Age-associated cognitive decline, or normal cognitive ageing, is a significant aspect of human life, with individual differences in the extent of decline. The factors contributing to these differences are not fully understood, but research across biomedical and psychosocial sciences is advancing. Normal cognitive ageing involves some mental abilities remaining stable into old age, while others, such as processing speed, reasoning, memory, and executive functions, decline. These declines are partly due to a general cognitive factor and are influenced by genetics, health, inflammation, neurobiology, diet, and lifestyle. Many effect sizes are small and not consistently replicated, with potential for reverse causation. Emerging research focuses on genome-wide scans to identify genetic contributions, vascular factors, diet, biomarkers like inflammation, and lifestyle factors such as exercise. Advances in brain imaging allow better in vivo studies of cognitive changes. Factors affecting general bodily ageing also influence cognitive functions in old age. Diseases like Alzheimer's are considered extreme ends of the cognitive decline spectrum. Dementia and mild cognitive impairment are often distinguished by diagnostic criteria, but the distinction is not always clear. Cognitive decline is influenced by prior intelligence, health, and lifestyle factors. Studies on non-pathological cognitive ageing must consider these complexities. Genetic studies show that general cognitive ability has a heritability of around 50%, with genetic influences on both intelligence and cognitive decline. Candidate genes like APOE are associated with cognitive decline, but few associations are replicable. Genome-wide association studies are more promising for identifying genetic contributions. Cardiovascular disease is linked to cognitive decline, with stroke and peripheral arterial disease affecting cognitive function. Inflammation is also associated with cognitive decline, though the relationship is less clear. Inflammatory biomarkers like CRP and fibrinogen show some associations with cognitive ability, but reverse causation may explain these. Neurobiological changes, such as brain atrophy and white matter integrity loss, contribute to cognitive decline. These changes are influenced by factors like hypertension, oxidative stress, and inflammation. Cognitive reserve, defined by early cognitive ability, education, and occupation, may buffer against cognitive decline. Diet and lifestyle factors, including B-vitamins, antioxidants, omega-3 fatty acids, physical activity, and mental stimulation, are important for cognitive health. A Mediterranean diet is recommended for cognitive benefits. However, cognitive intervention trials have not shown robust results, and more research is needed. In conclusion, understanding and mitigating age-associated cognitive decline requires a multifaceted approach, considering genetic, biological, lifestyle, and environmental factors. Future research should focus on longitudinal studies, genetic factors, and lifestyle interventions to improve cognitive health in older adults.Age-associated cognitive decline, or normal cognitive ageing, is a significant aspect of human life, with individual differences in the extent of decline. The factors contributing to these differences are not fully understood, but research across biomedical and psychosocial sciences is advancing. Normal cognitive ageing involves some mental abilities remaining stable into old age, while others, such as processing speed, reasoning, memory, and executive functions, decline. These declines are partly due to a general cognitive factor and are influenced by genetics, health, inflammation, neurobiology, diet, and lifestyle. Many effect sizes are small and not consistently replicated, with potential for reverse causation. Emerging research focuses on genome-wide scans to identify genetic contributions, vascular factors, diet, biomarkers like inflammation, and lifestyle factors such as exercise. Advances in brain imaging allow better in vivo studies of cognitive changes. Factors affecting general bodily ageing also influence cognitive functions in old age. Diseases like Alzheimer's are considered extreme ends of the cognitive decline spectrum. Dementia and mild cognitive impairment are often distinguished by diagnostic criteria, but the distinction is not always clear. Cognitive decline is influenced by prior intelligence, health, and lifestyle factors. Studies on non-pathological cognitive ageing must consider these complexities. Genetic studies show that general cognitive ability has a heritability of around 50%, with genetic influences on both intelligence and cognitive decline. Candidate genes like APOE are associated with cognitive decline, but few associations are replicable. Genome-wide association studies are more promising for identifying genetic contributions. Cardiovascular disease is linked to cognitive decline, with stroke and peripheral arterial disease affecting cognitive function. Inflammation is also associated with cognitive decline, though the relationship is less clear. Inflammatory biomarkers like CRP and fibrinogen show some associations with cognitive ability, but reverse causation may explain these. Neurobiological changes, such as brain atrophy and white matter integrity loss, contribute to cognitive decline. These changes are influenced by factors like hypertension, oxidative stress, and inflammation. Cognitive reserve, defined by early cognitive ability, education, and occupation, may buffer against cognitive decline. Diet and lifestyle factors, including B-vitamins, antioxidants, omega-3 fatty acids, physical activity, and mental stimulation, are important for cognitive health. A Mediterranean diet is recommended for cognitive benefits. However, cognitive intervention trials have not shown robust results, and more research is needed. In conclusion, understanding and mitigating age-associated cognitive decline requires a multifaceted approach, considering genetic, biological, lifestyle, and environmental factors. Future research should focus on longitudinal studies, genetic factors, and lifestyle interventions to improve cognitive health in older adults.