Flaxseed could boost lung health, animal study

By Stephen Daniells

- Last updated on GMT

Related tags: Omega-3 fatty acids, Omega-3 fatty acid

A dietary supplement of flaxseed, a rich source of lignans and
omega-3 fatty acids, could prove useful to reduce lung inflammation
and oxidative stress, if results from a mice study can be expanded
to humans.

Flaxseed contains high concentrations of both omega-3 fatty acids and lignans, particularly secoisolariciresinol diglucoside (SDG), which is converted into enterodiol and enterolactone in the colon. There is some evidence that enterolactone, a phytoestrogen, may have a beneficial effect on bone health, breast health, heart health, hair loss, acne, inflammation, with the main focus being for prostate and menopause health, and as an antioxidant.

If the preliminary results from the mice studies can be applied to humans, this could be open up a new outlet for flaxseed. The North American market for flax lignan-containing specialty supplements saw growth of 8.1 per cent overall in 2004 over over the previous year, and annual sales were over $2.9bn.

"To our knowledge, our study shows here the first supporting evidence to indicate that dietary supplementation with flaxseed can ameliorate oxidative tissue damage and inflammation in certain forms of experimental acute lung injury,"​ wrote lead author Paul Kinniry in the Journal of Nutrition​ (Vol 136, pp 1545-1551).

The researchers, from the University of Pennsylvania and North Dakota State University, supplemented the diet of female mice with five and ten per cent flaxseed (Purina Mills) for up to ten weeks. The mice were divided into two groups; one group received the supplemented diet (test group) while the other received only the standard AIN-93G diet (control group).

Vitamin E was removed from the diet mix and, because flaxseed contains a small amount of the vitamin, each diet was standardised to contain a constant 3.35 mg per kg, attained by adding appropriate amounts of dl-alpha-tocopheryl acetate.

The mice were further divided into four different groups; three groups had induced lung damage by acid aspiration, administration of lipopolysaccharide solution (LPS), or hyperoxic (excess oxygen in the tissues) conditions. The fourth group was untouched and used as control. The degree of lung damage was evaluated by measuring malondialdehyde (MDA) concentrations, a reactive carbonyl compound.

The researchers, led by Professor Melpo Christofidou-Solomidou, found that both doses of flaxseed supplementation resulted in decreased levels of MDA after acid aspiration and hyperoxia, but not LPS conditions.

Supplementation with ten per cent flaxseed, for example, reduced MDA levels by a significant three micromoles per gram of lung tissue, compared to unsupplemented mice exposed to acid aspiration.

MDA levels also decreased in lung tissue of mice eating the ten per cent flaxseed diet after hyperoxia, falling from 7.5 micromoles per gram of lung tissue in the untouched mice, to 5 micromoles per gram of lung tissue in the hyperoxia mice.

"Acid aspiration results in a dramatic increase in lung permeability,"​ explained the authors. "Aspiration of gastric contents [which are acidic] is one of the most common causes of acute injury or acute respiratory distress syndrome (ARDS), and is reported to be associated with a 25 to 35 per cent incidence of ARDS."

Over 150000 Americans are diagnosed with ARDS every year, which is equivalent to 17 people per hour, according to the ARDS Foundation. The syndrome is defined as an acute process that leads to moderate to severe loss of lung function.

Since flaxseed contains both omega-3 fatty acids and flax lignans the authors were unable to determine which were the bioactive components. But the researchers did suggest that the possible protective mechanism could be due to the antioxidant activity of the flax lignans.

"The flaxseed lignan SDG and its metabolites (enterodiol and enterolactone) have known antioxidant activities, shown both in vitro and in vivo systems, that are exerted mainly through the inhibition of lipid peroxidation,"​ said Kinniry.

Lipid peroxides can then undergo further decomposition to produce compounds like MDA, said the researchers, adding to the oxidative stress on the tissues. This by inhibiting the lipid peroxidation process, oxidative stress on the lungs may be reduced.

Further study should focus on determining tissue lignan levels. Prof Christofidou-Solomidou told NutraIngredients.com that work was continuing in this field with "even more exciting data with dietary flaxseed in additional, clinically relevant disease models (in mice),"​ already generated.

"We are very excited to pioneer the work of flaxseed in the context of acute lung disease,"​ she said.

However, Professor Michael Crawford, director of London Metropolitan University's Institute of Brain Chemistry and Human Nutrition, warned that caution was needed when interpreting these results since mice are especially efficient at converting alpha-linolenic acid (the only omega 3 in flax seed) to docosahexaenoic acid.

"In mice the efficiency of the conversion leads to high levels of docosahexaenoic acid throuhgout cell membranes in the body.

It is not the same in large mammals including humans in whom only a very small proportion of the alpha-linelenic acid is converted to docosahexaenoic acid. So the quote "Flaxseed could boost lung health" may be relevant to mice but achieved by the docosahexaenoic acid. It may not be seen in humans where the bulk of the alpha-linolenic acid is oxidised,"​ Professor Crawford told NutraIngredients.com.

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