Cognitive Impairment in Australia and Latin American and Caribbean Countries: Life Expectancy, Diet and Physical Activity, and the Potential for Prevention

Abstract

The prevalence of moderate or severe cognitive impairment (CIm) rises steeply with age. It is well documented that our populations (both in developed and low- and middle-income countries) are ageing and that lifestyle factors may hold the key to preserving mental and functional status. This thesis adopts a cross-national approach between Australia and seven Latin American and Caribbean (LAC) countries and focuses on two modifiable lifestyle factors – diet and physical activity.

Two data sets are utilised in this thesis – the Australia Diabetes, Obesity and Lifestyle Study (AusDiab)and the Survey on Health, Well-Being, and Ageing in LAC (SABE). AusDiab represents the largest Australian longitudinal population-based study examining the natural history of diabetes, pre-diabetes, heart disease and kidney disease. Three Waves of data have been collected thus far with cognitive function examined at the most recent Wave only. The SABE is a 7-country survey conducted in LAC in 2000. The SABE represents the only comprehensive health-related data set for persons over the age of 60 in the region that takes into account cognitive status.

Using the Sullivan Method for calculating health expectancies, it was found that in Australia females live longer than males and males spend more time with CIm. In LAC, substantial differences in the absolute years lived and the proportion of remaining life spent free of CIm were observed. Total life expectancy (TLE) and cognitive impairment-free life expectancy (CIFLE) at age 60 years were highest in Brazil and Mexico and lowest in Uruguay and Cuba.

Both a priori and a posteriori methods were used to examine the relationship between diet, physical activity and cognition. In the first instance, greater adherence to the Mediterranean Diet (MeDi), engagement in physical activity, and television viewing time were not predictive of CIm among older adults in the Australian sample.

In the second instance using principal component analysis (PCA), complex patterns of associations between dietary factors and cognition were evident in the Australian sample. The most consistent finding was the protective effects of high vegetable and plant-based food item consumption and negative effects of ‘Western’ patterns on cognition. Among LAC countries, weekly consumption of milk and cheese, eggs, peas and beans, meat, fish or poultry, and fruits or vegetables were significantly associated with CIm. Regular exercise or participation in vigorous physical activity such as playing a sport, dancing or heavy housework three or more times a week was significantly associated with CIm in Chile, Mexico and Uruguay.

Using a modified population attributable risk formula which accounts for non-independence of risk factors, an estimated 39.0% of dementia cases in Australia may be attributable to five modifiable risk factor (excess alcohol consumption, midlife obesity, physical inactivity, smoking and low educational attainment). In the LAC region, diabetes mellitus, physical inactivity and smoking were estimated to be attributable to 21.9% of cases in Barbados, 14.7% in Mexico, and 26.2% in Cuba. If each risk factor were to be reduced by 10% and 20% every 10 years to 2050, dementia prevalence could be reduced by up to 24.7% in Australia and up to 16.3% in LAC countries.

This thesis highlights the need for greater investment in research, interventions and policies targeting modifiable lifestyle factors to reduce CIm risk factor prevalence at the population level. In addition, the need for more research in the LAC region (particularly longitudinal studies) is highlighted. Overall, the findings suggest that there is a need for further studies to better understand more nuanced topics, such as the effect of composite dietary patterns on cognitive decline and the nutrition-cognition link in different populations, as there is a general paucity of data sources designed to address these issues.