Plant lignans, found widely in plants and seeds, such as flax seed, whole grain cereals, berries, vegetables and fruits, are converted into enterodiol and enterolactone in the colon. There is some evidence that enterolactone, a phytoestrogen, may have a beneficial effect on prostate health, bone health, breast health, menopause symptoms, heart health, hair loss, acne and inflammation.
A previous clinical trial, also from Finland, reported that high serum levels of enterolactone could reduce the risk of death from coronary heart disease by 55 per cent, and cardiovascular disease by 45 per cent (The Lancet, 1999, Vol. 354, pp. 2112-2115).
The authors of the new study, published in the American Journal of Epidemiology (Vol. 163, pp. 687-693), say that other studies into the effects of lignans and enterolactone on heart health have been inconsistent.
The researchers, led by Annamari Kilkkinen from the National Public Health Institute, Helsinki, followed-up participants from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study - a randomized, double-blind, placebo-controlled trial looking at the effects of vitamin E (50 mg per day), beta-carotene (20 mg per day), both, or a placebo.
The ATBC study only recruited smokers. Of the 29,133 men who were randomized in the initial study, only 340 cases and 420 members of a subcohort with available serum enterolactone sample analysis were used in the current study.
When the researchers calculated the risk factor for coronary heart disease with respect to enterolactone intake, men who had highest serum enterolactone levels (average 40.9 nanomoles per litre) had a 42 per cent lower risk than men with the lowest serum enterolactone levels (average 2.6 nanomoles per litre).
When the scientists accounted for "classic risk factors" they say that the relationship was "no longer statistically significant", despite the highest group having an apparent 37 per cent risk reduction, compared to the lowest enterolactone level group.
"The results of this case-cohort study support only weakly the hypothesis that a high serum enterolactone concentration is associated with the reduced risk of coronary heart disease," wrote Kilkkinen.
The difference in results between the results published in The Lancet and the new results may be due the differences in study populations. The Lancet study's population was typically four years younger, had higher serum enterolactone levels, and was not focussed on smokers (43 per cent of cases and 27 per cent of controls), which prevents the new study from being a generalised result.
Kilkkinen pointed out however that the smokers in the Lancet study actually had lower risk rates than non-smokers with regards the enterolactone-coronary heart disease relationship.
This study measured serum lignan levels and was not an intervention by design, but there is increasing interest from consumers making a concerted effort to consume lignans. Use of lignans in the specialty supplements sector is increasing.
Flax lignan products sales in the US were up 8.1 per cent overall in 2004 over 2003 to more than $2.9bn in 2004, according to Flax Canada.
The lignan market is currently dominated by Acatris' SDG (secoisolariciresinol diglucoside) flax lignan but competition is increasing with the launch of Linnea's HMRlignan.
However much of the research on the health benefits of lignans has been conducted using SDG, and Acatris is at pains to point out that it should not be presumed that all sources deliver the same results.
Laurent Leduc, president of Acatris' North America division told NutraIngredients.com that, in any case, heart health is not the main health area for flax lignans. Rather the focus is on prostate and menopause health, and their antioxidant properties.
Moreover he said that rye, not flaxseed, is a more common source of lignans in Finland.