March 22, 2005 -- There is new evidence that
Currently, there is no cure for Alzheimer's disease, the most common form of mental decline in older adults. The latest findings -- which are based on a study of lab mice -- don't change that. But they enhance fish oil's reputation as a "brain food" that may help protect the brain from the ravages of Alzheimer's disease.
Researchers worldwide are hot on the trail of an Alzheimer's cure. They're studying everything from diet to mental activity, while working on new Alzheimer's drugs.
The need has never been greater. About 4.5 million people in the U.S. have Alzheimer's disease, says the Alzheimer's Association. By the year 2050, that number may rise to 11-16 million people, the association estimates.
Alzheimer's disease is a progressive condition. Gradually, it damages areas of the brain involved in memory, intelligence, language, judgment, and behavior. Alzheimer's becomes more common with age, striking one in 10 people over age 65 and nearly half of those over 85.
But Alzheimer's disease is not an inevitable part of aging. It's less common in some populations that eat a lot of fish, researchers have noticed.
Those studies don't prove that fish oil prevents Alzheimer's disease. But they have sparked curiosity about one of the fish oils called DHA (docosahexaenoic acid).found in abundance in cold-water fish such as salmon, mackerel, herring, and sardines.
Omega-3 Fatty Acids in the Spotlight
You may have heard about omega-3 fatty acids before. They're getting lots of attention, with studies probing their effects on depression, arthritis, and heart health, besides Alzheimer's disease.
The body needs omega-3 fatty acids and their relative -- omega-6 fatty acids -- to function properly. But the typical U.S. diet -- which isn't strong on fish -- tends to overload on omega-6 oils (due to increased use of vegetable oils) and skimp on omega-3s.
What if that changed? Could getting a little more DHA boost the brain's odds against Alzheimer's disease? That's what Giselle Lim, PhD, and colleagues wanted to learn.
Lim's team studied elderly mice with genes linked to an Alzheimer's-like brain condition. The mice were split into three groups.
One group of mice was fed normal chow. A second group got a diet low in DHA. The third group ate a diet high in DHA.
After three to five months -- the equivalent of several years for people -- the group that ate the most DHA had the healthiest brains. That is, they had the least amount of senile plaque and harmful proteins, which clump and knot in the brain in Alzheimer's disease.
Brain imaging showed that the high-DHA diet cut brain plaque by 40%. The largest drops were seen in brain areas vulnerable to Alzheimer's disease, according to the study.
The high-DHA diet also delivered the biggest drop (70%) in levels of beta-amyloid protein in the brain, a building block of plaque, compared to the other groups.
How Much Does It Take?
There is no official recommended daily allowance of DHA (or any omega-3 fatty acid). If you choose to eat fish, you may want to keep an eye on your intake due to concerns about contaminants such as mercury.
DHA and another omega-3 fatty acid, EPA, are found in fish, eggs fortified with omega-3 fatty acids, and fish oil supplements. Another omega-3 fatty acid, ALA, is found in walnuts, soybean oil, and flax seeds.
What About People?
Swedish researchers are studying the safety and tolerability of omega-3 fatty acids on people with mild to moderate Alzheimer's disease. Two studies are also comparing omega-3 fatty acids with placebos, note Lim and colleagues.
Lim is a postgraduate researcher at the University of California Los Angeles (UCLA). Other researchers included Greg Cole, PhD. He's a UCLA professor of medicine and neurology. Cole is also the associate director for research with the Geriatric Research, Education, and Clinical Center at the Greater Los Angeles Veteran's Administration Healthcare System.
The study appears in The Journal of Neuroscience's online edition for March 23.