People with dementia have difficulties with their memory, attention, thinking, and reasoning that interfere with everyday activities. These cognitive difficulties are not part of the typical aging process.
According to the Centers for Disease Control and Prevention (CDC), in 2014, around 5 million adults in the United States had dementia. However, the CDC estimate this number may be close to 14 million by 2060.
The World Health Organization (WHO) report that there are around 50 million dementia cases globally, with around 10 million new cases being diagnosed every year.
Alzheimer’s disease is the most common cause of dementia, accounting for 60–70% of cases.
About 5–10% of cases are associated with impaired blood flow to the brain — for example, as a result of a stroke — and are known as vascular dementia.
Genetic and environmental factors, including diet and lifestyle, are known to affect the development and progression of dementia.
Previous research links people’s overall meat consumption to their risk of developing the condition.
However, a new study from scientists at the University of Leeds in the United Kingdom suggests there is a link between eating processed meat in particular and an increased risk of developing dementia.
Processed meats include products such as sausages, bacon, salami, and corned beef.
That said, the research also indicates that red meat may have a protective effect against dementia.
The study appears in The American Journal of Clinical Nutrition.
Diet, genetics, and lifestyle
The scientists analyzed data from the UK Biobank, a database of genetic and health information from around half a million volunteers in the U.K. aged 40–69 years.
On recruitment to the project, every participant filled out a dietary questionnaire and completed 24-hour dietary assessments.
This allowed the researchers to estimate the total amount of meat each participant regularly consumed and how much of each type they ate.
The database also allowed them to identify which participants had thegene variant APOE ε4 allele, which is known to increase a person’s risk of dementia.
They then used hospital and mortality records to identify subsequent cases of dementia from all causes, Alzheimer’s disease, and vascular dementia during the follow-up period of around 8 years.
Of the 493,888 participants, 2,896 had all-cause dementia. These included 1,006 cases of Alzheimer’s disease and 490 cases of vascular dementia.
To estimate the role of meat consumption, the researchers had to account for a wide range of other factors that are known to affect a person’s likelihood of having dementia.
These included age, gender, ethnicity, education, and socioeconomic status. In addition, the researchers accounted for lifestyle factors, such as smoking, physical activity, and consumption of fruits and vegetables, fish, tea, coffee, and alcohol.
After these adjustments, they found that each additional 25-g portion of processed meat eaten per day was associated with a 44% increase in the risk of dementia from all causes.
This intake was also associated with a 52% increased risk of Alzheimer’s disease.
By contrast, each additional 50-g portion of unprocessed meat eaten per day was linked to a 19% reduction in the risk of all-cause dementia and a 30% reduced risk of Alzheimer’s disease.
The results for unprocessed poultry and total meat consumption were not statistically significant.
Eating large amounts of processed meat was also associated with a higher risk of vascular dementia, but the link with steadily increasing daily consumption was not significant.
As expected, the researchers noted that having the APOE ε4 allele increased the risk of dementia 3–6-fold. However, it did not significantly affect the observed associations between diet and dementia.
Processed meat and disease risk
A large body of evidence has linked consumption of processed meat to cancer. In 2015, the WHO even went so far as to define it as a carcinogen.
“Worldwide, the prevalence of dementia is increasing, and diet as a modifiable factor could play a role,” says Huifeng Zhang, a Ph.D. student at the School of Food Science and Nutrition at the University of Leeds, who was the lead researcher of the new study.
“Our research adds to the growing body of evidence linking processed meat consumption to increased risk of a range of nontransmissible diseases,” she adds.
It is important to note that the researchers have reported their results as percentage increases in the risk of developing dementia, or “relative risk.”
This is in contrast to the change in “absolute risk,” or how many extra cases there will be per 1,000 individuals, for example.
Ms. Zhang told Medical News Today that data from the UK Biobank are unsuitable for calculating absolute risk, because it is not a representative sample of the entire population.
For example, she said, it does not contain a sufficiently high proportion of individuals aged over 70 years.
The risk of dementia rises with age, so this imbalance would skew any calculation of absolute risk.
It is also worth noting that this was an observational study, so it could not prove that consuming processed meat causes dementia. It does, however, demonstrate a statistical association between the two.
“It’s always important to remember when looking at studies like this that they can’t attribute causation and [that] important confounding factors might account for apparent associations,” says Prof. Robert Howard, professor of old age psychiatry at University College London in the U.K., who was not involved in the study.
“As a doctor who works clinically with people with dementia and conducts research into potential dementia treatments, the data wouldn’t persuade me to give up my breakfast bacon,” he adds.
Medical reference: Medical News Today