Clinical studies show a clear correlation between Alzheimer’s Disease and low selenium status. Lower selenium status is associated with worse cognitive decline [Aaseth 2016].
In many regions of Europe and the Middle East, there is poor selenium content in the soil and, accordingly, lower intake of selenium from food sources [Stoffaneller & Morse 2015; Winther 2020].
Adequate levels of selenium are essential for brain function; in fact, the brain is one of the organs that is supplied with selenium at the expense of other organs and tissues in times of low selenium intake. Selenoprotein P plays a special role in delivering selenium to the brain and the neurons. Some of the glutathione peroxidase and thioredoxin reductase selenoenzymes are important intracellular antioxidants in neurons and glia cells of the central nervous system.
The daily intake of selenium from food in many European countries iswell below the amount needed for optimal function of important selenoproteins. The needed intake of selenium from food is estimated to be at least 105 mcg per day [Winther 2020, fig. 2].
Brain cells are especially vulnerable to oxidative stress, which could be a factor in the pathology of neurodegenerative disorders. The danger of oxidative damage caused by free radicals (oxygen reactive species) is great because 1) the neurons use large quantities of oxygen, 2) the brain has high iron content, 3) neuronal mitochondria produce large quantities of hydrogen peroxide, and 4) neuronal membranes are full of polyunsaturated fatty acids, which are susceptible to oxidative stress [Shichiri, 2014]. Adequate supply of selenium and synthesis of antioxidant selenoproteins are necessary to counteract the harmful effects of oxidative stress.A review of the research literature on selenium and selenoprotein function in brain disorders reveals that selenium deficiency is associated with impaired cognitive function and impaired motor function [Pillai].
It is interesting to note that selenium concentrations are preferentially maintained in the brain even when the selenium concentrations in the blood circulation, in the liver, and in the skeletal tissues are depleted [Pillai].
Selenium supplementation may help to reduce the progression of the pathology of neurodegenerative diseases: Alzheimer’s, Huntington’s, and Parkinson’s [Pillai].
Selenium and Selenoproteins
What do we know about the trace element selenium and its incorporation into selenoproteins?read more
Brain tissue produces many free radicals (reactive oxygen species). The oxidative stress caused by an imbalance between potentially harmful free radicals and antioxidants to neutralize them is associated with ageing and with the onset of Alzheimer’s disease. Reduced levels of the selenium-dependent antioxidant enzyme glutathione peroxidase correlate strongly with cognitive decline and the risk of Alzheimer’s disease.
Blood selenium concentrations are significantly lower in patients with Alzheimer’s disease compared to healthy controls. This reduction in selenium concentration is directly associated with the observed reduced levels of the important antioxidant selenoprotein, glutathione peroxidase, in Alzheimer’s disease patients.
These are the conclusions of the authors of a 2017 meta-analysis of 12 case-control studies of selenium concentrations in Alzheimer’s disease patients and healthy controls. The 12 case-control studies comprised 594 Alzheimer’s disease patients and 472 healthy controls [Reddy].
Significantly decreased selenium levels were seen in the blood circulation of Alzheimer’s disease patients as compared to healthy controls.
Decreased selenium levels were also seen in the red blood cells and cerebrospinal fluid of Alzheimer’s patients as compared to healthy controls. However, the difference in selenium concentrations did not reach the level of statistical significance.
Age matching between the Alzheimer’s disease patients and healthy controls showed decreased selenium levels regardless of the age of the patients. This is interesting because advanced age is considered a risk factor for Alzheimer’s disease.
Controlling for socio-economic, geographical, and environmental differences also showed the decreased selenium levels in Alzheimer’s disease patients compared to the healthy controls.
A direct association was seen between decreased selenium levels and glutathione peroxidase levels in Alzheimer’s disease patients.
What is glutathione peroxidase, and why is it important?
The glutathione peroxidases (abbreviated GPx) are a family of antioxidant enzymes (selenoproteins) that reduce and thus neutralize potentially harmful radicals like hydrogen peroxide and lipid hydroperoxides. In so doing, the GPx enzymes lessen the extent of oxidative stress damage.read more
Pictured: A healthy brain and a brain suffering from severe Alzheimer’s disease. The question: what is the role of the selenium-dependent antioxidant seleno-enzymes in the prevention of Alzheimer’s disease? Professors Aaseth and Alehagen offer an explanation.
There is no reliable method to prevent the development and progression of Alzheimer’s. There is no known cure for Alzheimer’s. The approaches that we have tried over the past 20-25 years have not prevented or inhibited the decline in cognitive function that is associated with Alzheimer’s.
Now, Professor Jan Aaseth (Norway) and Professor Urban Alehagen (Sweden) propose selenium supplementation as a prophylactic measure to inhibit the decline of cognitive function, especially in the selenium-poor regions of the world. They hypothesize that the optimal functioning of the selenoproteins SEPP, GPx, and TrxR is necessary to protect against the cognitive decline associated with Alzheimer’s disease.read more
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