Red meat has been previously linked to higher rates of cancer, identified as a contributor to climate change through production methods, and now a long-term study has linked it to an increased risk of dementia.

The findings come from researchers led by a team at the Harvard TH Chan School of Public Health in Boston, and are based on records of 133,771 people in two US health databases. The participants were followed for up to 43 years, with dietary patterns charted against the likelihood of developing dementia.

Based on the 11,173 people in the study who did develop dementia over the research period, averaging a quarter of a serving or more of processed red meats every day – about half a slice of bacon – means a 13 percent higher risk compared to those who only ate a small amount of red meat.

As cognitive assessments are included in the health databases, the researchers could look at this too. For every extra serving of processed red meat averaged per day – one additional hot dog per day, roughly – speeds up cognitive aging by about 1.6 years.

"Higher intake of red meat, particularly processed red meat, was associated with a higher risk of developing dementia and worse cognition," write the researchers in their published paper.

"Reducing red meat consumption could be included in dietary guidelines to promote cognitive health."

It's important to recognize that studies of this type don't show direct cause and effect. All kinds of factors can play into dementia risk – from sleep quality to alcohol intake to genetic variants – and this research didn't cover all of them.

That means it can't be said that eating more red meat was directly responsible for a greater likelihood of developing dementia. Because the study involved such a large group of people, it does provide strong evidence for a link between the two.

Unprocessed red meat – such as beef, lamb, or pork that hasn't been preserved – wasn't shown to be associated with dementia risk. However, there was a link between processed and unprocessed meat and self-reported subjective cognitive decline.

The team behind the study isn't stopping there. The researchers want to take a closer look at why red meat might lead to dementia – including changes the meat makes to the gut microbiome – and are also keen to expand the analysis to a more diverse group of people.

"Dietary guidelines tend to focus on reducing risks of chronic conditions like heart disease and diabetes, while cognitive health is less frequently discussed, despite being linked to these diseases," says epidemiologist Daniel Wang, from the Harvard TH Chan School of Public Health.

"We hope our results encourage greater consideration of the connection between diet and brain health."

The research has been published in Neurology.