Linseed and Linseed Oil

Also indexed as: Lignan, Linum usitatissimum

What is it?

Linseed, called linseed in some countries, is a good source of dietary fibre, omega-3 fatty acids, and lignans. Each of these components may contribute to the health effects of eating linseed, but linseed oil contains no fibre and very little lignan.

Like most vegetable oils, linseed oil contains linoleic acid, an essential fatty acid needed for survival. But unlike most oils, it also contains significant amounts of another essential fatty acid, alpha linolenic acid (ALA).

ALA is an omega-3 fatty acid. To a limited extent, the body turns ALA into eicosapentaenoic acid (EPA)—an omega-3 fatty acid found in fish oil—which in turn converts to beneficial prostaglandins. (Prostaglandins are hormone-like substances made in many parts of the body rather than coming from one organ, as most hormones do.)

While fish oil has been shown to have anti-inflammatory activity, an anti-inflammatory effect of linseed oil has not been demonstrated conclusively. Some doctors have argued that, because ALA can be converted to EPA and DHA (the fatty acids found in fish oil), linseed oil should be useful for the same conditions as fish oil. However, the conversion of ALA to EPA and DHA is limited, so that argument may turn out to be incorrect. For example, while numerous studies have shown that fish oils are beneficial for rheumatoid arthritis, linseed oil failed to work for this condition in the only known trial.¹ In 1994, a diet purportedly high in ALA was successful in preventing heart disease,² but this study altered many dietary factors, so ALA may not have been solely responsible for the outcome.³ Linseed oil does not appear to be a good replacement for fish oil for people with elevated triglycerides.⁴ ⁵ ALA does not reduce excess platelet aggregation ("sticky platelets"), another risk factor for heart disease, the way fish oil does.⁶ However, linseed oil may help lower cholesterol,⁷ and research specific to linseed oil indicates that it may also lower blood pressure.⁸

Linseed is the most abundant food source of lignans, a family of phytochemicals that is drawing the interest of many health researchers.⁹ ¹⁰ ¹¹ Lignans are not actually present in linseed; rather intestinal bacteria produce them from precursors in linseed.¹² ¹³ Lignans have antioxidant activity,¹⁴ and test tube and animal research suggests they may also have significant effects on the metabolism and function of the hormone oestrogen.¹⁵ ¹⁶ ¹⁷

Where is it found?

In addition to its presence in linseed oil, small amounts of ALA are also found in canola, soya, black currant, and walnut oils. Small amounts of lignans are present in a wide variety of foods of plant origin.

Linseed and linseed oil has been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings	Health Concerns
	Constipation (flaxseed) Systemic lupus erythematosus (flaxseed)
	High cholesterol (flaxseed)
	Benign prostatic hyperplasia (BPH) (flaxseed oil) Constipation (flaxseed oil) Ulcerative colitis (flaxseed)
Reliable and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit. For a herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Who is likely to be deficient?

ALA deficiencies are possible but believed to be rare, except in infants who are fed formula that is omega-3 deficient. Lignan is not an essential nutrient, so deficiencies are not possible.

How much is usually taken?

For promoting bowel regularlity, 1 tablespoon (15 ml) of whole or ground linseed is taken one or two times per day, accompanied by a full glass of water. When used to treat other health conditions, it is used in amounts of 30 to 35 grams (1 to 2 ounces) per day.

Although it is not suitable for cooking, linseed oil (unlike fish oil) can be used in salads. Some doctors recommend that people use 1 tablespoon (15 ml) of linseed oil per day as a supplement in salads or on vegetables to ensure a supply of essential fatty acids. Some conversion of ALA to EPA does occur,¹⁸ and this conversion can be increased by restricting the intake of other vegetable oils.¹⁹

For those who wish to replace fish oil with linseed oil, research suggests taking up to ten times as much ALA as EPA.²⁰ Typically, this means 7.2 grams of linseed oil equals 1 gram of fish oil. However, even if taken in such high amounts, linseed oil may not have the same effects as fish oil. But, linseed oil will not cause a fishy-smelling burp (a possible side effect of fish oil).

Are there any side effects or interactions?

Linseed oil toxicity has not been reported. However, there is conflicting information about the effect of linseed oil and one of its major constituents, ALA, on cancer risk.

While most test tube and animal studies suggest a possible protective role for ALA against breast cancer,²¹ ²² ²³ ²⁴ ²⁵ one animal study²⁶ and a preliminary human study²⁷ suggested increased breast cancer risk from high dietary ALA. Another preliminary human study reported that higher breast tissue levels of ALA are associated with less advanced breast cancer at the time of diagnosis.²⁸ For prostate cancer, a test tube study reported ALA promoted cancer cell growth,²⁹ but preliminary human studies have shown ALA to be associated with either an increased³⁰ ³¹ or decreased risk,³² or no change³³ at all.

Advocates of linseed oil speculate that a potential association between ALA and cancer may be due to the fact that meat contains ALA, thus implicating ALA when the real culprits are probably other components of meat. In some studies, however, saturated fat (and therefore probably meat) were taken into consideration, and ALA still correlated with increased risk. The associations between ALA and cancer might eventually be shown to be caused by substances found in foods rich in ALA rather than by ALA itself. However, ALA has been reported to become mutagenic (able to cause precancerous changes) when heated,³⁴ which concerns some doctors.

The effect of ALA as an isolated substance, and of linseed oil on the risk of cancer in humans remains unclear, with most animal and test tube studies suggesting protection, and some preliminary human trials suggesting cause for concern. It is premature to suggest that ALA and linseed oil will either cause or protect against human cancer at this time.

Linseed oil is not suitable for cooking and should be stored in an opaque, airtight container in the refrigerator or freezer. If the oil has a noticeable odour it is probably rancid and should be discarded.

As with any source of fibre, linseed should not be taken if there is possibility that the intestines are obstructed. People with scleroderma (systemic sclerosis) should consult a doctor before using linseed. Although a gradual introduction of fibre in the diet may improve bowel symptoms in some cases, there have been several reports of people with scleroderma developing severe constipation and even bowel obstruction requiring hospitalisation after fibre supplementation.³⁵

Animal research suggests that large amounts of linseed or lignans consumed during pregnancy might adversely affect the development of the reproductive system.³⁶ No studies have attempted to investigate whether this could be a problem in humans.

Allergic reactions to linseed have occasionally been reported, but are considered very uncommon.³⁷ ³⁸

At the time of writing, there were no well-known drug interactions with linseed oil.

References
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3. Rice RD. Mediterranean diet. Lancet 1994;344;893-4 [letter].

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5. Abbey M, Clifton P, Kestin M, et al. Effect of fish oil on lipoproteins, lecithin: cholesterol acyltransferase, and lipid transfer protein activity in humans. Arterioscler 1990;10:85-94.

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22. Munõz SF, Silva RA, Lamarque A, et al. Protective capability of dietary Zizyphus mistol seed oil, rich in 18:3, n-3, on the development of two murine mammary gland adenocarcinomas with high or low metastatic potential. Prostaglandins Leukot Essent Fatty Acids 1995;53:135–8.

23. Thompson LU, Rickard SE, Orcheson LJ, Seidl MM. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis 1996;17:1373–6.

24. Fritsche KL, Johnston PV. Effect of dietary alpha-linolenic acid on growth, metastasis, fatty acid profile and prostaglandin production of two murine mammary adenocarcinomas. J Nutr 1990;120:1601–9.

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28. Bougnoix P. Alpha-linolenic acid content of adipose breast tissue: a host determinant of the risk of early metastasis in breast cancer. Br J Cancer 1994;70:330–40.

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36. Tou JC, Chen J, Thompson LU. Flaxseed and its lignan precursor, secoisolariciresinol diglycoside, affect pregnancy outcome and reproductive development in rats. J Nutr 1998;128:1861–8.

37. Alonso L, Marcos ML, Blanco JG, et al. Anaphylaxis caused by linseed (flaxseed) intake. J Allergy Clin Immunol 1996;98:469–70.

38. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergol Immunopathol (Madr) 2003;31:47–9.

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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or chemist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires March 2007.

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