A 25-year longitudinal study, the National Institute for Longevity Sciences – Longitudinal Study of Aging (NILS-LSA), reveals that specific dietary habits, lifestyle choices, and psychological factors significantly impact cognitive function and higher-level functional capacity in aging individuals. Notably, higher intake of certain fatty acids, soybeans, green tea, and dairy, coupled with dietary diversity, not smoking, moderate alcohol consumption, regular physical activity, adequate sleep, healthy BMI, maintaining a sense of purpose (Ikigai), regular health checkups, and post-retirement employment are associated with better brain health and reduced functional decline.
1. The NILS-LSA Cohort Study
- Duration and Scope: Initiated in 1997, the NILS-LSA is an ongoing longitudinal study with over 25 years of follow-up data.
- Participants: Includes individuals from middle age (starting at 40 years old) through older adulthood (up to 70+).
- Investigated Factors: The study examines a wide range of influences: Medical science Nutrition (including specific nutrients and dietary patterns) Genetics Psychology (e.g., depressive symptoms, Ikigai) Morphology Exercise physiology
- Outcomes Measured: Cognitive function (using MMSE, WAIS-R-SF) Higher-level functional capacity (using Tokyo Metropolitan Institute of Gerontology Index of Competence – TMIG-IC) Age-related conditions: Dementia, locomotive syndrome, sarcopenia, frailty, mental health issues, falls/fractures, malnutrition, and mortality.
2. Key Findings on Cognitive Function
Longitudinal analysis identified several dietary and lifestyle factors associated with cognitive function:
2.a. Protective Dietary Factors:
- Short-Chain Fatty Acids (SCFA) & Medium-Chain Fatty Acids (MCFA): Higher intake is associated with a lower probability of cognitive decline (MMSE score < 27).
- Soybeans: Higher intake (specifically >49.3g/day vs. <49.3g/day of soy protein isolate) is linked to reduced risk of cognitive decline (Odds Ratio [OR] 0.29).
- Green Tea: Consuming green tea 2-3 times per week or more is associated with a lower risk of cognitive decline compared to less than once per week (OR 0.71-0.72 for ≥2-3 times/week).
- Dairy Products: Higher intake of milk and dairy products (≥128 g/day) is associated with a reduced risk of cognitive decline (OR 0.80) compared to lower intake (<128 g/day).
- Dietary Diversity (QUANTIDD Score): A greater variety of foods consumed is protective. Individuals in the highest quartile of dietary diversity had a significantly lower risk of cognitive decline (OR 0.56, p-trend=0.001) compared to the lowest quartile.
- Specific Amino Acids: Adequate intake of certain amino acids appears protective. Low intake of Lysine, Phenylalanine, Tyrosine, Threonine, Tryptophan, Alanine, and Arginine was associated with higher odds ratios for cognitive decline, suggesting these amino acids are important for maintaining cognitive health.
2.b. Dietary Risk Factors:
- Cereals: Higher intake of cereals (>130 g/day) was associated with an increased risk of cognitive decline (OR 1.43) compared to lower intake.
2.c. Psychological and Lifestyle Factors:
- Depressive Symptoms: The presence of depressive symptoms (in individuals aged ≥65 years) accelerates cognitive decline over 12 years, as measured by both general knowledge tests (slope difference, p<0.05) and processing speed tests (slope difference, p<0.01).
- Employment After Retirement: Continued employment post-retirement is associated with better cognitive function (higher Digit Symbol Substitution Test scores, p<0.01) compared to being unemployed post-retirement.
3. Key Findings on Higher-Level Functional Capacity
Adherence to multiple healthy lifestyle practices significantly reduces the risk of decline in higher-level functional capacity.
3.a. Healthy Lifestyle Practices and Thresholds:
3.b. Impact of Combined Healthy Practices:
- Individuals adhering to 5-6 healthy practices had a 37% reduction in risk (OR 0.63) of higher-level functional capacity decline.
- Those adhering to 7-8 healthy practices experienced a 46% reduction in risk (OR 0.54) compared to individuals with 0-4 healthy practices.
4. Clinical Implications and Summary
- Early Intervention: The inclusion of middle-aged participants (from 40 years) highlights the importance of adopting healthy lifestyles early, potentially from elementary or junior high school age, for long-term brain health.
- Modifiable Factors: Many factors influencing cognitive and functional decline are modifiable through diet and lifestyle.
- Holistic Approach: Both physiological (diet, exercise, BMI) and psychological (mental health, Ikigai, personality, post-retirement engagement) aspects are crucial for cognitive outcomes.
- Dementia Prevention: Modifiable lifestyle factors and mental health interventions could be effective strategies for dementia prevention. Life transitions like retirement can accelerate cognitive decline if not managed with continued engagement.
TL;DR: A >25-year Japanese study (NILS-LSA) found that higher intake of SCFA/MCFA, soybeans, green tea, dairy, and diverse diets, along with non-smoking, moderate alcohol, high physical activity (≥32 METs-hrs/day), 6-8 hrs sleep, healthy BMI (21.5-<25), Ikigai, regular checkups, and post-retirement employment significantly reduce cognitive and functional decline. Conversely, high cereal intake and depressive symptoms accelerate cognitive decline.