This is the conclusion from the Norwegian Scientific Committee for Food and Environment (VKM), in a new benefit and risk assessment of fish in the Norwegian diet commissioned by the Norwegian Food Safety Authority.

Background

VKM has previously, in 2006 and 2014, conducted benefit and risk assessments of fish in the Norwegian diet. The availability of new knowledge, including new tolerable weekly intakes for exposure to contaminants (dioxins and dioxin-like PCBs, perfluoroalkyl substances (PFAS), including perfluorooctanesulfonic acids (PFOS) and perfluorooctanoic acids, PFOA), triggered the Norwegian Food Safety Authority to commission a new benefit and risk assessment.

The tolerable weekly intake (TWI) is the amount of a substance a person can ingest weekly throughout life without risking negative effects on their health.

The Norwegian Food Safety Authority wanted to know, for the Norwegian population, which health consequences people would have if they were to:

• continue with the same fish consumption levels as of today, or
• increase the consumption of fish to match the recommendations given by the Norwegian Directorate of Health.

The Directorate recommends eating fish for dinner two to three times a week and using fish as a spread on bread. This amounts to 300 - 450 grams of prepared fish per week for adults. At least 200 grams should comprise fatty fish such as salmon, trout, mackerel, and herring.

Systematic reviews of fish and health outcomes

The benefit and risk assessment is based on comprehensive systematic reviews of fish intake and health outcomes.

The health outcomes included are public health diseases and conditions common in the population in Norway, such as various cardiovascular diseases (CVD), coronary heart disease (CHD), mortality, neurological development in children, cognitive decline in adults, type 2 diabetes, overweight and obesity, birth outcomes, asthma and allergies, cancer, multiple sclerosis, and rheumatoid arthritis. The systematic reviews cover both individual studies, and previous systematic review articles and meta-analyses.

VKM has also made systematic reviews of associations between long-chain omega-3 fatty acids and several health outcomes.

This benefit and risk assessment consists of a quantitative analysis of benefits and risks from fish consumption, a semi-quantitative benefit assessment of nutrients in fish, and a semi-quantitative risk assessment of contaminants in fish.

The nutrients are long-chain omega-3 fatty acids, vitamin D, iodine, selenium and vitamin B12. The environmental toxins that have been assessed are dioxins and dioxin-like polychlorinated biphenyls (PCBs), PFASs and methylmercury.

An increased intake of fish benefits health

VKM has estimated that in Norway, women eat an average of 240 grams of fish per week, and men eat 350 grams.

As shown in the quantitative analysis, a reduction in the weekly fish intake from the current mean intake among adult men and women to 150 grams per week would result in an increase in annual numbers of incident cases or deaths estimated for all outcomes included in the quantitative model (CVD mortality, CHD mortality, all-cause mortality, incidence of CHD, stroke, dementia, Alzheimer’s disease and preterm birth).

“This indicates that a lower consumption of fish poses a potential health risk, and that beneficial health effects of eating fish are not obtained at the current levels of fish intake,” says Lene Frost Andersen, scientific leader of the project.

The quantitative analysis indicates that increasing the intake of fish to recommended levels, especially up to the upper range of recommended intake (450 grams per week in scenario 3) will reduce the probable incidence of stroke and CHD, diseases which largely contribute to the burden of disease in Norway.

“We have estimated that an increase of fish intake to recommended levels will reduce the number of new cases of dementia and Alzheimer’s disease. Both cognitive disorders are increasing in the population as the proportion of elderly is growing,” adds Frost Andersen.

An increased intake of fish will also lead to a decrease in the proportion of the population that ingests too little iodine and selenium. Large parts of the population have too low an intake of vitamin D and iodine. Increased intake of oily fish can also be important for those who ingest too little vitamin D, and increased intake of lean fish is positive for those who ingest too little iodine.

“All age groups would benefit from increasing levels from their current intake to the recommended intake of fish,” concludes Frost Andersen.

Risk of environmental contaminants

On the other hand, increasing fish intake to recommended intake levels would cause almost all age groups to exceed the tolerance limit for the environmental toxins that have been assessed.

Critical effects of being exposed to dioxins and dioxin-like PCBs and to PFASs include poorer sperm quality and lower effects of vaccines in children, respectively. The contribution of the critical effects to the combined death and disability burden has not been estimated.

“Lower vaccine responses are often used as a marker for reduced immune function, but it is not known to what extent this may lead to an increased risk of infections, by a project group in VKM and approved by VKM steering committee says Frost Andersen. “Moreover, there are many dietary sources of these contaminants, so although a reduction of fish intake will probably cause some reduction in exposure to these, it will not be enough to reduce exposure to below the tolerable weekly intake levels.

The benefit and risk assessment has been prepared by a project group in VKM, and approved by the Scientific Steering Committee.