• Researchers have recently investigated the link between inflammatory diets and the risk of dementia in older individuals in Greece.
• They found that those consuming highly inflammatory diets were over three times more likely to develop dementia than those consuming anti-inflammatory diets.
• The researchers caution that because their study was observational, it cannot confirm a direct link between inflammatory diets and dementia risk.

According to the United Nations (UN), the worldwide population of those aged 60 years and over will grow from 962 million in 2017 to 2.1 billion by 2050. Experts expect the rates of dementia to increase alongside this aging population.

As people age, they experience a form of chronic low-grade inflammation in their immune system. Experts have linked this kind of age-related inflammation to dementia and cognitive decline.

Research suggests that different foods can influence rates of inflammation both acutely and chronically.

Some foods linked to high rates of inflammation include:

• processed foods
• sugar
• unhealthy oils
• excess amounts of red meat
• alcohol

Some foods that are known for their anti-inflammatory properties include:

• fish
• fruits
• vegetables
• nuts and seeds
• tea
• legumes, such as lentils

Being able to measure the inflammatory potential of different diets may help clinicians recommend dietary interventions for cognitive health.

However, until now, there has been little research into the effects of an inflammatory diet on cognitive health. Although some studies suggest that increased intakes of inflammatory diets have negative effects on cognitive ability and memory, others have found no link.

Furthermore, the only prospective population-based study to have explored the issue so far included women alone. This limits the generalizability of its results.

Recently, researchers from the United States, Greece, and Ireland conducted a population based-study involving men and women to investigate the effects of inflammatory diets on cognitive decline.

“There may be some potent nutritional tools in your home to help fight the inflammation that could contribute to brain aging,” said study author Dr. Nikolaos Scarmeas, Ph.D., of the National and Kapodistrian University of Athens in Greece. Dr. Scarmeas is also a Fellow of the American Academy of Neurology.

“Diet is a lifestyle factor you can modify, and it might play a role in combating inflammation, one of the biological pathways contributing to risk [of] dementia and cognitive impairment later in life.”

“There has been previous conflicting literature on associations between inflammatory aspects of diet and cognition. Our study adds to the scientific argument favoring a potentially important role of inflammation,” he told Medical News Today.

The study appears in the journal Neurology.

Aging and diet

The researchers selected individuals from the Hellenic Longitudinal Investigation of Aging and Diet, which is a population-based study that tracks the epidemiology of dementia and other neuropsychiatric conditions in the aging Greek population.

In this study, the researchers evaluate the participants every 3 years. So far, there have been two evaluations per person.

Altogether, the researchers selected 1,059 individuals for their analysis. None of the participants had dementia at their first evaluation, and they all provided dietary information on the main food groups they had consumed within the past month.

The researchers assessed the participants’ diets using the Dietary Inflammatory Index (DII), which is a tool that can assess the inflammatory potential of a person’s diet. It includes 45 food parameters, such as macronutrients and micronutrients, bioactive compounds, and spices.

The researchers split the participants into three equal groups according to how inflammatory their diets were:

• The first group, which had the least inflammatory diets, had DII scores ranging from -5.83 to -1.76.
• The second group had DII scores of between -1.76 and 0.21.
• The third group, which had the most inflammatory diets, had scores of between 0.21 and 6.01.

Per week, those with the most anti-inflammatory diets consumed an average of:

• 20 servings of fruit
• 19 servings of vegetables
• 4 servings of beans and other legumes
• 11 servings of coffee or tea

Meanwhile, those with the most inflammatory diets consumed an average of:

• 9 fruit servings per week
• 10 vegetable servings per week
• 2 legume servings per week
• 9 coffee and tea servings per week

Among the 1,059 individuals the researchers included in the analyses, 62 developed dementia during the 3-year follow-up period.

The researchers found that those with the most inflammatory diets were 3.43 times more likely than those with the least inflammatory diets to develop dementia.

They also found that each 1-point increase in DII score was linked to a 21% higher dementia risk.

Inflammaging

To explain the results, the researchers say that after around 40 years of age, the immune system starts to decline.

In what is known as “inflammaging,” the immune system increases the production of pro-inflammatory mediators, which may reach the central nervous system and reduce brain-derived neurotrophic factor (BDNF) levels. BDNF is a protein that supports the growth, maturation, and maintenance of neurons.

Inflammaging is also linked to oxidative stress and the induction of apoptosis, or programmed cell death. These effects, note the researchers, make up some of the main neuroinflammatory and neurodegenerative pathways involved in dementia.

Although inflammaging is a common factor of aging, research suggests that food components could exacerbate it.

When MNT asked Prof. Con Stough, a professor of cognitive neuroscience at Swinburne University in Australia, what might cause the link between inflammatory diets and dementia, he said:

“If you rule out a non-causative explanation, i.e., that people with dementia or who are already at risk [of] dementia show behaviors [that] exacerbate their poor diets (e.g., not cooking nutritional foods, eating out at fast food places more often, etc.) then there could be many mechanisms. Many of these we simply don’t really understand.”

Prof. Stough was not involved in the recent study.

“Certainly, the microbiome could have a huge impact. What we eat seems to impact […] the diversity of our microbiome, i.e., what bacteria live in our microbiome. Gut bacteria appear to have a role for inflammation themselves and produce peptides that can increase inflammation (bad bacteria).”

“As we get older, too, there is greater leakage from the gut [that] also causes inflammation, so having a bad diet could increase the number of pro-inflammatory bacteria in the gut,” he added.

“Different foods can also increase the levels of pro-inflammatory cytokines. […] Increased inflammation or systemic inflammation can directly damage neurons as well as impact cardiovascular function. Both direct damage to the brain and changes in cardiovascular function could contribute to cognitive decline as well as increase dementia risk,” Prof. Stough explained.

The researchers conclude that more inflammatory diets are positively linked to a risk of dementia in community-dwelling older adults without a history of cognitive decline.

Strengths and limitations of the study

A limitation to the recent study is that 689 of the participants did not turn up for follow-up evaluations, meaning that the results may be skewed. Cognitively healthy individuals may have been more likely to overlook a secondary evaluation, as they may not have felt the need for further examination.

“From the present study, it seems that if a section of the population adopts dietary habits toward a more anti-inflammatory nature, then future dementia cases could be conceivably fewer,” Dr. Scarmeas told MNT.

“However, we should note that the study was an observational one, not a clinical trial. Also of a relatively short duration, only 3 years. Therefore, it does not prove that eating an anti-inflammatory diet prevents brain aging and dementia, it only shows an association.”

The researchers also say that the epidemiological nature of their study means that they cannot confirm causation and that the short follow-up period of just 3 years may not portray the lasting impacts of inflammatory diets.

“The study has both advantages and disadvantages,” said Dr. Stough.

“Firstly, it is an epidemiological study, which means that it is observational. It asks questions at different time points and tries to ascertain whether differences in diet at time 1 [predict] dementia risk at time 2. As far as epidemiological studies go, it is well constructed, but one of the problems with this type of study is that [the researchers] may have missed an important variable that may explain the results.”

“For instance, they didn’t measure the amount of exercise or cognitive training each participant [had] been doing over that period of time. Could those variables also predict diet quality? They both could potentially account for the reported relationships between diet and dementia risk. There could be many others,” he continued.

“It also doesn’t connect the dots, so it assumes that certain foods are related to an increase in certain pro-inflammatory cytokines, such as Il-6. While I think there is great logic in doing this, as there have been previous studies standardizing this approach, it is still an assumption.”

“The other issue is that this study doesn’t really offer the mechanisms by which diet and inflammation degrade cognition in this sample,” he explained.

When MNT asked how these findings could influence public health, Dr. Stough replied:

“We need to have a serious look at pro-inflammatory foods that we consume in Western diets. There has recently been a lot of attention paid to research on Mediterranean diets, which are anti-inflammatory and seem to have positive effects against cognitive decline and dementia risk.”

”Diets that comprise takeaway foods and fast foods are generally leading to pro-inflammatory diets,” added Dr. Stough. ”We need to consider healthier diets that focus on vegetables and fruits, in general, whole foods, etc. Given that we are all busy, this will not be an easy goal to achieve, but we need to find ways to promote healthier diets.”

”Certainly, studies like this offer us a huge opportunity to explain to the community the potential long-term damage of pro-inflammatory diets,” he concluded.

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