Study details

For the study, researchers analyzed data on more than 133,000 American adults who were tracked for over 40 years. The participants were healthcare professionals enrolled in two major studies: the Nurses' Health Study and the Health Professionals Follow-Up Study.

Every two to four years, the participants filled out dietary surveys asking about their intake of more than 150 foods and were asked questions about their weight, physical activity, and other lifestyle habits.

The participants were also administered tests that evaluated their memory, recall, and cognitive function at different points throughout the follow-up period. They filled out questionnaires investigating any self-reported problems with memory and mental abilities that can detect early stages of worsening cognitive decline. Diagnoses of dementia and deaths from the disease were also tracked.

The researchers found that people who ate a quarter of a serving of processed red meat or more a day — equivalent to at least three quarters of an ounce of processed red meat each day — had a 13% higher risk of developing dementia compared to people who ate little to no processed red meat.

In addition, those who ate at least a quarter of a serving of processed red meat a day had a 14% higher risk of subjective cognitive decline, and each additional serving of processed red meat each day was linked to an extra 1.69 years of cognitive aging in a participant's ability to understand and remember words and sentences.

The study also found that replacing one daily serving of processed red meat with plant proteins like nuts and legumes was associated with a 19% lower risk of dementia and 1.37 fewer years of cognitive aging. 

Discussion

Other research has resulted in similar findings regarding the link between processed meats and dementia.

One study, which tracked half a million adults in the United Kingdom over around eight years, found that eating the equivalent of one ounce of processed meat or more a day was associated with a 44% higher risk of developing dementia and a 52% higher risk of developing Alzheimer's disease. However, eating unprocessed meat was found to be protective against dementia and Alzheimer's.

According to Daniel Wang, a senior author of the study and an assistant professor in the department of nutrition at the Harvard T.H. Chan School of Public Health, there are several reasons why processed red meats could impact brain health.

Wang noted that cured meats typically contain high sodium levels, which can increase blood pressure and cause vascular problems that can impact the brain. They also contain nitrites, nitrates, and other preservatives and chemical additives that can lead to oxidative stress.

Processed red meats also contain large amounts of saturated fat, which can increase cholesterol levels and disrupt neuron function in the brain and nervous system. Previous research has suggested that diets high in saturated fat could reduce levels of brain-derived neurotrophic factor, a protein that can trigger the growth of new brain cells.

Yian Gu, an associated professor of neurological sciences at the Columbia University Irving Medical Center, said the study findings were "very important."

Gu noted that it's often difficult for people to change their longtime dietary habits but encouraging them to make small changes like cutting back on processed red meat could lead to significant health benefits. Gu has found in her own research that eating more fruits, vegetables, fish, nuts, whole grains, and legumes was associated with less brain atrophy as people age.

Wang said that he recommends people try to reduce the amount of processed red meat in their diets and replace it with other proteins. "There's quite a range of healthier options for you," he said. "You can replace it with chicken, fish, nuts, low-fat dairy, and legumes."

"The take-home message is that if you can limit your red meat intake, then please do it," Wang added. "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."