Although the link between seafood consumption and improved health has been known for decades, research sheds 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 the Developing Infant
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 now finds 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 6-month-old performed on a standard test of mental development.
Overall, babies' scores on the test climbed by 4 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.
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. Benefits for Young Children
Findings from Child Asthma Prevention Study
Study findings from the Childhood Asthma Prevention Study in Australia also reported that the consumption of omega-3 fatty acids was linked to a reduction in asthma symptoms in children.
Published in the October 2004 issue of the Journal of Allergy & Clinical Immunology and conducted by researchers at the University of Sydney, the study examined 616 children at high risk for developing asthma and found that those children whose diets were high in omega-3 fatty acids were much less likely to develop a cough, one of the major triggers for asthma attacks. Moreover, the study concluded that increasing the proportion of omega-3 fatty acids in the diet significantly reduced airway inflammation in children as young as age 3. Other research has found omega-3 fatty acids to be beneficial in other lung diseases such as cystic fibrosis.
3. 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. This includes postpartum depression, where a 1998 study published in the Lancet, found that women in 23 countries whose breast milk was rich in omega-3 fatty acids because they had consumed fatty fish were less likely to suffer from this condition. Researchers noted that there was an inverse relationship between the consumption of fatty fish and the occurrence of postpartum depression. That means that women eating fatty fish were less likely to develop post partum depression.
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 26 percent 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 3 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 5 ounces of seafood per week according to National Marine Fisheries data.
4. 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 minimal 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.
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 23, 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.
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, the Dietary Guidelines Advisory Committee estimates that there could be a 30 percent reduction in coronary deaths if people increased their intake of omega-3 fatty acids.
5. 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.
6. 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.
At a time when an estimated 2.5 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 2 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 1 gram of EPA, and noted significant improvements in depressive symptoms, sleep, anxiety, lassitude, libido, and thoughts of suicide.
Funded by an unrestricted educational grant from the U.S. Tuna Foundation.
Reprinted with permission from the NWHRC. 1-877-986-9472 (toll-free). On the Web at: www.healthywomen.org .