The idea that omega-3s from fish support brain health in middle-aged and older adults … even in younger people … keeps on accumulating evidence.
Still, we currently lack clear proof that omega-3s can treat Alzheimer’s disease, possibly because it develops over decades ... and because the disease appears resistant to their effects in people with common genetic risk factors (See “Omega-3 Didn't Delay Alzheimer's Decline”).
Now, the intriguing results of a study from Columbia University Medical Center suggest that diets high in omega-3 fatty acids from fish lower blood levels of a protein related to Alzheimer's disease.
The protein, called beta-amyloid, forms a neuron-killing “plaque” that abounds only in the brains of Alzheimer's patients, along with so-called “tangles” made of tau protein.
It’s not clear what causes beta-amyloid to accumulate and form a plaque – or whether that process is the underlying cause of the disease. In fact, clinical trials that have tested drugs or antibodies targeting amyloid production have been inconclusive (Reitz C 2012).
Instead, as a recent paper from the Boston University School of Medicine noted, “Late-onset Alzheimer's disease might result from the cumulative effects of at least four different factors: beta-amyloid accumulation, cardiovascular disease, aging, and the associated loss of synaptic plasticity, and inflammation.” (Wolozin B 2012)
Columbia study links omega-3-rich diets to lower beta-amyloid levels
A team led by Nikolaos Scarmeas, M.D., M.S., recruited 1,219 people over age 65 who were free of dementia symptoms (Gu Y et al. 2012).
The volunteers provided information about their diet for an average of 1.2 years before their blood was tested for beta-amyloid protein.
“While it's not easy to measure the level of beta-amyloid deposits in the brain in this type of study, it is relatively easy to measure the levels of beta-amyloid in the blood, which, to a certain degree, relates to the level in the brain," said Dr. Scarmeas.
The researchers estimated the participants’ intakes of 10 nutrients, including saturated fatty acids, omega-3 and omega-6 polyunsaturated fatty acids, monounsaturated fatty acid (as from olive and canola oils), vitamin E, vitamin C, beta-carotene, vitamin B12, folate, and vitamin D.
The results showed that the more omega-3 fatty acids a person consumed, the lower were their blood beta-amyloid levels.
Specifically, diets that provided one gram of omega-3s daily more than the participants’ average daily omega-3 intake was associated with 20 to 30 percent lower blood beta-amyloid levels.
The average American consumes only 91mg (0.91 grams) of omega-3s daily (AHRQ 2004). For reference, you would get one gram of omega-3s from a 3.5 oz (100 gram) serving of wild salmon, tuna, sardines, mackerel, or sablefish, or from two to three servings of richer white fish (e.g., cod or halibut) or most shellfish.
None of the other nine nutrients whose intakes were estimated were associated with having lower beta-amyloid levels.
Importantly, the results persisted after they were adjusted to account for major risk factors for Alzheimer's disease, including age, education, gender, ethnicity, average calories consumed, and APOE gene status.
As Dr. Scarmeas said, “Determining through further research whether omega-3 fatty acids or other nutrients relate to spinal fluid or brain beta-amyloid levels or levels of other Alzheimer's disease related proteins can strengthen our confidence on beneficial effects of parts of our diet in preventing dementia.”
Are you listening, NIH and other research funders?
Agency for Healthcare Research and Quality (AHRQ). Evidence Report/Technology Assessment: Number 94. Effects of Omega-3 Fatty Acids on Cardiovascular Disease. 2004. Accessed at http://www.ahrq.gov/downloads/pub/evidence/pdf/o3cardio/o3cardio.pdf
Cosentino SA, Stern Y, Sokolov E, Scarmeas N, Manly JJ, Tang MX, Schupf N, Mayeux RP. Plasma ß-amyloid and cognitive decline. Arch Neurol. 2010 Dec;67(12):1485-90. Epub 2010 Aug 9.
Gu Y et al. Nutrient intake and plasma β-amyloid. Neurology WNL.0b013e318258f7c. Published online before print May 2, 2012, doi: 10.1212/WNL.0b013e318258f7c2
Reitz C. Alzheimer's disease and the amyloid cascade hypothesis: a critical review. Int J Alzheimers Dis. 2012;2012:369808. Epub 2012 Mar 17.
Wolozin B. Statins and therapy of Alzheimer's disease: questions of efficacy versus trial design. Alzheimers Res Ther. 2012 Jan 16;4(1):3.