After taking into account all the negative results that went unpublished, there appears to be no benefit for major depression or for preventing suicide, as I explored in my video Is Fish Oil Just Snake Oil? [Visit Nutrition Facts/Videos to watch all of Dr. Greger's videos.]
Image Credit: Pixabay. This image has been modified.
In the landmark Global Burden of Disease study, researchers compiled the
top 20 causes of death and disability. Number one on the list was high blood
pressure, two and three was smoke, and the fourth leading cause of loss of
life and health was not eating enough fruit. Lack of exercise was number 10,
followed by too much sodium, not enough nuts and seeds, not enough whole
grains, and then not enough vegetables. Number 18 on the top 20 list was not
getting enough long-chain omega-3 fatty acids like DHA and EPA found in
seafood, due to their purported protective effect against heart disease. As
I discuss in my video Is Fish “Brain Food” for Older Adults?, even years ago
when the study was published, researchers were already questioning the
benefits of these fish fats, as more and more randomized controlled trials
put them to the test and they failed, culminating in the meta-analysis I
profiled in my video Is Fish Oil Just Snake Oil? that appeared to put the
issue to rest.
Consumption of fish and fish oil wasn’t only hyped for cardiovascular
protection, though. Omega-3s have also been touted to treat depression.
However, after taking into account all the negative results that went
unpublished, there appears to be no benefit for major depression or for
preventing suicide, as I explored in my video Fish Consumption and Suicide.
What about omega-3s for the prevention of cognitive decline or dementia? The
available randomized controlled trials show no benefit for cognitive
function with omega-3 supplementation in studies lasting from 6 to 40 months
among healthy older adults.
It may sometimes even make things worse. “Higher current fish consumption
predicted worse performance on several cognitive speed constructs. Greater
fish consumption in childhood predicted slower perceptual speed and
simple/choice reaction time.” This may be due to neurotoxic contaminants,
such as mercury, in seafood. We’ve known that the developing brain is
particularly sensitive to the damaging effects of mercury, but maybe the
aging brain is as well.
This would explain results that have shown higher omega-3 levels to be
associated with high levels of cognitive impairment and dementia. More EPA
(eicosapentanoic acid) was found in the cognitively impaired, and more DHA
(docosahexanoic acid) was found in the demented, presumably because of
pollutants like mercury and polychlorinated biphenyls (PCBs) in seafood that
have been related to cognitive impairment and Alzheimer’s disease.
The same cognitive “functions disrupted in adults, namely attention,
fine-motor function and verbal memory, are similar to some of those
previously reported in children with prenatal exposures,” that is, exposed
in the womb. And, the adults exposed to mercury through fish consumption
didn’t have only subtle EEG brain wave changes, but “observable deficits in
neurobehavioral performance measures,” such as poorer performance on tests
of fine motor speed and dexterity, as well as concentration, for example.
“Some aspects of verbal learning and memory were also disrupted by mercury
exposure,” and the greater the mercury levels, the worse they did.
That study, however, was done downstream of a gold mining operation, which
uses a process that uses lots of mercury. Other such studies were done on
people eating fish next to chemical plants or toxic spills, or eating whale
meat. What about a more mainstream population? An “elite group of
well-educated participants”—most were corporate executives like CEOs and
CFOs––all living in Florida and wealthy enough to afford so much seafood
that at least 43 percent exceeded the U.S. Environmental Protection Agency’s
safety limit for mercury were studied. Researchers found that excessive
seafood intake, which they defined as more than three to four servings per
month of large-mouth fish like tuna, snapper, and bass, elevates mercury
levels and causes cognitive dysfunction, resulting in about a 5 percent drop
in cognitive performance. This may not seem like much, but it’s “a decrement
that no one, let alone a health-conscious and achievement-oriented person,
is likely to welcome.”
“It is worth noting the irony in the situation; that is, the fact that
corporate executives who chose to overconsume seafood for health reasons
sustained a drop in their executive functions. Yet, if a 4.8% drop in
executive function due to excessive seafood intake occurs in highly
functioning, healthy adults with ample cognitive reserve, the major concern
for further study is whether similar [mercury] level elevations in
individuals already suffering from cognitive decline might result in
substantially greater declines,” particularly with cognitive decline,
dementia, and seafood consumption on the rise.
Fruit deficiency is the number-one dietary risk factor? For more, see
Inhibiting Platelet Aggregation with Berries.
But what about the Inuit? See Omega-3s and the Eskimo Fish Tale.
For more on the shift of the evidence on fish and heart disease, see my Is
Fish Oil Just Snake Oil? video.
The greatest danger of mercury exposure may be for children, as I discuss in
Mercury vs. Omega-3s for Brain Development and How Long to Detox from Fish
Before Pregnancy?
Other videos on the effect of fish contaminants and health among adults
include Fish and Diabetes and Fish Consumption and Suicide.
Mercury is not the only neurotoxic contaminant of seafood, though. See Diet
and Amyotrophic Lateral Sclerosis (ALS) and ALS (Lou Gehrig’s Disease):
Fishing for Answers.
In health,
Michael Greger, M.D.
Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.
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