In a large prospective cohort study published in JAMA Neurology, healthy dietary patterns in midlife were associated with a lower risk of subjective cognitive decline (SCD) and better objectively measured cognitive function later in life. 

The analysis drew on data from over 150,000 participants in 3 long-running US cohorts – the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow-up Study – with dietary intake assessed repeatedly over decades. Investigators evaluated adherence to six established healthy dietary patterns, including the Dietary Approaches to Stop Hypertension (DASH) diet, the Alternate Healthy Eating Index (AHEI-2010), and plant-based and inflammatory indices. 

Across cohorts, higher adherence to all six dietary patterns was associated with a lower risk of SCD, an early marker of cognitive aging. The strongest association was observed for the DASH diet: participants in the highest adherence range had a 41% lower risk of SCD compared with those in the lowest range. Associations were most pronounced when healthier diets were followed during midadulthood, particularly between ages 45 and 54 years. 

In a subset of older participants who underwent telephone-based cognitive testing, higher DASH diet adherence was also linked to modestly better global cognitive performance, as well as improvements in verbal fluency and working memory. While effect sizes were small, the authors note that they were comparable to differences typically seen with several years of cognitive aging. 

Analysis of individual food groups highlighted higher intake of vegetables and fish as being associated with better cognitive outcomes, whereas greater consumption of red and processed meats, fried potatoes, and sugar-sweetened beverages was associated with poorer cognitive performance. Unexpectedly, higher intake of nuts and seeds was associated with increased SCD risk, a finding the authors caution should be interpreted carefully given potential residual confounding. 

The authors emphasize that SCD captures perceived cognitive change rather than diagnosed impairment, but note that it has been shown to correlate strongly with objective cognitive measures and may represent an early window for prevention. Long latency analyses – assessing diet up to 26 years before SCD assessment – helped reduce concerns about reverse causation. 

Although the cohorts were predominantly white and composed of health professionals, the authors argue that this relative homogeneity may strengthen internal validity by limiting socioeconomic confounding. They caution that the observational design precludes causal inference and that randomized dietary intervention trials will be needed to confirm cognitive benefits. 

Source: JAMA Neurology