The prevalence of neurodegenerative diseases
Many studies carried out in recent years have ascertained that nutritional factors are linked with dementia, in particular with AD, both as risk or protective factors in the onset of the disease and as elements able to modify the course of the disease.
Vitamin B12, vitamin B6 and folate play an important role in DNA synthesis and their deficiency may lead to increased levels of HCY that are correlated with an increased risk for AD. This may be due to HCY-induced apoptosis of hippocampal neurons consequent to DNA damage. However the use of supplements, with folic acid, vitamin B12 and B6, did not show positive results for the prevention of AD.
The link between obesity and AD may be separately considered in two different periods of life: midlife and old age. For obesity in the elderly, the data are not definitive and different studies reached different conclusions. The available data are more conclusive considering the relation between obesity in middle age and future risk of dementia. The link between obesity and dementia may be explained by different pathogenetic mechanisms. Cardiovascular disease and diabetes, frequently associated with or caused by obesity, may be a reason for an increased risk of dementia with adiposity. Moreover, an inflammatory status is frequently present in patients with increased adiposity and may have a direct effect on neuronal degradation (cerebral atrophy, white matter hyperintensity). Adipocytokines may first affect the integrity of the blood brain barrier where the receptors for them are located, suggesting an influence and a role in the central nervous system. Adipose tissue-related compounds (steroid hormones, insulin, interleukins, neurotrophins, growth factors, adipocytokines, fatty acids) then cross the blood-brain barrier leading to a dysregulation in hippocampus, hypothalamus and, ultimately, to dementia symptoms and AD
Oxidative stress plays a role in neuronal loss associated with different neurological disorders (Parkinson’s disease, AD, amyotrophic lateral sclerosis) and the neurotoxicity caused by amyloid-ß-peptide in AD is a result of its associated free radicals. Many studies demonstrate the neuroprotective actions of vitamin C and E (radical scavenging activity, suppression of COX-2 activity) and some epidemiological studies show that high dietary intake of these vitamins lowers the risk of AD. However, current knowledge provides insufficient support for antioxidant supplementation as a means of delaying the aging process and for any major beneficial effect on cognitive functions
Different studies show a relationship between cognitive functions and the ω-3-PUFA. In particular, elderly people who frequently eat fish are at lower risk of developing dementia, including AD. The role of ω-3-PUFA as protective factors in the onset of AD may be explained by their ability to provide vascular protection, reduce inflammation in the brain and facilitate the regeneration of nerve cells. Once more, the results of supplementation with ω-3-PUFA are not consistent and, at the moment, there is no good evidence to support the use of dietary or supplemental ω-3-PUFA for the prevention of cognitive impairment or dementia.
Meditarranean diet and dementia
Diet may play an important role in the prevention or delay of the onset of dementia. However, the results of epidemiological data are conflicting: many nutritional factors may be involved in the pathogenesis of dementia as protective factors but in all cases, supplementation with these factors don’t give consistent results either for the prevention or the delay in onset of the disease. The effect is much stronger and consistent for foods rich in antioxidant or ω-3-PUFA than for single vitamin supplements.
This is probably due to the fact that foods contain compounds and phytochemicals whose intake enhances the action of the single nutrient factor with possible additive and interactive effects among nutritional components. Both prospective studies and reviews on this topic show that a healthy and socially integrated lifestyle involving regular exercise and a balanced and regular diet, rich in antioxidants (vitamin C, vitamin E, flavonoids) and unsaturated fatty acids, with at least five portions of fruits and vegetables per day and one portion of fish per week, as in Mediterranean diet, seems to be the key to the prevention of several age-related diseases including dementia.
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