The assertion that increased omega-3 intake can lead to higher scores on measures of cognition among children is not new. But the researchers, who are associated with the University of Pennsylvania, said their study was the first to examine whether better sleep among those children who ate more fish may be a mediating mechanism by which the cognition boost is achieved.
Large scale longitudinal study
The longitudinal study collected data from 514 children aged 12 who were part of the second wave of an ongoing prospective longitudinal study called the China Jintan Cohort Study. Slightly more boys than girls were included in the study. The children and their families filled out self-reported food frequency questionnaires, had an IQ measurement done and the parents provided sleep evaluations.
Fish consumption for the period when the children were aged 9-11 was graded in the questionnaires on a three part scale: often, sometimes and rarely or never. Similarly, sleep patterns were ranked on a three tier scale. The parents were also asked to score eight sleep parameters on a 1 (rarely/never) to 3 (five to seven times a week) scale. The parameters were: bedtime resistance, sleep-onset delay, sleep duration, sleep anxiety, night waking, parasomnias, sleep-disordered breathing, and daytime sleepiness.
The children’s cognitive performance was evaluated with the Wechsler Intelligence Scale for Children-Revised (WISC-R), a version of which has been validated for Chinese children. The WISC-R consists of six verbal subtests (Information, Comprehension, Arithmetic, Vocabulary, Similarities and Digit Span) that are summed to form Verbal IQ, and six non-verbal subtests (Picture Arrangement, Picture Completion, Object Assembly, Block Design, Coding and Mazes), that are summed to form Performance IQ. The Verbal and Performance IQs are combined to produce a Full-Scale IQ score.
Results: more fish = better sleep, higher IQ
The researchers found that 25% of the children ate fish at least once a week, 58% ate fish two or three times a month and 18% rarely or never consumed fish. The children who frequently ate fish had both higher IQ scores and lower sleep disturbance scores than those who rarely or never consumed fish. The IQ increases showed a linear relationship with dosage. The children who frequently consumed fish when they were aged 9–11 years scored 4.75 points higher in verbal IQ, 3.79 points higher in performance IQ, and 4.80 points higher in full scale IQ compared to those who never or seldom consumed fish.
“Sleep was found to partially mediate the relationship between fish consumption and cognitive outcomes, suggesting that frequent fish consumption may improve sleep quality, which results in better long-term cognitive outcomes. These conclusions are supported by the finding of dose-response relationships between quantity of fish consumption and degree of increased IQ scores, relationships that were again found to be mediated by better sleep quality as indicated by less sleep disturbances. These findings thus have potentially significant implications for public health attempts to promote healthy dietary habits in children and adolescents,” the researchers wrote.
The researchers noted that while the sleep mediation effect they were investigating is novel, in other aspects their findings are consistent with existing literature. Evidence from European cohorts supports the relationship of omega-3 intake and cognitive performance, and other studies have investigated the link between omega-3 intake and better sleep.
One limiting factor could be that omega-3 intake specifically was not measured. Research has shown that the omega-3 content of fish can vary widely depending on species and habitat or feeding protocols for farmed fish. There was no attempt by the researchers to evaluate the quality of the fish eaten, nor any indication of what kinds of species are typically consumed among the families that made up the cohort.
More research on specific aspects of sleep called for
An interesting aspect of the results was that higher fish consumption and better sleep was linked with better verbal IQ scores, but did not have a statically significant effect on performance IQ. “This partial mediation may reflect how the effects of fish consumption on sleep differentially affects specific neurocognitive domains rather than a global deficit. However, these potential effects on VIQ versus PIQ remain mixed and unclear,” the researchers wrote. They speculated that higher fish consumption may have improved only those aspects of sleep that affect verbal IQ performance. But they said more research is called for, because other studies have suggested that EPA and DHA enhance cognitive functioning in children in a global fashion.
“Clearly, more research identifying the relationships between cognitive functioning with both objective and subjective measures of sleep in children is warranted,” they wrote.
Source: Scientific Reports
“The mediating role of sleep in the fish consumption – cognitive functioning relationship: a cohort study”
Dec. 21, 2017 doi:10.1038/s41598-017-17520-w
Authors: Liu J, Cui Y, Wu L, et al.