The study tracked Dietary Inflammatory Index scores measured at three time points over 10 years.
Diets higher in inflammatory foods were tied to an increased incidence of dementia in older adults, longitudinal data from the Framingham Heart Study Offspring cohort showed.
Over 13 years of follow-up, higher Dietary Inflammatory Index (DII) scores averaged across three time points were linearly associated with an increased incidence of all-cause dementia (HR 1.21, 95% CI 1.10-1.33, P<0.001), reported Debora Melo van Lent, PhD, of UT Health San Antonio in Texas, and co-authors.
Similarly, higher DII scores were linearly associated with an increase in Alzheimer's disease dementia (HR 1.20, 95% CI 1.07-1.34, P=0.002), the researchers reported in Alzheimer's & Dementia. Findings were adjusted for demographic, lifestyle, and clinical covariates.
"Although these promising findings need to be replicated and further validated, our results suggest that diets that correlate with low DII scores may prevent late-life dementia," van Lent and colleagues noted.
Previous cross-sectional research from the Framingham Heart Study Offspring cohort showed that higher DII scores -- indicating more pro-inflammatory foods consumed -- correlated with smaller total brain and gray matter volumes and larger lateral ventricular volume.
Other cohort studies, including a 3-year study in Greece, tied diets with high inflammatory potential to an increased risk of incident dementia. And clinical trial data showed the MIND diet -- a hybrid of the Mediterranean diet and the DASH (Dietary Approaches to Stop Hypertension) diet that is rich in anti-inflammatory foods -- had a similar effect on cognition and brain MRI outcomes as mild caloric restriction over 3 years, possibly due to high adherence of the control group to lifestyle advice.
However, there's limited information about the long-term relationship between diet-driven inflammation and incident dementia, van Lent and co-authors noted.
The researchers evaluated 1,487 participants in the Framingham Heart Study Offspring study who were age 60 or older at baseline with no prevalent dementia. More than half (53%) were women, and mean baseline age was 69. About 22% carried an APOE4 allele.
DII scores were calculated using the 126-item Harvard semi-quantitative food frequency questionnaire, which was administered at three points over 10 years from 1991 to 2001.
The DII used in the analysis consisted of 36 dietary components including nutrients, whole foods, and caffeine from food intake. Components were categorized as anti-inflammatory or pro-inflammatory.
Anti-inflammatory components included alcohol, beta-carotene, caffeine, dietary fiber, folic acid, magnesium, thiamin, riboflavin, niacin, zinc, monounsaturated fat, polyunsaturated fat, omega-3 fat, omega-6 fat, selenium, flavan-3-ol, flavones, flavonols, flavanones, anthocyanidins, green or black tea, pepper, garlic, and vitamins B6, A, C, D, and E.
The mean DII score was -0.30, indicating that participants' diets were anti-inflammatory, on average. DII scores were grouped into quartiles. Education, body mass index, total energy intake, and smoking status varied across the four groups.
Follow-up was a maximum of 22.3 years and a mean of 12.8 years. In that span, 246 participants developed all-cause dementia, mostly Alzheimer's dementia (187 people). There were no significant interactions between DII scores and APOE4, sex, hypertension, type 2 diabetes, or cardiovascular disease in relation to incident all-cause and Alzheimer's dementia, the researchers noted.
"The most pro-inflammatory components of the DII (i.e., saturated fat, trans fats, and total energy intake) are present in the pro-inflammatory 'Western diet' -- a summary term for dietary patterns consumed in Western societies -- which has shown an association with increased concentrations of biomarkers of systemic inflammation and risk factors of all-cause and Alzheimer's disease dementia, and also with neurodegenerative disease-related outcomes," they wrote. "Western diets having inflammatory potential especially known to be pro-inflammatory may have enormous implications for preventive dietary interventions."
The study had several limitations, van Lent and colleagues acknowledged. Its design was observational and the study cannot show causality. The findings relied on food frequency questionnaire data that may have measurement error or recall bias. In the Framingham Heart Study Offspring study, only 36 of 45 possible DII components could be assessed.
The DII was created based on studies of micro- and macronutrients and bioactive compounds in relation to inflammatory markers, not specific disease outcomes. "A limitation of this approach is that some individual DII components may have an opposite effect on the health outcome under study," the researchers pointed out. "For example, vitamin B12 is considered pro-inflammatory in the DII score, but the vitamin has been hypothesized to be protective for dementia risk."