Study finds that eating seafood once a week may slow memory loss
(Chicago) – Eating a meal of seafood or other foods containing omega-3 fatty acids at least once a week may protect against age-related memory loss and thinking problems in older people, according to a team of researchers at Rush University Medical Center and Wageningen University in the Netherlands.
Their research findings were published in the May 4 online issue of Neurology, the medical journal of the American Academy of Neurology. The study was supported by the National Institute on Aging and the Judith Zwartz Foundation.
The age-related memory loss and thinking problems of participants in the study who reported eating seafood less than once a week declined more rapidly compared to those who ate at least one seafood meal per week.
“This study helps show that while cognitive abilities naturally decline as part of the normal aging process, there is something that we can do to mitigate this process,” says Martha Clare Morris, ScD, a Rush nutritional epidemiologist and senior author of the paper.
Four types of seafood, five types of brain function
The researchers followed 915 people with a mean age of 81.4 years for an average of five years. At study enrollment, none had signs of dementia. The participants were recruited from people already taking part in the Rush Memory and Aging Project, a study of residents of more than 40 retirement communities and senior public housing units across northern Illinois, plus older adults identified through church groups and social service agencies.
During the course of the study, each person received annual, standardized testing for cognitive ability in five areas — episodic memory, working memory, semantic memory, visuospatial ability and perceptual speed. The study group also completed annual food frequency questionnaires, allowing the researchers to compare participants’ reported seafood intake with changes in their cognitive abilities as measured by the tests.
The questionnaires included four types of seafood: tuna sandwiches; fish sticks, fish cakes and fish sandwiches; fresh fish as a main dish; and shrimp, lobster and crab. The participants were divided into two groups: those who ate at least one of those seafood meals per week and those who ate less than one of those seafood meals per week.
Participants in the higher seafood consumption group ate an average of two seafood meals per week. Those in the lower group ate an average of 0.5 meals per week.
Making closer associations
Seafood is the direct nutrient source of a type of omega-3 fatty acid (docosahexaenoic acid) that is the main structural component of the brain. While epidemiologic studies have shown the importance of seafood and omega-3 fatty acids in preventing dementia, few prior studies have examined their associations with specific types of cognitive ability.
In the new Neurology article, the researchers report associations between seafood consumption and two of the areas of cognitive ability that they tested. People who ate more seafood had reduced rates of decline in the semantic memory, which is memory of verbal information. They also had slower rates of decline in a test of perceptual speed, or the ability to quickly compare letters, objects and patterns.
The study did not find a significant difference in the rate of decline in episodic memory (recollection of personal experiences), working memory (short-term memory used in mental function in the immediate present) and visuospatial ability (comprehension of relationships between objects).
The results were the same after researchers adjusted for other factors that could affect memory and thinking skills, such as education, physical activity, smoking and participating in mentally stimulating activities.
Further, the protective association of seafood was even stronger among individuals with a common genotype (APOE-ε4) that increases the risk of developing Alzheimer’s disease. The APOE is a gene involved in cholesterol transport to neurons. About 20 percent of the population carries the APOE-ε4 gene, although not everyone who has the gene will develop Alzheimer’s disease.
The news release is a recap of a recent journal article published in the journal Neurology, and reports that older adults who eat seafood at least once per week saw slower declines in two specific cognitive areas (semantic memory and perceptual speed) than older adults who eat less than one serving of seafood per week. The release provides a good measured overview of the study but does not quantify the benefits or address the limitations of the study.
Most people plan on aging; it happens whether we like it or not. And many people have experiences with loved ones whose cognitive abilities — such as memory — have declined with age. In short, issues regarding cognitive decline associated with aging are relevant to almost everyone. Research that offers simple steps that could slow memory loss are, therefore, of widespread interest. For the same reason, it’s important to approach these simple solutions with caution. How much does it slow loss, for example? That’s not clear from the release, and yet it’s likely the most pertinent question for many readers.
Cost isn’t discussed. And because it’s about a widely-consumed food that is a staple for many diets, we’ll rate it not applicable. However, it’s worth noting that seafood can be more expensive than many other types of food. What’s more, since the story discusses seafood primarily as a vehicle for omega-3 fatty acids, cost becomes even more of an issue. And when it comes to omega-3 fatty acids, not all seafood is created equal. Salmon, for example, has a lot more omega-3 fatty acids than a similar serving size of catfish — but it’s also a lot more expensive. There is also the issue of accessibility. People living in so-called “food deserts,” which are often found in socioeconomically challenged areas, may have difficulty even reaching stores or restaurants that sell seafood.
Benefits are discussed using only vague language. For example: “age-related memory loss and thinking problems of participants in the study who reported eating seafood less than once a week declined more rapidly compared to those who ate at least one seafood meal per week.” How much more rapidly? Or: “People who ate more seafood had reduced rates of decline in the semantic memory, which is memory of verbal information. They also had slower rates of decline in a test of perceptual speed, or the ability to quickly compare letters, objects and patterns.” But how much less decline was there of semantic memory? And how much slower was the decline in regard to perceptual speed? The release doesn’t tell us.
It would have been helpful for the news release to present the raw numbers relating to cognitive decline in each group and to provide some context to help readers understand their significance (such as “performance on the semantic memory test dropped by X amount in this group and Y in the other group,” for example).
The study population in this specific study was made up of older adults (mean age of 81.4 years old). There are few, if any, risks associated with eating one seafood meal per week for older adults. However, the release might have warned that both the FDA and the EPA, while encouraging pregnant and breastfeeding women to consume two to three servings of fish weekly, now recommend that they choose fish that is low in mercury (which include salmon, shrimp, pollock, tuna (light canned), tilapia, catfish, and cod).
The news release does a good job of explaining the size and design of the study. However, it doesn’t point out that the study is observational which means it doesn’t show there is a cause and effect between seafood consumption and cognitive decline. In some instances the release uses active verbs: “may protect,” “may slow” which imply causality that isn’t proven in observational studies.
The release would also have been stronger if it had addressed the study’s limitations. For example, data on the diet of study participants was collected via an annual questionnaire completed by study participants. This presents two challenges. First, it relies on the memory of the study participants, which introduces significant room for reporting errors. Second, the questionnaire categories are extremely broad (e.g., “fish sticks, fish cakes and fish sandwiches” and “fresh fish as a main dish”). These broad categories are problematic because eating a salmon filet and eating a serving of popcorn shrimp are given the same weight, even though they are nutritionally dissimilar. Also, while the release tells readers the number of study participants (951), it doesn’t offer readers any insight into whether that’s a big number or a small one. As the Neurology paper itself notes: “Another limitation of the study is the relatively small sample size to detect modest associations within subgroups.”
The opening paragraph talks about protecting against “thinking problems.” Readers could be excused if they translate “thinking problems” to mean senility or dementia. But the story quickly notes that “cognitive abilities naturally decline as part of the normal aging process” — and that’s what we wanted to see. This study was about slowing that normal decline, not addressing specific medical conditions such as Alzheimer’s disease.
The story clearly and prominently lists the sources of funding for the work, and there are no apparent conflicts of interest.
The story says that “researchers adjusted for other factors that could affect memory and thinking skills, such as education, physical activity, smoking and participating in mentally stimulating activities.” It doesn’t tell us which are potentially good (and which are bad), but it’s sufficient for a Satisfactory rating.
The release would have been stronger if it had addressed the question (probably on some on readers’ minds) about whether fatty acid supplements could possibly have the same effect that the researchers observed with seafood consumption. These supplements are widely used, not to mention costly, so this may have been worth including.
People have been eating fish for rather a long time, so we’ll rate this Not Applicable.
The story states that: “While epidemiologic studies have shown the importance of seafood and omega-3 fatty acids in preventing dementia, few prior studies have examined their associations with specific types of cognitive ability.” That gets it a satisfactory rating. However, it’s worth noting that the story does not get to the novel aspect of the findings — the “associations with specific types of cognitive ability” — until the sixth paragraph. If that’s what’s new in the news, one wonders why it wasn’t addressed higher.
This is a close one, but mainly because of the headline. Declines in semantic memory and perceptual speed weren’t prevented, or even postponed, they were simply slowed down. That said, we’ll give the release the benefit of the doubt. The body of the release used language that was measured and appropriate.