Flaxseed oil is derived from the hard, tiny seeds of the flax plant. It has been proposed as a less smelly alternative to fish oil. Like fish oil, flaxseed oil contains omega-3 fatty acids, a type of fat your body needs as much as it needs vitamins.

However, it's important to realize that the omega-3 fatty acids in flaxseed oil aren't identical to what you get from fish oil. Flaxseed oil contains alpha-linolenic acid (ALA), while fish oil contains eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The effects and potential benefits may not be the same.

Whole flaxseeds contain another important group of chemicals known as lignans.Lignans are being studied for use in preventing cancer. However, flaxseed oil contains no lignans. 1

Requirements/Sources

Flaxseed oil contains both omega-3 and omega-6 fatty acids, which are essential to health. Although the exact daily requirement of these essential fatty acids is not known, deficiencies are believed to be fairly common. 2 Flaxseed oil may be an economical way to ensure that you get enough essential fatty acids in your diet.

The essential fatty acids in flax can be damaged by exposure to heat, light, and oxygen (essentially, they become rancid). For this reason, you shouldn't cook with flaxseed oil. A good product should be sold in an opaque container, and the manufacturing process should keep the temperature under 100 degrees Fahrenheit. Some manufacturers combine the product with vitamin E because it helps prevent rancidity.

Therapeutic Dosages

A typical dosage is 1 to 2 tablespoons of flaxseed oil daily. It can be taken in capsule form or made into salad dressing. Some people find the taste pleasant, although others would politely disagree.

For whole flaxseed, a typical dose is 1 tablespoon of the seed (not ground) with plenty of liquid 2 to 3 times daily.

Therapeutic Uses

The best use of flaxseed oil is as a general nutritional supplement to provide essential fatty acids. There is little evidence that it is effective for any specific therapeutic purpose.

Flaxseed oil has been proposed as a less smelly alternative to fish oil for the prevention of heart disease . However, there is as yet no consistent evidence that it works. One double-blind study of 56 people failed to find that flax oil improved cholesterol profile . 19 Other studies did find improvements in cholesterol and/or blood pressure , but these were small trials and suffered from serious problems in study design. 19-20

One study found that a diet high in ALA (from sources other than flaxseed oil) was associated with a reduced risk of heart disease. 6 However, there were so many other factors involved that it is hard to say what caused what. 7

Sjogren’s syndrome is an autoimmune condition in which the immune system destroys moisture-producing glands, such as tear glands and salivary glands. It can occur by itself, or in conjunction with other autoimmune diseases, such as lupus . One small, double-blind study found preliminary evidence that use of flaxseed oil at a dose of 1-2 g daily can improve dry eye symptoms in Sjogren’s syndrome. 21

One very preliminary study hints that flaxseed oil may enhance the effects of conventional treatments for bipolar disorder when combined with conventional medications. 9 But, another study did not find flaxseed oil to be beneficial for treating bipolar disorder in children. 23

It has been suggested that flaxseed oil may have anticancer effects due to its ALA and lignan content. However, the supporting evidence for this belief is incomplete and somewhat contradictory (some studies actually found weak evidence of increased cancer risk with higher ALA intake). 11-17 Although fish oil appears to be effective for reducing symptoms of rheumatoid arthritis , one study failed to find flaxseed oil helpful for this purpose. 8 One study failed to find flaxseed oil helpful for preventing premature birth . 18

One small randomized trial found flaxseed oil ineffective for reducing blood sugar in people with type 2 diabetes . 22

Safety Issues

Flaxseed oil appears to be a safe nutritional supplement when used as recommended. However, due to the contradictory evidence regarding its effects on cancer (as described above), it should not be taken by people at high risk of cancer except on physician’s advice.