Fish oil is also used for diabetes, prediabetes, asthma, a movement and coordination disorder called dyspraxia, dyslexia, eczema, autism, obesity, weak bones (osteoporosis), rheumatoid arthritis (RA), osteoarthritis, psoriasis, an autoimmune disease called systemic lupus erythematosus (SLE), multiple sclerosis, HIV/AIDS, cystic fibrosis, gum disease, Lyme disease, sickle cell disease, and preventing weight loss caused by some cancer drugs.
The supplements contain omega-3 fatty acids, the polyunsaturated oils prominent in fatty cold water fish like salmon, sardines and mackerel. In many observational studies, people who regularly consumed fish two or more times a week were less likely to suffer heart attacks, strokes and cardiovascular deaths than those who ate fish infrequently or not at all.

Although there are no randomized data on fish oil consumption and protection from sudden death, observational studies have linked omega-3 FA with the prevention of sudden death. In a population-based, case-control study of sudden cardiac death victims, the mean red blood cell membrane omega-3 FA level of the lowest quartile, when compared with the mean level of the third quartile, was associated with a relative risk reduction of 70%.33 A similar finding was appreciated in a nested, prospective, case-control study of the Physician Health Study cohort of 22,000 healthy males. In the 119 patients that succumbed to sudden death, baseline omega-3 FA blood levels were significantly lower than in matched controls.34 Finally, in an analysis of data from the Nurses Health Study, a cohort study of 84,688 women, an inverse association was shown between fish consumption and CAD-related death. The investigators concluded that the reduction in CAD deaths was likely due to a reduction in sudden deaths, as there was no difference in the rate of MI when comparing high and low fish consumption.35
In 2016, AHRQ reviewed 143 studies that evaluated the effects of giving omega-3 supplements to pregnant or breastfeeding women or giving formulas with added DHA to infants. They found that when women took omega-3 supplements during pregnancy, their babies’ birth weight was slightly higher, but the risk of an undesirably low birth weight did not change. Also, when women took omega-3 supplements during pregnancy, their pregnancies lasted a little longer, but there was no effect on the risk of premature birth. Omega-3s were not found to have effects on any other aspects of the mothers’ or infants’ health or the infants’ long-term development. Aspects of the infants’ health that were not shown to be affected by omega-3s include growth after birth, visual acuity, long-term neurological and cognitive development, and the risks of autism, ADHD, learning disorders, and allergies.

Fish oil is FDA approved to lower triglycerides levels, but it is also used for many other conditions. It is most often used for conditions related to the heart and blood system. Some people use fish oil to lower blood pressure, triglycerides and cholesterol levels. Fish oil has also been used for preventing heart disease or stroke, as well as for clogged arteries, chest pain, irregular heartbeat, bypass surgery, heart failure, rapid heartbeat, preventing blood clots, and high blood pressure after a heart transplant.
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