Brain changes that can eventually lead to dementia may begin many years before anyone notices symptoms such as memory problems, missed appointments or difficulty finding words.
This is where blood biomarkers are becoming important. Biomarkers are measurable signs of biological activity in the body. In dementia research, some blood biomarkers can give clues about biological processes related to brain changes. These can include Alzheimer’s-related protein alterations, damage to nerve cells or changes in cells that support and protect nerve cells.
But these cannot predict with certainty whether an individual will develop dementia. Higher levels may suggest increased risk, but some people with biological signs never develop dementia, while others do. That raises an important question: once early brain-related changes have begun, can lifestyle still influence dementia risk?
Diet and dementia
Our research suggests diet may still be relevant. We followed nearly 1,900 adults aged 60 and older in Sweden for up to 15 years. None had dementia at the start. During that time, 240 developed dementia.
Participants’ diets were assessed several times. We then looked at whether healthier eating patterns were linked to lower dementia risk among people with different levels of blood markers related to Alzheimer’s disease, nerve cell damage and biological stress in the brain.
We found that people with healthier dietary patterns generally had a lower risk of dementia. Importantly, this pattern was also seen among people whose blood markers suggested higher biological risk, including Alzheimer’s-related changes.
Rather than focusing on single foods or nutrients, we studied overall dietary patterns. This is useful because people eat combinations of foods, rather than isolated nutrients. Previous work from our group has also linked diet quality with blood markers related to Alzheimer’s disease in cognitively healthy older adults.
We examined three ways of describing diet quality: how closely people followed a Mediterranean-style diet, how closely their diet matched general healthy eating guidelines, and how likely their diet was to promote inflammation in the body. This allowed us to ask whether different aspects of diet quality were more relevant for people with different biological profiles.
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The strongest and most consistent finding among people at higher biological risk involved the inflammatory potential of the diet. Among people with higher levels of these risk-related biomarkers, diets with lower inflammatory potential were associated with up to a 30% lower relative risk of dementia. A relative reduction describes a difference between groups. It cannot tell any individual person whether they will avoid dementia.
The finding also has an important caveat. Our study was observational, which means it can show links between diet, biomarkers and dementia risk, but it cannot prove cause and effect.
Still, the results suggest that inflammation may be one pathway through which diet remains relevant, even after disease-related changes have begun.
Lower-inflammatory diet
A lower-inflammatory diet is a broad way of eating rather than a special medical diet. In this kind of research, it generally means eating more foods such as vegetables, fruits, whole grains, legumes, tea and coffee, and fewer foods such as red and processed meat, refined grains and sugary drinks. Similar work has linked lower dietary inflammatory potential with lower dementia risk in older adults with cardiometabolic diseases, such as type 2 diabetes, heart disease or stroke.
Why might this affect the brain? Inflammation is part of the body’s normal defence system. It helps us respond to infection and injury. The concern is chronic, low-grade inflammation that remains active for years.
Scientists are increasingly interested in how this kind of long-term inflammation may contribute to brain ageing and dementia. It may affect the brain directly, through immune activity around brain cells, and indirectly, through blood vessels, insulin resistance and heart health.
Other dietary patterns showed a different picture. A Mediterranean-style diet and a healthy diet based on general nutrition guidelines were more strongly linked to lower dementia risk among people with lower biomarker levels.
Even so, these diets may still be relevant for people at higher biological risk. The results suggest that different aspects of diet quality may operate in different ways, depending on a person’s biological profile.
Our study had several strengths. We used repeated information on diet, followed people for many years, identified dementia cases carefully, and compared several dietary patterns in the same group of older adults.
There were limitations too. Diet was measured with questionnaires, which are useful but imperfect. The participants came from one urban area in Sweden and were, on average, relatively healthy and well educated, so the findings may not apply in the same way to all populations.
The message should be modest: a healthy diet cannot erase dementia risk. Age, genes, cardiovascular health, social conditions and chance all play a part.
But our findings suggest that diet may still be relevant for brain health even when early biological signs linked to higher risk are already present. The next task is to identify which foods and nutrients are driving these associations, so future advice on dementia prevention can become more precise and more useful.
