Dementia disrupts the lives of patients and caregivers alike, dramatically.
Alzheimer's disease and other forms of dementia also drain personal and public accounts.
It's a fearsome enough prospect in the U.S., but dementia could truly devastate rapidly aging nations such as China and Japan.
Some 50 million adults are affected worldwide, and that number is rising by almost 8 million new cases each year.
The term "dementia” simply means a progressive deterioration of memory and ability to perform everyday cognitive tasks.
Alzheimer's disease accounts for about two thirds of dementia diagnoses worldwide. Since there's no cure, prevention becomes even more important.
Most — though not all — population and clinical studies suggest that seafood and omega-3 fish oils can help prevent, delay, or diminish dementia.
However, few studies have looked for links between seafood-rich diets and preservation of specific types of cognitive ability.
A new American-Dutch study was designed to detect specific brain-performance effects from seafood, which makes its results especially important.
Before we delve into the details of the new study, let's take a look at one published earlier this year by the American half of the team.
Chicago group leads the search for lifestyle answers
Researchers at Chicago's Rush University Medical Center – led by Martha Clare Morris, Sc.D. – have been looking for links between diet or lifestyle and dementia.
Last February, they reported the results of the first study to look for links between seafood consumption, mercury levels in the brain, and risk of dementia (Morris MC et al. 2016).
That Dutch-American investigation was groundbreaking, because it included the results of autopsies on study participants who died during the five-year study.
Encouragingly, the results linked higher seafood consumption to lower risk for Alzheimer's disease ... despite higher brain-mercury levels among seafood-lovers.
And the results of the autopsies linked higher seafood intakes to lower risk for two signs associated with Alzheimer's disease: amyloid "plaque” and brain-cell "tangles”.
Our summary of that report explains why — thanks to its omega-3 fats, and despite its mercury content — all but a very few species of fish actively help brain health.
The uncommon exceptions to that rule — for reasons explained in our report on this earlier Rush Center study — are swordfish, shark, tile fish, and king mackerel.
New American-Dutch study links fishy diets to memory benefits
The team at Rush has just released a companion study, also conducted with scientists from Wageningen University in the Netherlands.
In their second study, the researchers looked at the effects of eating seafood on specific aspects of brain function (van de Rest O et al. 2016).
The Chicago-based researchers recruited 915 elderly volunteers whose average age was 81.4 years. None of the participants had signs of dementia at the outset of the study.
They were recruited from people taking part in the Rush Memory and Aging Project, mostly involving people at more than 40 Illinois retirement communities and senior housing units.
Every year, the participants took standard tests designed to measure four indicators of brain performance: episodic memory, working memory, semantic memory, visuo-spatial ability, and perceptual speed.
The participants also answered questionnaires designed to measure their seafood consumption during the five-year study.
The questionnaires presented four categories of seafood: tuna sandwiches; fish sticks, cakes or sandwiches; fresh fish as a main course; and shellfish (shrimp, lobster, and crab).
The participants were divided into two groups, defined by their average weekly seafood consumption:
- Average of 0.5 seafood meals per week
- Average of two seafood meals per week
After five years, the participants who reported eating seafood more than twice a week retained more capacity in two brain-performance categories:
- Semantic memory, or the capacity to remember verbal information.
- Perceptual speed, or the ability to quickly compare objects, letters or patterns.
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.
"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,” said nutritional epidemiologist Martha Clare Morris, Sc.D., senior author of the paper.
The researchers did not detect a significant difference in the rate of decline in episodic memory (recollection of personal experiences), working memory (short-term memory used in the present) and visuo-spatial ability (comprehension of relationships between objects).
Greatest benefit in people at risk for Alzheimer's
Perhaps the most interesting finding was that these brain-protecting effects were strongest among the participants with the highest genetic for Alzheimer's disease.
The gene in question, called APOE, is involved in transporting cholesterol to neurons (brain cells).
About one in five Americans carries a variant of the APOE gene called APOE-ε4, which significantly raises the risk of developing Alzheimer's disease.
Importantly, the study participants who carried the APOE-ε4 gene variant showed the most benefit from eating seafood at least twice a week.
These results confirm the many prior findings that eating a seafood-rich diet brings brain benefits that outweigh the risks of consuming more mercury.
And the findings provide special hope for people at the highest gene-related risk of developing Alzheimer's.
Why would seafood help?
Fish and shellfish are the only food sources of omega-3 DHA.
DHA is a critical structural and functional component of brain cells, and also plays a key role in preventing chronic inflammation, which has been tied to Alzheimer's disease.
- Beydoun MA, Kaufman JS, Satia JA, Rosamond W, Folsom AR. Plasma n-3 fatty acids and the risk of cognitive decline in older adults: the Atherosclerosis Risk in Communities Study. Am J Clin Nutr. 2007 Apr;85(4):1103-11.
- Björnberg KA, Vahter M, Grawé KP, Berglund M. Methyl mercury exposure in Swedish women with high fish consumption. Sci Total Environ. 2005 Apr 1;341(1-3):45-52.
- Connor WE, Connor SL. The importance of fish and docosahexaenoic acid in Alzheimer disease. Am J Clin Nutr. 2007 Apr;85(4):929-30.
- Dangour AD, Allen E, Elbourne D, Fasey N, Fletcher AE, Hardy P, Holder GE, Knight R, Letley L, Richards M, Uauy R. Effect of 2-y n-3 long-chain polyunsaturated fatty acid supplementation on cognitive function in older people: a randomized, double-blind, controlled trial. Am J Clin Nutr. 2010 Jun;91(6):1725-32. doi: 10.3945/ajcn.2009.29121. Epub 2010 Apr 21.
- Karimi R, Silbernagel S, Fisher NS, Meliker JR. Elevated blood Hg at recommended seafood consumption rates in adult seafood consumers. Int J Hyg Environ Health. 2014 Sep;217(7):758-64. doi: 10.1016/j.ijheh.2014.03.007. Epub 2014 Apr 6.
- Morris MC, Brockman J, Schneider JA, Wang Y, Bennett DA, Tangney CC, van de Rest O. Association of Seafood Consumption, Brain Mercury Level, and APOE ε4 Status With Brain Neuropathology in Older Adults. JAMA. 2016 Feb 2;315(5):489-97. doi: 10.1001/jama.2015.19451.
- Morris MC, Evans DA, Bienias JL, Tangney CC, Bennett DA, Wilson RS, Aggarwal N, Schneider J. Consumption of fish and n-3 fatty acids and risk of incident Alzheimer disease. Arch Neurol. 2003 Jul;60(7):940-6.
- Morris MC, Evans DA, Tangney CC, Bienias JL, Wilson RS. Fish consumption and cognitive decline with age in a large community study. Arch Neurol. 2005 Dec;62(12):1849-53. Epub 2005 Oct 10.
- Nielsen SJ, Aoki Y, Kit BK, Ogden CL. More than half of US youth consume seafood and most have blood mercury concentrations below the EPA reference level, 2009-2012. J Nutr. 2015 Feb;145(2):322-7. doi: 10.3945/jn.114.203786. Epub 2014 Dec 17.
- Nielsen SJ, Kit BK, Aoki Y, Ogden CL. Seafood consumption and blood mercury concentrations in adults aged ≥20 y, 2007-2010. Am J Clin Nutr. 2014 May;99(5):1066-70. doi: 10.3945/ajcn.113.077081. Epub 2014 Feb 12.
- Schaefer EJ, Bongard V, Beiser AS, Lamon-Fava S, Robins SJ, Au R, Tucker KL, Kyle DJ, Wilson PW, Wolf PA. Plasma phosphatidylcholine docosahexaenoic Acid content and risk of dementia and Alzheimer disease: the framingham heart study. Arch Neurol. 2006 Nov;63(11):1545-50.
- van de Rest O, Wang Y, Barnes LL, Tangney C, Bennett DA, Morris MC. APOE ε4 and the associations of seafood and long-chain omega-3 fatty acids with cognitive decline. Neurology. 2016 May 31;86(22):2063-70. doi: 10.1212/WNL.0000000000002719. Epub 2016 May 4.
- van Gelder BM, Tijhuis M, Kalmijn S, Kromhout D. Fish consumption, n-3 fatty acids, and subsequent 5-y cognitive decline in elderly men: the Zutphen Elderly Study. Am J Clin Nutr. 2007 Apr;85(4):1142-7.