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Lijnzaad tegen hoog cholesterol*
Uit een analyse van 28 studies van de laatste 20 jaar over lijnzaad en cholesterol blijkt dat het regelmatig eten van lijnzaad inderdaad het slechte (LDL) en totaal cholesterol doet dalen, vooral bij postmenopauzale vrouwen en bij personen die al een hoog cholesterol hebben. Lijnzaadolie daarentegen heeft weinig invloed op cholesterolwaarden.
Flaxseed Reduces Blood Lipids 
Whole flaxseed and flaxseed lignans significantly reduce circulating total cholesterol and low-density lipoprotein (LDL) cholesterol levels, showing their greatest effect in postmenopausal women and individuals with high initial cholesterol concentrations, according to the results of a meta-analysis published in the American Journal of Clinical Nutrition.
"Owing to the promising results in preclinical models, many clinical trials have been performed to determine the outcomes of flaxseed intervention (whole flaxseed, flaxseed oil, or lignans) on various cardiometabolic risk factors, particularly blood lipids," write An Pan, MSc, from the Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Chinese Academy of Sciences, Shanghai, China, and colleagues. "However, the findings from most of the previous clinical trials were inconsistent, and the discrepancies could be attributed to small sample size, insufficient study duration, variation in study designs, and diversity of the test product."
Total, LDL Cholesterol Levels Reduced 
The aim of this study was to evaluate whether administration of flaxseed or its derivatives could improve total, LDL, and high-density lipoprotein (HDL) cholesterol levels and triglyceride levels by making use of the increased statistical power afforded by a meta-analysis.
The researchers searched all randomized controlled trials of flaxseed or its derivatives on lipid profiles in adults, which were published in English from January 1990 to October 2008. They also attempted to contact authors of unpublished data. Study quality was assessed with use of the Jadad score; 16 studies were classified as high quality (Jadad score of 4 or 5), and 12 studies were classified as low quality (Jadad score of 2 or 3).
The 28 trials used in the meta-analysis comprised a total of 1381 study subjects. Five were conducted exclusively in postmenopausal women, 1 was done in premenopausal women, 10 trials were conducted in men, 10 trials were conducted in both sexes, 1 trial did not indicate the sex composition of the study sample, and 1 trial reported results separately by sex.
The median duration of the trials was 8.5 weeks, (range, 2 - 52 weeks). Flaxseed in whole, ground, or defatted form was tested in 10 of the 28 trials in doses that ranged from 20 to 50 g (2 - 5 tablespoons), and flaxseed oil was tested in 13 of the trials.
A significant reduction in total cholesterol levels was found in studies using whole flaxseed, with a net change of –0.19 mmol/L (95% confidence interval [CI], –0.29 to –0.09 mmol/L) and also in studies using lignan supplements, where the net change was –0.28 mmol/L; (95% CI, –0.55 to –0.01 mmol/L). Similarly, a significant reduction in LDL cholesterol levels was found with whole flaxseed, (net change, –0.16 mmol/L; 95% CI, –0.25 to –0.06 mmol/L) and lignan supplements (–0.16 mmol/L; 95% CI, –0.31 to –0.01 mmol/L). However there were no significant changes in total and LDL cholesterol levels with the intervention of flaxseed oil, the study authors report.
Women vs men had greater reductions in total cholesterol levels with flaxseed. The mean reduction for women was –0.24 mmol/L (95% CI, –0.36 to 0.12 mmol/L), and for men, the mean reduction was –0.09 mmol/L (95% CI, –0.05 to 0.23 mmol/L). The same was found with reductions in LDL cholesterol levels: for women, the mean reduction was –0.17 mmol/L (95% CI, –0.28 to –0.06 mmol/L), and for men, the mean reduction was –0.07 mmol/L (95% CI, –0.04 to 0.18 mmol/L).
The authors also report that total and LDL cholesterol levels were reduced to a greater degree in the high-quality studies (net change, –0.13 mmol/L; 95% CI, –0.24 to –0.02 mmol/L) vs the low-quality studies (net change, –0.08 mmol/L; 95% CI, 0.16 to –0.01 mmol/L). No significant changes were detected in the low-quality studies, they add.
When the studies were stratified according to initial lipid status, significant reductions in total cholesterol levels were found in the studies including subjects with high initial concentrations, as defined as 5.7 mmol/L for total cholesterol and 3.4 mmol/L for LDL cholesterol. For these individuals, the mean change in total cholesterol level was –0.17 mmol/L (95% CI, –0.32 to –0.03 mmol/L), and the mean change in LDL cholesterol level was –0.13 mmol/L (95% CI, – 0.23 to –0.02 mmol/L). In comparison, the mean change in total cholesterol levels for subjects with lower initial concentrations was 0.03 mmol/L (95% CI, –0.11 to 0.17 mmol/L), and the mean change in LDL cholesterol levels was 0.00 mmol/L (95% CI, –0.12 to 0.12 mmol/L).
There were no significant changes in HDL cholesterol or triglyceride levels.
Interpret Findings With Caution 
The authors point out that the limitations of their study include the heterogeneity of the studies in the meta-analysis, and a lack of information on the quality, quantity, and bioavailability of the flaxseed that was used. Therefore, they write, their findings must be interpreted with caution.
The results of this meta-analysis indicate that flaxseed consumption may be a useful dietary approach for the prevention of hypercholesterolemia, especially in some patient subgroups, the authors conclude. They add that further studies should be done to investigate the effectiveness of flaxseed supplementation on cardiometabolic risk factors other than blood lipids and, ultimately, on cardiovascular disease–related morbidity and mortality.
Dr. Pan has disclosed no relevant financial relationships. 
Am J Clin Nutr. 2009;90:288-297. Abstract 
Clinical Context
Flaxseed is an edible oil, seed, or grain with a potential effect on preventing cardiovascular disease. It is a rich plant source of alpha-linolenic acid and lignans and is an excellent source of dietary fiber, of which 25% is in soluble form. Previous studies have suggested that flaxseed reduces both total and LDL cholesterol levels, but it is unclear which forms of flaxseed are more effective and if benefits are seen for all patient populations.
This is a meta-analysis of studies published between 1990 and 2008 to examine the effect of flaxseed and its derivatives on lipid profile and the factors that influence this effect.
Study Highlights
· 2 researchers independently searched PubMed, the Cochrane library, clinical trials, the World Health Organization, and other databases for studies comparing flaxseed and its derivatives vs placebo or other products.
· Study characteristics and participant information were extracted with lipid data, and the Jadad score was used to rate quality.
· Participants with fish oil as the intervention were excluded.
· The estimated principal effect was the mean difference in lipid concentrations between those assigned to flaxseed and its derivatives and those assigned to control regimens.
· 160 citations were identified, of which 82 were evaluated and 28 studies were included for analysis.
· 1539 subjects were assigned to flaxseed.
· 6 trials were conducted exclusively in women (5 in postmenopausal women), 10 trials in men, and 10 in both sexes.
· Flaxseed in whole, ground, or defatted form (whole flaxseed) was tested in 10 of 28 trials with doses from 20.0 to 50.0 g.
· Wheat, wheat bran/germ, manioc flour, or sunflower seed were the control regimens in these studies.
· Those in the control groups adhered to dietary measures.
· Flaxseed oil was tested in nearly half of the trials with doses of 1.0 to 38.0 g for alpha-linolenic acid.
· Flaxseed lignan was tested in doses from 200 to 600 mg.
· Trials varied in length from 2 to 52 weeks, with a median duration of 8.5 weeks.
· 16 were of high quality and 12 of low quality by Jadad score.
· There were no significant differences between groups in weight or lipid levels at baseline.
· Total cholesterol results were reported in 36 comparisons from 28 studies for 1548 participants.
· LDL levels were reported in 35 comparisons from 27 studies including 1471 subjects.
· For the overall population, total cholesterol levels decreased by 0.10 mmol/L (P = .06), and LDL cholesterol levels decreased by 0.08 mmol/L (P = .04).
· Concentrations of HDL cholesterol were reported in 35 comparisons from 27 studies involving 1353 participants.
· Triglyceride levels were reported in 33 comparisons from 26 studies including 1359 subjects.
· A significant reduction in total cholesterol levels was seen for studies involving whole flaxseed (change, –0.19 mmol/L) and lignan supplement (change, –0.28 mmol/L) but not for flaxseed oil.
· LDL cholesterol level also declined significantly for whole flaxseed (–0.16 mmol/L) and lignan (–0.16 mmol/L) but not for flaxseed oil.
· Reductions were greater in women (–0.24 mmol/L) vs men (–0.09 mmol/L), and only moderate reductions were seen in studies involving both sexes.
· LDL cholesterol reductions were also larger in women (–0.17 mmol/L) and in both sexes (–0.14 mmol/L) vs men (–0.07 mmol/L) and postmenopausal women.
· When stratified by baseline lipid status, significant reductions in total cholesterol levels were seen in studies with subjects with high initial total cholesterol levels and not in those with low initial cholesterol levels.
· The same pattern was seen for LDL cholesterol levels.
· The authors noted that studies involving women vs studies involving men were more likely to include subjects with higher cholesterol levels at baseline and to use flaxseed and lignan vs flaxseed oil.
· No significant changes were seen for HDL cholesterol or triglyceride levels across all groups or subgroups.
· The authors concluded that whole flaxseed and lignan, but not flaxseed oil, were associate with reductions in total and LDL cholesterol levels.
· Female sex higher baseline cholesterol levels were associated with greater reductions in total and LDL cholesterol levels.
Clinical Implications
· Whole flaxseed and lignan, but not flaxseed oil, are associated with lowering of total and LDL cholesterol levels but not with beneficial effects on HDL cholesterol or triglyceride levels.
· Lipid benefits seen with flaxseed and lignan are greater in women, especially in postmenopausal women, and in those with high baseline cholesterol levels. (September 2009)