Conceived and designed the experiments: XL AP JS ZY YW WD YL. Performed the experiments: XL AP JS YC XY HL WG XZ XC. Analyzed the data: AP YC XY ZY. Wrote the paper: XL AP XY HL ZY WD YL. Other: Dietary data analyses: YC. Laboratory management: HL. Patient recruitment: YW. Laboratory assistant: WG. Patient recruitment, follow-up management: AP JS YC XZ XC.
The authors have declared that no competing interests exist.
Flaxseed consumption has been shown to improve blood lipids in humans and flaxseed-derived lignan has been shown to enhance glycemic control in animals. The study aimed to investigate the effect of a flaxseed-derived lignan supplement on glycemic control, lipid profiles and insulin sensitivity in type 2 diabetic patients.
This was a randomized, double-blind, placebo-controlled, cross-over trial and it was conducted between April and December 2006 in Shanghai, China. Seventy-three type 2 diabetic patients with mild hypercholesterolemia were enrolled into the study. Patients were randomized to supplementation with flaxseed-derived lignan capsules (360 mg lignan per day) or placebo for 12 weeks, separated by an 8-week wash-out period. HbA1c, lipid profiles, insulin resistance index and inflammatory factors were measured. Sixty-eight completed the study and were included in the analyses. The lignan supplement significantly improved glycemic control as measured by HbA1c (-0.10±0.65 % vs. 0.09±0.52 %,
Daily lignan supplementation resulted in modest, yet statistically significant improvements in glycemic control in type 2 diabetic patients without apparently affecting fasting glucose, lipid profiles and insulin sensitivity. Further studies are needed to validate these findings and explore the efficacy of lignans on type 2 diabetes.
ClinicalTrials.gov
Type 2 diabetes is a serious and economically devastating disease. Over the past few decades its worldwide prevalence has increased dramatically, especially in the developing countries such as China and India
Recently, phytoestrogens have gained increasing attention because of accumulating evidence suggesting their protective roles against numerous chronic diseases, including cancers, CVD, dyslipidemia and diabetes
To our knowledge, no clinical trials thus far have determined the effect of SDG on glycemic control or lipid profiles in type 2 diabetic patients. This is particularly intriguing among Asians who already consume high intakes of soy-derived isoflavone and may respond differently to lignan supplements compared to Westerners
The protocol for this trial and supporting CONSORT checklist are available as supporting information; see
A total of 581 type 2 diabetic patients were screened for inclusion at the local community medical service centers in urban districts of Shanghai. Participants were considered eligible if they met the following criteria: 1) 50–79 years of age (women were required to be postmenopausal for at least 1-year); 2) LDL-C level ≥2.9 mmol/L; and 3) diagnosis of type 2 diabetes, but not using exogenous insulin for glycemic control. Exclusion criteria were: 1) current or previous (preceding 6 months) estrogen-use; 2) regularly taking phytoestrogen-containing supplements; 3) antibiotic-use in the preceding 3 months; 4) severe renal, liver, heart, pituitary, thyroid or mental diseases, alimentary tract ulceration or diseases affecting absorption; or 5) history of cancer, history of drug or alcohol abuse.
The study protocol was approved by the Ethics Committee of Institute for Nutritional Sciences, Chinese Academy of Sciences. All participants provided signed informed consents.
Thirty-seven subjects began lignan supplements and 36 subjects started on the placebo for 12 weeks. After an 8-week wash-out period, the participants received the alternative treatment for another 12 weeks. While on study, participants were instructed to maintain their habitual diets, levels of physical activity, and use of prescribed medications. During the 12 weeks, participants assigned to the lignan supplements were instructed to take three lignan capsules (0.6 g/capsule) each day that provided a daily amount of 360 mg isolated flaxseed lignan. The raw materials of lignan were donated by Frutarom Netherlands BV (LinumLife™ Extra, Veenendaal, The Netherlands) and were produced by Jarrow Formulas Inc (Flax Essence™ , Los Angeles). The three capsules provided 3.7 kilocalories and were comprised of 20% SDG, 15.6% fat, 3.2% protein, 2.6% fiber and 30% carbohydrate. Participants randomly assigned to the placebo group were instructed to take 3 placebo capsules per day, which were comprised of rice flour (98%) and provided a total of 5.8 kilocalories. Subjects were asked to return any unused capsules and adherence was assessed by pill counts, as well as by urinary concentrations of lignan metabolites (for SDG-specific adherence).
The objective of the study was to investigate the effect of a flaxseed-derived lignan supplement on indexes of glycemic control, insulin resistance and lipid profiles in type 2 diabetic patients.
All participants were scheduled to visit Huadong Hospital every 3 weeks to obtain new capsules, and their adherence and physical status were evaluated. Dietary intakes were assessed using 3-day food records which ascertained intakes during 2-weekdays and 1-weekend day at four timepoints throughout the study (1 week prior to and during the last week of each intervention period). All food records were reviewed for completeness and coded by the trained dietitians who were blinded to the study arms. Energy and nutrient intakes were calculated using the SY Nutrition Software (Fudan University, Shanghai, China) based on the local food composition database. Physical activity level was evaluated by asking the average times per week spent on several common activities (e.g. running, jogging, dancing, bicycling) in the last month and each activity was assigned a metabolic equivalent value (MET) according to accepted standards
Serum total cholesterol, HDL cholesterol (HDL-C), LDL-C, triacylglycerol, and glucose were measured using reagents purchased from Wako Pure Chemical Industries (Osaka, Japan), serum lipoprotein(a) [Lp(a)], apolipoprotein A-1 and B (apoA1 and apoB) were measured using kits from Roche Diagnostics (Mannheim, Germany). All the above assays were performed on an automatic analyzer (Hitachi 7080, Japan) within one day. HbA1c was determined by turbidometric immunoinhibition on packed red blood cells on the automatic analyzer using kits from Roche Diagnostics
Lp(a) concentrations were measured in 245 serum samples due to reagent shortage. The values of urinary excretion of lignan or isoflavone metabolites were replaced by 0.05 µg/mL (half of the lowest detectable limit) when not detectable.
As there were no extant studies that had investigated the effect of flaxseed-derived lignans on HbA1c, the sample size was calculated based on the previous studies of flaxseed on LDL-C concentrations. Using a one-sided 5% significance level, a sample of 67 patients was needed for this cross-over trial, assuming a 10% drop-out rate. This gave the study 90% power to detect a 5% difference (0.2 mmol/L) in LDL-C between treatments (assuming a common SD of 0.5 mmol/L).
The random allocation sequence was developed using computer program by a statistician who was not involved in the study. After enrollment, each participant was randomly given a unique study number. Randomization and allocation to the treatment or placebo group was based on the study number. Participants were randomized to the intervention or the placebo arms using stratification factors of gender and tertiled LDL-C concentrations from screening. In detail, women and men were sorted by their levels of LDL-C, respectively. Then randomization was performed using a block size of 3 and length of 10 for men and length of 16 for women, respectively. Placebo capsules were almost identical to the lignan capsules in size, shape, color, and taste. Each bottle of capsules was marked with the participant's study number, but no product identifier. Participants, health professionals, statisticians, and other research staff involved in the trial were blinded to the assignments.
Differences between values after 12-week intervention were analyzed in Stata 9.2 (Stata ™, Texas) using a mixed model analysis of covariance with treatment (lignan or placebo) and period (first or second period) as fixed factors, subjects as random factors, and baseline measurements as covariates. Further fixed terms corresponding to treatment/period interactions were included to test for any carry-over effect between periods, and treatment/covariate interaction was included to test whether the treatment effect of flaxseed lignan varied according to the baseline values of the covariate. Given the weight-dependent nature of the study endpoints, weight and weight changes were incorporated into the model as covariates. However the results were not affected and the data are therefore not shown. Data that were not normally distributed, as assessed by the Shapiro-Wilks test, were natural-logarithmically transformed prior to analysis (see table footnotes for details). Differences before and after treatments were analyzed using paired Student's t-test. Pre-post differences in physical activity level, and habitual energy and nutrient intake were analyzed using ANOVA. Differences were considered significant at
A total of 581 type 2 diabetic patients were screened for inclusion in the study (
Study flow chart of the lignan intervention trial.
The baseline characteristics of participants are given in
Variable | Total (n = 68) | Group A (n = 34) | Group B (n = 34) |
Age (years) | 63.2±7.4 | 63.4±7.1 | 63.0±7.8 |
Male gender (n, %) | 25 (36.8%) | 14 (41.2%) | 11 (32.4%) |
Height (cm) | 159.7±8.2 | 160.5±8.6 | 158.9±7.8 |
Weight (kg) | 64.2±11.0 | 64.7±11.4 | 63.8±10.6 |
BMI (kg/m2) | 25.1±3.3 | 25.0±3.3 | 25.2±3.3 |
Waist circumference (cm) | 86.9±9.4 | 87.1±9.6 | 86.7±9.2 |
Hip circumference (cm) | 94.5±7.0 | 94.5±7.4 | 94.5±6.6 |
Data are mean±Standard Deviation. BMI, body mass index.
No carry-over effect was identified for any of the observed results. Both the lignan capsules and placebo were well-tolerated, and the overall adherence was 96% during the lignan treatment phase and 94% during the placebo phase.
Pre- post dietary intakes of energy, fat, specific classes of fatty acids, protein, carbohydrate, total fiber and cholesterol are featured according to treatment (
Variable | Lignan treatment | Placebo treatment | ||
Week 0 | Week 12 | Week 0 | Week 12 | |
Energy (kcal/day) | 1911±329 | 1858±365 | 1840±327 | 1866±321 |
Fat (% of energy) | 32±6 | 31±7 | 31±6 | 31±6 |
SFA (g/d) | 10±4 | 10±4 | 10±3 | 10±3 |
MUFA (g/d) | 14±5 | 14±6 | 14±5 | 14±6 |
PUFA (g/d) | 22±9 | 20±9 | 21±9 | 21±9 |
Protein (% of energy) | 17±3 | 18±3 | 17±3 | 17±3 |
Carbohydrate (% of energy) | 51±6 | 52±7 | 52±6 | 51±6 |
Total fiber (g/d) | 10±4 | 10±3 | 10±4 | 9±4 |
Dietary cholesterol (mg/d) | 394±153 | 439±206 | 403±195 | 410±171 |
Physical activity level(MET-hours/week) | 88.0±32.7 | 92.3±37.7 | 89.4±32.4 | 87.6±35.4 |
Data are mean±Standard Deviation. SFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; MET, metabolic equivalent value.
Data of the study endpoints are shown in
Variable | Lignan treatment | Placebo treatment | Treatment difference ( | ||||
Baseline | 12 weeks | Absolute change | Baseline | 12 weeks | Absolute change | ||
Weight (kg) | 64.0±11.0 | 64.5±10.8 | 0.5±1.3 | 64.1±10.9 | 64.4±11.0 | 0.3±1.3 | 0.354 |
BMI (kg/m2) | 25.0±3.3 | 25.2±3.3 | 0.2±0.5 | 25.1±3.3 | 25.2±3.5 | 0.1±0.5 | 0.478 |
Systolic BP (mmHg) | 139.3±21.4 | 138.9±19.9 | −0.4±15.1 | 138.0±18.6 | 138.6±18.2 | 0.7±11.6 | 0.268 |
Diastolic BP (mmHg) | 79.2±10.7 | 77.7±9.5 | −1.5±6.7 | 79.3±10.3 | 79.0±9.9 | −0.3±6.9 | 0.751 |
HbA1c (%) | 7.17±1.42 | 7.06±1.15 | −0.10±0.65 | 7.01±1.10 | 7.11±1.29 | 0.09±0.52 | 0.001 |
Glucose (mmol/L) | 8.12±2.60 | 7.83±2.33 | −0.29±1.61 | 7.90±2.31 | 8.04±2.52 | 0.14±1.37 | 0.829 |
Insulin (µU/mL) | 13.37±4.54 | 13.08±5.38 | −0.29±3.22 | 13.28±5.02 | 13.27±4.93 | −0.01±2.87 | 0.169 |
HOMA-IR | 4.74±1.86 | 4.49±2.06 | −0.25±1.55 | 4.59±1.91 | 4.65±1.88 | 0.06±1.20 | 0.142 |
Cholesterol (mmol/L) | 5.97±0.92 | 5.81±0.90 | −0.17±0.70 | 5.83±0.85 | 5.75±0.85 | −0.08±0.77 | 0.367 |
LDL-C (mmol/L) | 4.19±0.89 | 4.08±0.79 | −0.11±0.74 | 4.10±0.73 | 4.01±0.76 | −0.09±0.71 | 0.404 |
HDL-C (mmol/L) | 1.38±0.34 | 1.36±0.30 | −0.02±0.24 | 1.37±0.32 | 1.35±0.34 | −0.02±0.25 | 0.243 |
Triacylglycerol (mmol/L) | 2.25±1.23 | 2.05±1.10 | −0.20±1.12 | 2.08±1.18 | 2.11±1.29 | −0.01±0.89 | 0.720 |
ApoA1 (mg/dL) | 152.2±23.2 | 149.6±23.8 | −2.5±20.0 | 152.4±24.8 | 148.7±23.9 | −3.7±19.7 | 0.751 |
ApoB (mg/dL) | 111.5±21.2 | 109.9±21.1 | −1.6±16.4 | 110.3±20.1 | 108.0±20.5 | −2.3±15.4 | 0.528 |
Lp(a) (mg/dL) | 44.3±37.0 (n = 62) | 41.8±34.8 (n = 62) | −2.52±9.85 (n = 62) | 43.6±35.3 (n = 62) | 43.2±34.7 (n = 59) | −0.59±9.86 (n = 59) | 0.339 |
Urine lignans (µg/mL) | 1.21±2.39 | 14.20±18.1 | 13.0±18.2 | 1.37±2.50 | 2.33±7.32 | 0.97±7.12 | <0.001 |
Urine isoflavones (µg/mL) | 2.70±3.94 | 2.69±3.67 | −0.01±4.56 | 2.77±4.15 | 2.66±2.54 | −0.11±4.25 | 0.962 |
Data are mean±Standard Deviation. BMI, body mass index; BP, blood pressure; HOMA-IR, homeostasis model assessment of insulin resistance; LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; apoA1, apolipoprotein A-1; apoB, apolipoprotein B; Lp(a), lipoprotein(a).
Data were not normally distributed.
Changes of serum concentrations of total cholesterol, LDL-C, HDL-C, triacylglycerol, Lp(a), apoA1 and apoB did not differ over time or between treatment phases (
As anticipated, the flaxseed lignan supplement significantly increased the urinary excretion of lignan metabolites compared to the baseline and thus validated pill count results during the lignan supplement phase. No difference was seen over time during the placebo phase. Urinary excretion of isoflavone metabolites showed no differences over time or between the treatment phases. Likewise, no differences were observed between treatments for weight, BMI, systolic BP and diastolic BP (
None of the three participants who withdrew from the study was considered related to the study treatment. Similar numbers of adverse events occurred during both treatment phases and they were predominantly gastrointestinal (percentages of the participants who reported diarrhea, flatulence and nausea were 23%, 32% and 4%, respectively). Blinded reviews conducted on adverse events found that these occurrences were not attributable to the capsules, but rather the participants' health status.
To the best of our knowledge, the present study is the first to investigate the effect of flaxseed-derived lignan on glycemic control, lipid profiles and inflammatory status in type 2 diabetes. We showed that 12-week supplementation of a flaxseed-derived lignan complex, which provided 360 mg/day SDG, statistically significantly reduced HbA1c concentrations in type 2 diabetic patients as compared with the placebo. However, no effect was observed on fasting glucose and insulin concentrations, HOMA-IR and blood lipid profiles.
HbA1c, also known as glycosylated hemoglobin, is an indicator of long-term glycemic control over the past six-to-eight weeks, and has been strongly related to micro- and macro-vascular complications in diabetic patients
The lignan capsules used in the present study were specifically selected to avoid potential effects of other nutrients and constituents in flaxseed, such as fiber and α-linolenic acid, which are also highly concentrated in flaxseed. Owing that the maximum safety dose of lignan has not been studied in human subjects thus far, we selected 360 mg/day of SDG, corresponding to 27–60 g of whole flaxseed
The major class of phytoestrogens in Asian diets are isoflavones from soy-rich foods, while in Western diets it is lignan from various plant-origin foods
One limitation of the present study is that the randomization was based upon the screening results (LDL-cholesterol) rather than the baseline measurements. However, since the recruitment for eligible participants was completed within 6 weeks, it was assumed that the characteristics of the participants would not vary greatly. Secondly, two interventions were done in the spring and the autumn, and the possible influence of seasonal variations may not be fully adjusted even with the cross-over design. Additionally, the relatively modest changes of HbA1c in the lignan treatment might not be clinically sufficient and could be artifact or the effect of regression towards the mean, even when the baseline values have been incorporated into the statistical models.
In agreement with previous studies
CONSORT Checklist
(0.05 MB DOC)
Trial Protocol
(1.28 MB PDF)
We thank Dr. Marian Verbruggen of Frutarom Netherlands BV and Mrs. Peilin Guo of Jarrow Formulas Inc. for their support in supplying the study capsules. We appreciate Lihua Chen, Ying Wu, Jing Wang, Qibin Qi, Liang Sun, Ling Lu, Hongyu Wu and Chen Liu for their assistants in the field work, data entry and laboratory assays, and all the professionals in Nutrition Division of Huadong Hospital for recruitment and management of the study participants.