Seafood:
New Research on Its Health Benefits
Although
the link between seafood consumption and improved health
has been known for decades, a number of recent studies are
shedding new light on the many health benefits of the omega-3
fatty acids found in fish. Considered essential nutrients
because the body does not make them, omega-3 fatty acids
are fundamental molecules in the structure and activity
of cell membranes, especially in the brain and retina of
the eye.
The
following summarizes some important research findings that
show the omega-3 fatty acids in fish play a major health
role at every stage of life, from healthy infant development
through the prevention and management of certain diseases
and chronic conditions that may appear later on.
1.
Benefits for Infants and Young Children
A recent federally-funded report recently released by the Institute of Medicine (IOM) showed that the heart benefits of seafood outweigh the risks in infants as well as adults.
The report showed that omega-3 fatty acids found in fish promote healthy vision and brain development in infants whose mothers consume seafood while they are pregnant or nursing. These healthy fats also appear to lower the risk of delivering a preterm or low-birth-weight baby.
Findings from Harvard Medical School
When
it comes to the developing fetus, extensive research shows
that one of the essential omega-3 fatty acids in fish—DHA (docosahexaenoic acid)—is a critical component for
building brain tissue, for nerve growth, and for the retina.
In fact, research finds that when babies are developing
during the last third of pregnancy, the brain and nervous
system rapidly accumulate DHA. Before birth, babies get
the DHA they need from their mother. After birth they obtain
it mainly from breast milk.
However, a study by researchers at Harvard Medical School found that the importance of DHA to the developing brain is significant during the second trimester of pregnancy. According to a research article—Maternal Fish Consumption, Hair Mercury, and Infant Cognition in a U.S. Cohort—published in the October 2005 issue of Environmental Health Perspectives, the study of 135 mothers and their infants reported that the greater a woman's fish intake during the second trimester, the better her six-month-old performed on a standard test of mental development. Overall, babies' scores on the test climbed by four points for each weekly serving of fish their mothers had during the second trimester, after findings were adjusted for maternal hair mercury and other confounding factors. Examining the impact of mercury, the study found that elevated maternal mercury levels were associated with deficits in infant cognition, but in spite of that, greater fish consumption was associated with better cognition. These results suggest that higher consumption of fish low in mercury is beneficial for infant cognition.
New
Data from the National Institute of Environmental Health
Sciences (NIEHS)
In
July 2004, researchers with the National Institute of Environmental
Health Sciences (NIEHS) published a research article in
the Journal of Epidemiology based on assessing the fish
intake of more than 7,400 mothers in the United Kingdom
and found that those who ate fish regularly during pregnancy
had children with better language and communication skills
by the age of 18 months. Using standard tests of language,
comprehension, motor and social skills to assess childhood
development at 15 and 18 months, the study found a subtle
but consistent link between eating fish during pregnancy
and a child's early cognitive development, even after adjusting
for factors such as the age and education of the mother,
whether she breastfed, and the quality of the home environment.
Moreover, the study revealed that the amount of fish associated
with these cognitive benefits was one to three servings
a week, which is consistent with the advice of the Food
and Drug Administration (FDA) and the Environmental Protection
Agency (EPA) that pregnant women should eat up to 12 ounces
a week of fish low in mercury.
2.
Omega-3 Fatty Acids and Women's Health
Lower
Prevalence of Postpartum Depression
Because the omega-3 fatty acids in fish enhance the ability of brain-receptors to comprehend mood-related signals from the brain, some researchers have observed that the likelihood of having depressive symptoms is significantly higher among infrequent fish consumers than among habitual fish eaters, and this connection seems to correlate with protection against post-partum depression as well.
Lower
Risk of Breast Cancer
At a time when more than 40,000 American women die each year from breast cancer, the "Singapore Chinese Health Study" published in the May 2004 issue of the British Journal of Cancer found that postmenopausal women who ate more fish had a lower risk of developing the disease. Conducted by researchers at the Keck School of Medicine at the University of Southern California and the National University of Singapore, the study examined the eating habits of 35,298 women aged 45 to 74 years over a five-year period and found that those who consumed an average of one and a half to three ounces of fish and shellfish daily were 30 percent less likely to develop breast cancer than women who ate less than one ounce of fish a day. Based on these observations, the study authors suggested that eating approximately 40 grams of seafood a day—about 10 ounces of fish a week—could reduce breast cancer risk by 25 percent. As a comparison, the average American consumes less than five ounces of seafood per week according to National Marine Fisheries data.
3.
Reducing the Risk of Heart Disease and Stroke
Protection
Against Heart Disease
The
cardiovascular benefits of omega-3 fatty acids have been
documented in many prospective studies and randomized clinical
trials. For example, the findings of a small clinical trial
published in the Annals of Internal Medicine found
that patients who were given fish oil concentrate for two
years had lower triglyceride levels and less artery blockage
when compared to those receiving a placebo. Moreover, in
a 1998 issue of Diabetes Care, a meta-analysis of
studies on diabetes and fish oils found a 30 percent reduction
in patient triglyceride levels, particularly among subjects
with Type I diabetes who are at greatly increased risk of
heart disease than people without the disease.
Along
with these smaller studies, there have been a number of
large trials reporting that omega-3 fatty acids in fish
provide a protective mechanism of reducing the risk of irregular
heartbeats. One major study called the GISSI-Prevenzione
secondary prevention trial is particularly noteworthy. Reported
in 2002 in the journal Circulation, this study of
11,323 subjects who survived their first heart attack demonstrated
that even a small amount (about one gram a day) of the omega-3
fatty acids found in fish was effective in cutting the chance
of cardiac death by 45 percent-nearly half.
Most recently and perhaps most significantly, a team of scientists at Harvard School of Public Health reported that the death rate from heart disease was 36 percent lower among people who ate fish twice a week compared with people who ate little or no seafood. The study, which was published in the October 18, 2006 issue of the Journal of the American Medical Association, also showed that overall mortality was 17 percent lower among the seafood eaters.
Preventing
Stroke
Although
less is known about the relationship between the omega-3
fatty acids in fish and the prevention of stroke, findings
from the Nurses Health Study, which were published in the
January 2001 issue of the Journal of the American
Medical Association, found that women who ate fish more
than once per month had a lower risk of stroke when compared
with those who ate fish less than once a month. Moreover,
women who ate fish two or more times per week had a significantly
reduced risk of thrombotic infarction, the type of stroke
most common in the U.S. Fish consumption is also linked
to lower risk of stroke in men according to a major epidemiological
study.
New
Conclusions in 2005 Dietary Guidelines for Americans
Based in part on this body of evidence, the 2005 Dietary Guidelines for Americans recommend that Americans aged two and over get two eight-ounce servings a week of foods rich in the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). In making this recommendation, the 13-member 2005 Dietary Guidelines Advisory Committee whose scientific review formed the basis for updating the government's nutrition advice, concluded that higher levels of EPA and DHA are associated with the reduced risk of both sudden death and death from coronary heart disease in adults. Specifically, according to the National Heart, Lung, and Blood Institute, there could be a 30 percent reduction in coronary deaths if people increased their intake of omega-3 fatty acids.
4.
Improved Eye Function
Age-related
macular degeneration (AMD) is a leading cause of loss of
vision in older persons in developed countries. Although
the exact causes of AMD are still unknown, many researchers
believe that certain nutrients, such as the omega-3 fatty
acids in fish, help lower the risk for AMD or slow down
its progression. Towards this end, the August 2001 issue
of Archives of Ophthalmology reported findings that
consumption of omega-3 fatty acids had a protective effect
against advanced macular degeneration. The Age-Related Eye
Disease Study (AREDS) confirmed this finding in 2003. In
this case-control study of 4,513 participants aged 60 to
80 years at enrollment, total fish consumption of more than
two servings per week was associated with a decreased risk
for AMD compared with no fish in the diet.
5.
Improved Brain Function
Halting
Mental Decline Later in Life
Growing
scientific evidence now suggests that the omega-3 fatty
acids found in seafood improve brain function in middle
aged people and may actually lower the risk of mental impairment
as people age. The latest research comes from researchers
with Utrecht and Maastricht Universities in the Netherlands
and was published in the journal Neurology in 2004.
Tracking more than 1,600 Dutch men and women aged 45 to
70 over a six-year period, the researchers found that those
who ate fish regularly scored higher on a battery of tests
for memory, psychomotor speed, cognitive flexibility, and
overall cognition. Moreover, the study concluded that the
specific factors contributing to better brain function were
fatty fish and the consumption of two essential omega-3
fatty acids found in canned tuna, EPA (eicosapentaenoic
acid) and DHA (docosahexaenoic acid).
Slowing
the Progression of Alzheimer's Disease
Reported
in the September 2, 2005 issue of the journal Neuron,
neuroscientists at UCLA showed for the first time, in animals
with Alzheimer's disease, that a diet high in DHA helps
protect the brain against the memory loss and cell damage
caused by the condition, which now affects an estimated
4.5 million Americans. In the study, the researchers bred
mice with genetic mutations that cause the brain lesions
linked to advanced Alzheimer's disease. When the mice aged
and showed brain lesions but displayed no major loss of
brain-cell activity, the scientists then fed one group a
diet high in omega-3 fatty acids and the other a diet depleted
of these fatty acids. After five months, the researchers
compared each set of mice to a control group without the
disease and found extensive synaptic damage in the brain
cells of the Alzheimer's mice that ate the DHA-depleted
diet, but not in those consuming DHA.
Controlling
Epilepsy
At
a time when an estimated 2.7 million Americans have been
diagnosed with epilepsy, new research from the Emory University
School of Medicine finds that people with a common type
of seizure (refractory complex partial seizures) often have
significantly lower amounts of the omega-3 fatty acid DHA
(docosahexaenoic acid) in their blood. Because this form
of epilepsy is often resistant to drug treatment, the researchers
suggest that an important way to control these seizures
may be as simple as consuming more foods rich in DHA. These
preliminary findings suggest another area of brain function
that might be linked to omega-3 fatty acids that warrants
additional investigation.
Therapeutic
Effect on Depression
A
growing body of research finds a connection between the
intake of omega-3 fatty acids and a lower prevalence of
depression. This is because the brain and central nervous
system contain high levels of DHA and EPA to keep the pattern
of thoughts, reactions, and reflexes running smoothly and
efficiently. Although the precise mechanisms by which these
omega-3 fatty acids regulate mood are unknown, a number
of studies on omega-3 fatty acids and mood have reported
positive outcomes. In a 2002 study published in the American
Journal of Psychiatry, researchers showed that two grams
of EPA could improve the symptoms of treatment-resistant
depression. The researchers found that the EPA (versus placebo),
when added to an ineffective antidepressant for one month,
significantly improved depressive symptoms. A larger study
published in Archives of General Psychiatry in 2002
confirmed these findings using a daily dose of one gram of
EPA, and noted significant improvements in depressive symptoms,
sleep, anxiety, lassitude, libido, and thoughts of suicide.
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