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Chen C, Xun P, Kaufman JD, et al. Erythrocyte omega-3 index, environmental particulate matter pollution and brain aging.neurology. 2020;95(8):e995-e1007.
Objective
To determine whether omega-3 fatty acid levels reduce the potential neurotoxic effects of exposure to particles with diameters less than 2.5 µm (PM2.5) on normal-appearing brain volumes in dementia-free older women
Draft
Observational study
Participant
This observational study included a total of 1,315 women (aged 65 to 80 years; mean age 70 years at baseline) who participated in the WHIMS-MRI (Women's Health Initiative Memory Study - Magnetic Resonance Imaging) study and were free of dementia between 1996 and 1999. These participants underwent structural brain MRIs in 2005 to 2006. This cohort was a subset of the 7,427 people who participated in the Women's Health Initiative (WHI-CT) clinical trials of postmenopausal hormone therapy.
Exposure measures
Investigators calculated average PM2.5Exposure for each study participant based on their place of residence in the 3 years prior to their MRI. They determined long-chain omega-3 polyunsaturated fatty acids (LCn3PUFAs) intake and fish consumption using semi-quantitative food frequency questionnaires and then calculated the average amount of fish each woman consumed each week, including grilled or baked fish, canned tuna, tuna salad, tuna casserole, and non-fried shellfish. Investigators did not include any fried fish because research has shown that deep-frying damages omega-3 fatty acids.
Investigators measured baseline levels of omega-3 PUFA in participants' red blood cells (RBCs) and compared them to PM2.5Exposure and brain volumes as calculated from the MRIs.
Target parameters
The researchers calculated common associations of baseline omega-3 PUFAs in red blood cells and PM2.5Exposure to brain volumes in generalized linear models.
Key insights
After adjusting for potential confounders, women in this cohort who had higher levels of RBC LCn3PUFAs had significantly larger white matter and hippocampal volumes in their brains. For each interquartile increment (2.02%) in the omega-3 index, the average volume was 5.03 cm3(P<0.01) larger in white matter and 0.08 cm3(P=0.03) larger in the hippocampus. The associations with erythrocyte, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) levels were similar. Higher LCn3PUFA levels attenuated the inverse associations between PM2.5White matter exposure and volumes throughout the brain and in multimodal association areas (frontal, parietal, and temporal; allPfor interaction <0.05), while the associations with other brain regions were not modified. Consistent results were found for a linear relationship between dietary intake of LCn3PUFAs and non-fried fish.
These results suggest that in older women, the brain aging benefits of omega-3 PUFAs may include protection against the adverse effects of air pollution on white matter volume.
Clinical implications
In recent years we have seen the steady accumulation of evidence pointing to exposure to air pollutants, particularly superfine particulate matter2.5Produced by combustion increases the risk of various neurological disorders, including stroke, cognitive decline and accelerated brain aging. These particulate matter are also strongly linked to cardiovascular disease and all-cause mortality.1Exposure to ambient particulate matter2.5is now considered an environmental risk factor for cognitive decline in older people.2One of the more striking measures of this association is the link between PM2.5and reduced brain volume in older women, which the authors of the current study reported in 2015.3
PM2.5is tiny enough to enter the bloodstream directly through the respiratory tract. As blood flows through the body, these particles trigger inflammation that damages other systems, including the brain. LCn3PUFAs are important components of synaptic membranes and are critical for maintaining brain structure and function in aging, and these specific types of fat are associated with greater total brain volume and gray matter.4.5Fish oils have also been reported to reduce brain damage from a number of environmental toxins such as lead, organic solvents and mercury.6.7
In this report, Chen et al show that omega-3 fatty acid levels weaken the inverse association between PM2.5and volume of white matter in the brain. A simpler way to put this is that eating fish appears to protect against the brain damage caused by PM2.5Air pollution.
Even what many consider moderate fish consumption appears to be enough to counteract the harm associated with this air pollution: the omega-3 fatty acids in just 1 to 2 servings of fish per week were enough to provide significant benefit.
From 2009 to 2016, particulate matter levels in U.S. air fell by about 25%. According to a 2019 working paper from the National Bureau of Economic Research (NBER), this trend suddenly shifted in 2016, and PM2.5The level began to rise and increased by 5.5% by 2018.8This increase was caused by a nearly 30% increase in air pollutant levels in western states. A number of factors contributed to this increase, including increases in driving, natural gas burning and wildfires. The researchers also suggest that a contributor had reduced Clean Air Act enforcement from 2009 to 2016 and into 2018. This law and its updates were responsible for the strict air pollution standards set for power plants, factories, vehicles, etc. and other sources of pollution. Enforcement of these laws had significantly improved air quality across the country. A 2011 estimate by the Environmental Protection Agency found that these regulations would prevent 230,000 premature deaths by 2020.9In contrast, the authors of the NBER paper calculated that PM increased by 5.5%2.5The national level from 2016 to 2018 was associated with nearly 10,000 additional premature deaths during that time. These calculations do not take into account risks for diseases that have only recently been linked to air quality, such as the increased risk of brain volume effects found in the study by Chen et al. is described.
The omega-3 fatty acids in just 1 to 2 servings of fish per week were enough to provide significant benefit.
Two executive orders in early June 2020 further weakened environmental protections. The first order temporarily waived environmental reviews of infrastructure projects to encourage construction during the economic slowdown caused by Covid-19. The second rule changed the methodology used by EPA for cost-benefit analyzes arising from the Clean Air Act regulation and severely limited the strength of future air pollution controls.10
Given these measures and numerous other policy changes in recent years, we can expect air quality in our country to continue to deteriorate. Encouraging our patients to eat fish regularly - 2 servings per week, as in the study by Chen et al. suggested – is certainly prudent, pragmatic and advisable. This will provide our patients with some “place of control” and allow them to feel that they still have an opportunity to influence their future and their health. Still, as a naturopathic doctor who preachesgreat chewy(meaning find the cause), this fish eating ad feels like it's directing our attention in the wrong direction. We should strive to create a cleaner environment and reduce pollution. Increasing pollution is the problem, not a lack of fish.