The Role of Diet in Subjective Cognitive Complaints and Alzheimer’s Disease

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Dementia, a debilitating condition characterized by a decline in memory and other cognitive functions, poses a significant public health challenge.

Alzheimer’s disease (AD) stands as the most prevalent form of dementia, affecting millions of people worldwide. The year 2022 witnessed 6.5 million Americans aged 65 and older diagnosed with AD, and this number is expected to more than double by 2060. Interestingly, nearly two-thirds of AD cases are reported in women.

In recent years, researchers have increasingly focused on subjective cognitive complaints (SCCs), which refer to self-reported impairments in daily cognitive performance, notably memory loss. Although SCCs have been linked to non-neurodegenerative factors such as depression and anxiety, they are now considered indicative of mild cognitive impairment (MCI) and potential predictors for neurocognitive disorders, including AD. Examining risk factors for SCCs may offer insight into the pathology of AD and dementia, leading to improved risk assessment and early prevention.

Mid-Life Health Conditions and Cognitive Impairment

Recent data have revealed an intriguing connection between health conditions experienced during mid-life (typically between the ages of 40 and 60) and the risk of late-life cognitive impairment. This revelation suggests that the biological processes leading to neurodegeneration unfold over decades, rather than just in later life.

Consequently, epidemiological studies are increasingly emphasizing the assessment of risk factors in mid-life. Among the key factors associated with cognitive health in mid-life are obesity, hypertension, and diabetes. These conditions, when present during middle age, appear to contribute to the risk of late-life cognitive impairment. This insight underscores the importance of early intervention and prevention strategies.

Diet as a Modifiable Risk Factor

Diet is a modifiable risk factor that plays a significant role in maintaining brain health. Recent research has delved into the impact of specific food groups and nutrients on SCCs, offering promising findings. These studies have highlighted the potential benefits of dietary components such as carotenoids, flavonoids, protein intake, energy, and fat intake, as well as the consumption of fruits and vegetables, in preserving cognitive function. In addition to individual nutrients, dietary patterns have garnered attention.

The Mediterranean diet, characterized by its emphasis on whole grains, fish, olive oil, and abundant fruits and vegetables, has emerged as a dietary pattern associated with better late-life subjective cognitive function, particularly in men.

This suggests that adopting a Mediterranean diet in mid-life could contribute to cognitive resilience in later years. However, the role of other dietary patterns, such as the Dietary Approaches to Stop Hypertension (DASH) diet, remains less well-established.

DASH Diet and Cognitive Health

The DASH diet is designed to prevent and manage high blood pressure, a critical risk factor for cognitive decline and AD. This dietary plan focuses on increased consumption of plant-based foods rich in potassium, calcium, and magnesium while restricting saturated fat, cholesterol, sodium, and sugar intake. Research has shown its efficacy in reducing hypertension, but its potential impact on cognitive function remains an area of interest.

The Nurses’ Health Study (NHS) conducted a prospective study to investigate the effects of the DASH diet in mid-life on late-life SCCs. The findings of this study support the notion that adhering to the DASH dietary pattern over the long term has a beneficial role in subjective cognitive function, particularly among women. These results indicate that diet can be a critical factor in maintaining cognitive health as individuals age.

Future Research Directions

To gain a comprehensive understanding of the relationship between diet and cognitive health, further research is needed. Studies should aim to confirm the findings related to the DASH diet’s impact on cognitive function and explore potential effect modifiers. Demographic and lifestyle factors, as well as comorbidities such as cancer and depression, should be considered, as they have known associations with cognitive function, AD, dementia, and dietary patterns. Understanding the complex interplay between diet and cognitive health will be essential for improving prevention and intervention strategies in the face of the growing challenge of dementia and Alzheimer’s disease.

Discussion

In the study of women from the New York University Women’s Health Study (NYUWHS), the researchers observed a significant association between greater adherence to the Dietary Approaches to Stop Hypertension (DASH) diet in mid-life and a reduced risk of experiencing two or more subjective cognitive complaints (SCCs) in later life. After accounting for potential confounding variables, our findings suggested that adherence to the DASH diet was associated with approximately a 20% lower odds of having multiple SCCs in later life.

Notably, this inverse association was more pronounced among Black women and those without a history of cancer. These associations remained robust when different methods were employed to handle missing data and when adjusting for potential selection bias.

The relationship between adherence to the DASH diet and cognitive health has been the subject of previous research. While our study focused on SCCs, other longitudinal studies have examined the association between DASH diet adherence and the risk of objective cognitive decline or Alzheimer’s disease (AD).

The results from previous studies have been inconsistent. Some studies found a lower risk of mild cognitive impairment (MCI) among individuals with high DASH diet adherence, while others did not find significant associations with cognitive decline. Importantly, most of these previous studies focused on older populations, and the extent to which mid-life factors can impact cognitive function in later life remains a subject of debate.

The study adds to the existing literature by specifically exploring the association between mid-life adherence to the DASH diet and SCCs in later life, offering insights into cognitive health. The NYUWHS population is more diverse compared to other studies, with a substantial proportion of non-White participants.

The study findings indicated a stronger association between DASH scores and SCCs among Black women, emphasizing the need for further research on how different ethnic groups may be susceptible to dietary patterns’ effects on cognitive health.

Additionally, our study population was younger at the time of dietary assessment (mean age of 46 years), with an extensive follow-up period exceeding 30 years. This suggests that mid-life may provide a crucial window of opportunity for lifestyle modifications that can positively impact cognitive function in later life.

Furthermore, our findings indicated a stronger inverse association of DASH scores with the odds of having multiple SCCs among those without a history of cancer, suggesting that cancer or its treatments might mask the potential protective effect of the DASH diet on SCCs. Future research that includes detailed treatment and post-cancer dietary information is warranted to explore the relationship between diet and cognitive function in cancer survivors versus cancer-free individuals.

Several potential mechanisms could explain how the DASH diet impacts cognitive function. The diet’s emphasis on vegetables, fruits, legumes, and nuts provides essential nutrients and bioactive substances with anti-inflammatory and antioxidant properties, which may reduce oxidative stress, promote neurogenesis, and enhance neuronal connectivity.

The DASH diet’s potential to reduce hypertension, a known risk factor for cognitive decline, also plays a role. Moreover, by limiting the intake of red and processed meats and sweets, the diet may mitigate the adverse effects of high fat and sugar intake on brain inflammation and the production of amyloid beta protein. Perturbations in the gut microbiome, influenced by diet, may constitute another pathway for the diet’s impact on cognitive function.

Our findings align with previous research observations that higher intake of fruits, vegetables, nuts, and legumes, as well as lower intake of sweets, is associated with better subjective cognitive function. The observed higher odds of having multiple SCCs among women with high sweets intake is consistent with findings that lower consumption of sweets is linked to better verbal memory in later life.

Strengths of our study include the large sample size, diverse study population, prospective design, inclusion of middle-aged women, and long-term follow-up with dietary exposure measured over 30 years prior to SCC assessment. Despite these strengths, several limitations should be acknowledged. Dietary intake was self-reported, and we only assessed dietary intake at baseline.

Additionally, the time between the two SCC assessments was relatively short, limiting the assessment of longitudinal changes in SCCs. Selection bias due to non-response or loss to follow-up may have affected the results. Unmeasured confounders, including other lifestyle factors and behaviors, could influence the observed associations. We also did not account for family history of dementia, and we did not evaluate the presence of MCI or dementia at the time of SCC assessment.

In conclusion, our study provides compelling evidence of the potential impact of the DASH diet on cognitive health, particularly in mid-life. These findings underscore the importance of dietary patterns in shaping cognitive function in later life. Further research is needed to elucidate the interplay between diet, personality traits, and cognitive impairment, as well as to investigate the effects of dietary interventions on cognitive health in diverse populations. As the understanding of lifestyle factors that influence cognitive health continues to evolve, early dietary modifications may represent a crucial opportunity for enhancing later life cognitive function and mitigating the burden of cognitive impairment and dementia.


reference link :https://alz-journals.onlinelibrary.wiley.com/doi/10.1002/alz.13468

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