Does a mother's fish consumption affect whether the child develops arthritis?
Researchers are questioning whether environmental toxins in fish are the reason juvenile arthritis is twice as common in Northern Norway as in Southern Norway.
Norwegian researchers have found a link between a mother's fish consumption and juvenile arthritis. What does this mean?(Photo: Shutterstock / NTB)
Children of women who eat more than 250 grams of lean or semi-fatty fish per week during pregnancy have a higher risk of developing juvenile arthritis, according to a new study.
Vilde Øverlien Dåstøl, a PhD student at the rheumatology section of Oslo University Hospital, is the lead author of the study.
"We wondered whether the intake of fish and seafood during pregnancy could influence the risk of the child developing arthritis," she says.
For other autoimmune diseases as well, researchers see an increased risk in the north compared to the south of the country.
Annonse
Vilde Øverlien Dåstøl states that they cannot make any recommendations regarding fish intake for pregnant women based on their study.(Photo: Siw Ellen Jakobsen)
The risk increases with fish consumption
The suspicion that fish consumption and juvenile arthritis may be connected stems from a Swedish study from 2019.
In that study, researchers found an increased risk of juvenile arthritis if the mother ate fish more than once a week. This was also the case if the child ate fish more than once a week during its first year of life.
The Norwegian researchers also find this connection, but not as clearly as in the Swedish study.
"We find a somewhat increased risk of juvenile arthritis when the mother had a high intake of lean or semi-fatty fish during pregnancy. We define high intake as consuming more than 250 grams per week," says Dåstøl.
The connection is seen in both genders but is strongest for boys, according to the research group at Oslo University Hospital and the University of Oslo.
What is juvenile arthritis?
Juvenile arthritis, or juvenile idiopathic arthritis (JIA), is a chronic inflammatory rheumatic disease that affects the joints of children and adolescents under the age of 16.
It is an autoimmune disease, meaning that the immune system attacks the body's own joints.
The severity of the disease can vary. It may cause joint pain and swelling, morning stiffness, fatigue, and reduced energy levels.
The cause of the disease is still unknown, but it is believed to be a combination of genetic predisposition and environmental factors.
Juvenile arthritis primarily affects girls. 60 to 70 per cent of those diagnosed with the disease are girls. Researchers believe there is not enough knowledge about the reasons behind these gender differences.
Difficult to compare
The Swedish study does not specify how much fish the women consumed, making comparisons between the two studies difficult.
Additionally, the Swedish study does not distinguish between how fatty the fish is.
In contrast, the Norwegian researchers look at fatty fish, lean and semi-fatty fish, as well as shellfish. They do not find a connection between the intake of fatty fish during pregnancy and juvenile arthritis.
When it comes to shellfish, they find the connection only in boys.
Both genes and environment
Juvenile arthritis is partly caused by genetics.
However, genes do not explain everything. Researchers believe that environmental factors must also play a role.
In the Swedish study, researchers did not have genetic information.
"When we can now look at the interaction between genetic risk and environmental factors in juvenile arthritis, it's a clear strength. This has never been done before," says Dåstøl.
Researchers have actually found that the children with the highest risk of developing juvenile arthritis are those whose mothers ate fish but had a low genetic risk.
This strengthens the suspicion that there may be something in the environment that triggers the disease.
Found mercury in the blood
The Swedish researchers discovered that children with arthritis had higher levels of mercury and other heavy metals in their blood.
"It's often thought that fatty fish contain a lot of environmental toxins, but lean fish do as well. Mercury is the most significant environmental toxin in these fish," says Dåstøl.
The researchers now want to investigate this further and have received funding from the Norwegian Rheumatism Association.
"During the MoBa study, blood samples were taken from the mothers while pregnant. We will now go back and analyse them to see if the mothers of children who developed juvenile arthritis actually had higher levels of heavy metals in their blood. This will bring us closer to answering these questions," says Dåstøl.
According to a study from 2024, being exposed to environmental toxins in the womb may increase the risk of immune diseases, such as juvenile arthritis.
Could it be something else?
Dåstøl and colleagues believe that their study does not provide enough evidence to determine how much fish pregnant women should eat.
"Our study is an observational study. We can't establish cause and effect. There may be other things these women have in common that explain the connection, which we are unable to measure," she says.
The findings must be confirmed by more studies before researchers can conclude whether fish consumption is truly responsible for this link. This is the opinion of Helga Sanner, a professor at Oslo University Hospital's rheumatology department. She is the main supervisor and co-author of the study.
"An interesting finding"
"The idea that a mother's diet during pregnancy can influence the child's risk of developing arthritis is an interesting finding," Erik Kristoffer Arnesen writes in an email to sciencenorway.no.
He is an adviser at the Norwegian Directorate of Health.
"It's important to study the relationship between a mother's actions during pregnancy and health outcomes in children and to follow up with further research to see if other studies show the same results," he writes, adding:
"Single studies do not change guidelines and recommendations, as they often point in different directions. When enough research over time supports the same conclusion, it can form the basis for new recommendations."
Juvenile arthritis is very rare
It is also important to remember that juvenile arthritis is a very rare condition, says Arnesen.
"In the study referenced, only 0.3 per cent of the children developed the disease. Even though there was slightly higher odds with high fish intake in this study, the number of children who developed it was still very low. In other words, according to this study, it's still highly unlikely that a child will develop juvenile arthritis because the mother ate a lot of fish during pregnancy," he writes.
It is well-documented that eating fish has beneficial health effects. White, lean fish is an important source of iodine, which many pregnant women in Norway do not get enough of, writes Arnesen.
"It's therefore recommended that women – including pregnant women – eat 300 to 450 grams of fish per week to ensure an adequate intake of essential nutrients both for themselves and for the foetus," he writes.
According to the study, more women in Northern Norway than in Southern Norway had a high fish intake during the years 2002 to 2008.
Only 47 per cent ate fish or other seafood at least twice a week.
People from Eastern Norway topped the list with 58 per cent.
The survey indicates that sushi has contributed to increasing fish consumption in Eastern Norway.
Much we do not know
Juvenile arthritis is an area that has not been researched enough, according to Joachim Sagen. He is head of research at the Norwegian Rheumatism Association.
"The great mystery that remains unsolved is what causes some people to develop juvenile arthritis. In this context, this study can help piece together parts of the puzzle. That makes it valuable," he says.
Sagen believes that fish should still be part of a healthy and varied diet. However, the findings suggest that people might need to be more conscious of where their fish comes from and what it contains.
"This is probably only a small part of the explanation. But these are exciting findings that could inspire further research. And if research can help improve the lives of this group of patients, it will be of great significance," he says.
