Results in animals suggest favourable coronary vasomotor actions of isoflavones; however, the effects of isoflavones on the human coronary circulation have not been determined. In the present study, we therefore investigated the effects of short-term isoflavone-intact soya protein ingestion on basal coronary arterial tone and stimulated vasoreactivity and blood flow in patients with CHD (coronary heart disease) or risk factors for CHD. Seventy-one subjects were randomized, double-blind, to isoflavone-intact soya protein [active; n=33, aged 58±8 years (mean±S.D.)] or isoflavone-free placebo (n=38, aged 61±8 years) for 5 days prior to coronary angiography. In 25 of these subjects, stimulated coronary blood flow was calculated from flow velocity, measured using intracoronary Doppler and coronary luminal diameter before and after intracoronary adenosine, ACh (acetylcholine) and ISDN (isosorbide dinitrate) infusions. Basal and stimulated coronary artery luminal diameters were measured using quantitative coronary angiography. Serum concentrations of the isoflavones genistein, daidzein and equol were increased by active treatment (P<0.001, P<0.001 and P=0.03 respectively). Basal mean luminal diameter was not significantly different between groups (active compared with placebo: 2.9±0.7 compared with 2.73±0.44 mm, P=0.31). There was no difference in luminal diameter, flow velocity and volume flow responses to adenosine, ACh or ISDN between groups. Active supplement had no effect on basal coronary artery tone or stimulated coronary vasoreactivity or blood flow compared with placebo. Our results suggest that short-term consumption of isoflavone-intact soya protein is neither harmful nor beneficial to the coronary circulation of humans with CHD or risk factors for CHD. These results are consistent with recent cautions placed on the purported health benefits of plant sterols.

INTRODUCTION

Soya beans, the source of most soya protein consumed in the diet, contain soya protein and other constituents including isoflavones (sometimes termed phytoestrogens owing to their similar chemical structure to oestradiol and weak binding affinity for oestrogen receptor α and β [1,2]). Evidence suggests that isoflavones have health benefits in humans against hormone-dependent cancers of the breast and prostate, bone sparing effects, and some favourable effects on cardiovascular disease risk factors such as cholesterol concentrations in hypercholesterolaemic subjects [36]. The AHA (American Heart Association) dietary guidelines recommend “the consumption of soya protein containing isoflavones, along with other heart-healthy diet modifications” in “high-risk populations with elevated total and LDL (low-density lipoprotein)-cholesterol” [7], and the FDA (Food and Drug Administration) approved labels on foods containing 25 g of soya protein/day claiming a reduction in heart disease risk [8]. However, a recent AHA Dietary Advisory Committee counsels caution with regard to these recommendations [9].

Our group has demonstrated a relaxing effect of the isoflavone genistein in precontracted coronary arteries [10]. In vivo animal studies indicate a beneficial effect of soya protein with intact isoflavones on coronary reactivity in female, but not male, atherosclerotic monkeys, and indicate an endothelium-mediated effect [1113]. Investigation of the vascular effects of soya protein and isoflavones in humans have largely been confined to the peripheral circulation, mostly in healthy postmenopausal women [1417]. These studies show both positive and negative results using non-standard soya protein or isoflavone preparations and doses. In humans with risk factors for CHD (coronary heart disease) the results are also unclear. One uncontrolled study in hypercholesterolaemic non-smoking men showed increases in baseline brachial artery diameter and reactive hyperaemia after 6 weeks of a low-fat diet and soya protein substitution [18]. In contrast, a cross-over study in postmenopausal hypercholesterolaemic women showed no effect of 25 g of soya protein compared with placebo for 6 weeks on the lipid profile or brachial artery reactivity [19], and a recent study in hypertensive subjects showed no effect of isoflavone-intact soya protein on arterial function compared with placebo [20].

There are very few published studies investigating the effects of soya protein, with or without intact isoflavones, on the coronary circulation of humans [21]. We therefore investigated the effects of short-term isoflavone-intact soya protein ingestion on basal coronary artery tone and stimulated coronary vasoreactivity and blood flow in patients with CHD or risk factors for CHD undergoing clinically indicated coronary angiography.

MATERIALS AND METHODS

Subjects

Subjects aged 30–75 years with clinical indications for coronary angiography and on the waiting list for the procedure at the Royal Brompton and Harefield hospitals were invited to participate in the study. Female subjects were postmenopausal (follicular-stimulating hormone>40 i.u./l) and had not taken hormone-replacement therapy during the previous 6 months. Subjects with significant bradycardia, asthma, left ventricular hypertrophy or dysfunction, primary valvar heart disease or known three-vessel coronary disease were excluded. The study complied with the Declaration of Helsinki, the protocol was approved by the local research ethics committee and all subjects gave written informed consent to the full study.

Study design

Subjects were randomized in a double-blind parallel design to a twice daily isoflavone-intact soya protein drinks (Supro® Soy; The Solae Company) or isoflavone-free placebo drinks in addition to an unrestricted diet for 5 days before coronary angiography, with the last drink consumed approx. 5 h before cardiac catheterization. Blinding was achieved by having the drinks flavoured the same, labelled blindly, and randomized and dispensed by our pharmacy department. Cardiac medication and caffeine-containing beverages were withheld for at least 24 h prior to cardiac catheterization.

First, a 10 ml blood sample was taken from the in situ femoral artery sheath for evaluation of plasma isoflavone and lipid concentrations. All subjects then underwent clinically indicated coronary angiography and these images were used to measure the basal coronary artery mean luminal diameter (method described below). Subjects with risk factors for CHD and with at least one non-obstructed major coronary artery proceeded immediately to the intracoronary sub-study.

Intracoronary protocol

Following full heparinization, a 0.014 inch Doppler wire (Cardiometrics®) was positioned in the proximal portion of an unobstructed coronary artery from which continuous traces of average peak blood flow velocity were recorded. Arterial pressure, HR (heart rate) and ECG were displayed continuously. Baseline measurements were made, and then adenosine (30 μg) was given as a bolus intracoronary infusion. This was followed by infusions of increasing concentrations of intracoronary ACh (acetylcholine; 10−7–10−5 mol/l) for 2 min each or until peak velocity response. The study protocol was completed with an intracoronary bolus of 300 μg of ISDN (isosorbide dinitrate). Coronary angiograms were performed at baseline, then at peak response to each vasoactive substance. A rest period of at least 1 min was observed between each infusion to allow all measured parameters to return to baseline.

Quantitative coronary angiography and calculation of flow

Coronary angiograms were acquired digitally using a real-time digital image acquisition system (Siemens) and analysed off-line using QCA (quantitative coronary angiography; MEDIS). The basal luminal diameter of the entire coronary artery (mean luminal diameter) was measured for all subjects. For the intracoronary protocol angiograms, the mean luminal diameter and the luminal diameter approx. 4 mm distal to the tip of the Doppler wire were measured. The latter measurements were used to quantify volume flow as described previously [22].

Calculation of CFR (coronary flow reserve) and coronary resistance

In the intracoronary protocol, adenosine was infused to induce a maximal hyperaemic response. CFR was then calculated as the quotient of maximal coronary blood flow/baseline coronary blood flow. Coronary resistance was calculated as the quotient of MAP (mean arterial pressure; mmHg) and coronary blood flow (ml/min).

Soya preparation

The isolated soya protein drink (Supro® Soy) was prepared using water-washing to retain the isoflavones. One 65 g powdered beverage or one 316 g ready-to-drink beverage was consumed twice daily approx. 12 h apart. Each Supro® Soy drink (active) provided 25.8 g of soya protein containing 71 mg of isoflavones (aglycone weight). The placebo (control) was made with milk protein isolate and provided 25.7 g of milk protein with no isoflavones. The mucosal lining of the gut is necessary for the activation of the isoflavones in this form, which takes approx. 3–5 h. Each beverage (active or control) typically contained 210–240 calories, 1–2 g of fat (0 g of saturated fat), 24–30 g of carbohydrate (21–26 g of sugars), 26 g of protein (25 g from soya or milk), 170–260 mg of sodium, 480–800 mg of potassium and 900 mg of calcium.

Blood analysis methods

The isoflavones genistein, daidzein and equol were isolated and measured from serum using liquid-chromatographic tandem MS bioanalytical assays (HFL). Total cholesterol, HDL (high-density lipoprotein)-cholesterol and triacylglycerol (triglyceride) concentrations were measured using a Beckman CX7 analyser. LDL-cholesterol was estimated with the Friedewald formula [22a].

Statistics

Sample size

As there have been no previous studies of isoflavones in the human coronary circulation on which to base our calculations, the sample size calculation for the basal epicardial coronary artery tone end point was based on a previous study of 17β-oestradiol published by our laboratory [23], estimating a 12% difference in basal luminal diameter with an S.D. of 15% at 80% power and 5% significance level, giving an estimate of 38 subjects in each group.

The sample size calculation for the intracoronary study was determined by the treatment response of coronary luminal diameter to ACh, using in vivo animal data to estimate the difference between groups [12]. A mean difference of 12% with an S.D. of 7% required 13 subjects in each group, with assumptions of a 5% significance level and 80% power to detect a difference between groups.

Statistical methods

Outcome measures that were normally distributed were compared between groups using a two-sample Student's t test and are presented as means±S.D. The Mann–Whitney test was used to compare between groups when outcomes were not normally distributed and are presented as medians (interquartile range). P<0.05 was considered significant.

RESULTS

Subject characteristics

A total of 71 subjects consented to take part in the study and were randomized (Table 1). Thirty-three subjects did not have a coronary artery suitable for the intracoronary protocol (for example due to the extent of coronary atherosclerosis or difficulty placing the coronary catheter in a stable position), four did not comply with the study treatment regimen, one had severe chest pain on intracoronary contrast injections at diagnostic angiography, one had pre-procedural ST-segment changes, one had pre-procedural syncope, two had taken anti-anginal medication prior to angiography, and four had exclusion criteria that were unknown at randomization.

Table 1
Subject characteristics

Values are means±S.D. or numbers. BMI, body mass index; MI, myocardial infarction.

CharacteristicActive (n=33)Placebo (n=38)P
Age (years) 58±8 61±8 0.051 
Gender (n) (male/female) 31/2 31/7 0.12 
Previous MI (n10 10 0.69 
Hypercholesterolaemia (n21 26 0.51 
Hypertension (n18 18 0.7 
Diabetes mellitus (n0.83 
Cigarette smoking status (n  0.69 
 Current  
 Ex-smoker 19 17  
 Never 10  
 Unknown  
CHD (n  0.81 
 Unobstructed  
 One-vessel disease 10  
 Two-vessel disease 13  
 Three-vessel disease  
Height (cm) 175±6 174±9 0.62 
Weight (kg) 90±15 85±14 0.3 
BMI (kg/m229±4 28±3 0.46 
CharacteristicActive (n=33)Placebo (n=38)P
Age (years) 58±8 61±8 0.051 
Gender (n) (male/female) 31/2 31/7 0.12 
Previous MI (n10 10 0.69 
Hypercholesterolaemia (n21 26 0.51 
Hypertension (n18 18 0.7 
Diabetes mellitus (n0.83 
Cigarette smoking status (n  0.69 
 Current  
 Ex-smoker 19 17  
 Never 10  
 Unknown  
CHD (n  0.81 
 Unobstructed  
 One-vessel disease 10  
 Two-vessel disease 13  
 Three-vessel disease  
Height (cm) 175±6 174±9 0.62 
Weight (kg) 90±15 85±14 0.3 
BMI (kg/m229±4 28±3 0.46 

The remaining 25 subjects proceeded to the intracoronary protocol (Table 2). Thirteen received the active drink and, of these, two subjects had no significant coronary stenosis, nine had one-vessel disease (diameter stenosis ≥70% in a major epicardial coronary artery) and two had two-vessel disease. In the active group, the left anterior descending coronary artery was studied in one subject, the left circumflex in two subjects and the right coronary artery in ten subjects. Twelve subjects received placebo and, of these, two subjects had unobstructed coronary arteries, seven had one-vessel disease and three had two-vessel disease. In the placebo group, the left circumflex coronary artery was studied in two subjects and the right coronary artery in ten subjects. There was no significant difference between groups in the extent of coronary atherosclerosis (P=0.81), artery studied (P=0.62), risk factors for CHD, anthropometric measurements or cardiovascular medication (Table 2).

Table 2
Subject characteristics of individuals undergoing the intracoronary flow protocol

Values are means±S.D. or number. ACE, angiotensin-converting enzyme; BMI, body mass index; ISMN, isosorbide mononitrate; MI, myocardial infarction.

CharacteristicActive (n=13)Placebo (n=12)P
Age (years) 58±6 59±7 0.66 
Gender (n) (male/female) 13/0 9/3 0.13 
Previous MI (n0.11 
Hypercholesterolaemia (n0.85 
Hypertension (n0.54 
Diabetes mellitus (n0.32 
Cigarette smoking status (n  0.34 
 Current  
 Ex-smoker  
 Never  
Height (cm) 175±7 174±7 0.9 
Weight (kg) 90±15 84±12 0.2 
BMI (kg/m229±4 28±4 0.4 
Cardiovascular medications (n   
 ACE inhibitor 0.57 
 Statin 0.83 
 β-Blocker 0.32 
 Calcium antagonist 0.32 
 Potassium channel activator 0.26 
 ISMN 0.8 
CharacteristicActive (n=13)Placebo (n=12)P
Age (years) 58±6 59±7 0.66 
Gender (n) (male/female) 13/0 9/3 0.13 
Previous MI (n0.11 
Hypercholesterolaemia (n0.85 
Hypertension (n0.54 
Diabetes mellitus (n0.32 
Cigarette smoking status (n  0.34 
 Current  
 Ex-smoker  
 Never  
Height (cm) 175±7 174±7 0.9 
Weight (kg) 90±15 84±12 0.2 
BMI (kg/m229±4 28±4 0.4 
Cardiovascular medications (n   
 ACE inhibitor 0.57 
 Statin 0.83 
 β-Blocker 0.32 
 Calcium antagonist 0.32 
 Potassium channel activator 0.26 
 ISMN 0.8 

Serum isoflavone concentrations

Genistein [median (95% confidence interval): 340 (247, 515) compared with 3.9 (1.7, 5.8) ng/ml, P<0.001], daidzein [168 (108, 360) compared with 1.2 (0.5, 2) ng/ml, P<0.001] and equol [0.88 (0.72, 2.41) compared with 0.59 (0.35, 0.76) ng/ml, P=0.03] concentrations were greater in the active compared with placebo groups. Two subjects who consumed the isoflavone-intact soya protein drink produced significantly greater equol concentrations than the rest of the active group (282.2 and 171.3 ng/ml compared with a mean concentration of 1.2 ng/ml for the rest of the active group). There was no dietary explanation (e.g. vegetarianism, herbal supplements) for this variation.

Lipid profile

There was no difference in the lipid profile after treatment in either the main study group (active compared with placebo: total cholesterol, 4.5±0.9 compared with 5.1±1 mmol/l, P=0.06; HDL-cholesterol, 1.2±0.4 compared with 1.2±0.4 mmol/l, P=0.99; LDL-cholesterol, 2.7±1.1 compared with 3±0.9 mmol/l, P=0.17; and triacylglycerols, 1.8±1.5 compared with 1.8±1 mmol/l, P=0.98) or the intracoronary protocol group (active compared with placebo: total cholesterol, 5.1±0.9 compared with 4.5±1.2 mmol/l, P=0.19; HDL-cholesterol, 1.3±0.3 compared with 1.2±0.5 mmol/l, P=0.34; LDL-cholesterol, 3.2±0.8 compared with 2.7±1.4 mmol/l, P=0.29; and triacylglycerols, 1.5±0.8 compared with 2±2 mmol/l, P=0.44).

Luminal diameter

There was no difference in basal mean luminal diameter between the treatment groups (active compared with placebo: 2.9±0.7 compared with 2.73±0.44 mm, P=0.31).

Intracoronary protocol

Luminal diameter

Mean luminal diameter responses to adenosine, ACh (10−7–10−5 mol/l) and ISDN were significantly increased in both treatment groups but there was no difference in response between groups (Figure 1).

Coronary artery change in mean luminal diameter, blood flow velocity and volume blood flow after infusions of adenosine (AD), 10−7–10−5 mol/l ACh (A7, A6 and A5) and ISDN in subjects taking isoflavone-intact soya protein (black lines) or placebo (grey lines)
Figure 1
Coronary artery change in mean luminal diameter, blood flow velocity and volume blood flow after infusions of adenosine (AD), 10−7–10−5 mol/l ACh (A7, A6 and A5) and ISDN in subjects taking isoflavone-intact soya protein (black lines) or placebo (grey lines)

Values are means±S.D. **P≤0.01 and ***P≤0.001, active compared with the respective baseline; †P≤0.05, ††P≤0.01 and †††P≤0.001, control compared with the respective baseline. There was no significant difference in response between the two groups.

Figure 1
Coronary artery change in mean luminal diameter, blood flow velocity and volume blood flow after infusions of adenosine (AD), 10−7–10−5 mol/l ACh (A7, A6 and A5) and ISDN in subjects taking isoflavone-intact soya protein (black lines) or placebo (grey lines)

Values are means±S.D. **P≤0.01 and ***P≤0.001, active compared with the respective baseline; †P≤0.05, ††P≤0.01 and †††P≤0.001, control compared with the respective baseline. There was no significant difference in response between the two groups.

Velocity

Blood flow velocity responses significantly increased after each infusion in both treatment groups, except after 10−7 mol/l ACh in the active group (Figure 1). There was no significant difference between groups, but a trend towards a significantly lower peak velocity response to 10−7 mol/l ACh (P=0.07) and 10−5 mol/l ACh (P=0.09) in subjects taking the active drinks was observed.

Volume flow

Volume blood flow increased significantly compared with baseline after adenosine, ACh (10−6 mol/l and 10−5 mol/l) and ISDN in both treatment groups (Figure 1), but there was no difference between groups.

CFR and resistance

There was a trend towards a lower coronary vascular resistance in response to adenosine (0.94±0.33 compared with 1.24±0.5 ml/min per mmHg, P=0.09) and ISDN (1.12±0.29 compared with 1.58±0.7 ml/min per mmHg, P=0.06) in the active group compared with the placebo, but there was no difference in resistance after ACh infusions. CFR was not statistically different between treatment groups (active compared with placebo: 2.79±0.93 compared with 2.42±0.77, P=0.3).

Systemic haemodynamics

Baseline systolic blood pressure and diastolic blood pressure were not different between groups (active compared with placebo: 146±18 compared with 158±20 mmHg, P=0.59 and 79±7 compared with 76±5 mmHg, P=0.25). There was no difference in MAP (active compared with placebo: 100±9 compared with 97±11 mmHg, P=0.37) and HR (active compared with placebo: 69±11 compared with 67±9 beats/min, P=0.73) at baseline, and these measurements did not change significantly throughout the procedure.

DISCUSSION

The present study is the first to describe invasive in vivo coronary vasomotor and blood flow effects of soya-derived isoflavone consumption in humans. We found that isoflavone-intact soya protein and placebo-treated subjects with CHD or risk factors for CHD had a similar basal coronary luminal diameter, and comparable vasodilator and blood flow responses to adenosine, ACh and ISDN. Until now intracoronary studies of soya protein and isoflavones have been confined to animals, and studies in humans investigating vascular function after isoflavone-intact soya protein ingestion have largely been limited to the peripheral circulation, namely the brachial artery. A strength of the present study is the direct investigation of coronary vascular effects of isoflavone-intact soya protein in humans. Our results complement those of van der Schouw et al. [24], who found no effect of higher dietary intake of phytoestrogens on cardiovascular disease risk. Indeed recent evidence has cast uncertainty on the purported benefits of soya and isoflavone supplementation on cardiovascular health [9].

Effect of variations in isoflavone preparation and ingestion

Vascular responses to isoflavones vary depending on the preparation used (isoflavone-intact soya protein compared with isolated isoflavones for example), dose of isoflavones, duration of exposure and existence of risk factors for CHD compared with healthy subjects. Supro® Soy was a commercially available preparation containing isoflavone-intact soya protein at levels recommended for lipid lowering at the time that the present study was conceived [7,8]. We favoured this supplement over intracoronary infusions of isoflavones as the combination of soya protein together with isoflavones had been shown to result in enhanced lipid effects compared with isoflavones alone (summarized in Sacks et al. [9]) and in practice, therefore, isoflavone-intact soya protein would be the supplement of choice. We chose a relatively short treatment duration as pilot results showed that serum isoflavone levels were significantly raised after taking this supplement for 4 days, and that relaxation of pre-contracted isolated coronary arteries exposed to phytoestrogens occurred within a short time period [10]. It is possible that longer-term treatment may have different effects on the human coronary circulation; however, primate coronary results would argue against this [1113]. In the peripheral circulation of healthy postmenopausal women there does appear to be an effect of treatment duration but clear interpretation of a duration effect is complicated by use of non-uniform treatments (isolated isoflavones compared with red clover isoflavones compared with isoflavone-intact soya protein) [1417]. The present study population had a clinical indication for undergoing coronary angiography, to investigate chest pain, and all subjects had at least one risk factor for CHD. Whether a similar lack of effect on coronary artery tone and stimulated reactivity would be demonstrated in healthy subjects ingesting isoflavone-intact soya protein is unknown; however, results from the peripheral circulation would suggest that there may be a differing effect of isoflavone-intact soya protein on the coronary circulation of healthy subjects [1417].

Soya isoflavones and coronary endothelial function

A normally functioning endothelium is vital for the maintenance of vascular health. The age-related decline in endothelial function predisposes to vascular diseases; however, evidence suggests that diet assists in the preservation of endothelial function [25]. We observed no effect of isoflavone-intact soya protein consumption on stimulated coronary endothelium-derived NO. Results of previous coronary studies, using longer-term soya-isoflavone treatment in primates, suggest that endothelium-dependent responses in the coronary circulation may be gender-related [1113], although inhibition of atheroma progression appears unrelated to gender [11]. A recent observational study found that higher genistein levels in women referred for coronary angiography are associated with reduced coronary endothelium-dependent and -independent coronary vascular function [21]. The present study did not include a sufficient number of women to perform a gender-specific analysis so we cannot exclude this as a possible reason for the null result on endothelial function.

Isoflavone concentrations

Dietary isoflavones such as genistein and daidzein are metabolized by intestinal bacteria, conjugated in the liver, circulated in the plasma and excreted in the urine [26]. Daidzein is further converted into equol in approx. one-third of adults depending on gut microflora and/or intestinal conditions [27]. Equol has a higher oestrogenic potency than daidzein, with higher binding affinity for oestrogen receptors and lower binding to sex-hormone-binding globulin and albumin [28,29]. Serum concentrations of genistein measured in the present study are similar to those reported in a previous pilot study using the same preparation (1.6 μmol/l compared with 2.1 μmol/l respectively) [10]. In the present study only two subjects receiving the isoflavone-intact soya protein drinks produced significant amounts of serum equol, fewer than the previous report of one-third of the general population [27]. Investigation of coronary vasoreactivity and blood flow responses in active daidzein–equol metabolizers may clarify further the role of soya protein products in the coronary circulation.

Limitations

We acknowledge that pre-treatment data would have helped the interpretation of our results and this is a flaw in the present study design. Our protocol was of a parallel design, as performing cardiac catheterization before and after treatment raised ethical issues relating to risk/benefit of the additional procedure. We did not control the general diet of subjects enrolled in the study; however, measurement of serum isoflavone concentrations confirmed that the subjects in the placebo group did not consume significant amounts of isoflavone-intact soya protein. We feel that consumption of a supplemental isoflavone-intact soya protein drink in addition to an unrestricted diet better mimics the way in which isoflavones would generally be consumed in the diet and therefore enhances the application of our results. We also felt that consuming a supplement would provide more pertinent information than giving isolated isoflavones via intracoronary infusion as we have done in previous intracoronary studies [22,23]. We enrolled 12, and not the required 13, patients into the placebo group meaning that the intracoronary study is slightly underpowered. Whether our results would be replicated in a larger and longer-term study, possibly using non-invasive measures of coronary blood flow, is an area for further investigation.

Conclusions

In the present study, short-term ingestion of isoflavones together with soya protein did not affect coronary vascular tone or stimulated vasoreactivity and blood flow compared with isoflavone-free placebo. There was no effect on ACh-stimulated coronary luminal diameter and blood flow indicating no effect on endothelium-derived NO. Our results suggest that consumption of isoflavone-intact soya protein is neither harmful nor beneficial to the coronary circulation of humans with risk factors for, or established, CHD. A recent nutritional advisory committee has placed caution on past statements by national organizations asserting that consumption of plant sterols is recommended to combat diseases such as CHD [9], and our results provide further physiological evidence to support this advice.

Abbreviations

     
  • ACh

    acetylcholine

  •  
  • CFR

    coronary flow reserve

  •  
  • CHD

    coronary heart disease

  •  
  • HDL

    high-density lipoprotein

  •  
  • HR

    heart rate

  •  
  • ISDN

    isosorbide dinitrate

  •  
  • LDL

    low-density lipoprotein

  •  
  • MAP

    mean arterial pressure

We gratefully acknowledge the subjects who participated in this study, and the staff in the day-case unit and the cardiac catheterization laboratories of the Royal Brompton and Harefield Hospitals. Financial support was provided by The Solae Company, St. Louis, MO, U.S.A. C.M.W. was supported by the British Heart Foundation and is currently funded by the Victor Phillip Dahdaleh Charitable Foundation, U.K. C.S.H. was supported by an Overseas Research Fellowship from the National Heart Foundation of Australia.

References

References
1
Miksicek
 
R. J.
 
Interaction of naturally occurring nonsteroidal estrogens with expressed recombinant human estrogen receptor
J. Steroid Biochem. Mol. Biol.
1994
, vol. 
49
 (pg. 
153
-
160
)
2
Kuiper
 
G. G.
Lemmen
 
J. G.
Carlsson
 
B.
, et al 
Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor β
Endocrinology
1998
, vol. 
139
 (pg. 
4252
-
4263
)
3
Adlercreutz
 
H.
 
Phyto-oestrogens and cancer
Lancet Oncol.
2002
, vol. 
3
 (pg. 
364
-
373
)
4
Anderson
 
J. W.
Johnstone
 
B. M.
Cook-Newell
 
M. E.
 
Meta-analysis of the effects of soy protein intake on serum lipids
N. Engl. J. Med.
1995
, vol. 
333
 (pg. 
276
-
282
)
5
Arjmandi
 
B. H.
 
The role of phytoestrogens in the prevention and treatment of osteoporosis in ovarian hormone deficiency
J. Am. Coll. Nutr.
2001
, vol. 
20
 (pg. 
398S
-
420S
)
6
Lissin
 
L. W.
Cooke
 
J. P.
 
Phytoestrogens and cardiovascular health
J. Am. Coll. Cardiol.
2000
, vol. 
35
 (pg. 
1403
-
1410
)
7
Krauss
 
R. M.
Eckel
 
R. H.
Howard
 
B.
, et al 
AHA Dietary Guidelines: revision 2000: a statement for healthcare professionals from the Nutrition Committee of the American Heart Association
Circulation
2000
, vol. 
102
 (pg. 
2284
-
2299
)
8
Food and Drug Administration
Food labeling, health claims, soy protein, and coronary heart disease
Fed. Reg.
1999
, vol. 
57
 (pg. 
699
-
733
)
9
Sacks
 
F. M.
Lichtenstein
 
A.
Van Horn
 
L.
Harris
 
W.
Kris-Etherton
 
P.
Winston
 
M.
 
Soy protein, isoflavones, and cardiovascular health. An American Heart Association Science Advisory for Professionals from the Nutritional Committee
Circulation
2006
, vol. 
113
 (pg. 
1034
-
1044
)
10
Figtree
 
G. A.
Griffiths
 
H.
Lu
 
Y.-Q.
Webb
 
C. M.
MacLeod
 
K.
Collins
 
P.
 
Plant derived estrogens relax coronary arteries in vitro by a calcium antagonistic mechanism
J. Am. Coll. Cardiol.
2000
, vol. 
35
 (pg. 
1977
-
1985
)
11
Adams
 
M. R.
Golden
 
D. L.
Williams
 
J. K.
Franke
 
A. A.
Register
 
T. C.
Kaplan
 
J. R.
 
Soy protein containing isoflavones reduces the size of atherosclerotic plaques without affecting coronary artery reactivity in adult male monkeys
J. Nutr.
2005
, vol. 
135
 (pg. 
2852
-
2856
)
12
Honore
 
E. K.
Williams
 
J. K.
Anthony
 
M. S.
Clarkson
 
T. B.
 
Soy isoflavones enhance coronary vascular reactivity in atherosclerotic female macaques
Fertil. Steril.
1997
, vol. 
67
 (pg. 
148
-
154
)
13
Williams
 
J. K.
Clarkson
 
T. B.
 
Dietary soy isoflavones inhibit in vivo constrictor responses of coronary arteries to collagen-induced platelet activation
Coron. Artery Dis.
1998
, vol. 
9
 (pg. 
759
-
764
)
14
Squadrito
 
F.
Altavilla
 
D.
Morabito
 
N.
, et al 
The effect of the phytoestrogen genistein on plasma nitric oxide concentrations, endothelin-1 levels and endothelium dependent vasodilation in postmenopausal women
Atherosclerosis
2002
, vol. 
163
 (pg. 
339
-
347
)
15
Squadrito
 
F.
Altavilla
 
D.
Crisafulli
 
A.
, et al 
Effect of genistein on endothelial function in postmenopausal women: a randomized, double-blind, controlled study
Am. J. Med.
2003
, vol. 
114
 (pg. 
470
-
476
)
16
Teede
 
H. J.
Dalais
 
F. S.
Kotsopoulos
 
D.
Liang
 
Y. L.
Davis
 
S.
McGrath
 
B. P.
 
Dietary soy has both beneficial and potentially adverse cardiovascular effects: a placebo-controlled study in men and postmenopausal women
J. Clin. Endocrinol. Metab.
2001
, vol. 
86
 (pg. 
3053
-
3060
)
17
Teede
 
H. J.
McGrath
 
B. P.
DeSilva
 
L.
Cehun
 
M.
Fassoulakis
 
A.
Nestel
 
P. J.
 
Isoflavones reduce arterial stiffness: a placebo-controlled study in men and postmenopausal women
Arterioscler. Thromb. Vasc. Biol.
2003
, vol. 
23
 (pg. 
1066
-
1071
)
18
Yildirir
 
A.
Tokgozoglu
 
S. L.
Oduncu
 
T.
, et al 
Soy protein diet significantly improves endothelial function and lipid parameters
Clin. Cardiol.
2001
, vol. 
24
 (pg. 
711
-
716
)
19
Blum
 
A.
Lang
 
N.
Vigder
 
F.
, et al 
Effects of soy protein on endothelium-dependent vasodilatation and lipid profile in postmenopausal women with mild hypercholesterolemia
Clin. Invest. Med.
2003
, vol. 
26
 (pg. 
20
-
26
)
20
Teede
 
H. J.
Giannopoulos
 
D.
Dalais
 
F. S.
Hodgson
 
J.
McGrath
 
B. P.
 
Randomised, controlled, cross-over trial of soy protein with isoflavones on blood pressure and arterial function in hypertensive subjects
J. Am. Coll. Nutr.
2006
, vol. 
25
 (pg. 
533
-
540
)
21
Pepine
 
C. J.
von Mering
 
G. O.
Kerensky
 
R. A.
, et al 
Phytoestrogens and coronary microvascular function in women with suspected myocardial ischemia: a report from the Women's Ischemia Syndrome Evaluation (WISE) Study
J. Womens Health
2007
, vol. 
16
 (pg. 
481
-
488
)
22
Webb
 
C. M.
McNeill
 
J. G.
Hayward
 
C. S.
de Ziegler
 
D.
Collins
 
P.
 
Effects of testosterone on coronary vasomotor regulation in men with coronary artery disease
Circulation
1999
, vol. 
100
 (pg. 
1690
-
1696
)
22a
Friedewald
 
W. T.
Levy
 
R. I.
Fredrickson
 
D. S.
 
Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge
Clin. Chem.
1972
, vol. 
18
 (pg. 
499
-
502
)
23
Webb
 
C. M.
Ghatei
 
M.
McNeill
 
J. G.
Collins
 
P.
 
17β-Estradiol decreases endothelin-1 levels in the coronary circulation of postmenopausal women with coronary artery disease
Circulation
2000
, vol. 
102
 (pg. 
1617
-
1622
)
24
van der Schouw
 
Y. T.
Kreijkamp-Kaspers
 
S.
Peeters
 
P. H.
Keinan-Boker
 
L.
Rimm
 
E. B.
Grobbee
 
D. E.
 
Prospective study on usual dietary phytoestrogen intake and cardiovascular disease risk in Western women
Circulation
2005
, vol. 
111
 (pg. 
465
-
471
)
25
Brown
 
A. A.
Hu
 
F. B.
 
Dietary modulation of endothelial function: implications for cardiovascular disease
Am. J. Clin. Nutr.
2001
, vol. 
73
 (pg. 
673
-
686
)
26
Cassidy
 
A.
 
Potential risks and benefits of phytoestrogen-rich diets
Int. J. Vitam. Nutr. Res.
2003
, vol. 
73
 (pg. 
120
-
126
)
27
Setchell
 
K. D.
Brown
 
N. M.
Desai
 
P.
, et al 
Bioavailability of pure isoflavones in healthy humans and analysis of commercial soy isoflavone supplements
J. Nutr.
2001
, vol. 
131
 (pg. 
1362S
-
1375S
)
28
Nagel
 
S. C.
vom Saal
 
F. S.
Welshons
 
W. V.
 
The effective free fraction of estradiol and xenoestrogens in human serum measured by whole cell uptake assays: physiology of delivery modifies estrogenic activity
Proc. Soc. Exp. Biol. Med.
1998
, vol. 
217
 (pg. 
300
-
309
)
29
Shutt
 
D. A.
Cox
 
R. I.
 
Steroid and phyto- oestrogen binding to sheep uterine receptors in vitro
J. Endocrinol.
1972
, vol. 
52
 (pg. 
299
-
310
)