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Flaxseed has been used as a traditional food and remedy in Mediterranean cultures for thousands of years. It's now popular in the U.S. for many different health conditions. Flaxseed oil is made from crushed flaxseed. It shares some -- but not all -- of flaxseed's health properties.

Why do people take flaxseed?

Flaxseed and flaxseed oil contain alpha-linolenic acid (ALA), a precursor to the essential omega-3 fatty acid that partly and inefficiently converts into DHA and EPA -- more active omega-3s -- in the body. While flaxseed hasn't yet been shown to improve heart disease risk, there's good evidence that flaxseed and flaxseed oil may lower cholesterol levels.

Ground flaxseed -- but not flaxseed oil -- may also help with menopausal symptoms. Research has shown that 40 grams per day may be similar to hormone therapy for improving mild menopause symptoms, such as hot flashes and night sweats. Ground flaxseed may also ease constipation.

Flaxseed has also been shown to improve kidney function in people with lupus. If you have lupus -- or any other medical condition -- it's very important to talk with your doctor about any supplements you take.

Flaxseed oil, like fish oil, has been studied for lowering triglycerides. However, it is necessary to ingest a lot of flaxseed oil (38-60 grams) to have any noticeable effects.

Flaxseed is being studied for many other conditions, ranging from cancer to diabetes to osteoporosis. At this point, there is not enough evidence to support flaxseed for these conditions.

How much flaxseed should you take?

There is no set dose of flaxseed. In studies of people with high cholesterol, 40 to 50 grams of flaxseed per day has been used; 15 grams for improving kidney function in people with lupus; 40 grams for mild menopause symptoms. Flaxseed must be ground prior to ingestion or it won’t work for these conditions. Ask your doctor for advice. In order to lower triglycerides, 38-60 grams of flaxseed oil daily has been used.

Flaxseed can be mixed with liquid or food, such as muffins or bread. To be absorbed, however, it must me ground before using it to allow the oils to be available.   Some people use a small coffee grinder to grind daily doses as needed.

Can you get flaxseed naturally from foods?

While no other food sources contain flaxseed, flaxseed is itself sometimes added to foods. Ground flaxseed is sold as flour. Flaxseed oil might be added to salad dressing, but it should not be used for cooking.

What are the risks of taking flaxseed?

  • Side effects. At normal doses, flaxseed and flaxseed oil seem to be safe. Flaxseed -- and not flaxseed oil -- contains soluble fiber. It might cause diarrhea, cramping, gas, and bloating. High doses of flaxseed, especially when not taken with enough water, can cause constipation and, rarely, even bowel obstruction. 
  • Interactions. If you take any medicines or other supplements regularly, talk to your doctor before you start using flaxseed. Flaxseed may block the normal absorption of medicines. Always take medicines at least one hour before or two hours after using flaxseed. Flaxseed and flaxseed oil may also interact with drugs like blood thinners, NSAID painkillers, hormone treatments, and medicines for blood pressure, cholesterol, and diabetes. Use caution when taking flaxseed or flaxseed oil with supplements like St. John's wort and valerian. 
  • Risks. Never eat raw or unripe flaxseed -- it could be poisonous. People who have diabetes, bipolar disorder, high triglycerides, bleeding disorders, or prostate cancer should talk to a doctor before using flaxseed or flaxseed oil. Anyone with digestive problems (like Crohn's disease, IBS, or colitis) and women with hormone-sensitive diseases (like endometriosis, PCOS, breast cancer, and uterine cancer) should not use flaxseed.

Given the lack of evidence about its safety, flaxseed and flaxseed oil is not recommended for children or for women who are pregnant or breastfeeding.

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