Higher DHA Intakes and Blood Levels Associated with Lower Risk of Dementia in Older Adults

March 21, 2011


High Dietary and Plasma Levels of the Omega-3 Fatty Acid Docosahexaenoic Acid are Associated with Decreased Dementia Risk : the Rancho Bernardo Study
Lopez, L. B. et al., J. Nutrition , Health and Aging , 15: 25-31 , 2011
Dept. of Family and Preventive Medicine , Univ. of California , San Diego, La Jolla , Calif., USA


Dementia is characterized as a deterioration of intellectual faculties , including memory , mental concentration, judgement , others due to a disorder of the brain . Alzheimer’s Disease (AD) , the most common form of dementia , is a major cause of disability and mortality in those aged 65 years and older. The purpose of the present study was to determine the relationship between higher dietary intakes of DHA omega-3 fatty acid and fish as well as having higher blood levels of DHA and the prevalence of dementia in an aging population. For this purpose, food frequency questionnaires along with DHA and fish intakes were conducted on 266 men and women (average age of 80 years ranging from 67-100 years) living in the community of Rancho Bernardo in Southern California. Further, the subjects performed a battery of neuropsychological tests to screen for dementia (including a Mini-Mental Status Exam, testing of visuomotor tracking and attention, memory assessment, category fluency, and the ability to store and retrieve spoken words ).

The results indicated that higher dietary intakes of DHA and higher DHA levels in the blood samples were associated with a significantly reduced prevalence of dementia. Higher dietary DHA intakes were also associated with a significantly reduced risk of having Alzheimer’s Disease. While a trend for an inverse relation between fish intake and all-cause dementia as well as Alzheimer’s Disease was observed, this did not reach statistical significance. The average daily intake of DHA omega-3 fatty acid was only 90 mg in those with all-cause dementia as compared to 160 mg in those without the condition. The authors concluded that ‘ Increasing DHA intake from marine sources may be recommended for reducing dementia risk’.

Dr. Holub's Comments:

Previous research (Morris et al., Arch. Neurology, 60: 940-946 (2003)) observed that higher intakes of both DHA and fish were associated with a lower risk for Alzheimer’s Disease . The failure for increased fish intake to correlate with less dementia in the present study may be due to the smaller population studied , the relatively low intake of fish, along with other factors. It is noted that the average fish intake (all subjects) averaged at only approx. one-half fish serving/week. Also, the reported average DHA intake of approx. 150 mg/day is only a fraction of daily intakes in Japan. It remains to be seen if the potential benefits of increased DHA intakes in the aging population from supplements or functional foods can mimic those from fish/seafood which also contain selenium (antioxidant) , iodine , other nutrients.

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