Beta-carotene May Help Protect Some Against Alzheimer’s
A recent study in the Journal of Gerontology took a look at the potential protective effect of beta-carotene in people with Alzheimer’s disease (AD). The researchers found that those individuals with a specific genotype known to be associated with greater risk of developing AD had a significantly reduced risk of cognitive decline if serum beta-carotene levels were kept high.
Earlier studies have identified that people who have blood lipoproteins of the apoE4 genetic type are at greater risk of developing early-onset AD. Lipoproteins are molecules that help transport fats and cholesterol through the blood. There are three types of these particular lipoproteins: apoE2, apoE3, and apoE4.
Each person has two copies of the gene that codes for this lipoprotein, one from the mother and one from the father. If both copies of the gene code for apoE4, then one is considered homozygous for that trait. If only one of the parents’ genes code for it, then one is considered heterozygous for that trait. Those at highest risk are individuals who are homozygous for apoE4.
More on the different gene types here:
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ApoE4 is associated with a higher risk of Alzheimer’s. About a quarter of the population inherits one copy of the ApoE4 gene, which increases their risk of developing Alzheimer’s disease by up to four times.
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Two per cent of the population get a ‘double dose’ of the ApoE4 gene, one from each parent. Their risk of developing Alzheimer’s disease is increased by about ten times.
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Sixty per cent of the population have a ‘double dose’ of the ApoE3 gene and are at ‘average risk’. About half of this group develop Alzheimer’s disease by their late 80s.
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ApoE2 is least associated with Alzheimer’s disease. One in six people carry it. People with one ApoE2 gene and one ApoE3 gene (11 per cent of the population) have a 50 per cent chance of getting Alzheimer’s disease when they reach their late 90s.
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One in 200 people inherit two copies of the ApoE2 gene and are at a lower risk of developing Alzheimer’s disease.
The researchers in the beta-carotene study found that in those individuals who were either hetero- or homozygous for apoE4, high serum levels of beta-carotene reduced the risk of cognitive decline by 89%. Little effect (11% risk reduction) was observed in people with no apoE4.
The researchers hypothesize that the beta-carotene may help to reduce the oxidative stress and resulting tissue damage that is observed with the build-up of beta-amyloid plaque deposits in AD brains. Also, there is research that suggests that people with the apoE4 form of the gene are less able to prevent the buildup of the plaque deposits observed in AD.
Another hypothesis as to why people with apoE4 are at higher risk is that a primary difference between the three lipoprotein types is the number of cysteine amino acids in the lipoprotein’s amino acid chain. apoE2 has two cysteine amino acids, apoE3 has one, and apoE4 has none. Cysteine is a sulfur-containing amino acid. Mercury has a high affinity for sulfur. The absence of cysteine in the apoE4 form of the lipoprotein may make individuals with this form less able to remove heavy metals from the bloodstream and more susceptible to toxin exposure.
Regardless of the mechanism, antioxidants such as beta-carotene, seem to play an important role in helping to manage the oxidative stress observed in AD.
