Mercury, genes and the link with Alzheimer’s disease

cropped-IMG_7188-1.jpgMethyl mercury, a pollutant produced by various industrial activities, is a potent neurotoxin that has now caused serious contamination issues within our oceans. As a fat soluble molecule, methyl mercury enters the food chain and accumulates in the flesh of the fish that then may end up in our supermarkets. Consuming larger, longer living fish on a regular basis is now known to pose a serious health hazard, especially for children and pregnant women who are consequently advised to limit (or even avoid) the intake of some species such as fresh tuna or marlin.

The accumulation of mercury within the body can have profound long-term effects on the nervous system, and has been linked to a variety of conditions including Alzheimer’s disease where it is believed to play a part in nerve cell death. Lipoproteins, such as high density lipoprotein (HDL) and low density lipoprotein (LDL), are combinations of lipids (fat) and proteins that function to transport fat around via the blood, a function that is generally associated with cholesterol, and therefore cardiovascular health. However, approximately 1 in 7 people carry a gene that causes their body to produce a particular lipoprotein called apoE4, known to play a significant role in the development of Alzheimer’s disease. Those who inherit the apoE4 gene from one parent are three times more likely than average to develop Alzheimer’s disease, with those who inherit the gene from both parents having a tenfold risk of developing the disease (Donix et al, 2010). There are multiple hypotheses as to why those carrying the apoE4 gene are more likely to develop Alzheimer’s than those who carry the apoE3 or apoE2 genes; one such hypothesis regards the role that these lipoproteins play in mercury transport within the body, as mercury accumulation in the brain hasbeen linked to the progression of Alzheimer’s. Like all proteins, apolipoprotein is made of chains of amino acids. Cysteine is of particular relevance, as this amino acid contains sulphur, a member of a class of substances called ‘mercaptans,’ the Latin name for “mercury capture.” Because apoE2, the protective form of apoE, contains two cysteine amino acids, it is particularly efficient at removing mercury from the system. In contrast, apoE3 has only one cysteine, and apoE4 none, making it the most ineffective at removing excess mercury from the body.

Given that fish oils are thought to offer protection against neuronal death and therefore the onset of dementia, it seems that ingesting them in high doses may negate any beneficial therapeutic effects unless they are highly purified to ensure all heavy metals are removed. The growing omega-3 market means there are more products of differing qualities and strengths, and the processes used to isolate and purify oils can also differ quite significantly. It would certainly be advisable to choose fish oil supplements that have been purified under pharmaceutical grade conditions to ensure the product not only offers the best possible health benefits, but can also guarantee to be contaminant free.

Refrences

Dórea JG. Environmental contaminants as biomarkers of fish intake: a case for hair mercury concentrations. Eur J Clin Nutr. 2010 Sep 1. [Epub ahead of print]

Albert I, Villeret G, Paris A, Verger P. Integrating variability in half-lives and dietary intakes to predict mercury concentration in hair. Regul Toxicol Pharmacol. 2010 Aug 27. [Epub ahead of print]

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