WHAT WAS THIS STUDY ABOUT?

In the article “APOE ε4 and the associations of seafood and long-chain omega-3 fatty acids with cognitive decline,” van de Rest and colleagues examined the connection between the amount of seafood eaten per week and cognitive decline over approximately 5 years in older adults living in retirement communities. The researchers were also interested in learning more about how a gene called APOE ε4 might influence the effect that seafood consumption has on cognitive decline.¹ The community-based study was designed to better understand changes in thinking and motor abilities and the risk of Alzheimer disease (AD) in older adults. The study was called the Rush Memory and Aging Project or MAP.²

In 2015, 46.8 million people worldwide had dementia, and this number is expected to double every 20 years. AD is the most common type of dementia.³ There is currently no proven therapy that can prevent or cure AD, so it is important to understand and identify factors that might prevent or delay the onset of AD and other dementias. Researchers are interested in the fats contained in fish and seafood. These fats are called omega-3 fatty acids. These fats are of interest to researchers because the brain contains a high amount of omega-3 fatty acids. It is also known that these fatty acids are needed for a healthy brain. With aging, these fatty acids may decrease, so keeping healthy levels of them in the brain may prevent or delay cognitive decline. The APOE ε4 gene is involved in moving cholesterol to cells, including brain cells. This gene may also have an effect on how omega-3 fatty acids are moved into brain cells. People who have the APOE ε4 gene have an increased risk of AD. Those over age 65 are at the highest risk for AD.

WHO WERE THE PARTICIPANTS?

The participants were older adults without dementia in the MAP study whose information was collected every year for about 4.9 years. The average age of this group was 81.4 years and about 75% were women. The MAP study followed the same group of people who lived in retirement communities in the Chicago area from 2004 to 2013. Every year, they filled out a survey about their diet. Researchers also gave them tests to rate their thinking ability. The diet survey asked about eating things like tuna fish sandwiches, fish sticks or fish cakes, fresh fish, and shellfish like shrimp, crab, or lobster. Complete information from 915 participants on diet, thinking ability, and the APOE ε4 gene was used to produce the study results.

WHAT WERE THE RESULTS?

This study showed that older adults without dementia who eat one or more servings of seafood per week have less cognitive decline than those who eat less than one serving of seafood per week. The study showed that seafood consumption was related to 2 specific areas of brain function. One of these areas was the ability to remember facts, like knowing the names of different types of animals. This is important for clear communication. The other area was the ability to learn and process new information. This is important in difficult decision-making during tasks like driving. The researchers did not see an effect on overall cognitive function. A smaller group of participants reported taking fish oil supplements (17.5% of the total participants). They had less decline in overall cognitive function and “episodic memory” than those who did not supplement with fish oil. Episodic memory involves the ability to remember specific events, like where you parked your car or your wedding day. The researchers saw a similar and bigger effect in those participants that had the APOE ε4 gene (19.5% of the total participants). Because this APOE ε4 effect has not been seen in other studies, the researchers noted that more studies need to be done to better understand how this gene influences the protective effect of eating seafood.

WHY IS THIS STUDY IMPORTANT?

The study shows that older adults who reported eating at least one serving of seafood a week had less decline in specific thinking skills than those who ate little or no seafood. In addition, those who reported supplementing with fish oils showed less decline in overall thinking skills. Those people with the APOE ε4 gene seemed to benefit the most. How the APOE ε4 gene influences these effects remains unclear and needs further study. Earlier studies of dietary seafood have focused on overall thinking function. This study is important because it examines specific areas of cognitive function. This study simply tried to show whether there was a connection between seafood intake and cognition. The next step would be to study whether giving older people diets high in omega-3 fatty acids or fish oil supplements protects them from cognitive decline compared to a placebo group on a “normal” diet.