Study in older adults supports earlier evidence of anti-Alzheimer’s effects
by Craig Weatherby
Want to shave a few years off your chronological age, at least in terms of mental performance? Try eating fish one or two times a week.
Researchers at Rush University Medical Center analyzed six years of data from 3,718-plus participants in the Chicago Health and Aging Project aged 65 or older.
After accounting for possible confounding factors—including healthy lifestyle behaviors—participants who ate fish once a week slowed their age-associated loss of mental function by 10 percent per year, and those who ate fish twice a week slowed their loss of function by 13 percent per year.
As the authors put it, “The rate reduction is the equivalent of being 3 to 4 years younger in age.”
How the study worked
Over the course of the six-year study, researchers (Morris MC, Evans DA, Tangney CC, et al) visited participants at home three times, to administer tests of mental performance, and ask about consumption frequency of 139 different foods, their daily activities, exercise level, alcohol consumption, mental activity, sex, race, education, income, and medical history.
The questionnaire asked about participants’ consumption of tuna sandwiches, fried fish (sticks/cakes/sandwiches), and fresh fish as a main dish. The respondents’ consumption of shellfish (shrimp/lobster/crab) was recorded, but was not included in the calculation of weekly fish intake.
The results are considered especially reliable because the researchers administered multiple mental-performance tests over time: tactics designed to reduce bias and error.
Weak omega-3 link puzzles researchers
To their surprise, the Chicago researchers found no strong association between participants’ estimated intake of omega-3 fatty acids and measured reductions in cognitive decline—except among those who’d eaten the most fish for the longest time. They were surprised because earlier studies have found that higher blood levels of omega-3s correlate to a reduced risk of Alzheimer’s disease.
They proposed three possible reasons for the lack of a correlation between higher omega-3 consumption and delayed cognitive decline:
- “The absence of association with [omega-3] DHA raises the possibility that the observed fish association was due to some other dietary constituent or perhaps to another factor that is related to cognitive health and fish consumption.
- “We can only speculate that perhaps dietary -3 [omega-3] fatty acids have little impact on milder forms of cognitive decline.
- “Another plausible explanation is that our measure of DHA and EPA intake is too imprecise to detect an association with cognitive change. One large population-based study examined the fatty acid composition of erythrocyte (blood-cell) membranes in relation to 4-year change in Mini-Mental State Examination score and observed significant reductions in cognitive decline with increased levels of total -3 fatty acids, DHA, and EPA.
Despite the lack of a connection in this study, the strong brain-protective effects of omega-3s seen in many other studies make it likely that they were also responsible for the benefits seen in this study.
And, some of the beneficial effects seen in these fish eaters may have stemmed from the fact that it replaced meats in their diets. Red meats are high in the kinds of saturated fats that promote the vascular clogs linked to heart disease and dementia.
- Morris MC, Evans DA, Tangney CC, et al. Fish Consumption and Cognitive Decline With Age in a Large Community Study. Arch Neurol. 2005;62:(doi:10.1001/archneur.62.12.noc50161). Accessed online October 12, 2005 at http://archneur.ama-assn.org/cgi/content/full/62.12.noc50161v1
- Morris MC, Evans DA, Bienias JL, et al. Dietary fat intake and 6-year cognitive change in an older biracial community population. Neurology. 2004;62:1573-1579.
- Morris MC, Evans DA, Bienias JL, et al. Dietary fats and the risk of incident Alzheimer's disease. Arch Neurol. 2003;60:194-200.
- Albert M, Smith LA, Scherr PA, et al. Use of brief cognitive tests to identify individuals in the community with clinically-diagnosed Alzheimer's disease. Int J Neurosci. 1991;57:167-178.
- Barberger-Gateau P, Letenneur L, Deschamps V, et al. Fish, meat, and risk of dementia: cohort study. BMJ. 2002;325:932-933.
- Calon F, Lim GP, Yang F, et al. Docosahexaenoic acid protects from dendritic pathology in an Alzheimer's disease mouse model 1. Neuron. 2004;43:633-645.
- Connor WE. Importance of -3 fatty acids in health and disease. Am J Clin Nutr. 2000;71(1 suppl):171S-175S.
- Diggle PJ, Liang J-Y, Zeger SL. Analysis of Longitudinal Data. Oxford, England: Oxford University Press; 1994.
- Evans DA, Bennett DA, Wilson RS, et al. Incidence of Alzheimer's disease in a biracial urban community: relation to apolipoprotein E allele status. Arch Neurol. 2003;60:185-189.
- Folstein MF, Folstein SE, McHugh PR. "Mini-mental state": a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res. 1975;12:189-198.
- Gamoh S, Hashimoto M, Hossain S, Masumura S. Chronic administration of docosahexaenoic acid improves the performance of radial arm maze task in aged rats. Clin Exp Pharmacol Physiol. 2001;28:266-270.
- Gamoh S, Hashimoto M, Sugioka K, et al. Chronic administration of docosahexaenoic acid improves reference memory-related learning ability in young rats. Neuroscience. 1999;93:237-241.
- Gillum RF, Mussolino ME, Madans JH. The relationship between fish consumption and stroke incidence: the NHANES I Epidemiologic Follow-up Study (National Health and Nutrition Examination Survey). Arch Intern Med. 1996;156:537-542.
- Heude B, Ducimetiere P, Berr C. Cognitive decline and fatty acid composition of erythrocyte membranes—the EVA Study. Am J Clin Nutr. 2003;77:803-808.
- Iso H, Rexrode KM, Stampfer MJ, et al. Intake of fish and omega-3 fatty acids and risk of stroke in women. JAMA. 2001;285:304-312.
- Kalmijn S, Feskens EJ, Launer LJ, Kromhout D. Polyunsaturated fatty acids, antioxidants, and cognitive function in very old men. Am J Epidemiol. 1997;145:33-41.
- Kalmijn S, Launer LJ, Ott A, et al. Dietary fat intake and the risk of incident dementia in the Rotterdam Study. Ann Neurol. 1997;42:776-782.
- Keli SO, Feskens EJ, Kromhout D. Fish consumption and risk of stroke: the Zutphen Study. Stroke. 1994;25:328-332.
- Kohout FJ, Berkman LF, Evans DA, Cornoni-Huntley J. Two shorter forms of the CES-D depression symptoms index. J Aging Health. 1993;5:179-193.
- Lim S, Suzuki H. Changes in maze behavior of mice occur after sufficient accumulation of docosahexaenoic acid in brain. J Nutr. 2001;131:319-324.
- Lim SY, Suzuki H. Effect of dietary docosahexaenoic acid and phosphatidylcholine on maze behavior and fatty acid composition of plasma and brain lipids in mice. Int J Vitam Nutr Res. 2000;70:251-259.
- Morris MC, Colditz GA, Evans DA. Response to a mail nutritional survey in an older bi-racial community population. Ann Epidemiol. 1998;8:342-346.
- Morris MC, Evans DA, Bienias JL, et al. Consumption of fish and -3 fatty acids and risk of incident Alzheimer disease. Arch Neurol. 2003;60:940-946.
- Neuringer M, Anderson GJ, Connor WE. The essentiality of -3 fatty acids for the development and function of the retina and brain. Annu Rev Nutr. 1988;8:517-541.
- Orencia AJ, Daviglus ML, Dyer AR, et al. Fish consumption and stroke in men: 30-year findings of the Chicago Western Electric Study. Stroke. 1996;27:204-209.
- Rockett HR, Breitenbach M, Frazier AL, et al. Validation of a youth/adolescent food frequency questionnaire. Prev Med. 1997;26:808-816.
- Scherr PA, Albert MS, Funkenstein HH, et al. Correlates of cognitive function in an elderly community population. Am J Epidemiol. 1988;128:1084-1101.
- Smith A. Symbol Digit Modalities Test Manual. Revised. Los Angeles, Calif: Western Psychological; 1984.
- Sugimoto Y, Taga C, Nishiga M, et al. Effect of docosahexaenoic acid-fortified Chlorella vulgaris strain CK22 on the radial maze performance in aged mice. Biol Pharm Bull. 2002;25:1090-1092.
- Suzuki H, Park SJ, Tamura M, Ando S. Effect of the long-term feeding of dietary lipids on the learning ability, fatty acid composition of brain stem phospholipids and synaptic membrane fluidity in adult mice: a comparison of sardine oil diet with palm oil diet. Mech Ageing Dev. 1998;101:119-128.
- Willett W, Stampfer MJ. Total energy intake: implications for epidemiologic analysis. Am J Epidemiol. 1986;124:17-27.
- Wilson RS, Bennett DA, Beckett LA, et al. Cognitive activity in older persons from a geographically defined population. J Gerontol B Psychol Sci Soc Sci. 1999;54:P155-P160.