The Bioavailability of Flax Lignans from Flax Seeds and Supplements

Adding flaxmeal to your breakfast is the cheapest way of getting lignans. (Photo by thepinkpeppercorn)

In the previous post, we looked at the studies on flax lignans and their possible effect on hair growth. As promised, in this post we'll be looking at the issue of bioavailability: how well flax lignans are absorbed and whether supplements or natural sources are the best way to go.

Lignan content of flax supplements

As mentioned in the previous post, the company that funded the only study measuring the effect of flax lignans on hair loss is called Acatris. This unpublished study found that LinumLife EXTRA, a flax lignan supplement, improved hair loss condition in 9 out of 10 males. There was no mention of bioavailability in the press release, however.

Another study done for Acatris suggests that flax lignans are indeed absorbed by the body, at least when using their LinumLife product (link). The researchers concluded that the lignans are absorbed and that they increase serum levels of enterolactone (ENL) and enteroldiol (END), which are what secoisolariciresinol diglucoside (SDG) is eventually metabolized into. A quote from the press release:

The men in the study received a daily dose of 1 gram of LinumLife, equivalent to 40 mg of SDG. Their serum END and ENL levels were measured at baseline, three months and six months. At baseline, their average levels were 115 nmol/L. At three months they had increased 25% to 145 nmol/L, and at six months were around 136 nmol/L.

The baseline levels were quite high because the participants were from Japan, where lignan intake from diet is much higher than in much of the Western world. Note that in this study they used LinumLife instead of LinumLife EXTRA, which contains more lignans per gram. LinumLife has 40 mg of SDG, which is the main lignan in flax, while LinumLife extra contains 50 mg. The rather limited press releases don't mention whether the higher concentration of lignans resulted in better absorption.

Lignan content of flax seeds

So now we have two studies from a supplement company saying that supplemental forms of lignans are bioavailable and grow hair in humans. But what about getting your daily dose of flax lignans directly from flax seeds?

The SDG concentrations in flax seed varies from about 1% to 3%. Since one tablespoon of ground flax seed weighs 7 grams, it contains between 70 mg and 210 mg of SDG. So one tablespoon would have at least as much SDG than the supplements.

Indeed, the LinumLife website does not claim better absorption from using their product than from consuming flax seeds. They only state that their product contains 10-30 times more lignans than flax oil or ground flax seeds. Therefore, it supplementing with flax lignans seems unnecessary and more expensive than simply consuming flax seeds.

For example, a (discontinued) flax supplement from Jarrow contains 60 capsules with 40 mg of SDG and costs about $10. An 18 oz (510 grams) can of organic flax meal costs about $5; for half the price, you get more portions (72 tablespoons, to be exact) with more SDG in each portion.

It's difficult to find reliable information on the lignan content of flax seed oil, but it appears that the oil contains very little to zero lignans (link, link). The reason is that the lignans are in the fiber portion of the seed, and the oil is very low in fiber. There are flax seed oils with added lignans, but how much lignans they actually contain and how bioavailable they are is unclear.

Improving the bioavailability of lignans from flax seeds

Unfortunately, there are no studies directly comparing whether lignans from supplements are absorbed differently than from flax seeds. While I remain somewhat sceptical, it is possible that the supplement form has superior bioavailability compared to flax seeds.

However, even if it was true, in my opinion the scale still tips in favor of ordinary flax seeds. First, just two tablespoons of flax seeds daily would provide 3-6 times more SDG than either LinumLife or LinumLife EXTRA. My guess is that this would more than compensate for poorer bioavailability.

Second, the bioavailability of lignans from flax seed can be increased dramatically by crushing or grinding the seeds (link). Crushing flax seeds is better than consuming whole flax seeds, but ground flax seeds (i.e. flax meal) are superior in terms of lignan absorption. That's good news, because while I find the taste of whole flax seeds somewhat unpleasant and the taste of flax seed oil (or linseed oil) downright disgusting, flax meal actually tastes quite nice.

In the study linked to above, the participants were given 0.3 grams of flax seeds per kg body weight. For a 70 kg person, this would mean 21 grams (or 3 tablespoons) and 210-630 mg of SDG. After 10 days of consuming ground flax seed, enterodiol and enterolactone levels increased from 1.9 to 103 nmol/L and from 9.5 to 167 nmol/L, respectively. That's a much greater increase than what was seen in the LinumLife study. There was no significant difference between men and women.

The authors also report that steady-state plateau concentrations of enterolactone and enterodiol are reached when the supplemental interval is less than ~17 hours. In other words, if you want to keep enterolignan levels high, you should consume ground flax seeds twice per day with at least 7 hours in between.

Conclusion

Consuming 40-610 mg of SDG, the main flax lignan, raises serum enterolactone and enterodiol levels significantly, which indicates that flax lignans are absorbed by the human body. Lignans are bioavailable both in supplement and natural form.

While the taste of flax seeds may be unpleasant to some people, a tablespoon of flax meal (ground flax seeds) actually contains more SDG than most supplements. The lignans in crushed and whole flax seeds are absorbed less effectively, however.

For more information on hair growth, see these posts:

Emu Oil and Hair Growth: A Critical Look at the Evidence
Hair Growth with Vitamin E Tocotrienols from Palm Oil – Experiment Conclusion
Sesame Seeds Increase Absorption of Vitamin E Tocotrienols by Up to 500%
Hyaluronic Acid for Skin & Hair – Experiment Conclusion