Processed red meats—like bacon, deli meats, and hot dogs—are linked to a host of health ills. Now, the latest study finds that eating too much red meat may even harm the brain.
In a study published in the journal Neurology, Dr. Daniel Wang, an assistant professor of medicine at the Brigham and Women’s Hospital and Harvard Medical School, and his team report that people who eat more processed red meat had a 14% higher risk of developing dementia over more than four decades that those who consumed minimal amounts.
The study analyzed data from more than 130,000 health professionals enrolled in two major studies: the Nurses’ Health Study and the Health Professionals Follow-Up Study. Every two to four years, people filled out detailed dietary surveys asking about their intake of more than 150 foods. The researchers also collected health data on dementia diagnoses and asked people brief questions about their memory.
“Based on this data, we see that if people have higher processed red meat intake, they have a higher risk of dementia, a higher risk of subjective cognitive decline, and worse cognitive function,” says Wang.
The scientists saw increased risk of all of these outcomes with any consumption of processed red meat, and it continued to increase the more meat a person consumed. The 14% increased dementia risk was the upper threshold.
It didn’t take much meat to reach that upper limit. The 14% higher risk of dementia was linked to people who ate at least a quarter of a single 3-oz. serving of processed red meat daily—equivalent to two slices of bacon, one and a half slices of bologna, or a hot dog—compared to those who ate less than a tenth of a serving (less than a slice of bacon) a day.
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Wang plans to keep studying these populations to better understand how processed red meat affects the brain, and possibly dementia. One theory is that processed meat, because of its high saturated fat and sodium, can increase the risk of diabetes and heart conditions, in part by raising blood pressure, and thus harming the brain. Another is based on the fact that that some of the compounds the body makes when it breaks down processed red meat can increase the risk of dementia; in the lab, for example, some of these compounds cause the clumping of amyloid protein that is a hallmark of Alzheimer’s disease. Finally, the nitrites found in processed red meats may damage DNA, injuring brain cells.
Previous studies of processed red meat and dementia have been inconsistent, with some finding a connection and others not. Wang says those studies were smaller and followed people for less time, without evaluating people’s diets more than once. His team’s approach, on the other hand, “captured changes in dietary intake during decades-long follow up, which is the strength our study has,” he says.
The detailed dietary data also allowed them to estimate what effect replacing red meat would have on dementia risk. Substituting one serving a day of processed red meat with nuts or legumes contributed to a 19% lower risk of dementia over the study period; similarly, replacing red meat with fish was linked to a 28% lower risk of dementia. Eating chicken instead of red meat for one serving daily contributed to a 16% lower dementia risk.
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The data also allowed Wang’s team to compare people who ate more processed red meat to those who ate more unprocessed red meat. Those who ate more unprocessed red meat did show a slightly higher risk of dementia compared to people eating minimal amounts, but this association wasn’t statistically significant.
However, on the scale that measured people’s own assessments of their cognitive function, those who ate unprocessed red meat had a 16% higher risk of having memory issues than those who ate minimal amounts. This subjective assessment included six to seven yes-or-no questions, including whether they had more difficulty remembering the names of close friends in the past year compared to the previous year, or whether they had problems finding their way home in the past year.
While this subjective assessment does not measure dementia specifically, it measures memory problems and is “very sensitive,” says Wang, often detecting signs of cognitive decline earlier than more standardized tests. It may therefore be a useful tool for alerting doctors to potential emerging cognitive problems. Wang plans to continue following these populations in order to determine if the subjective assessments of memory issues lead to more dementia findings on standardized testing over time.
“The take-home message is that if you can limit your red meat intake, then please do it,” says Wang. “If you reduce your intake even a little bit, it will give you cognitive health benefits. And if you do it earlier, then even better.”
