Nutrition interventions for Alzheimer’s
The 2023 Alzheimer’s Awareness key theme was ‘never too early, never too late’, with a key focus on modifiable risk factors and risk reduction. Research in the nascent field of nutritional psychiatry continues to emerge, and the evidence base surrounding nutrition interventions, paired with lifestyle modifications, has yielded some interesting results with regards to Alzheimer’s prevention.
Diet and Lifestyle
Recent research by Jia et al. (2023) identified some modifiable diet and lifestyle risk factors for dementia. Their study followed 29, 072 participants for a period of ten years in China, to explore dietary and lifestyle factors which may prevent memory decline in older adults. Over a fifth of participants also had the APOE4 allele, a key genetic risk factor for development of Alzheimer’s disease. The study measured the following factors:
- a healthy diet (adherence to the recommended intake of at least 7 of 12 eligible food items, including – fruits, vegetables, fish, meat, dairy products, salt, oil, eggs, cereals, legumes, nuts, and tea)
- regular physical exercise (≥ 150 min of moderate intensity or ≥75 min of vigorous intensity, per week)
- active social contact (≥ twice per week)
- active cognitive activity (≥ twice per week), never or previously smoked, and never drinking alcohol.
Participants were categorised into the favourable group if they had four to six healthy lifestyle factors, into the average group for two to three factors, and into the unfavourable group for zero to one factor. Memory function was assessed using the World Health Organization/University of California-Los Angeles Auditory Verbal Learning Test, and global cognition was assessed via the Mini-Mental State Examination (MMSE). Results indicated that a healthy lifestyle was associated with a slower rate of memory decline, even in individuals with the APOE4 allele. Of all the factors assessed, healthy diet was indicated to be the most significantly protective factor (P<0.001), followed by, in order of statistical significance, active cognitive activity (P<0.001), regular physical exercise (P<0.001), active social contact (P<0.001), never or former smoker ( P=0.026), and never drinking alcohol (P=0.048).
Keeping Key Biomarkers within Healthy Ranges
Adopting the aforementioned nutrition and lifestyle interventions may be beneficial for keeping some key biomarkers associated with Alzheimer’s disease within healthy ranges. Below some of these markers are briefly delineated in terms of findings from the literature.
Lower HDL and higher triglyceride (a type of fat found in the blood) levels measured in blood in early adulthood, and high blood sugar levels in middle adulthood, have been indicated to contribute to future risk of developing Alzheimer’s. High LDL cholesterol has been indicated to increase accumulation of beta amyloid plaques in the brain, a key feature and driver of Alzheimer’s disease (Ferringa & Kant, 2021). However, a recent study observed that a 15 mg/dL increase in high density lipoprotein (HDL) cholesterol was associated with decreased AD risk during early (15.4%, P = 0.041) and middle (17.9%, P = 0.014) adulthood (Zhang et al., 2023).
Homocysteine has been established as an independent risk factor for Alzheimer’s disease (Sheshadri et al., 2002). Homocysteine is a sulphur containing intermediate metabolite produced during the metabolism of methionine (Met) to cysteine (Cys) (Kumar et al., 2017). Both high and low homocysteine are associated with increased Alzheimer’s risk. Elevated homocysteine increases levels of inflammation in the body, has a detrimental impact on the structural integrity of blood vessels, and also affects gene expression (Ganguly & Alam, 2015; Li et al., 2015). Bae et al. (2021) highlighted in their research how overuse of vitamin supplements could increase risk, and be explanatory, of incidence of low homocysteine, whilst acknowledging that high homocysteine should be addressed with appropriate health interventions.
Patients with type II diabetes who have poorly controlled blood glucose levels are at significantly increased risk of subsequent development of Alzheimer’s disease (Ngyuyen et al., 2020). High blood sugar causes inflammation. This may damage brain cells and cause Alzheimer’s disease to develop (Alzheimer’s Association, 2023). A prospective cohort study by Zhang et al. (2023) including 4,932 participants demonstrated that a 15 mg/dL increase in glucose, measured during middle adulthood, was associated with 14.5% increased Alzheimer’s disease risk (P = 0.00029) (Zhang et al., 2023).
Research has indicated that higher blood pressure is associated with poorer memory scores. Having elevated blood pressure has been indicated to be predictive of worse cognitive ability for those who have the APOE4 allele, even in otherwise healthy midlife adults (Oberlin et al., 2015). The link between elevated blood pressure and Alzheimer’s disease is well established, and addressing hypertension early is key for reducing risk of developing the disease.
Lempiere et al. (2022) found in their study that hypothyroidism was associated with an 81% increase in dementia risk. Although further research is required to explore the exact mechanisms, it appears that this link is mediated via the HPT (hypothalamic–pituitary–thyroid) axis, which is a bidirectional communication pathway between the brain and thyroid. Performing thyroid blood tests at regular intervals during midlife and older adulthood could be a supportive measure for identifying at risk individuals for Alzheimer’s disease.
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