less educated, overweight, and to eat less fruit and vegetables. Those things have been identified as risk factors for dementia in previous research.

“So, if people who eat more processed meat turn out to be more likely to be diagnosed with dementia, it could be because of these other differences in risk factors rather than because of their processed meat consumption.”

Researchers suggested consumption of a single 25g rasher of bacon was linked with a 44 per cent increased risk of the disease. 

However Prof McConway said: “It sounds pretty dramatic to say that consuming 25g of processed meat a day, about one rasher of bacon a day, increases the risk of developing dementia by 44 per cent. But what was the risk, in the context of this study?

“Yes, almost 500,000 people were followed up, but under 3,000 of them actually developed dementia during the study period. In other words, only about 6 in every thousand got a dementia diagnosis.

“Imagine a group of 1,000 people like those in the study. If we follow them up for eight years, the average follow-up time in this study, six of them would get a dementia diagnosis.

“Imagine for now that it really is the processed meat eating that increases dementia risk by the amount found in this study, and now imagine that all the 1,000 people ate an extra 25g of bacon every day for the eight years.

“The number who would get dementia would go up from six to eight. Actually there’s a bit of statistical uncertainty about that figure – it could be between seven and 10. So all that extra bacon eating would increase the number of dementia cases in our group of 1,000 people by between one and four cases. That’s an increase, but a pretty small one in my view.”

Researchers also found more men than women were diagnosed with dementia in the study population.

The findings suggested the risks from eating processed meat were the same whether or not a person was genetically predisposed to developing the disease.

Huifeng Zhang, lead researcher and PhD student from the University of Leeds School of Food Science and Nutrition, said further confirmation of the findings was needed.

“Worldwide, the prevalence of dementia is increasing and diet as a modifiable factor could play a role,” she said.

Globally, there are around 50 million dementia cases with around 10 million new cases diagnosed every year.

Alzheimer's disease makes up around two-thirds of cases, with vascular dementia accounting for a quarter.

This article was updated to include comments from Professor Kevin McConway, emeritus professor of applied statistics at the Open University.