You may want to rethink having a hot dog or a ham sandwich for lunch, based on the findings of a recent study published in the journal Neurology^®. The study found that those who ate more processed red meat daily on average had an increased risk of dementia.

The paper analyzed the diets, health, and lifestyle choices of more than 133,000 participants in two long-running population studies, the Nurses’ Health Study and the Health Professionals Follow-Up Study. Participants answered survey questions every two to four years, providing detailed health information over the course of 43 years.

More than 11,000 study participants were diagnosed with dementia in that time period. Researchers based that diagnosis on the participants’ own reports of cognitive decline and the listing of dementia on death certificates.

Participants who ate a quarter or more of a serving of processed red meat daily on average—about two slices of bacon, 1.5 slices of bologna, or a hot dog—had a 13 percent higher risk of developing dementia than those who ate only one-tenth of a serving each day. (A typical serving of red meat is 3 ounces, approximately the size of a deck of cards.)

Researchers say several factors could contribute to that link, including that diet can impact the microorganisms, including bacteria, that reside in the gut. Trimethylamine N-oxide, a byproduct of the breakdown of meat by bacteria, may increase cognitive dysfunction, too, although they note that research on that association is limited. The saturated fat and salt content of red meat also could impact the health of brain cells, researchers say. 

The researchers found that replacing processed red meat with plant-based protein sources, such as nuts and legumes, was associated with a 19 percent lower risk of dementia and 1.37 fewer years of cognitive aging. 

“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 study co-author Daniel Wang, MD, ScD, assistant professor in the department of nutrition at the Harvard T.H. Chan School of Public Health and Brigham and Women’s Hospital.

Some experts not involved with the study had questions about the findings. David Knopman, MD, FAAN, a clinical neurologist at the Mayo Clinic, expressed concern about the reliability of the dementia diagnosis based on some self-reporting by participants. The underlying cause of each case of dementia was not clearly accounted for in the study. In addition, he notes  “people’s food choices are often based on what they can afford, and poor socioeconomic status can impact health issues such as dementia.” Dementia also could play a role in the food choices people make, he adds.

Dr. Wang says, however, that self-assessments of cognitive decline may come years earlier than a clinical diagnosis and may therefore be important.

“Large, long-term cohort studies are essential for investigating conditions like dementia, which can develop over decades,” he adds. “We are continuing to piece together this story to understand the mechanisms causing dementia and cognitive decline.”