Do Fish Oil Supplements Really Work?

By Dace L. Trence, MD, FACE

One of the more common and popular nutritional supplements on the market today is fish oils, or omega-3 fatty acids. Fish oil is found in fish or supplements. Fish that have particularly high amounts of omega-3 fatty acids include mackerel, tuna, salmon, sturgeon, mullet, bluefish, anchovy, sardines, herring and trout. These fish contain approximately 1 gram of omega-3 fatty acids in about 3.5 ounces of fish. Supplements are usually made from mackerel, herring, tuna, halibut, salmon, cod liver, or the blubber of seals or whales and may be combined with calcium, iron, or vitamins A, B1, B2, B3, C, or D and, to better preserve freshness, often contain small amounts of vitamin E.

The interest in fish oil is likely due to research indicating that it can offer a variety of health advantages. Some reports suggest fish oils offer possible benefits in slowing changes in age-related memory and thinking disorders, in helping prevent heart disease, in boosting the immune system, even in contributing to muscle and bone strength.

Like the fountain of youth, let’s review the actual science.

From 1935 to 2010, United States population statistics showed that death rates decreased by 60 percent. If current trends continue, the number of U.S. citizens that will be 65 years or older by 2050 is estimated to be around 88 million, or 20 percent of the total population, and 4 percent, or 19 million citizens, will be age 85 years or older. Because some memory loss is anticipated and expected as a normal process of aging, these statistics reflect a large percentage of the population who want to preserve their cognitive skills. How often have you wished that you could remember where you parked the car? Or a person’s name? Or perhaps the name of that great restaurant you visited five years ago?

Researchers have examined whether a 12-month course of fish oil supplementation with concentrated DHA (docosahexaenoic acid, an omega-3 fatty acid which is essential for healthy brain function) might be beneficial in older individuals who already had shown signs of some thinking impairment — what is often called mild cognitive impairment (MCI). They measured a variety of different thinking and memory functions before and after fish oils were administered. Significant improvements were seen in research participants’ short-term and working memory, immediate verbal memory and delayed recall capability. Twelve-month memory testing also showed significant improvement after treatment, with the fish oils being well tolerated and with minimal side effects. Rate of learning also increased significantly after supplementation, but not mental processing speed, accuracy or mood. Available evidence generally supports a positive correlation between omega-3 status/supplementation and brain function, at least in older individuals.

Regarding heart function, individuals with a history of having had a heart attack who took in 1 gram of fish oil supplements daily for six months had a reduction in some, but not all, types of irregular heartbeats, enhancing the effect of anti-arrhythmic therapy. Additional positive heart function effects seen in other studies have included more stable heart rates and less heart failure in the groups taking fish oils.

Scientific evidence has long suggested the beneficial effects of fish oils decreasing blood triglyceride (sugar fats) levels — part of the cholesterol panel your doctor orders — resulting in various prescription forms of fish oils. These are generally more potent fish oil preparations, some containing more specific amounts of a particular fish oil than others. The role triglycerides play in the development of heart disease is not clear, but there is an association of higher triglyceride levels with increased coronary artery disease risk, more so in women than in men.

We know that inflammation in the body is associated with the risk of developing many diseases such as heart disease and diabetes. Research suggests that fish oils might have a beneficial effect in decreasing inflammation, but not all studies confirm this research. Some suggest that taking fish oils intravenously might be more effective than the much more commonly used capsule form, but there is no clear agreement. There is data that suggests a decreased cell mutation effect, and mutations are thought to be associated with the development of many cancers. But studies with specific cancers have been sparse thus far, preventing any firm conclusions as to possible benefit or lack of benefit.

Progressive loss of muscle mass and function, what is often referred to as sarcopenia, occurs in all of us as we get older. Approximately one to two percent of muscle mass per year is lost after the age of 50. This loss of muscle mass and strength is accompanied by fat accumulation in muscle, muscle thinning and an overall structural muscle change leading to loss of strength. Sarcopenia is a medical concern as it represents a considerable healthcare cost: about 1.5 percent of total healthcare costs were attributable to sarcopenia in the United States in 2000.

Muscle weakness is associated with an increased risk for falls and subsequent bone fracture, but the stimulation of muscle protein production by fish oil supplements could be useful for the treatment and prevention of sarcopenia. And there is some evidence that fish oils could help maintain muscle mass: A study of 300 participating older Italians suggested that omega-3 fatty acid blood levels, as well as supplementation, were strongly correlated with maintenance of muscle mass and function in these older adults. But not all muscle studies have shown a positive effect. For example, a 12-week study in older adults participating in a resistance training program showed no difference in muscle mass and strength between those taking fish oils versus those who were not. There were some differences seen between women and men regarding benefits in specific muscle and joint groups, but this was a short study of only three months. An important question is whether short-term results can be sustained over time, something we don’t know from currently available data.

Bone health has been reported to be significantly correlated with omega-3 status. But studies comparing those actually taking fish oils supplements versus those not taking them have yet to be conducted.

And there have been a number of studies looking at whether fish oils could improve or stabilize mood issues, although results have not been consistent enough to confirm their value in this regard.

Many of the benefits of fish oil appear to come from the omega-3 fatty acids it contains, which cannot be produced by the body but are essential to the body’s well-being and development. Nor can the body manufacture omega-3 fatty acids from omega 6-fatty acids, which are relatively common in a standard Western diet.

Fish oil supplements are felt to be safe for most people, including pregnant and breast-feeding women, when taken in low doses (3 grams or less per day). However, there is a flip side to over-supplementation. For some, fish oils may increase your blood sugar, although this tends to be a short-term effect. In high doses of more than 3 grams per day, bleeding can be seen due to fish oil’s capacity to keep blood from clotting. Also, high doses of fish oil might also reduce the immune system’s activity, reducing the body’s ability to fight infection. So if you are taking medication to prevent blood clots or to decrease your immune system’s activity (organ transplant patients, for example), discuss fish oil safety with your medical team before taking. In addition, if you are allergic to seafood, this may also increase your risk of allergy to fish oil supplements.

At the end of the day, if you eat a well-balanced diet that regularly includes fish, you might not need to supplement your diet with fish oil at all. In fact, it might actually be more beneficial to start introducing more fatty fish into your diet before considering a visit to your local supplement aisle.

Dr. Dace Trence, FACE, is Director of the Diabetes Care Center and Professor of Medicine at the University of Washington Medical Center in Seattle. She is also the University of Washington Endocrine Fellowship Program Director and Director of Endocrine Days, a medical education program for endocrinologists practicing in the Pacific Northwest. She is on the American College of Endocrinology Board of Trustees and chairs the CME Committee and is also chair of the AACE Publications Committee.