Researchers found in a 2018 survey that there just wasn't enough solid evidence to definitively conclude that certain dietary factors — like, for example, coffee, or supplements — impacted dementia risk one way or another.
The number of people living with dementia is projected to more than triple by 2050, soaring to 152 million cases worldwide. Not all types of dementia are preventable, but mounting evidence points to the possibility that some cases are. With certain environmental and lifestyle interventions, that could be as substantial as two in five dementia cases delayed or avoided altogether. When it comes to a specific, clear set of instructions on How to Prevent Dementia, however, the research leaves much to be desired. Despite decades of study there is still broad consensus that the links between brain function and foods or food groups are, as of yet, inconclusive. Even with so encouraging evidence, there are still studies that find the total opposite: no correlation between eating healthy food and having less of a chance of developing dementia.
For example, in a 2018 study, health officials in England determined there was not enough evidence to support a link between diet and dementia after reviewing studies on diet, supplements like omega-3 and caffeine. To be clear, they’re not ruling out the potential effects of diet on brain health—there’s just not sufficient evidence to show that there is a cause and effect relationship.
The report, put together by the Scientific Advisory Committee on Nutrition, acknowledged that a Mediterranean diet is associated with a lower risk of cognitive impairment and dementia, but concluded that the observational model of most nutrition studies limits how much we can attribute to cause and effect. After publishing the review, Public Health England said that following a healthy diet was still recommended, because it can help people maintain a healthy blood pressure and weight, two factors that have been shown to reduce risk of dementia.
As far as supplements and caffeine intake, the report said evidence is limited and inconclusive. In other words, there is no magic pill or amount of coffee that will or won’t improve your chances of developing dementia.
“There’s no evidence that eating a certain food, or taking a specific vitamin or supplement can affect the risk of dementia, but we do know that people who eat a Mediterranean style diet tend to have a lower risk of dementia,” said Doug Brown, Chief Policy and Research Officer at Alzheimer’s Society. “Dementia is set to be the 21st century’s biggest killer, and with no way yet to cure the condition, prevention is key.”
Both the National Health Service and Alzheimer’s Society recommend sticking to a healthy diet, despite the lack of conclusive evidence.
“We recommend eating plenty of fresh fruit, vegetables and whole grains, having fish twice a week, and using healthier fats like olive oil. It’s also a good idea to cut down on red meat, saturated fats, refined sugar and salty foods,” said Brown.
Fixing the problem with research into diet and dementia risk
Researchers acknowledge that getting an accurate picture of the link between diet and dementia is very, very hard to do. And in 2022, a Nutrition for Dementia Prevention Working Group made up of 27 leading researchers in the Alzheimer’s and dementia field laid out recommendations to help solidify the science around the relationship between nutritional diets and lower dementia risk. The group’s guidelines were published in The Lancet Health Longevity, where the authors also highlight the limitations of existing research.
“Many trials have not found that making people eat healthy or exercise is translating into benefits in the ways that is expected from the epidemiological research,” said Dr. Hussein Yassine, associate professor of medicine and neurology at the Keck School of Medicine of USC, said. “That means either there is no causal connection, or that these studies have not been properly designed.”
The researchers involved in creating these guidelines spent two years looking at the vast body of evidence linking nutrition and dementia risk. The results of nutritional research, they found, are not always straightforward. For example, it is known that a Mediterranean-style diet is healthy and that study participants who adhere to this diet are less likely to develop Alzheimer’s or other forms of dementia. But is the diet itself the protector? Or are there other factors at work behind the scenes?
What if, for example, the consumption of a Mediterranean diet were linked to some other influential but unmeasured factor, such as socioeconomic status, which is also linked to brain health? In addition to unmeasured variables, Yassine notes that studies may often be too short to spot any meaningful effects of a dietary intervention on cognition. “If it takes five to 10 years,” he said, “then studies that lasted for two years or less are not accurately reflecting the effect of the diet on cognition.”
Dementia risk and omega-3 fish oil
While this 2018 study found differently, other studies have repeatedly linked eating more fish to better brain health — and to lower risk of developing dementia. That’s because fish — in particular, cold-water, fatty fish, like salmon, for example — is rich in omega-3 fatty acids. (Specifically, we’re talking about docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) — important building blocks for cells.) As a result, many companies now market DHA and EPA as omega-3 fish oil supplements in the nutrients, vitamins and supplements aisle at your local pharmacy, hailing the compounds’ brain-boosting potential. Around 8 percent of Americans take omega-3 supplements daily to boost their brain health.
There is a caveat, however: Although omega-3 fish oils have shown great results in the lab — improving brain health measurably in lab specimens of rats, mice, and brain cells in Petri dishes — the same may not be true for humans. Clinical trials of omega-3 fish oils and of these specific omega-3 fatty acid compounds DHA and EPA have so far failed to show any particular brain benefits for healthy adults, nor for people with Alzheimer’s, dementia, or cognitive decline. Read more about the current verdict on omega 3s for brain health and Alzheimer’s dementia risk here.
Dementia risk and coffee
The 2018 study found no particular association between coffee and dementia risk — but coffee is a heavily studied area and there have been many other studies that have found all manner of results.
For new Alzheimer’s treatments, scientists run randomized, blinded trials. This is impossible to do for coffee drinkers because most Americans drink coffee every day. Instead, many of these studies on coffee and dementia risk look at large populations to see whether people who drink a certain amount of coffee are more likely to develop Alzheimer’s than non-drinkers. These studies can’t provide a clear verdict because many variables are not measured: Are people taking their coffee with cream or milk? Are they drinking an espresso or a latte? How strong do they enjoy their brew? To make matters even more intricate, recent research also suggests that certain genetic traits are linked to coffee metabolism and drinking more coffee; it may be difficult to separate out this genetic factor when considering the impact of coffee consumption on the brain.
Ultimately these studies provide scientists with a few clues; none have shown that drinking a certain amount of coffee will affect brain health. So, what have we learned? Firstly, that articles proclaiming some clear, definitive link between a daily habit like coffee and your dementia risk are likely oversimplifying the issue; and secondly, that if you are looking to improve your brain health, turn your attention from your caffeine habit to better known lifestyle opportunities: like a healthy diet, exercise, and good sleep to name a few. Read more on coffee and Alzheimer’s risk here.