This observational study drawing a link between higher fish consumption, better sleep and higher scores on an IQ test has many potential variables that could influence the research results. Those variables as well as alternative explanations for the outcomes observed should have been included in the news release.
While this is important research, appropriate caveats are missing here, and further details could have helped readers make better sense of the difficulties involved in this research. Note that this study was done in China, where the other aspects of a daily diet may differ markedly from those in North America.
If simple dietary changes, such as an increased intake of fish, could result in better sleep and better cognitive development, then it follows that new dietary recommendations should be taken seriously. But this kind of observational, short-term research in a relatively small number of school children makes it difficult to draw conclusions and, while maybe hypothesis-generating, it would be premature to make any conclusive recommendations about how the diet of a nation’s children should change.
We’ve prepared some tips to keep in mind when reading or writing about observational studies. Observational studies that draw connections between health and food intake sometimes raise more questions than answers and need to be treated with a high degree of caution.
No details are provided that would let a reader estimate the cost of including more fish in a diet such as type of fish or the amount to be consumed.
We are told that children who said they ate fish weekly “scored 4.8 points higher on the IQ exams than those who said they “seldom” or “never” consumed fish.” The children who reportedly “sometimes” ate fish consumers scored 3.3 points higher. How big is a 4-point difference on the IQ test and would it translate to better school performance or other outcomes that would be meaningful for the children? That question isn’t addressed.
The release also claims that those who consumed fish had fewer sleep disturbances but doesn’t give us any clue as to how sleep disturbances changed — from what to what?
It would also be useful to know how much fish they ate and what kinds.
Current dietary recommendations include warnings about some commonly eaten types of fish that are high in mercury, but this or any other potential drawbacks associated with consuming fish were not mentioned.
The news release notes that the researchers want to “add to this current observational study to establish, through randomized controlled trials, that eating fish can lead to better sleep, better school performance and other real-life, practical outcomes.” But elsewhere it assumes that fish consumption is already proven to be beneficial — for example when a researcher is quoted as stating, “If the fish improves sleep, great. If it also improves cognitive performance — like we’ve seen here — even better. It’s a double hit.” The release should have informed readers that a randomized controlled trial would be required to prove cause and effect.
In terms of the changes or lack of change in IQ among children who ate fish weekly, sometimes or never, we aren’t told how many ate fish weekly. How much fish did they eat? How many never ate fish? These numbers are needed to weigh the evidence.
In addition, some of the study data were collected using questionnaires completed by students and their parents. Questionnaires are not very reliable sources of scientific data since they are subject to recall bias. This should have been pointed out in the release as a limitation.
There is no evidence of disease mongering here.
We learn the connections between the funders of the research and the investigators and there is no sense that a conflict of interest exists here.
The important question about the role of omega-3s supplementation versus fish consumption was mentioned, but there were no details how the supplements compared in IQ or sleep improvements.
It’s pretty clear that fish is a common food source, available everywhere.
We rate this marginally satisfactory for the release’s description of how this study differs from earlier work.
“Previous studies showed a relationship between omega-3s, the fatty acids in many types of fish, and improved intelligence, as well as omega-3s and better sleep. But they’ve never all been connected before. This work, conducted by Jianghong Liu, Jennifer Pinto-Martin and Alexandra Hanlon of the School of Nursing and Penn Integrates Knowledge Professor Adrian Raine, reveals sleep as a possible mediating pathway, the potential missing link between fish and intelligence.”
Generally the language was satisfactory, but based on the observational nature of the research alone it seems the concluding advice may be premature:
“The researchers recommend incrementally incorporating additional fish into a diet; consumption even once a week moves a family into the “high” fish-eating group as defined in the study.”
Current US dietary guidelines already recommend at least 8 ounces of fish and shellfish at least once a week. The release could have clarified this.