Higher DHA levels associated with reduced risk of dementia
A report published in the November issue of the American Medical Association journal Archives of Neurology revealed the finding of Ernst J. Schaefer, MD, of Tufts University in Boston and his colleagues that having a higher blood level of the omega-3 fatty acid docosahexaenoic acid (DHA) may have a protective effect against the development of dementia and Alzheimer’s disease.
“The level of DHA in the brain has been shown to be very important for learning ability and memory in early life in studies of rodents, baboons and humans," writes Martha Clare Morris, ScD, of Rush University Medical Center in an editorial in the same issue of the journal. "It is only recently that the omega-3 fatty acids have been investigated for their importance to the aging brain. The DHA composition of the brain decreases with age as a result of increased oxidative damage to the lipid membranes."
The current study included 899 participants in the Framingham Heart Study. The subjects, who were an average of 76 years of age and free of dementia at the beginning of the study, underwent neuropsychological tests and provided blood samples that were analyzed for DHA levels. Four hundred eighty-eight of these participants also completed a dietary questionnaire. The group was followed for approximately nine years during which they received mental examinations every two years to screen for dementia.
During the follow-up period, 99 participants developed dementia. Of these, 71 were diagnosed with Alzheimer’s disease. After controlling for other factors including homocysteine levels, Dr Schaefer’s team found that subjects whose DHA levels were in the highest one-fourth of participants had a 47 percent lower risk of developing dementia and a 39 percent lower risk of Alzheimer’s disease than the rest of the subjects. Individuals in the top 25 percent reported eating more fish than the other three groups, with an mean intake of three times per week, providing an average of 180 milligrams DHA per day.
"In our study, the correlation between [blood] DHA content and fish intake was significant, indicating that fish intake is an important source of dietary DHA," the authors observed. "In the future, it will also be important to determine whether combined dietary supplementation with DHA can decrease further mental deterioration in patients with established dementia.”
Over the past 10 years, scientific studies have revealed the remarkable effects that fish consumption has on neurological function. Fish oils contain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both of which are omega-3 oils. DHA is essential to brain health because it constitutes between 30 and 50 percent of the total fatty acid content of the human brain (Young G et al 2005).
Deficiencies in DHA have been linked to cognitive decline, and human cell studies have shown that DHA reduces beta-amyloid secretion (Lukiw WJ et al 2005). DHA has been documented to increase phosphatidylserine, a naturally occurring component found in every cell membrane of the body (Akbar M et al 2005). DHA may also improve the memory of animals with Alzheimer's disease by suppressing oxidative damage in the brain (Hashimoto M et al 2005). In a 10-year study that tracked the DHA levels of 1188 elderly subjects, Alzheimer's disease was 67 percent more likely to develop in those whose DHA levels were in the lower half of the distribution (Kyle DJ et al 1999).
Scientists have recently developed a compound that takes DHA and binds it to a lecithin extract that has itself been shown to reduce the risk of cognitive dysfunction in the elderly. Laboratory studies document that this patented compound delivers higher DHA concentrations to brain cells.
The October 18, 2006 issue of the Journal of the American Medical Association published the conclusion of Dariush Mozaffarian, MD and Eric B. Rimm, MD of Harvard School of Public Health that any risks associated with eating fish are far outweighed by the benefits of consuming them.
"Overall, for major health outcomes among adults, the benefits of eating fish greatly outweigh the risks," Dr Mozaffarian stated. "Somehow this evidence has been lost on the public."
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