What Really Happens When You Take A Fish Oil Supplement Every Day

When it comes to dietary supplements, fish oil is one of the most popular. That's because fish oil is a great source of omega-3 fatty acids — specifically, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). According to the National Institutes of Health (NIH), more than seven percent of adults regularly take a supplement that contains fish oil, omega-3s, or EPA and DHA. Because most people don't consume enough fatty fish to get significant amounts of EPA and DHA from their diet, adding fish oil supplements can help. Health officials recommend healthy adults get between 250 and 500 mg of EPA and DHA each day.

According to WebMD, fish oil supplements come in two forms: over-the-counter dietary supplements and prescription medications, which contain much higher levels of EPA and DHA. While individuals taking prescription-strength fish oil may be instructed to take up to 15 grams a day for certain medical conditions, people taking OTC fish oil usually take much lower doses. Although fish oil is commonly seen as safe, it can have negative interactions with certain medications, such as birth control pills and drugs used to control high blood pressure. It's always best to speak with your doctor before beginning any dietary supplement.

Fish oil has powerful anti-inflammatory effects

Most of fish oil's supposed health benefits stem from the fact that it has anti-inflammatory properties. As a 2017 paper in Biochemical Society Transactions explained, EPA and DHA have properties that partly block inflammatory processes at a cellular level. In addition, "EPA and DHA give rise to anti-inflammatory and inflammation resolving mediators called resolvins, protectins and maresins."

When it comes to inflammation, the ratio of pro-inflammatory omega-6 fats to anti-inflammatory omega-3 fats may play a critical role. Humans evolved eating an omega-6 to omega-3 ratio of about 1:1. The modern American diet, however, produces a ratio between 15:1 and 16.7:1. Taking fish oil supplements can help reduce the disparity between these two types of fat.

Although it often gets a bad rep, inflammation isn't always a bad thing. Acute inflammation occurs immediately after an injury and produces warmth, redness, swelling, and pain. This brings white blood cells to the area, where they can begin the healing process. But if the inflammatory response becomes chronic, the body can get confused and begin attacking healthy tissue. Chronic, low-grade inflammation is believed to cause or worsen a number of conditions, many of which fish oil is purported to help.

Fish oil could improve the health of your heart

A lot of the hype surrounding fish oil centers on its potential for improving heart health. As a 2018 paper published in Clinical and Experimental Pharmacology and Physiology explained, EPA and DHA are able to combat inflammation, dilate blood vessels, control irregular heartbeats, lower blood pressure, and lower triglycerides — all of which can help manage heart disease. The paper's authors noted that the American Heart Association recommends individuals with diagnosed heart disease consume one gram of EPA and DHA daily. It's unclear, however, if fish oil can help prevent heart disease in healthy individuals. One 2017 meta-analysis of past research published in Circulation noted: "There are no reports from RCTs [randomized controlled trials] that have targeted exclusively the primary prevention of CHD [coronary heart disease], that is, the effects of omega-3 PUFA supplements in the general population of patients without prior CHD."

Heart disease is a big problem in the United States. According to the Centers for Disease Control and Prevention (CDC), it's the "leading cause of death," killing approximately 655,000 people each year. More than 18 million Americans have coronary artery disease, the most common form of heart disease.

You may lose weight, but fish oil isn't a magic bullet

If you're hoping fish oil will help you shed those extra pounds, you may get a little boost, but that's it. In one 2005 study, 324 overweight participants were put on a calorie-restricted diet supplemented with either lean fish, fatty fish, fish oil, or sunflower oil (the control). After four weeks, those consuming the fish oil had lost the most weight (4.96 kg compared to 3.55–4.50 kg for the other groups). It's important to remember, however, that these individuals were on a reduced-calorie diet. So while fish oil may make a diet more effective, it doesn't magically melt away body fat on its own.

A 2015 meta-analysis published in PLoS One reviewed 21 previously published studies and concluded that "current evidence cannot support an exact anti-obesity role of n-3 polyunsaturated fatty acids (PUFAs) in overweight/obese subjects." The authors did note, however, that fish oil in combination with certain lifestyle changes may help reduce levels of abdominal fat.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, more than two-thirds of American adults are overweight or obese. Obesity is a major risk factor for a number of chronic conditions, including heart disease and diabetes.

Your bones could benefit from fish oil

When it comes to building strong bones, calcium and vitamin D tend to get all the attention. But the omega-3s found in fish oil also appear to play an important role. As a 2014 paper published in Current Osteoporosis Reports explained, omega-3s and other polyunsaturated fatty acids (PUFAs) assist with bone remodeling on a cellular level. Although we think of bones as hard and unchanging, they're constantly being broken down and rebuilt, and omega-3s help with the latter. Omega-3s reduce bone and muscle loss as we age, and higher intake of omega-3s has been linked to stronger bones and muscles in older adults.

Another study, published in 2011, examined the role of fish oil specifically. Subjects were divided into two groups: One group received 4 grams of safflower oil each day, while the other received 4 grams of fish oil, supplying 1,600 mg of EPA and 800 mg of DHA. After six weeks, researchers measured the level of N-terminal cross-linked telopeptide (NTx) in subjects' urine. NTs are a marker of bone breakdown. Those taking the fish oil had significantly reduced levels of NTs in their urine, suggesting that their bones weren't being broken down as quickly.

Fish oil may help manage blood sugar levels in those with diabetes

According to the American Diabetes Association, there are approximately 34.2 million Americans living with diabetes. If poorly managed, diabetes can lead to serious complications such as blindness, foot or limb amputations, and kidney disease. It's the seventh leading cause of death in the United States.

Some researchers suspect that fish oil may be useful in controlling blood glucose levels. As a 2015 meta-analysis published in PLoS One noted, studies in animals suggest that fish oil may help improve insulin sensitivity. The researchers noted that among the 20 previously published human trials they reviewed, "relatively high ratio of EPA/DHA contributed to a greater decreasing tendency in [hemoglobin A1C] and [insulin]." Hemoglobin A1C is a protein used as a marker for how well the body is handling blood sugar in the long term.

What does appear to be certain is that fish oil can dramatically lower triglyceride levels in those with type 2 diabetes, which in turn may improve their overall health and ability to manage their condition. A landmark paper published in Diabetes Care concluded that fish oil reduced triglyceride levels among diabetics by as much as 30 percent.

Fish oil may protect your aging eyes

Move over vitamin A; fish oil may be the nutrient your eyes need most. A 2014 study published in Investigative Ophthalmology & Visual Science found that individuals with the lowest dietary intake of EPA and DHA were most at risk for age-related macular degeneration (AMD). Even if you already have AMD, fish oil supplements may help. 

In another study, published in PharmaNutrition the same year, researchers gave patients with AMD high-dose omega-3s containing 3.4 grams of EPA and 1.6 grams of DHA every day for 6 months. The researchers noted that "significant improvement in vision acuity occurred in 100 percent of patients ... within four and half months after omega-3 supplementation." But not all research has come to the same conclusion. A 2013 study published in the Journal of the American Medical Association found that EPA and DHA had no ability to slow the progression of advanced AMD.

So it may be that fish oil can help prevent AMD or reverse mild forms of it, but once the condition is more advanced, fish oil may not be effective.

If you have psoriasis, fish oil could help

According to the Mayo Clinic, psoriasis is "a skin disease that causes red, itchy scaly patches, most commonly on the knees, elbows, trunk and scalp." It's a chronic condition that tends to flare up for weeks or months at a time before subsiding. It's also extremely common, affecting more than 8 million Americans.

Although fish oil on its own may not be enough to manage psoriasis symptoms, it may give conventional treatments a boost. A 2020 meta-analysis published in Nutrition Reviews of 18 previously published studies found that using fish oil alone had no effect on the size, severity, or itchiness of psoriasis lesions. When combined with conventional treatments, however, decreases in lesion size and severity were greater than with the conventional treatment alone. The researchers also noted that the fish oil helped regulate certain inflammatory factors involved in the condition.

A 2018 review published in JAMA Dermatology found that fish oil was among the most effective complementary and alternative medicine (CAM) treatments for psoriasis. Other top contenders included curcumin (the active compound found in the spice turmeric) and acupuncture.

Fish oil could help prevent or manage asthma

If you're pregnant, getting enough omega-3s through fish oil supplements may decrease the chances that your child will develop asthma. According to a paper published in PLoS One in 2013, children born to mothers who consumed omega-3s during pregnancy had a 29 percent decreased risk of asthma. (Those born to mothers who ate fish during pregnancy had a 24 percent decreased risk.)

But what if you're an adult already living with asthma? Can fish oil help you manage your symptoms? The research is mixed. One meta-analysis published in the Journal of Alternative and Complementary Medicine found that prescription-strength omega-3 supplements did reduce overreactions in the airways of asthmatic athletes during exercise. On the other hand, a 2018 study published in the Annals of the American Thoracic Society found no such benefit. Researchers gave overweight and obese individuals with uncontrolled asthma 4 grams of omega-3s daily for 24 weeks. The study authors concluded: "We did not find evidence that n3PUFA use improves most asthma-related outcomes and cannot recommend it as a prevention strategy for overweight/obese patients with asthma."

Fish oil may prevent flare-ups of autoimmune diseases

When you have an autoimmune disease, the immune system becomes confused and begins attacking healthy tissue as if it were a harmful invader. Although the exact cause of autoimmune conditions is unknown, it's likely that certain bacteria, viruses, or medications may trigger the immune system's confusion. Common autoimmune conditions include type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and certain forms of thyroid disease.

Although autoimmune diseases can't be cured, fish oil may help some individuals manage symptoms. A paper published in Nutrition & Food Science noted that omega-3s can help suppress an overreactive immune system. The authors concluded: "Although fish oils may not be as effective as either steroidal or non‐steroidal anti‐inflammatory [NSAID] medications, they may prove useful in reducing the dosage (and associated side‐effects) of these medications required."

But how exactly do omega-3s keep an overactive immune system in check? According to a paper published in the Journal of the American College of Nutrition, EPA and DHA can reduce levels of interleukin 1 (IL-1), a type of pro-inflammatory immune cell seen in high numbers in certain autoimmune conditions.

Fish oil could help with PCOS

According to the Office of Women's Health, polycystic ovary syndrome (PCOS) is a medical condition caused by an imbalance of reproductive hormones. As the name implies, it can cause cysts on the ovaries, but can also cause irregular periods, infertility, acne, excess body hair, and weight gain, among other symptoms. These symptoms are caused by a combination of high levels of androgens (male sex hormones) and high insulin levels. It's also surprisingly common, affecting approximately 1 in 10 women of reproductive age.

If you're a woman with PCOS, fish oil may help manage some of your symptoms and improve overall health. One study, published in 2017 in the Journal of Research in Medical Sciences, split women with PCOS into two groups. One group received two grams of fish oil a day for six months, while the other group received olive oil as a control. At the end of the experiment, the fish oil group had smaller waist circumferences, higher HDL ("good") cholesterol, lower LDL ("bad") cholesterol, and lower triglycerides than the control group. The time between periods was also significantly decreased in the fish oil group (an average of 29.83 days versus 47.11 days for the control group).

Fish oil may improve your chances of conceiving, especially later in life

Infertility, defined as the inability to conceive after a year of trying, affects approximately 11 percent of women and 9 percent of men. Infertility can have many causes, including age. Both male and female fertility decreases with age. But while the decline in men is gradual, women experience a precipitous drop in their 30s. Women in this age group are only half as fertile as they were in their 20s.

But fish oil may be able to extend the "reproductive lifespan" of women. A 2017 paper published in Aging Cell noted that a lifelong diet rich in omega-3s prolonged fertility among female rodents. The authors noted that "even short-term dietary treatment with a diet rich in omega-3 fatty acids initiated at the time of the normal age-related rapid decline in murine [rodent] reproductive function is associated with improved oocyte [egg] quality," It's possible that omega-3s could have the same fertility-extending effect in humans.

Fish oil may also improve men's baby-making abilities. A 2020 study of more than 1,600 men found that fish oil supplementation was correlated with higher sperm count and semen volume, larger testicular size, and higher levels of testosterone.

Fish oil may reduce symptoms of depression

The Depression and Bipolar Support Alliance estimate that major depressive disorder affects 7.1 percent of American adults. While fish oil is no substitute for medication or psychotherapy, it may lessen symptoms for some individuals.

A 2019 meta-analysis published in Translational Psychiatry analyzed 26 previously published studies with a total of 2,160 participants to see what effect omega-3s had on depression. They concluded that supplements that were at least 60 percent EPA had a beneficial impact, while supplements that were predominantly or only DHA had no effect. In fact, the ideal ratio of EPA to DHA appears to be 2:1 or 3:1.

But how does EPA improve depression, and why is DHA not as effective? DHA is highly concentrated in brain tissue. But, as the authors noted, EPA can easily cross the blood-brain barrier. Inflammation has been linked to depression, and EPA has significant anti-inflammatory abilities in the brain. It also increases levels of N-acetyl-aspartate, a chemical that helps maintain the balance of neurotransmitters in the brain. Interestingly, the researchers found that there was no additional benefit to taking a higher dose of EPA (more than one gram per day), so even over-the-counter fish oil supplements may be useful for those with depression.

Could fish oil protect you from cognitive decline and dementia?

As we get older, it can be hard to tell if our memory lapses and moments of confusion are simply the result of aging or something more serious. According to Healthline, occasional forgetfulness or difficulty paying attention are normal as we age. Mild cognitive impairment (MCI), on the other hand, may also involve some difficulty with language and higher-level tasks or planning. Alzheimer's disease (the most common form of dementia) is marked by much more severe impairments that affect everyday tasks, basic communication, motor skills, personality, and self-awareness.

A 2017 paper published in Current Opinion in Clinical Nutrition and Metabolic Care concluded that fish consumption or omega-3 supplementation (specifically DHA) may help prevent MCI and Alzheimer's in healthy individuals and improve symptoms of MCI in older adults. While DHA may help some individuals with mild or moderate Alzheimer's, overall omega-3s appeared to have little effect on those with dementia.

The idea that fish oil may prevent, but not treat, Alzheimer's was reflected in another study published in the Archives of Neurology. It found that, among those who already had mild to moderate Alzheimer's, omega-3s didn't slow the rate at which the condition's severity progressed.

Proceed with caution if you're allergic to fish

If you're allergic to fish, you may also need to avoid fish oil. Unlike many other common food allergies, seafood allergies are more common in adults than in children. Approximately one percent of individuals are allergic to seafood (fish and/or shellfish). Common symptoms include hives, wheezing, vomiting, diarrhea, and difficulty breathing. For some individuals, reactions may be severe, including life-threatening anaphylaxis.

As Healthline explained, individuals with a fish allergy are reacting to parvalbumin, a protein found in the muscles (meat) of fish. In theory, fish oil shouldn't contain any protein and should be safe to consume, but cross-contamination is a possibility. It's also theoretically possible to be allergic to fish oil itself. While there are eight foods that make up the vast majority of food allergies (fish, shellfish, eggs, soy, milk, wheat, peanuts, and tree nuts), it's possible to develop an allergy to almost any food. WebMD lists anaphylaxis as a rare, but possible, side effect of taking fish oil.

A study published in Asthma & Allergy Proceedings found that individuals with a fish allergy didn't have an allergic response to fish oil. The study was extremely small, however, using only six participants and two brands of fish oil.