Lifelong diet quality predicts cognitive ability and dementia risk in older age

A new longitudinal analysis suggests that the quality of a person’s diet throughout their entire lifespan shares a significant link with their cognitive abilities as they age. The research indicates that individuals who maintain lower quality dietary habits from childhood into adulthood may face a higher likelihood of cognitive struggles and dementia in later years. These findings were published in Current Developments in Nutrition.

Scientists have established that diet is a modifiable risk factor for dementia and cognitive decline. However, the majority of existing research focuses on dietary habits in older adults, often after cognitive issues have already begun to surface. This leaves a gap in understanding how nutrition across the entire lifespan might influence brain health.

Symptoms of conditions like Alzheimer’s disease can begin to develop in the brain decades before memory loss becomes apparent. Consequently, researchers suspect that dietary improvements made earlier in life might be more effective at preventing neurodegeneration than changes made in old age.

A research team led by Kelly C. Cara of the Friedman School of Nutrition Science and Policy at Tufts University sought to map the long-term relationship between what people eat and how well their brains function over time. They aimed to determine if dietary patterns established in childhood and mid-life predict cognitive outcomes decades later.

The researchers analyzed data from the 1946 British Birth Cohort. This is a long-running project following individuals born in England, Scotland, and Wales during a single week in March 1946. The study provides a rare opportunity to observe health trends over nearly seventy years.

The final analytical sample included 3,059 participants. The team assessed dietary intake at five specific ages: 4, 36, 43, 53, and between 60 and 64 years old. At age four, dietary data was collected via recalls provided by parents or caregivers. In adulthood, participants completed food diaries recording their intake over several days.

To evaluate diet quality, the researchers utilized the Healthy Eating Index-2020. This scoring system measures how closely a diet aligns with the Dietary Guidelines for Americans. It assigns higher scores for the consumption of adequate components like fruits, vegetables, whole grains, dairy, and proteins.

The index simultaneously lowers scores for high intakes of moderation components. These include refined grains, sodium, added sugars, and saturated fats. Total scores on this index range from 0 to 100, with higher numbers indicating a healthier diet.

Cognitive ability was measured at seven time points: ages 8, 11, 15, 43, 53, 60-64, and 68-69. The researchers used a variety of tests appropriate for each developmental stage. In childhood, assessments focused on reading comprehension, vocabulary, and arithmetic.

In adulthood, the testing focus shifted to functional performance. These measures included word list recalls to test memory, visual search speed tests, and reaction time assessments. To allow for comparison across these different tests and ages, the researchers converted the results into global cognitive ability percentile ranks.

Using a statistical method called group-based trajectory modeling, the researchers identified distinctive trends in the data. This technique groups individuals who follow similar patterns of change over time. The analysis revealed three distinct trajectories for diet quality.

The first group, comprising about 31 percent of the sample, followed a lower diet quality trajectory. The second group, representing about 50 percent, followed a moderate quality trajectory. The third group, making up roughly 19 percent, maintained a higher quality diet trajectory throughout life.

Similarly, the researchers identified four distinct trajectories for cognitive ability. These ranged from consistently lower performance to consistently higher performance relative to peers. The largest portion of the sample fell into the highest cognitive trajectory.

Cara and her colleagues found a clear association between these dietary and cognitive paths. Participants who followed the lowest cognitive ability trajectory were most likely to belong to the lower or moderate diet quality groups. Specifically, 58 percent of the lowest cognitive group came from the lower diet trajectory.

In contrast, those in the highest cognitive ability trajectory were primarily composed of individuals with moderate or higher diet quality. Only a small fraction of the high cognitive performers belonged to the low diet quality group. This suggests that maintaining a high-quality diet is common among those who maintain high cognitive function.

The researchers examined specific dietary components that differed between the groups. Throughout adulthood, participants in the higher cognitive trajectory tended to eat more whole fruits and whole grains. They also consumed fewer refined grains compared to their peers in lower cognitive groups.

At ages 53 and 60-64, the high cognitive group also showed lower sodium intake. They consumed more vegetables, specifically greens and beans. These specific food choices appear to contribute to the overall difference in diet quality scores.

The study also investigated the risk of dementia in later life. At age 68-69, participants completed the Addenbrooke’s Cognitive Examination-III. This is a comprehensive test used in clinical settings to screen for cognitive impairment.

The researchers found that 9.8 percent of participants in the lower diet quality group showed indications of likely dementia, compared to the 6 percent observed in the moderate diet quality group. It was also notably higher than the 2.4 percent seen in the higher diet quality group.

The analysis highlighted early life factors that predicted these outcomes. Higher childhood social class was a strong predictor of being in a higher cognitive trajectory. It also predicted membership in a higher diet quality trajectory.

Engagement in leisure activities at age 11 also played a role. Children who participated in more intellectual and social activities were more likely to follow higher cognitive trajectories later in life. Being female was associated with a greater chance of belonging to the moderate or higher diet quality groups.

The researchers posit several biological mechanisms that might explain these findings. Nutrients found in high-quality diets, such as fatty acids, B vitamins, and antioxidants, are essential for brain health. These compounds support the maintenance of neurons and protect against neurodegeneration.

While the findings provide evidence for a link between life-course diet and cognition, the study has limitations. The research is observational, meaning it cannot definitively prove that a poor diet causes lower cognitive ability. It is possible that individuals with higher cognitive abilities are simply better equipped to make healthier food choices.

Another limitation involves the study population. The sample consisted entirely of individuals born in Britain in 1946. This group was not racially or ethnically diverse, limiting the generalizability of the results to other populations.

Additionally, dietary data was self-reported. Self-reports can be subject to memory errors or social desirability bias. The study also experienced attrition over the decades, as some participants passed away or withdrew from the research.

The researchers note that diet quality at age four was generally similar across all groups. Differences only began to emerge and widen in adulthood. This may be due to the lingering effects of post-war food rationing in Britain, which standardized diets during that era.

Despite these limitations, the study offers evidence that long-term dietary habits matter. It suggests that consistent alignment with dietary guidelines from childhood through adulthood is associated with better cognitive outcomes. This supports the idea that nutritional interventions could be a viable strategy for preserving brain health.

Future research is needed to confirm these trends in more diverse populations. Studies that track diet and cognition starting from very early childhood in modern contexts would be particularly beneficial. Understanding these life-course relationships is essential for developing public health strategies to combat the rising rates of dementia.

The study, “Associations between diet quality and global cognitive ability across the life course: Longitudinal analysis of the 1946 British Birth Cohort,” was authored by Kelly C. Cara, Tammy M. Scott, Mei Chung, and Paul F. Jacques.