Why has fish consumption been associated with cognitive impairment and loss of executive function?
Is Fish “Brain Food” for Older Adults?
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In the landmark Global Burden of Disease study, researchers compiled the top 20 causes of death and disability. Number one on the list was high blood pressure, two and three were smoking. The number four leading cause of loss of life and health was not eating enough fruit. Lack of exercise was number ten, then too much sodium, then not enough nuts and seeds, not enough whole grains, not enough vegetables, and number 18 was not getting enough long-chain omega 3 fatty acids found in seafood due to its purported protective effect against heart disease.
Even years ago, when this was published, however, they were already questioning the benefits of these fish fats, as more and more randomized controlled trials put them to the test and they failed, culminating in the recent meta-analysis that I profiled previously, that appeared to put the issue to rest.
Cardiovascular protection isn’t the only thing fishes and fish oil consumption were hyped for, though. Omega-3s have also been touted to treat depression. But after taking into account all the negative results that went unpublished, there appears to be no benefit for major depression, or for preventing suicide—as I explored previously in my video on fish consumption and suicide.
But what about for the prevention of cognitive decline, or dementia? The available randomized controlled trials show no benefit for cognitive function with omega-3 supplementation in studies lasting from six months to 40 months among healthy older adults.
It may sometimes even make things worse. Higher current fish consumption predicted worse cognitive performance, and greater past fish consumption in childhood predicted slowed perceptual speed and reaction time. This may be due to neurotoxic contaminants, such as mercury, in fishes. We’ve known that the developing brain is particularly sensitive to the damaging effects of mercury, but maybe the aging brain is as well.
This would explain results like this, where higher omega-3 levels were associated with high levels of cognitive impairment and dementia. More EPA found in the cognitively impaired, and more DHA found in the demented—presumably because of pollutants like mercury and PCBs in seafood that have been related to cognitive impairment and Alzheimer’s disease.
The same cognitive functions disrupted in adults, like attention, fine motor function, and verbal memory, are similar to some of those previously reported in children exposed in the womb. And the adults exposed to mercury through fish consumption didn’t just have subtle EEG brain wave changes or something, but observable deficits in neurobehavioral performance measures—for example, poorer performance on tests of fine motor speed, and dexterity, and concentration. Some aspects of verbal learning and memory were also disrupted by mercury exposure, and the greater the mercury levels, the worse they did.
But look, this study was done downstream of a gold mining area, a process that uses lots of mercury. Other such studies were done on people eating fishes next to chemical plants or toxic spills or eating whale meat. What about a more mainstream population, an elite group of well-educated participants, really well educated—most were corporate executives like CEOs, all living in Florida, and wealthy enough to afford so much seafood that at least 43% exceeded the EPA’s safety limit for mercury. And it had an effect.
Excessive seafood intake, which they defined as like more than three to four servings per month of fishes, like tunas or snappers, elevates mercury levels and causes cognitive dysfunction. Not much, only about a 5% drop in cognitive performance, but a decrement that no one, let alone a health conscious and achievement-oriented person, is likely to welcome.
It’s worth noting the irony of the situation; the fact that corporate executives who choose to overconsume seafood for health reasons instead sustained a drop in their executive functions as a result. Yet, if a 4.8% drop in executive function due to excessive seafood intake occurs in highly functioning, healthy adults with ample cognitive reserve, the major concern is whether similar mercury level elevations in individuals already suffering from cognitive decline might result in substantially greater declines—particularly with cognitive decline and dementia, and seafood consumption, on the rise.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
Please consider volunteering to help out on the site.
- E Sydenham, A D Dangour, W S Lim. Omega 3 fatty acid for the prevention of cognitive decline and dementia. Cochrane Database Syst Rev. 2012 Jun 13;6:CD005379.
- V Danthiir, D Hosking, N R Burns, C Wilson, T Nettelbeck, E Calvaresi, P Clifton, G A Wittert. Cognitive performance in older adults is inversely associated with fish consumption but not erythrocyte membrane n-3 fatty acids. J Nutr. 2014 Mar;144(3):311-20.
- J W Chang, M C Pai, H L Chen, H R Guo, H J Su, C C Lee. Cognitive function and blood methylmercury in adults living near a deserted chloralkali factory. Environ Res. 2008 Nov;108(3):334-9.
- E M Yokoo, J G Valente, L Grattan, S L Schmidt, I Platt, E K Silbergeld. Low level methylmercury exposure affects neuropsychological function in adults. Environ Health. 2003 Jun 4;2(1):8.
- D Laurin, R Verreault, J Lindsay, E Dewailly, B J Holub. Omega-3 fatty acids and risk of cognitive impairment and dementia. J Alzheimers Dis. 2003 Aug;5(4):315-22.
- S C Masley, L V Masley, C T Gualtieri. Effect of Mercury Levels and Seafood Intake on Cognitive Function in Middle-aged Adults.
- S S Lim, T Vos, A D Flaxman, G Danaei, K Shibuya, H Adair-Rohani, M Amann, H R Anderson, K G Andrews, M Aryee, C Atkinson, L J Bacchus, A N Bahalim, K Balakrishnan, J Balmes, S Barker-Collo, A Baxter, M L Bell, J D Blore, F Blyth, C Bonner, G Borges, R Bourne, M Boussinesq, M Brauer, P Brooks, N G Bruce, B Brunekreef, C Bryan-Hancock, C Bucello, R Buchbinder, F Bull, R T Burnett, T E Byers, B Calabria, J Carapetis, E Carnahan, Z Chafe, F Charlson, H Chen, J S Chen, A T Cheng, J C Child, A Cohen, K E Colson, B C Cowie, S Darby, S Darling, A Davis, L Degenhardt, F Dentener, D C Des Jarlais, K Devries, M Dherani, E L Ding, E R Dorsey, T Driscoll, K Edmond, S E Ali, R E Engell, P J Erwin, S Fahimi, G Falder, F Farzadfar, A Ferrari, M M Finucane, S Flaxman, F G Fowkes, G Freedman, M K Freeman, E Gakidou, S Ghosh, E Giovannucci, G Gmel, K Graham, R Grainger, B Grant, D Gunnell, H R Gutierrez, W Hall, H W Hoek, A Hogan, H D Hosgood 3rd, D Hoy, H Hu, B J Hubbell, S J Hutchings, S E Ibeanusi, G L Jacklyn, R Jasrasaria, J B Jonas, H Kan, J A Kanis, N Kassebaum, N Kawakami, Y H Khang, S Khatibzadeh, J P Khoo, C Kok, F Laden, R Lalloo, Q Lan, T Lathlean, J L Leasher, J Leigh, Y Li, J K Lin, S E Lipshultz, S London, R Lozano, Y Lu, J Mak, R Malekzadeh, L Mallinger, W Marcenes, L March, R Marks, R Martin, P McGale, J McGrath, S Mehta, G A Mensah, T R Merriman, R Micha, C Michaud, V Mishra, K Mohd Hanafiah, A A Mokdad, L Morawska, D Mozaffarian, T Murphy, M Naghavi, B Neal, P K Nelson, J M Nolla, R Norman, C Olives, S B Omer, J Orchard, R Osborne, B Ostro, A Page, K D Pandey, C D Parry, E Passmore, J Patra, N Pearce, P M Pelizzari, M Petzold, M R Phillips, D Pope, C A Pope 3rd, J Powles, M Rao, H Razavi, E A Rehfuess, J T Rehm, B Ritz, F P Rivara, T Roberts, C Robinson, J A Rodriguez-Portales, I Romieu, R Room, L C Rosenfeld, A Roy, L Rushton, J A Salomon, U Sampson, L Sanchez-Riera, E Sanman, A Sapkota, S Seedat, P Shi, K Shield, R Shivakoti, G M Singh, D A Sleet, E Smith, K R Smith, N J Stapelberg, K Steenland, H Stöckl, L J Stovner, K Straif, L Straney, G D Thurston, J H Tran, R Van Dingenen, A van Donkelaar, J L Veerman, L Vijayakumar, R, Weintraub, M M Weissman, R A White, H Whiteford, S T Wiersma, J D Wilkinson, H C Williams, W Williams, N Wilson, A D Woolf, P Yip, J M Zielinski. A D Lopez, C J Murray, M Ezzati, M A AlMazroa, Z A Memish. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet. 2012 Dec 15;380(9859):2224-60.
- A C Tsai, M Lucas, O I Okereke, E J O'Reilly, F Mirzaei, I Kawachi, A Ascherio, W C Willett. Suicide mortality in relation to dietary intake of n-3 and n-6 polyunsaturated fatty acids and fish: equivocal findings from 3 large US cohort studies. Am J Epidemiol. 2014 Jun 15;179(12):1458-66.
- M H Bloch, J Hannestad. Omega-3 fatty acids for the treatment of depression: systematic review and meta-analysis. Mol Psychiatry. 2012 Dec;17(12):1272-82.
- M H Bloch, J Hannestad. Response to critiques on ‘Omega-3 fatty acids for the treatment of depression:systematic review andmeta-analysis’ . Molecular Psychiatry 17, 1163-1167 (December 2012).
- Evangelos C. Rizos, MD, PhD; Evangelia E. Ntzani, MD, PhD; Eftychia Bika, MD; Michael S. Kostapanos, MD; Moses S. Elisaf, MD, PhD, FASA, FRSH. Association Between Omega-3 Fatty Acid Supplementation and Risk of Major Cardiovascular Disease EventsA Systematic Review and Meta-analysis
Image thanks to samkerridge via Pixabay
In the landmark Global Burden of Disease study, researchers compiled the top 20 causes of death and disability. Number one on the list was high blood pressure, two and three were smoking. The number four leading cause of loss of life and health was not eating enough fruit. Lack of exercise was number ten, then too much sodium, then not enough nuts and seeds, not enough whole grains, not enough vegetables, and number 18 was not getting enough long-chain omega 3 fatty acids found in seafood due to its purported protective effect against heart disease.
Even years ago, when this was published, however, they were already questioning the benefits of these fish fats, as more and more randomized controlled trials put them to the test and they failed, culminating in the recent meta-analysis that I profiled previously, that appeared to put the issue to rest.
Cardiovascular protection isn’t the only thing fishes and fish oil consumption were hyped for, though. Omega-3s have also been touted to treat depression. But after taking into account all the negative results that went unpublished, there appears to be no benefit for major depression, or for preventing suicide—as I explored previously in my video on fish consumption and suicide.
But what about for the prevention of cognitive decline, or dementia? The available randomized controlled trials show no benefit for cognitive function with omega-3 supplementation in studies lasting from six months to 40 months among healthy older adults.
It may sometimes even make things worse. Higher current fish consumption predicted worse cognitive performance, and greater past fish consumption in childhood predicted slowed perceptual speed and reaction time. This may be due to neurotoxic contaminants, such as mercury, in fishes. We’ve known that the developing brain is particularly sensitive to the damaging effects of mercury, but maybe the aging brain is as well.
This would explain results like this, where higher omega-3 levels were associated with high levels of cognitive impairment and dementia. More EPA found in the cognitively impaired, and more DHA found in the demented—presumably because of pollutants like mercury and PCBs in seafood that have been related to cognitive impairment and Alzheimer’s disease.
The same cognitive functions disrupted in adults, like attention, fine motor function, and verbal memory, are similar to some of those previously reported in children exposed in the womb. And the adults exposed to mercury through fish consumption didn’t just have subtle EEG brain wave changes or something, but observable deficits in neurobehavioral performance measures—for example, poorer performance on tests of fine motor speed, and dexterity, and concentration. Some aspects of verbal learning and memory were also disrupted by mercury exposure, and the greater the mercury levels, the worse they did.
But look, this study was done downstream of a gold mining area, a process that uses lots of mercury. Other such studies were done on people eating fishes next to chemical plants or toxic spills or eating whale meat. What about a more mainstream population, an elite group of well-educated participants, really well educated—most were corporate executives like CEOs, all living in Florida, and wealthy enough to afford so much seafood that at least 43% exceeded the EPA’s safety limit for mercury. And it had an effect.
Excessive seafood intake, which they defined as like more than three to four servings per month of fishes, like tunas or snappers, elevates mercury levels and causes cognitive dysfunction. Not much, only about a 5% drop in cognitive performance, but a decrement that no one, let alone a health conscious and achievement-oriented person, is likely to welcome.
It’s worth noting the irony of the situation; the fact that corporate executives who choose to overconsume seafood for health reasons instead sustained a drop in their executive functions as a result. Yet, if a 4.8% drop in executive function due to excessive seafood intake occurs in highly functioning, healthy adults with ample cognitive reserve, the major concern is whether similar mercury level elevations in individuals already suffering from cognitive decline might result in substantially greater declines—particularly with cognitive decline and dementia, and seafood consumption, on the rise.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
Please consider volunteering to help out on the site.
- E Sydenham, A D Dangour, W S Lim. Omega 3 fatty acid for the prevention of cognitive decline and dementia. Cochrane Database Syst Rev. 2012 Jun 13;6:CD005379.
- V Danthiir, D Hosking, N R Burns, C Wilson, T Nettelbeck, E Calvaresi, P Clifton, G A Wittert. Cognitive performance in older adults is inversely associated with fish consumption but not erythrocyte membrane n-3 fatty acids. J Nutr. 2014 Mar;144(3):311-20.
- J W Chang, M C Pai, H L Chen, H R Guo, H J Su, C C Lee. Cognitive function and blood methylmercury in adults living near a deserted chloralkali factory. Environ Res. 2008 Nov;108(3):334-9.
- E M Yokoo, J G Valente, L Grattan, S L Schmidt, I Platt, E K Silbergeld. Low level methylmercury exposure affects neuropsychological function in adults. Environ Health. 2003 Jun 4;2(1):8.
- D Laurin, R Verreault, J Lindsay, E Dewailly, B J Holub. Omega-3 fatty acids and risk of cognitive impairment and dementia. J Alzheimers Dis. 2003 Aug;5(4):315-22.
- S C Masley, L V Masley, C T Gualtieri. Effect of Mercury Levels and Seafood Intake on Cognitive Function in Middle-aged Adults.
- S S Lim, T Vos, A D Flaxman, G Danaei, K Shibuya, H Adair-Rohani, M Amann, H R Anderson, K G Andrews, M Aryee, C Atkinson, L J Bacchus, A N Bahalim, K Balakrishnan, J Balmes, S Barker-Collo, A Baxter, M L Bell, J D Blore, F Blyth, C Bonner, G Borges, R Bourne, M Boussinesq, M Brauer, P Brooks, N G Bruce, B Brunekreef, C Bryan-Hancock, C Bucello, R Buchbinder, F Bull, R T Burnett, T E Byers, B Calabria, J Carapetis, E Carnahan, Z Chafe, F Charlson, H Chen, J S Chen, A T Cheng, J C Child, A Cohen, K E Colson, B C Cowie, S Darby, S Darling, A Davis, L Degenhardt, F Dentener, D C Des Jarlais, K Devries, M Dherani, E L Ding, E R Dorsey, T Driscoll, K Edmond, S E Ali, R E Engell, P J Erwin, S Fahimi, G Falder, F Farzadfar, A Ferrari, M M Finucane, S Flaxman, F G Fowkes, G Freedman, M K Freeman, E Gakidou, S Ghosh, E Giovannucci, G Gmel, K Graham, R Grainger, B Grant, D Gunnell, H R Gutierrez, W Hall, H W Hoek, A Hogan, H D Hosgood 3rd, D Hoy, H Hu, B J Hubbell, S J Hutchings, S E Ibeanusi, G L Jacklyn, R Jasrasaria, J B Jonas, H Kan, J A Kanis, N Kassebaum, N Kawakami, Y H Khang, S Khatibzadeh, J P Khoo, C Kok, F Laden, R Lalloo, Q Lan, T Lathlean, J L Leasher, J Leigh, Y Li, J K Lin, S E Lipshultz, S London, R Lozano, Y Lu, J Mak, R Malekzadeh, L Mallinger, W Marcenes, L March, R Marks, R Martin, P McGale, J McGrath, S Mehta, G A Mensah, T R Merriman, R Micha, C Michaud, V Mishra, K Mohd Hanafiah, A A Mokdad, L Morawska, D Mozaffarian, T Murphy, M Naghavi, B Neal, P K Nelson, J M Nolla, R Norman, C Olives, S B Omer, J Orchard, R Osborne, B Ostro, A Page, K D Pandey, C D Parry, E Passmore, J Patra, N Pearce, P M Pelizzari, M Petzold, M R Phillips, D Pope, C A Pope 3rd, J Powles, M Rao, H Razavi, E A Rehfuess, J T Rehm, B Ritz, F P Rivara, T Roberts, C Robinson, J A Rodriguez-Portales, I Romieu, R Room, L C Rosenfeld, A Roy, L Rushton, J A Salomon, U Sampson, L Sanchez-Riera, E Sanman, A Sapkota, S Seedat, P Shi, K Shield, R Shivakoti, G M Singh, D A Sleet, E Smith, K R Smith, N J Stapelberg, K Steenland, H Stöckl, L J Stovner, K Straif, L Straney, G D Thurston, J H Tran, R Van Dingenen, A van Donkelaar, J L Veerman, L Vijayakumar, R, Weintraub, M M Weissman, R A White, H Whiteford, S T Wiersma, J D Wilkinson, H C Williams, W Williams, N Wilson, A D Woolf, P Yip, J M Zielinski. A D Lopez, C J Murray, M Ezzati, M A AlMazroa, Z A Memish. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet. 2012 Dec 15;380(9859):2224-60.
- A C Tsai, M Lucas, O I Okereke, E J O'Reilly, F Mirzaei, I Kawachi, A Ascherio, W C Willett. Suicide mortality in relation to dietary intake of n-3 and n-6 polyunsaturated fatty acids and fish: equivocal findings from 3 large US cohort studies. Am J Epidemiol. 2014 Jun 15;179(12):1458-66.
- M H Bloch, J Hannestad. Omega-3 fatty acids for the treatment of depression: systematic review and meta-analysis. Mol Psychiatry. 2012 Dec;17(12):1272-82.
- M H Bloch, J Hannestad. Response to critiques on ‘Omega-3 fatty acids for the treatment of depression:systematic review andmeta-analysis’ . Molecular Psychiatry 17, 1163-1167 (December 2012).
- Evangelos C. Rizos, MD, PhD; Evangelia E. Ntzani, MD, PhD; Eftychia Bika, MD; Michael S. Kostapanos, MD; Moses S. Elisaf, MD, PhD, FASA, FRSH. Association Between Omega-3 Fatty Acid Supplementation and Risk of Major Cardiovascular Disease EventsA Systematic Review and Meta-analysis
Image thanks to samkerridge via Pixabay
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Is Fish “Brain Food” for Older Adults?
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Content URLDoctor's Note
Fruit deficiency as the #1 dietary risk factor? For more, see Inhibiting Platelet Aggregation with Berries.
But what about those healthy Eskimos? See Omega-3s and the Eskimo Fish Tale.
For more on the shift of the evidence on fish and heart disease, see Is Fish Oil Just Snake Oil?
The greatest danger of mercury exposure may be for children; see
Other videos on the effect of fish contaminants and health among adults include Fish and Diabetes and Fish Consumption and Suicide.
Mercury is not the only neurotoxic contaminant of seafood, though. See Diet and Amyotrophic Lateral Sclerosis (ALS) and ALS (Lou Gehrig’s Disease): Fishing for Answers.
Are Fish or Fish Oil Supplements Good for the Heart? Check out the video.
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