People who follow a Mediterranean-style diet tend to have higher HDL (good) cholesterol levels, which help promote heart health. Inuit Eskimos, who get high amounts of omega-3 fatty acids from eating fatty fish, also tend to have increased HDL cholesterol and decreased triglycerides (fats in the blood). Several studies show that fish oil supplements reduce triglyceride levels. Walnuts, which are rich in alpha linolenic acid or ALA, which can convert to omega-3s in the body, have been reported to lower total cholesterol and triglycerides in people with high cholesterol levels.
High blood pressure
Several clinical studies suggest that diets rich in omega-3 fatty acids lower blood pressure in people with hypertension. An analysis of 17 clinical studies using fish oil supplements found that taking 3 or more grams of fish oil daily may reduce blood pressure in people with untreated hypertension. Doses this high, however, should only be taken under the direction of a physician.
The role of omega-3 fatty acids in cardiovascular disease is well established. One of the best ways to help prevent heart disease is to eat a diet low in saturated fat, and to eat foods that are rich in monounsaturated and polyunsaturated fats (including omega-3 fatty acids). Clinical evidence suggests that EPA and DHA (eicosapentaenoic acid and docosahexaenoic acid), the two omega-3 fatty acids found in fish oil help reduce risk factors for heart disease, including high cholesterol and high blood pressure. Fish oil has been shown to lower levels of triglycerides (fats in the blood), and to lower the risk of death, heart attack, stroke, and abnormal heart rhythms in people who have already had a heart attack. Fish oil also appears to help prevent and treat atherosclerosis (hardening of the arteries) by slowing the development of plaque and blood clots, which can clog arteries.
Large population studies suggest that getting omega-3 fatty acids in the diet, primarily from fish, helps protect against stroke caused by plaque build up and blood clots in the arteries that lead to the brain. Eating at least 2 servings of fish per week can reduce the risk of stroke by as much as 50%. However, high doses of fish oil and omega-3 fatty acids may increase the risk of bleeding. People who eat more than 3 grams of omega-3 fatty acids per day (equivalent to 3 servings of fish per day) may have higher risk for hemorrhagic stroke, a potentially fatal type of stroke in which an artery in the brain leaks or ruptures. Studies also suggest that omega-3 fatty acids may have antioxidant properties that improve endothelial function and may contribute to heart benefits.
People with diabetes often have high triglyceride and low HDL levels. Omega-3 fatty acids from fish oil can help lower triglycerides and apoproteins (markers of diabetes), and raise HDL. So eating foods or taking fish oil supplements may help people with diabetes. Another type of omega-3 fatty acid, ALA (from flaxseed, for example) may not have the same benefit as fish oil. Some people with diabetes can't efficiently convert ALA to a form of omega-3 fatty acids that the body can use. Also, some people with type 2 diabetes may have slight increases in fasting blood sugar when taking fish oil. So talk to your doctor to see if fish oil is right for you.
Most clinical studies examining omega-3 fatty acid supplements for arthritis have focused on rheumatoid arthritis (RA), an autoimmune disease that causes inflammation in the joints. Several small studies have found that fish oil helps reduce symptoms of RA, including joint pain and morning stiffness. One study suggests that people with RA who take fish oil may be able to lower their dose of non-steroidal anti-inflammatory drugs (NSAIDs). However, unlike prescription medications, fish oil does not appear to slow progression of RA, only to treat the symptoms. Joint damage still occurs.
Laboratory studies suggest that diets rich in omega-3 fatty acids (and low in the inflammatory omega-6 fatty acids) may help people with osteoarthritis. More study is needed. New Zealand green lipped mussel (Perna canaliculus), another potential source of omega-3 fatty acids, has been reported to reduce joint stiffness and pain, increase grip strength, and improve walking pace in a small group of people with osteoarthritis. For some people, symptoms worsened before they improved.
An analysis of 17 randomized, controlled clinical trials looked at the pain-relieving effects of omega-3 fatty acid supplements in people with RA or joint pain caused by inflammatory bowel disease (IBS) and painful menstruation (dysmenorrhea). The results suggest that omega-3 fatty acids, along with conventional therapies, such as NSAIDs, may help relieve joint pain associated with these conditions.
Systemic lupus erythematosus (SLE)
Several small studies suggest that EPA and fish oil may help reduce symptoms of lupus, an autoimmune condition characterized by fatigue and joint pain. However, two small studies found that fish oil had no effect on lupus nephritis (kidney disease caused by lupus, a frequent complication of the disease).
Some studies suggest that omega-3 fatty acids may help increase levels of calcium in the body and improve bone strength, although not all results were positive. Some studies also suggest that people who do not get enough of some essential fatty acids (particularly EPA and gamma-linolenic acid (GLA), an omega-6 fatty acid) are more likely to have bone loss than those with normal levels of these fatty acids. In a study of women over 65 with osteoporosis, those who took EPA and GLA supplements had less bone loss over 3 years than those who took placebo. Many of these women also experienced an increase in bone density.
Research is not clear on whether taking omega-3 fatty acids can help relieve depression symptoms. Several studies show that people who took omega-3 fatty acids in addition to prescription antidepressants had a greater improvement in symptoms than those who took antidepressants alone. Other studies suggest that omega-3 fatty acid intake helps protect against postpartum depression, among other benefits. However, some studies found no benefit.
Studies are also mixed on whether omega-3 fatty acids alone have any effect on depression. Depression is a serious illness and you should not try to treat it on your own. See a doctor for help.
In a clinical study of 30 people with bipolar disorder, those who took fish oil in addition to standard prescription treatments for bipolar disorder for 4 months experienced fewer mood swings and relapses than those who received placebo. But another 4-month long clinical study treating people with bipolar depression and rapid cycling bipolar disorder did not show that EPA helped reduce symptoms.
Preliminary clinical evidence suggests that people with schizophrenia take omega-3 fatty acids, they experience an improvement in symptoms. However, more recent research found that EPA supplements were no better than placebo in improving symptoms of this condition.
Attention deficit/hyperactivity disorder (ADHD)
Children with ADHD may have low levels of certain essential fatty acids (including EPA and DHA). In a clinical study of nearly 100 boys, those with lower levels of omega-3 fatty acids had more learning and behavioral problems (such as temper tantrums and sleep disturbances) than boys with normal omega-3 fatty acid levels.
However, studies examining whether omega-3 fatty acids help improve symptoms of ADHD have produced mixed results. A few studies show that omega-3 fatty acids help improve behavioral symptoms. But most of these studies were not well designed. One study that looked at DHA in addition to stimulant therapy (standard therapy for ADHD) found no effect. More research is needed. In the meantime, eating foods that are high in omega-3 fatty acids is a reasonable approach for someone with ADHD.
Several studies show that reduced intake of omega-3 fatty acids is associated with increased risk of age-related cognitive decline or dementia, including Alzheimer disease. Scientists believe the omega-3 fatty acid DHA is protective against Alzheimer disease and dementia.
In one clinical study, 13 people with sun sensitivity known as photo dermatitis showed less sensitivity to UV rays after taking fish oil supplements. However, topical sunscreens are much better at protecting the skin from damaging effects of the sun than omega-3 fatty acids. In another study of 40 people with psoriasis, those who took EPA with their prescription medications did better than those treated with the medications alone. However, a larger study of people with psoriasis found no benefit from fish oil.
Inflammatory bowel disease (IBD)
Results are mixed as to whether omega-3 fatty acids can help reduce symptoms of Crohn disease and ulcerative colitis, two types of IBD. Some studies suggest that omega-3 fatty acids may help when added to medication, such as sulfasalazine (a standard medication for IBD). Others show no effect. More studies are needed. Fish oil supplements can cause side effects that are similar to symptoms of IBD (such as flatulence, belching, bloating, and diarrhea).
Studies examining omega-3 fatty acids for asthma are mixed. In one small, well-designed clinical study of 29 children with asthma, those who took fish oil supplements rich in EPA and DHA for 10 months experienced fewer symptoms compared to children who took placebo. However, most studies have shown no effect.
A questionnaire given to more than 3,000 people over the age of 49 found that those who ate more fish were less likely to have macular degeneration, a serious age-related eye condition that can progress to blindness, than those who ate less fish. Similarly, a clinical study comparing 350 people with macular degeneration to 500 without the eye disease found that those with a healthy dietary balance of omega-3 and omega-6 fatty acids, as well as more fish in their diets, were less likely to have macular degeneration.
In one study of 42 women, participants had less menstrual pain when they took fish oil supplements than when they took placebo.
Eating foods rich in omega-3 fatty acids seems to reduce the risk of colorectal cancer. For example, Eskimos, who tend to have a high fat diet, but eat significant amounts of fish rich in omega-3 fatty acids, have a low rate of colorectal cancer. Animal studies and laboratory studies have found that omega-3 fatty acids prevent worsening of colon cancer. Preliminary studies suggest that taking fish oil daily may help slow the progression of colon cancer in people with early stages of the disease. If you have colorectal cancer, ask your doctor before taking any supplements.
Although not all experts agree, women who eat foods rich in omega-3 fatty acids over many years may be less likely to develop breast cancer. More research is needed to understand the effect that omega-3 fatty acids may have on the prevention of breast cancer.
Population-based studies of groups of men suggest that a low-fat diet including omega-3 fatty acids (from fish or fish oil) may help prevent the development of prostate cancer.