The health effects of farmed salmon consumption

2004

YEAR BOOK

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Food Safety Authority of Ireland

Wayne Anderson

The health effects of farmed salmon consumption

On 8 January 2004, researchers in the USA reported the outcome of the largest study to date on the presence of persistent organic pollutants (POPs) in farmed and wild salmon ¹ . They concluded that European farmed salmon was more contaminated with these POPs, particularly dioxins and PCBs, than salmon reared in North and South America and that, in general, farmed salmon was more contaminated than wild salmon. They also concluded that farmed salmon from Scotland and the Faroe Isles were the most contaminated salmon tested, and advised that it should only be consumed at a rate of 'less than one half meal of salmon per month'.

These research findings were not new and were previously known from a number of smaller studies around the world, including a study carried out by the Food Safety Authority of Ireland. However, in contrast to the US researchers' advice, national food agencies around the world concluded that current nutritional advice to consume one portion of oily fish per week would not lead to intakes of dioxins and dioxin-like PCBs above the agreed international safe limits.

The difference between health advice based on essentially the same data lies in the risk assessment approach. The US researchers used a risk assessment approach adopted by the US Environmental Protection Agency (EPA): Guidance for Assessing Chemical Contamination Data for use in Fish Advisories ² . This approach provides for fish consumption advice designed to maintain the cancer risk at a tolerable level of 1 in 10,000. It assumes that any level of exposure to a carcinogen presents a degree of risk and that the toxic effect of related chemicals is either additive or synergistic. Neither of these assumptions is accepted internationally by toxicologists, and their effect is to lead to an overly conservative assessment of risk. In contrast, both the EU and the World Health Organization (WHO) have concluded that a number of the pollutants characterised by the US EPA are non-genotoxic (don't have an effect on the DNA in cells of the body) and hence a threshold intake can be established below which adverse health effects are very unlikely. This safe limit is expressed as a tolerable weekly (in the case of the EU) or monthly (in the case of WHO) intake over a lifetime of 70 years.

Part of the difficulty in assessing the risks to general health of consuming farmed salmon is that we tend to only look at health in one dimension, in this case the potential for a contaminant to cause cancer. The problem with this approach is that it fails to recognise the complexity of overall nutrition and its health effects. For example, the diet also includes compounds that protect against the risk of cancer � e.g. flavenoids, antioxidants and even omega-3 polyunsaturated fatty acids (PUFAs) themselves. As a result, a definitive answer on how risky a food is to health remains elusive. Fish is highly nutritious and contains minerals (calcium, iron, selenium and zinc), vitamins A, B3, B6, B12, E and D, as well as PUFAs and proteins of high biological value ³ . Atlantic salmon contains around 5.4g fat per 100g edible fish, of which 1.2g are omega-3 PUFAs ⁴ : these have been shown to reduce the risk of coronary heart disease, decrease mild hypertension, prevent certain cardiac arrhythmias, lower the incidence of diabetes, and also appear to alleviate the symptoms of rheumatoid arthritis. Evidence is emerging that the omega-3 PUFAs play a role in the development and function of the brain, vision and reproductive system3. They have also been reported to reduce the risk of a number of digestive cancers ⁵ and cancer of the uterus ⁶ .

There can be no denying that the salmon farming industry needs to reduce the levels of contaminants in their fish, and this also requires the levels of contaminants to be reduced in the commercial fish feed. Alternative oil sources for fish feed need to be investigated. There is also emerging data on other non-cancer toxicological effects of dioxins and dioxin-like PCBs that may need to be taken into account ⁷ . Consequently, further risk assessment work will need to be done in this area in future as new data emerges.

References

1. Hites R.A., Foran J.A., Carpenter D.O., Hamilton M.C., Knuth B.A., Schwager S.J. (2004), Global assessment of organic contaminants in farmed salmon. Science, 303, 226-229.

2. US EPA (2000), Guidance for assessing chemical contaminant data for use in fish advisories. Volume 2: risk assessment and fish consumption limits. US EPA, Washington DC. www.epa.gov/ost/fishadvice/volume2/index.html

3. Sidhu K.S. (2003), Health benefits and potential risks related to consumption of fish or fish oil. Regulatory Toxicology and Pharmacology, 38 , 336-344.

4. Hepburn F.N., Exler J., Weihrauch J.L. (1986), Provisional tables on the content of omega-3 fatty acids and other fat components of selected foods. Journal of the American Dietetic Association, 86 , 6, 788-793.

5. Jahangiri A., Leifert W.R., McMurchie E.J. (2002), Omega-3 polyunsaturated fatty acids: recent aspects in relation to health benefits. Food Australia, 54 , 3, 74-77.

6. Terry P., Wolk A., Vainio H., Weiderpuss E. (2002), Fatty fish consumption lowers the risk of endometrial cancer: a nationwide case-control study in Sweden. Cancer Epidemiology, Biomarkers and Prevention, 11 , 143-145.

7. SCF (2001), Opinion of the scientific committee on food on the risk assessment of dioxins and dioxin-like PCBs in food. http://europa.eu.int/comm/food/fs/sc/scf/out90_en.pdf

Contact: Dr Wayne Anderson, Food Safety Authority of Ireland, Abbey Court, Lower Abbey Street, Dublin 1;
Tel: 01-8171300; Fax: 01-8171301;
E-mail: [email protected] ; Web: www.fsai.ie