Lead study author Dr. Cyrus Raji, PhD, from the University of Pittsburgh Medical Center, said this is the first study to establish a direct relationship between fish consumption, brain structure, and the risk of Alzheimer's disease.
"What MRI does that makes this study unique is that it shows the relationships between these lifestyle factors and the brain in ways that had never been seen before," Raji told AuntMinnie.com. "We can tell exactly what parts of the brain are being affected based on the different lifestyle factors, and how these increases in brain volume with good lifestyle factors -- such as eating baked or broiled fish -- reduce the risk of Alzheimer's disease. From a radiology standpoint, [MRI] was absolutely crucial for understanding these relationships."
Over the past several years, Raji and his colleagues have used MRI in similar research on mild cognitive impairment and Alzheimer's disease, focusing on how obesity can shrink the volume of gray matter in the brain, and how physical activity can promote larger brain volume and potentially reduce the risk for Alzheimer's disease.
Gray-matter volume is crucial to brain health; when it increases, brain health is maintained. Decreases in gray-matter volume indicate that brain cells are shrinking.
This study used the same 260 patients from the Cardiovascular Health Study - Cognition Study (CHS-CS) who contributed to the previous research. "This is what makes all these different studies possible, because we have this cohort of individuals whom we started following 20 years ago in their mid-60s up to their 80s," Raji explained. "We have 20 years worth of clinical data, such as physical activity, vascular disease, and obesity. We also have dietary information on the consumption of different types of foods."
Each patient underwent a 3D volumetric MRI exam of the brain. Voxel-based morphometry, a brain-mapping technique that measures gray-matter volume, was used to model the relationship between weekly fish consumption at baseline and brain structure 10 years later.
The 260 individuals also received a standard National Cancer Institute questionnaire at the beginning of the CHS-CS study on, among other things, their food consumption, including how often they ate fish and whether it was baked, broiled, or fried.
"The reason the preparation is important is because the thinking is that the omega-3 fatty acids in the fish are benefiting the brain, giving the brain better structure and neural strength, so it can resist diseases such as Alzheimer's, allowing the brain to age better," Raji said. "You will get a better delivery of omega-3s if you have baked or broiled fish than if you have fried fish."
The researchers found that 163 (63%) of the 260 subjects consumed baked or broiled fish on a weekly basis, typically between one to four times per week. MR images showed that those individuals have increased gray-matter brain volume in the same areas that are responsible for memory, learning, and executive function. Those regions include the frontal lobes, hippocampus, orbital frontal cortex, and posterior cingulate gyrus.
"We found that if our subjects receive the benefits of more gray-matter volume with fish consumption, then the risk for Alzheimer's disease went down over a five-year period three- to fivefold," Raji said.
The researchers found no statistically significant relationship between consumption of fried fish and brain structure or cognitive decline. In other words, eating fried fish did not increase brain volume or protect against cognitive decline.
Raji noted that the study controlled for other brain-affecting lifestyle factors, such as waist-to-hip ratio, physical activity, age, gender, education, race, and the presence or absence of apolipoprotein E4 (a gene that increases the risk of developing Alzheimer's disease), all of which the group has previously researched.
"Even after accounting for all these variables, we found that fish consumption as little as one time a week can increase the volume of the brain," Raji added.
The main message of the study is that the more baked or broiled fish individuals consume, the more gray-matter brain volume they will have as they age. Having more gray matter in the future, in turn, lessens their risk for Alzheimer's disease, the researchers concluded.