11:09am Wednesday 13 December 2017

Food and environmental contaminants in the blood

Illustration photoOily fish contributes most to the intake of PCBs and dioxins in most people, since this is a food that is commonly eaten. The calculations were done as part of the recent doctoral dissertation for clinical nutritionist and researcher Helen Engelstad Kvalem at the Norwegian Institute of Public Health.

Engelstad Kvalem has also analysed the eating habits (dietary patterns) of individuals with the highest concentration of these substances in the blood.

Which foods contribute to high levels of dioxins and PCBs? 

  • Oily fish is a major source because it is a popular food 
  • The foods that contain most dioxins and PCBs are gull eggs, cod liver and fish liver pâtè. These foods contribute significantly to the total intake of contaminants in those who eat large amounts. 
  • People with a dietary pattern containing fish liver and gull eggs had much higher concentrations of these contaminants in their blood than those with a high score in the oily fish pattern. 
  • Most people who exceeded the tolerable intake of dioxins and PCBs ate gull eggs and / or fish liver.

Other findings: 

  • The relationship between intake of these substances through the diet and the concentration in blood is stronger for men than women. 
  • Increasing age and body mass was related to higher concentrations of the substances in the blood of the women. 
  • For men, age and dietary intake were the main determinants of the blood concentrations. 
  • This may be related to differences in the metabolism of these substances in women and men.

Should we stop eating oily fish?

– No, oily fish is still healthy. It is just a question of quantity. Intake of oily fish for dinner twice a week is considered safe according to the Scientific Committee for Food Safety’s overall evaluation of the health effects of eating fish. The levels of dioxins and PCBs in blood from the average Norwegian is low. Based on our findings, oily fish is the main source for most people, but intake of oily fish does not give the same clear increase in blood levels as intake of fish liver or gull eggs, said Helen Engelstad Kvalem

Should we stop eating gull eggs completely?

– For children or women of child-bearing age, the answer is yes. For men it is ok with a few eggs, but the advice is to limit intake. This is because eating one gull egg a year for many years can increase the body levels of dioxins and PCBs by 10 percent.

Are some types of fish worse than others?

– Yes, large halibut and eels as well as liver from lean fish such as cod and pollock contain more dioxins and PCBs than, for example, herring, mackerel, salmon and sardines.

Is it dangerous to eat a can of mackerel in tomato sauce every day?

– It depends on the total diet. If you do not eat much oily fish, a can of mackerel in tomato sauce every day is fine, but if you eat oily fish for dinner regularly in addition to a can of mackerel in tomato every day over a long period (years) you may be exposed to more dioxins and PCBs than is recommended.

What health effects can we expect if we have a high intake of dioxins and PCBs?

– Moderate over-exposure to dioxins and PCBs will probably not cause any health effects. Tolerable intake is determined by the effects in laboratory animals. There is a quite large safety margin between the level that provides a low degree of effect in laboratory animals and that which is considered safe in humans. If you ingest more dioxins and PCBs than is considered tolerable the safety margin becomes less.

How was the study conducted?

Measurement of environmental pollutants in blood is very expensive and requires more blood than is usually available in research projects. This new method is thus particularly useful.

Engelstad Kvalem used data from the “Fish and Game Study” and the “Lake Mjøsa Study” in which a total of approximately 250 people from across Norway provided blood samples and detailed information about what they have consumed during the previous year. Engelstad Kvalem has compiled an extensive database of concentrations of dioxins and PCBs in Norwegian food.

The doctoral work demonstrates that the models for calculating blood levels of dioxins and PCBs are ideal for population studies where blood analysis is impossible.

Dissertation title

From food to blood – diet as a predictor of blood concentrations of dioxins and PCBs. Characterisation of dietary intake and blood concentrations in two Norwegian studies and development and validation of prediction models for blood concentrations of dioxin and PCBs.


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