A diet with an appropriate ratio of omega-3 and omega-6 fatty acids, rich in healthy oils and antioxidants, but low in cholesterol-containing foods, may be a beneficial component in the prevention of Alzheimer's disease, according to a new review.
The review, published in Molecular Nutrition & Food Research, reports on recent findings concerning the modulation of Alzheimer's disease (AD) development by dietary lipids in animals and humans, focusing on the destructive role of lipid oxidation products.
The authors of the review, led by Fiorella Biasi, from the University of Turin, Italy, conclude that the balance between omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) and cholesterol “surely plays a crucial role in AD's onset,” and offered support to the emerging idea that certain antioxidants should be included in nutritional strategies for the prevention and early treatment of AD.
However, Biasi and his colleagues also noted that such nutritional factors must be weighed with many other factors, including genetics, education and lifestyle considerations.
“Considerable experimental data suggest the importance, in the pathogenesis of AD, of persistent oxidative stress associated with the presence of oxidation end-products,” said Biasi and colleagues.
“However, it may be said that a dietary regimen low in ω-6 PUFA and cholesterol, together with the use of antioxidants, including polyphenols, is valuable within a general strategy of prevention of neurodegenerative diseases,” they added.
Alzheimer's disease (AD) is the most common form of dementia in the elderly – affecting between 20 and 30 million people worldwide, with nearly half of those affected above the over the age of 85 years.
The disease is characterized by memory dysfunction, loss of lexical access, spatial and temporal disorientation, and impaired judgment.
Whilst the cause of AD is still not fully understood, and there are currently no curative treatments yet available, the reviewers noted that “a growing body of literature points to an important role of nutrition in the development of AD.”
They said that changes in the metabolism of lipids, such as cholesterol and ω-6 polyunsaturated fatty acids (PUFAs), with the accumulation of their oxidized derivatives, have been suggested to contribute to the onset and progression of this disease.
“This would provide mechanistic support for the widely held opinion that appropriate dietary supplementation with ω-3 PUFAs and antioxidants, which counteract lipid oxidation products, is helpful in preventing or delaying the development of AD,” they noted.
Nutrition and Alzheimer’s
The authors comprehensively reviewed recent animal and human studies focused on the potential role of PUFAs and cholesterol-oxidized products in the molecular pathogenesis of AD – finding that there is strong evidence to suggest diet may influence both the development and the prevention of AD.
They noted that a suitably balanced intake of omega-3 and omega-6 PUFA “is essential for brain homeostasis, while a significantly reduced omega-3/omega-6 PUFA ratio appears to contribute to the onset of AD.”
“It is reported that the daily intake of omega-3 PUFAs among the world population is significantly lower than that recommended by the World Health Organization ... It cannot be excluded that the incidence and prevalence of AD are increased in populations with a dietary intake of EPA and DHA below the recommended doses,” said Biasi and colleagues.
“A dietary regimen including the intake of a recommended amount of ω-3 PUFA or, better, an appropriate omega-6/omega-3 PUFA ratio, could certainly help to prevent cognitive impairment and, in patients with early AD, would help to delay progression of the disease,” they added.
The review team noted that an altered cholesterol metabolism is most likely implicated not only in the pathogenesis of vascular dementia but also in the onset of AD and of the mixed degenerative and vascular types of dementia. They also offered further support for the emerging opinion that certain flavonoids should be included in nutritional strategies of prevention and early treatment of AD and other neurodegenerative diseases.
“Several epidemiological studies indicate that the consumption of flavonoids, such as quercetin and the catechins, is associated with a lower incidence of Parkinson's disease and of AD,” said Biasi and co-workers.
Source: Molecular Nutrition & Food Research
Volume 55, Issue Supplement 2, Pages S161–SS172, doi: 10.1002/mnfr.201100208
“Dietary lipids and their oxidized products in Alzheimer's disease”
Author: L. Corsinovi, F. Biasi, G. Poli, G. Leonarduzzi, G. Isaia