Impact of nutritional status and diet on cognitive decline and survival

Abstract

This doctoral thesis investigated the complex relationship between nutritional status and survival and the impact of dietary intake on cognitive decline in older Swedish adults. The data used in the four studies (I‒IV) in this thesis were derived from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). SNAC-K is a population-based prospective cohort study of 3,363 people aged ≥60 years in Stockholm, Sweden. The major findings are summarized below.

Study I. Nutritional status (by MNA-SF) and its relationship to survival were investigated using 11 years follow-up data. The multi-adjusted hazard ratios (95% confidence interval) of mortality was 2.40 (1.56−3.67) for those with malnutrition, and 1.49 (1.29−1.71) for those at risk for malnutrition. The median age at death was about 3 years younger in people with malnutrition and 1.5 years younger in people at risk for malnutrition than in those with normal nutritional status. Survival was shortened by an additional year in those who had suboptimal haemoglobin and/or albumin levels in addition to malnutrition or risk for malnutrition.

Study II. The hypothesis that the prudent diet may attenuate the adverse effects of the Western diet on cognitive decline was verified using 6-year follow-up data. The highest adherence to the prudent pattern was related to less MMSE decline (β: 0.106, P=0.011) than the lowest adherence, whereas the highest adherence to the Western pattern was associated with more MMSE decline (β: -0.156, P<0.001) than the lowest adherence. The decline associated with the Western diet was attenuated when accompanied by high adherence to the prudent pattern.

Study III. Six-year follow-up data were used to identify a dietary pattern index that predicts preserved cognitive function in a Nordic country, the Nordic Prudent Dietary Pattern (NPDP). Moderate (β: 0.139, 95% CI: 0.077−0.201) and high adherence (β: 0.238, 95% CI: 0.175−0.300) to the NPDP was associated with less cognitive decline than moderate or high adherence to four other dietary indices. High adherence to the NPDP was associated with the lowest risk of MMSE decline to ≤24 and had the greatest ability to predict such decline.

Study IV. The joint effect of a healthy diet and an active lifestyle on cognitive decline was examined using 6-year follow-up data. Moderate to high adherence to the NPDP was associated with less cognitive decline (β: 0.19, 95% CI: 0.14−0.24) than low adherence. This association became stronger when combined with moderate to intense physical (β: 0.34, 95% CI: 0.23−0.45), mental (β: 0.29, 95% CI: 0.21−0.37), or social (β: 0.27, 95% CI: 0.19−0.34) activity. An active lifestyle more than doubled the protective effect of the NPDP against cognitive decline, and further lowered the risk of MMSE decline to ≤24 by 30%.

Conclusions. Poor nutritional status (by MNA-SF) is presented in about a quarter of the older adults’ population and associated with shorter survival, especially in those with suboptimal levels of biomarkers reflecting disease severity and inflammation (i.e. haemoglobin and albumin). Although high adherence to the Western diet is associated with cognitive decline, high adherence to the prudent diet may diminish these effects. Moderate to high adherence to the NPDP may predict better preserved cognitive function in Nordic countries than adherence to other healthy dietary indices. These findings lend further weight to the growing evidence of a link between a healthy diet and healthy brain aging. Finally, an active lifestyle may reinforce the protective effect of a healthy diet (i.e. NPDP) against cognitive decline.