Subclinical Atherosclerosis and Polycystic Ovary Syndrome

Abstract

Polycystic ovary syndrome (PCOS) impacts approximately 6–10% of women worldwide, with hallmark features of hyperandrogenism, irregular menses, infertility and polycystic appearing ovaries on ultrasound. In addition, PCOS is associated with several endocrine and metabolic disorders, including obesity, insulin resistance and diabetes mellitus, hypertension, dyslipidemia and metabolic syndrome, which all increase the risk for subclinical cardiovascular disease (CVD), the presence of altered vascular endothelium without overt CVD. In this review, we summarize the most recent literature regarding subclinical CVD in PCOS women, including markers such as flow-mediated dilation (FMD), arterial stiffness, coronary artery calcium (CAC) scores, carotid intima-media thickness (CIMT) and visceral and epicardial fat.

Capsule statement

PCOS women are at increased risk of subclinical cardiovascular disease as measured by altered arterial flow-mediated dilation, arterial stiffness, coronary artery calcium, carotid intima-media thickness, and visceral and epicardial fat.

Introduction

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders of reproductive age women, affecting 6–10% of women globally and a common cause of infertility.(1, 2) PCOS is a multifactorial condition, with oligo/anovulation (OA), appearance of polycystic ovaries on ultrasound (PCOM) and hyperandrogenism (HA) as central features. Four phenotypes of PCOS have been defined based upon the presence of specific diagnostic criteria: phenotype A (OA+PCOM+HA), phenotype B (OA+HA), phenotype C (HA+PCOM) and phenotype D (OA+PCOM).(3) PCOS is strongly associated with various cardiometabolic comorbidities including diabetes mellitus (DM), dyslipidemia, hypertension, obesity, and metabolic syndrome (MetS) that all increases the risk for developing cardiovascular disease (CVD)(1). Previous literature also indicates that women of reproductive age with PCOS have increased subclinical CVD compared to women without PCOS.(1)

Subclinical CVD occurs early in the progression of atherosclerosis when abnormal physiological changes occur to the blood vessel, yet no manifested disease is present. Subclinical CVD may precede clinical symptomatology providing a unique time period to capture prevention before disease sets in. There are several ways subclinical CVD is measured including abnormalities in arterial dilation and distensibility, flow velocity and wall thickness. While there are various methods to measure subclinical CVD, they are all based on the evaluation of the function of the vascular endothelium, the inner lining of the blood vessel wall. The vascular endothelium is a semipermeable barrier that is metabolically active and the interface that determines vascular health by regulating homeostasis through the exchange of nutrients and fluids.(4)

In a healthy endothelium, dilation will occur in response to (1) reactive hyperemia via increased shear stress (flow-mediated dilation or FMD), (2) the effects of endothelium-dependent vasodilators such as acetylcholine, bradykinin, or serotonin, or (3) vasoactive substance release from the endothelium, such as nitric oxide. In diseased endothelium, dilation via these endothelial-dependent mechanisms can be blunted or absent. Additionally, the response to vascular smooth muscle vasodilators (i.e., adenosine), which are non-endothelial dependent, can also be impaired.(4) Endothelial dysfunction is defined as loss of vascular integrity, increased expression of adhesion molecules, prothrombotic phenotype, cytokine production, and upregulation of human leukocyte antigen molecules.(5) There is cytokine-mediated alteration of endothelial cell function, most notably through the effects of interleukin-1 and tumor necrosis factor alpha (TNF-α),(6) and impaired nitric oxide production.(5) Given the association of PCOS with low-grade inflammation, there have been recent research efforts geared towards the discovery of novel biomarkers to elucidate the complex pathophysiology of PCOS(7). Among the native markers associated with hyperandrogenic PCOS, especially in cases of elevated BMI, are leptin, RBP-4, DPP-IV, and adiponectin.(7) In addition, an increased expression of the proinflammatory and proatherogenic cytokine intercellular adhesion molecule-1 (ICAM-1) has also been seen in women in PCOS.(8) Endothelial dysfunction is a crucial component of early active inflammation in atherosclerosis, predicts prognosis of future CVD atherosclerosis, and is strongly and independently associated with CVD events.(9) In this current review we aim to summarize the contemporary literature and current evidence on PCOS and subclinical CVD.

Methods

Primary articles included in this systematic review were obtained through a PUBMED search from January 2017 through December 2021. The year 2017 was selected as a start date to evaluate the current literature beyond the most recent systematic review of subclinical atherosclerosis in PCOS women.(1) PUBMED search terms included “subclinical cardiovascular disease” and “PCOS” or “polycystic ovary syndrome” and each of the following: carotid intimamedia thickness (CIMT), endothelial dysfunction, flow-mediated dilation (FMD), arterial compliance, arterial distensibility, pulse wave velocity (PWV), coronary artery calcium (CAC), visceral fat thickness (VFT), epicardial fat thickness (EFT) and nitroglycerin-induced dilation (NGT). Articles were included if they were peer-reviewed and published in the English language. Due to the relatively limited number of articles published in this timeframe, we did not exclude any articles based upon the study design or the diagnostic criteria used to establish a diagnosis of PCOS. Data from the primary articles, including author, year, study design, definition of PCOS, age and BMI, and study outcomes, were extracted and compiled into a table (Table 1).

Table 1.

Studies examining markers of subclinical cardiovascular disease in women with PCOS

Study	Study Design	PCOS Definition and n	Age (y) and BMI (kg/m2)	Outcomes (measured at follow-up)	Results
Tosun et al., 2021, Turkey	PS, patients of the gynecology outpatient clinic of Giresun University Maternal and Children Education and Training Hospital, outpatients with non-endocrinological gynecologic problems formed control group, Feb-Mar 2021	ESHRE/ASRM Rotterdam Criteria; PCOS: n = 47; Control: n = 35	Age PCOS: 25.0 ± 4.8; Control: 30.2 ± 5.1 p<0.0001 BMI PCOS: 28.1 ± 6.4; Control: 25.9 ± 4.6; p=0.071	CIMT (total, right, left)	Total CIMT: PCOS 0.535 ± 0.137 mm vs. control 0.471 ± 0.100 mm (p=0.021) Right CIMT: PCOS 0.546 ± 0.171 mm vs. control 0.465 ± 0.108 mm (p=0.015) Left CIMT: PCOS 0.562 ± 0.182 mm vs. control 0.471 ± 0.100 mm (p=0.009)
Gonulalan et al., 2021, Turkey	CS, women with symptoms of menstrual irregularity and/or hyperandrogenism and controls, admitted to outpatient clinic of Endocrinology and Metabolism Disorders in Konya Research and Training Hospital and age and BMI-matched controls; Sept 2018-Apr 2020	2003 Rotterdam Criteria; PCOS: n = 53; Control: n = 35	Age PCOS: 25.8 ± 7.1; Control: 27.3 ± 5.9; p=0.299 BMI PCOS: 28.22 ± 6.64; Control: 29.92 ± 6.72; p=0.698	CIMT	CIMT: PCOS 0.5 ± 0.06 mm vs. control 0.43 ± 0.1 mm (p<0.01)
Bahat et al., 2021, Turkey	Cohort study	Rotterdam; PCOS: n = 100; Control: n = 100	Age: pre-menopausal, 18–35 PCOS: 24.8 (IQR 19.4–30.2) Control: 25.2 (IQR 20.6–29.7) BMI PCOS: 25.9 (IQR 22.0–29.8) Control: 25.1 (IQR 21.2–29.0)	CIMT	CIMT, mean: PCOS 0.51 mm vs. controls 0.43 mm, p<0.001 Correlation between CIMT and FG score in PCOS women (r=0.4.89, p<0.001)
Krentowska et al., 2021, Poland	Prospective cohort study	Rotterdam (mFG score ≥8, PCOM with ovarian vol >10 ml and/or ≥12 follicles/ovary); PCOS: n = 154 Control: n = 113	Age: pre-menopausal, 18–35 PCOS: 24 (IQR 22–28) Control: 24 (IQR 22–28) BMI PCOS: 24.2 (IQR 21.6–28.8) Control: 22.7 (IQR 21.5–25.1)	Prevalence of MetS (IDF/AHA criteria) Brachial artery flow-mediated dilation (FMD) Common carotid artery intima-media thickness (CIMT)	MetS: PCOS 14.29% vs. controls 5.31%, p = 0.019 FMD: PCOS 10.58% vs. controls 11.39%, p = 0.645 PCOS patients with MetS had lower FMD than PCOS patients without MetS (6.29% vs. 11.16%, p=0.02) CIMT: PCOS 0.454 mm vs. controls 0.448 mm, p=0.517 No differences in FMD or CIMT between patients with different PCOS phenotypes (p=0.268, p=0.668)
Pandurevic et al., 2021, Italy	Cross sectional; data collected as part of ongoing longitudinal study of PCOS women	Rotterdam (oligo/anovulation with cycles <21d or >35d, mFG ≥8, tT>0.7ngmL, fT>9.52pg/mL, PCOM with ovarian vol >10 ml and/or >12 follicles/ovary); PCOS: n = 102 Phenotype A (HA+OA+PCOM): n = 38 B (HA+OA): n = 7 C (HA + PCOM): n = 46 D (OA + PCOM): n = 11	Age: pre-menopausal Overall mean age: 38.9 (IQR 31.5–46.3) Phenotype A: 38.7 (IQR 30.9–46.5) Phenotype B: 35.0 (IQR 29.4–40.6) Phenotype C: 38.8 (IQR 31.2–46.4) Phenotype D: 42.3 (IQR 37.2–47.4) BMI Phenotype A: 30.6 (IQR 21.9–39.3) Phenotype B: 26.8 (IQR 19.9–33.7) Phenotype C: 28.4 (IQR 21.3–35.5) Phenotype D: 32.6 (IQR 24.3–40.9) BMI Groups: (I): Normal weight, 18.5–24.9 kg/m2 (II): Overweight, 25–29.9 kg/m2 (III): Obese, >30 kg/m2	CIMT FMD Nitroglycerin-induced dilation (NTG) Epicardial Fat Thickness (EFT)	CIMT, mean (Phenotypes A/B/C/D): 0.61 mm vs. 0.50 mm vs. 0.56 mm vs. 0.60 mm, p=0.269 FMD, mean (Phenotypes A/B/C/D): 12.19% vs. 9.99% vs. 11.30% vs. 11.41%, p=0.820 NTG, mean (Phenotypes A/B/C/D): 24.25% vs. 19.54% vs. 25.51% vs. 23.95%, p=0.446 EFT, mean (Phenotypes A/B/C/D): 0.95 cm vs. 0.71 cm vs. 0.81 cm vs. 0.86 cm, p=0.165 CIMT, mean (BMI Groups I/II/III): 0.49 mm vs. 0.55 mm vs. 0.67 mm, p<0.001 FMD, mean (BMI Groups I/II/III): 12.52% vs. 13.66% vs. 9.17%, p=0.006 NTG, mean (BMI Groups I/II/III): 26.02% vs. 26.16% vs. 21.85%, p=0.052 EFT, mean (BMI Groups I/II/III): 0.63 cm vs. 0.82 cm vs. 1.07 cm, p<0.001
Jabbour et al., 2020, Austria	CS, patients of the endocrine department of Vienna General Hospital and age-matched health controls, July-Sept 2015	Rotterdam ESHRE/ASRM criteria; PCOS: n = 41; Control: n = 43	Age PCOS: 24 ± 4; Control: 25 ± 4; p=0.296 BMI PCOS: 26.33 ± 7.30; Control: 21.91 ± 3.22; p=0.001	CIMT	CIMT: PCOS 0.49 ± 0.04 mm vs. control 0.37 ± 0.04 mm (p<0.001)
Meun et al., 2019, Netherlands, Colombia	CS, women aged > 45 with PCOS and age-matched controls in 3 participating university hospitals, controls from the third cohort of the Rotterdam Study 2006–2008	Rotterdam Criteria; PCOS: n = 200; Control: n = 200	Age PCOS: 50.5; Control: 51.0; p=0.35 BMI PCOS: 28.4; Control: 26.3; p=0.02	CIMT	CIMT: PCOS 612.8 um, SD=93.6 vs. control 721.7 um, SD=118.4 (p<0.001)
Meun et al., 2018, the Netherlands	Prospective population-based cohort study, part of the Rotterdam Study	Reported history of cycle irregularities at age 25, and testosterone or free androgen index (FAI) in highest quartile PCOS: n = 106 Control: n = 171	Age: post-menopausal, ≥55 PCOS: 69.6 (IQR 60.9–78.3) Control: 69.2 (IQR 60.6–77.8) BMI PCOS: 27.9 (IQR 23.4–32.5)* Control: 26.8 (IQR 23.0–30.7) *p=0.03	Pulse wave velocity CIMT	Pulse wave velocity: highest quartile FAI associated with higher pulse wave velocity (beta-coefficient 0.009, 95%CI 0.000–0.018) CIMT: highest quartile of DHEA and androstenedione associated with lower CIMT (beta-coefficient −0.008, 95% CI −0.015–0.001 and −0.010, 95% CI −0.017–0.003, respectively)
Kim et al., 2018, USA	SA, Diabetes Prevention Program (DPP) and the Diabetes Prevention Program Outcomes Study (DPPOS) across 27 clinical centers in USA, women with sex hormone measurements without exogenous estrogen use, 1996–1999	Overweight, nondiabetic glucose-intolerant participants, n = 1422	Age ≥ 25 y BMI 35.8 ± 7 (regular menses, premenopausal), 37.1 ± 7.6 (irregular menses, premenopausal), 34.4 ± 6.3 (regular menses, postmenopausal), 37.3 ± 8.1 (irregular menses, postmenopausal)	CAC	Irregular menses was not associated with increased risk of CAC (OR 0.89; 95% CI, 0.53–1.49). Free Androgen Index was not associated with increased odds of CAC (OR 1.06; 95% CI, 0.92–1.23).
Tripathy et al., 2017, India	Cohort study	Rotterdam; PCOS: n = 124; Control: n = 118	Age: pre-menopausal, 18–37 PCOS: 27.22 (IQR 22.45–31.98) Control: 26.81 (IQR 22.06–31.56) BMI PCOS: 25.98 (IQR 22.84–29.12) Control: 25.86 (IQR 22.55–29.17)	Presence of visceral fat thickness (VFT) CIMT FMD	VFT: PCOS women had increased VFT (mean, 86 mm) vs. controls (mean, 78.5 mm) p=0.01 CIMT: higher in PCOS women (mean 53.9 mm) vs. controls (mean, 44.7 mm) p<0.001 FMD: lower in PCOS women (mean 10.89%) vs. controls (11.72%) p=0.02 In PCOS women, VFT is correlated to CIMT (beta coefficient 0.347, p=0.001)
Ramoglu et al., 2017, Turkey	PS, women presenting to the Gynecology Clinics at Marmara University Pendik Training and Research Hospital and age-matched health women controls, Oct 2012-Mar 2013	2003 ASRM/ESHRE (Rotterdam) Criteria; PCOS: n = 52; Control: n = 45	Age PCOS: <20 y (n = 10), 20-<30 y (n = 39), ≥30 y (n = 3) Control: <20 y (n = 8), 20-<30 y (n = 30), ≥30 y (n = 7) <20 y (p=0.511), 20-<30 y (p=0.613), ≥30 y (p=0.103) BMI PCOS: normal weight (n = 32), overweight (n = 12), obese (n = 8) Control: normal weight (n = 25, overweight (n = 10), obese (n = 10) Normal weight (p=0.702), overweight (p=0.943), obese (p=0.764)	CIMT	CIMT: PCOS 0.49 ± 0.07 mm vs. control 0.50 ± 0.07 mm (p=0.626)
Patel et al., 2017, US	Cohort study	NIH Criteria adapted for adolescents (OA <8 cycles/year, at least 2 years after menarche + hyperadrogenism); PCOS: n = 36; Control: n = 17	Age: adolescents, 12–21 PCOS: 14.7 (IQR 13.25–16.37) Control: 13.9 (IQR 12.2–15.7) BMI PCOS: 35.6 (IQR 31.94–39.26)* Control: 32.2 (IQR 29.59–34.73) *p=0.001	CIMT Beta stiffness index Arterial compliance	CIMT, mean: PCOS 0.49 mm vs. controls 0.44, p=0.038 Beta Stiffness Index, mean: PCOS 5.1 U vs. controls 4.4 U, p=0.037 Carotid compliance, mean: PCOS 1.95 mm2/mmHg vs. control 2.13 mm2/mmHg, p=0.047

Summary of Current Evidence

Flow-mediated Dilation (FMD)

FMD, a marker of endothelial dysfunction, has been shown to be a strong predictor of CVD events beyond traditional risk factors in multiple large studies in the general population.(10–13) In a study of 2,264 menopausal women, the lower FMD tertile was associated a 4-fold increased risk of adverse CVD outcomes.(11) Another cohort study of older adults aged 72 to 98 years (The Cardiovascular Health Study) also showed significantly higher event-free survival rates for CVD events for patients with higher FMD compared to those below the median (p=0.006).(14)

Arterial FMD was previously found to be 3.4% lower in PCOS reproductive age women compared to controls in a 2013 meta-analysis (21 studies; PCOS n = 908)(15). Given the substantial degree of heterogeneity (I²=96%) between studies, the authors performed a separate analysis of seven studies including only women diagnosed with PCOS using the Rotterdam criteria (PCOS n=402), with specific age and BMI matched controls. In this subanalysis, the heterogeneity between studies was improved (I²=81%) and arterial FMD was 4.1% lower in the PCOS women(15). More recently, a prospective cohort study found that reproductive age PCOS women did not differ from controls in regard to FMD, nor was there a significant difference in FMD between women with different PCOS phenotypes.(16) However, the authors found that PCOS women with MetS had a 4.87% lower FMD than PCOS women without MetS (p=0.02), and that the individual components of MetS were associated with lower FMD (Table 1)(16). Of note, the PCOS women with MetS in this study had a higher mean BMI than the PCOS women without MetS (31.0 kg/m² vs. 23.3 kg/m², p<0.001), and thus obesity may be a confounding factor. Another recent cross-sectional study found no significant difference in FMD between women with different PCOS phenotypes (Table 1); however, when comparing groups of PCOS women based upon BMI, they found that obese (BMI>30 kg/m²) PCOS women had a lower FMD (9.2%) than overweight (13.7%) and normal weight (12.5%) PCOS women, p=0.006 (Table 1).(17) Thus, there are conflicting results of an association between lower FMD amongst PCOS women compared with controls, however, the presence of obesity and MetS may put PCOS women at higher risk of a lower FMD.

Another marker of arterial dilation is the nitroglycerin test (NTG), an assessment of arterial dilation after the administration of nitroglycerin which works through an endothelium-independent mechanism.(18) Nitroglycerin-induced dilation is impaired in individuals with cardiovascular risk factors and CVD.(18) In a 2021 cross-sectional study, NTG did not differ among the four PCOS phenotypes and had borderline significance when comparing PCOS women of different BMI classes.(17) (Table 1). Research is needed to determine the utility of NTG in PCOS women.

Arterial Stiffness

Arterial stiffening is another subclinical marker of cardiovascular disease. Pulse wave velocity (PWV) is the gold standard for the measurement of arterial stiffness,(19) and has an incremental role in CVD risk stratification independent of the Framingham Risk Score.(20) A higher PWV increases risk for total CVD events, CVD mortality and all-cause mortality.(21) Prior publications have shown that PCOS women have higher PWV compared to controls; however, these results may be confounded by age and obesity.(22, 23) A 2002 cohort study of reproductive age PCOS women (n=19, 1990 NIH Criteria) compared to BMI-matched controls, PWV was significantly elevated. However, age is a larger driver of elevation of PWV, and the controls were significantly older than the PCOS women (34 years vs. 26 years, p=0.001)(22). Further, in a 2016 cross-sectional study of PCOS adolescents (n=121, 2013 Endocrine Society criteria), PWV was higher in obese adolescents regardless of PCOS status compared to normal weight, non-PCOS controls(23). Both studies suggest that age and obesity play a larger role in elevation of PWV independent of PCOS status.

In a recent prospective cohort study of menopausal women, women with the highest quartile of free androgen index (FAI) had an elevated PWV compared to women with a FAI in the 25–75% quartiles (Table 1).(24) When comparing menopausal women with the highest quartile of FAI who also had a history of oligomenorrhea (the two criteria used to define PCOS in this study) to control women (FAI in the 25–75^% quartiles without a history of oligomenorrhea), there was no significant difference in PWV (beta-coefficient −0.016, 95% confidence interval: −0.036–0.004).(24)

Arterial stiffness index is a measure of the relative timing of diastolic and systolic components of PWV, and is known to have good correlation with central PWV.(25–27) A recent prospective cohort study of obese adolescents (12–21 years of age) with PCOS found that PCOS adolescents had a higher arterial stiffness index and lower arterial compliance compared to obese adolescent controls, suggesting that subclinical CVD may begin as early as in adolescence (Table 1).(28) Although all adolescents in this study were considered obese, the mean BMI between the two groups were statistically different (mean BMI of obese PCOS participants 35.6 kg/m² vs. obese controls 32.2 kg/m², p=0.001), which potentially confounds the results.(28) Thus, there continues to be mixed evidence suggesting women with PCOS have higher arterial stiffness.

Carotid Intima-Media Thickness (CIMT)

Carotid intima-media thickness (CIMT) refers to the ultrasound measurement of the distal wall of the common carotid artery. Epidemiological studies in both the general population and women with PCOS have found that CIMT thickness correlates with CVD risk factors,(29) progression of atherosclerosis,(30) and CVD events,(31) including stroke and myocardial infarction (MI).(1) A 2007 meta-analysis had quantified this relationship as a 15% risk increase in MI and 18% risk increase in stroke per 0.10-mm of CIMT difference.(32) Similarly, CIMT was also shown to be a significant predictor of CVD in a Japanese study, noting a hazard ratio for CVD of 2.37 for every 0.1 mm/year CIMT increment(33).

In the most recent meta-analysis by Cooney and Dokras in 2018, women with PCOS were noted to have higher CIMT compared with controls, with mean age in most studies being the late 20s(1).

In the past few years, several cohort and cross-sectional studies have been published that examines CIMT in PCOS (Table 1). A majority of these recent publications cite a significantly higher CIMT in women with PCOS compared to matched controls.(28, 34–39) This association was present in the reproductive age with mean age 24–27 years,(28, 34–37) and appeared to be similarly present in the younger age group of adolescents in females aged 12–21 years old.(28) Current literature also demonstrates that CIMT does not differ across different PCOS phenotypes, and appears to have a strong correlation with BMI.(17)

Two recent smaller studies by Ramoglu (PCOS n = 52) and Krentowska (PCOS n = 154) were also published failing to show consistent findings; that is, no significant association was found between CIMT and PCOS.(16, 40) While this could be due to the power of the studies given the relatively small sample size in each group, Krentowska also hypothesizes that the dissimilarities could be partially explained by the inherent characteristic of their cohort which included leaner women (median BMI 24; IQR 22–28), compared to others.(16, 40)

In contrast to findings in young women, CIMT was reported to be lower in women with PCOS with a mean age of 50.5 years compared to age-matched controls.(38) In this study, PCOS women were diagnosed during reproductive years by Rotterdam criteria. This difference could have been due to the smaller proportion of women with PCOS that were postmenopausal at the time of the study, when an larger increase in CIMT is seen. Another study draws attention to possibly the hormonal shift in PCOS after menopause may have a role.Finding the highest quartile of dehydroepiandrosterone and androstenedione was associated with lower CIMT in postmenopausal women aged ≥ 55 years old, suggesting that after menopause the androgen to estrogen ratio may play a role in a lower CIMT.(24) This is also supported by studies in non-PCOS women finding higher androgen concentrations are associated with lower CIMT.(41)

In summary, data from earlier meta-analysis suggests consistently increased CIMT in women with PCOS compared to controls, recent data shows more heterogeneity in findings. While majority of the recent studies show an increased CIMT in the PCOS group, a few smaller studies did not. This difference, as mentioned, could be either due to the studies’ power limitation or patients’ baseline characteristics, particularly BMI. One area of interest remains the role of PCOS and androgens after menopause with respect to CIMT progression.

Visceral and Epicardial Fat Thickness

The relationship between obesity and cardiovascular disease is defined not only by volume of body fat, but also by distribution.(42) Adipose tissue accumulation, especially in the visceral cavity, plays a major role in the pathogenesis of cardiovascular disease and metabolic syndrome,(43) highlighting the utility of visceral fat thickness (VFT) measurement in clinical practice. In PCOS, visceral fat has been previously shown to be elevated and associated with MetS and CVD.(44) A 2017 study found that PCOS women had increased VFT, but not pre-peritoneal fat thickness or subcutaneous fat thickness when compared to age and BMI-matched controls without PCOS (Table 1).(34) Furthermore, in this study, VFT was the strongest independent predictor of CIMT in PCOS women, suggesting its synergistic role in subclinical CVD.(34)

Epicardial fat thickness (EFT) is a measure of fat between the outer wall of the myocardium and visceral layer of the pericardium and is a novel marker for CVD risk.(45) It is emerging as a novel risk factor for predicting obstructive coronary artery disease, and has been found to be associated with coronary artery calcification(46, 47) Considered an analogue to VFT, the appeal of EFT is less expense and time associated with the study when compared to the use of magnetic resonance imaging, the gold standard for assessment of visceral fat thickness.(17) There are few studies published prior to 2017 on the value of EFT in PCOS women, with conflicting results. A 2014 cohort study of reproductive age women (n=64) diagnosed with PCOS using the Rotterdam criteria had similar mean EFT to controls, but when comparing obese (BMI>25 kg/m²) PCOS women to obese controls, the EFT was thicker in the PCOS group (p=0.026).(48) A 2015 cohort study found that PCOS women (n=35) had similar EFT to controls, and EFT was correlated with BMI, but not markers of metabolic dysfunction.(49) In another recent study, EFT did not differ significantly among women with different PCOS phenotypes but it strongly correlated with BMI (r=0.695, p<0.001), more so than other markers of subclinical CVD such as CIMT and FMD (Table 1).(17) Thus, research will be needed to determine the utility and value of measuring EFT in PCOS women.

Coronary Artery Calcium (CAC)

Coronary artery calcification (CAC) measured by computed tomography (CT) is a finding that implies coronary atherosclerosis and can be identified in asymptomatic individuals. In the large Multi-Ethnic Study of Atherosclerosis (MESA) Study, CAC proved to be a more powerful predictor of coronary heart disease with a 2.5-fold increased risk per standard deviation increment, compared to the 1.2-fold increased risk observed with CIMT.(50)

While small studies of young women have shown that PCOS is correlated with increased CAC, some did not and knowledge in this area remains limited.(1) Related to this, prior work has demonstrated a weak but independent relationship of higher testosterone to estradiol ratio to subclinical atherosclerosis measured by CAC in the general population.(51) Prior meta-analysis by Cooney and Dokras published in 2018 outlined several small studies of CAC in PCOS women revealing contrasting findings regarding the incidence of CAC in PCOS; some reported higher CAC in PCOS women, while others did not(1).

Since this time, one large single center of the observational cohort, Diabetes Prevention Program Outcomes Study (DPPOS), studied 2,029 participants at 10 years, showed that neither irregular menses, nor free androgen index, were associated with an increased CAC (OR 0.89, 95% CI 0.53–1.49, and OR 1.06, 95% CI 0.92–1.23, respectively).(52) Of note, the participants who underwent CAC studies in this cohort were reported to be slightly younger with modestly lower body mass index, lower systolic blood pressure, and with less smokers compared to those who did not have CAC scan performed,(52) which could be potential sources of bias.

In summary, while there is a higher prevalence of increased CAC in PCOS women found in smaller studies, it remains unclear to date whether this observation is reproducible given paucity of existing data. In the one larger study published in recent years, this specific association was not demonstrated.

Mechanisms for Increased CVD Risk in PCOS

As discussed above, women with PCOS are at increased risk of subclinical CVD as measured by various cardiovascular factors. The mechanisms behind the elevated subclinical CVD risk in PCOS women appear to be multi-factorial and interrelated, including insulin resistance and hyperinsulinemia, elevated levels of circulating androgens, inflammation, hypertension, visceral obesity and MetS(1).

Women with PCOS are at increased risk of insulin resistance, with a recent meta-analysis demonstrating an odds ratio of 3.26 (95% CI: 2.17–4.90) with minimal heterogeneity between studies(53). In 375 women with PCOS diagnosed by Rotterdam Criteria, 75% of women were diagnosed with insulin resistance using the gold-standard hyperinsulinemic euglycemic clamp(54). Prior work demonstrates that PCOS women with insulin resistance have decreased synthesis and release of NO and enhanced inactivation of NO following its release, preventing normal vasodilation.(55) Additionally, women with PCOS without overt CVD have altered reactivity of resistance arteries after administration of insulin.(22) In a 2002 cohort study, PCOS women were found to have an attenuated vasodilatory response to insulin after the administration of norepinephrine when compared to non-PCOS, BMI-matched controls, suggesting that PCOS women have impaired endothelium dependent vasodilation(22). Dokras et al. studied the response of forearm vasculature to endothelium dependent (Ach, bradykinin) and endothelium independent (nitroprusside and verapamil) drugs, and found no difference between the vasodilatory response in PCOS versus non-PCOS women; however, there was a significant difference between obese PCOS and non-obese PCOS women(56). The authors concluded that obesity and insulin resistance contribute to impaired vascular function in PCOS women(56). Insulin resistance is further exacerbated by hyperinsulinemia in a vicious cycle via two main mechanisms. Elevated insulin levels stimulate androgen production in ovarian theca cells and suppress liver production of sex hormone binding globulin (SHGB), both of which result in higher levels of free circulating androgens which act directly on peripheral tissues contributing to insulin resistance and endothelial dysfunction.(57–59)

Hyperandrogenism impacts approximately 75% of women with PCOS and is a contributor to endothelial dysfunction in PCOS. Women with subtypes of PCOS that include hyperandrogenism (phenotypes A-C) have increased plasma endothelin-1 (ET-1) levels, signifying endothelial injury, which has been shown to be independent of BMI (p=0.01).(58) Elevated levels of circulating androgens promote insulin resistance and visceral fat accumulation by inhibiting lipolysis and promoting lipogenesis,(60) contributing to endothelial dysfunction through the NO pathway as described above. Endothelial dysfunction in PCOS phenotypes with hyperandrogenism is also mediated through impaired function of the endothelin receptor ET_BR pathway in the microcirculation.(58) In a small physiological study, investigators demonstrated that both lean and obese PCOS women with elevated androgens had compromised microvascular function, alleviated in the presence of the ET_BR blocker, BQ-788(58). Further, when the women were given ethynyl estradiol, microvascular function improved, most notably in the lean PCOS women(58). These findings were of interest because they indicated endothelial dysfunction was present not only with obese, insulin resistant women with PCOS as described earlier, but this dysfunction was also found in lean, insulin sensitive women with PCOS, suggesting an important component of the endothelial dysfunction was due to their elevated androgens.

PCOS is associated with an inflammatory activation, with increased formation of reactive oxygen species and decreased levels of anti-inflammatory cytokines such as adiponectin and omectin.(58, 61) Inflammatory markers including C-reactive protein (CRP), interleukin-18, TNF- α, interleukin-6 and ferritin are higher in PCOS women compared with age- and BMI-matched controls.(61) CRP, an important marker vascular inflammation, was found to be 96% higher in PCOS women compared to controls in a meta-analysis of over thirty studies.(62) Substantial evidence demonstrates the role of immune-mediated inflammation in atherosclerosis and CVD. Immune cells are present and adhesion molecules are activated on the vascular endothelium which further recruit pro-inflammatory immune cells in early stages of atherosclerosis including CD4 T cells(63). Elevated levels of CRP have also been correlated with the degree of visceral fat accumulation in women with PCOS.(44) Visceral fat accumulation in particular has an associated elevated risk of atherosclerosis, insulin resistance, and is significantly higher in PCOS women than in controls.(44, 64) Visceral adipose tissue strongly correlates with markers of subclinical CVD such as CIMT and FMD.(34, 44) Together, these mechanisms increase the cardiovascular risk for women with PCOS.

Controversies and Areas of Future Research

Although there is evidence that women of reproductive years have elevated subclinical CVD, new data further highlight the controversy regarding how this translates into increased CVD risk in later life. While some authors suggest an interplay of genetic protective mechanisms, possible protective effect of hyperandrogenism, and an early worsening of risk and subsequent lack of risk progression as explanations, the mechanism for this age-related observation remains poorly understood.(38)

The contribution of androgens to the development of cardiovascular dysfunction has yet to be isolated in humans, although women with PCOS phenotypes that include hyperandrogenism have greater CV dysfunction than other PCOS phenotypes.(65) As stated earlier, young PCOS women with hyperandrogenism commonly manifest a spectrum of covert CVD risk markers, therefore it is likely that androgen excess in young women is a major driver of endothelial dysfunction.(58) Data in lean, insulin-sensitive (IS) PCOS women with hyperandrogenism support this androgen-dependent vascular pathology hypothesis,(58) such that peripheral subclinical CVD is more pronounced in this lean phenotype compared their obese, IR counterparts. However, this lean, IS, hyperandrogemic PCOS population comprises 25% of PCOS women who develop significant hypertension in their 20s and 30s. Thus, testing the direct impact of androgens in the larger, obese, IR PCOS women with hyperandrogenism is an area for future research using both humans and animal models.

Although there is evidence that women of reproductive years have elevated subclinical CVD, what remains controversial is whether this translates into CVD risk after menopause. Independent of PCOS, CVD is a leading cause of death and loss of independence in older women.(66, 67) As described earlier, subclinical CVD has been well characterized in young, premenopausal women with PCOS. With the NIH diagnostic criteria for PCOS being published in 1990 and subsequently, the Rotterdam Criteria in 2003, women diagnosed with these criteria are just now entering phases of life associated with greater CVD risk. Thus, a clear focus should be understanding the impact of PCOS in aging women. Aging is also associated with subclinical CVD,(67, 68) as well as endothelial dysfunction as measured by FMD although not all older individuals see a decline in FMD.(69) Thus, an exploration of this heterogeneity within older women, and whether PCOS contributes to greater risk of atherosclerosis would be of great interest, especially given the potential differences in immune function and NO availability in younger populations of women with PCOS. There has also been data to suggest that women with PCOS go through menopause at later age, thus providing a longer exposure to estrogen and some CVD protection in their later years. Indeed, several observational studies have suggested that CVD risk in women with PCOS may decrease with aging when compared with age matched groups.(1, 70) These studies should be followed up with physiological studies with a closer eye on mechanism. That said, diagnosis of PCOS is rarely and clearly established post menopause, so these studies that have examined CVD post menopause have relied on earlier diagnosis. It is quite likely that exposure to CVD risks, including insulin resistance, obesity and endothelial dysfunction is likely to increase CVD in older women who have had PCOS.

Another important area for research is the impact on subclinical CVD in the children of women with PCOS. There is some evidence of cardiometabolic dysfunction in the young children of women with PCOS, including dyslipidemia and higher carotid intima-media thickness compared to controls.(71) Recent data in hyperandrogemic rats have demonstrated adult male offspring of PCOS mothers may be at increased risk of cardiometabolic disease, due to greater plasma total cholesterol and HDL with greater proteinuria and lower nitrate/nitrite excretion compared to controls.(72) Data also demonstrates pregnancy protects hyperandrogemic rats against age-related hypertension,(73) suggesting that pregnancy may also protect PCOS from angiotensin II and salt sensitive hypertension,(74) although may be at risk for renal injury with aging.(74) These issues have not been examined in humans, so studies to determine whether adult and postmenopausal children of women with PCOS are at risk for hypertension are of interest.

Conclusions

Our current review of the data indicates that women with PCOS have subclinical CVD as measured by alterations in flow-mediated dilation (FMD), arterial stiffness, coronary artery calcium (CAC) scores, carotid intima-media thickness (CIMT) and visceral and epicardial fat. The contribution of these factors to increased risk for future overt cardiovascular events and mortality is largely unknown. Confounding factors such as age and metabolic syndrome components such as obesity, dyslipidemia and glucose intolerance can make the data more difficult to interpret, as they are not consistently controlled for in the cross-sectional studies in present literature. Larger population studies have demonstrated lower cardiovascular event-free survival, increased risk of incident myocardial infarction, angina and stroke in women with PCOS(75). Future longitudinal studies with extended follow-up periods are needed to better understand the role of subclinical CVD markers and future risk of major cardiovascular events in women with PCOS. These studies support current guideline recommendations for early screening in this patient population with early glucose and lipid screening, consideration of measurement of markers for subclinical CVD, as well as initiation of targeted interventions such as weight and blood pressure management and smoking cessation. An aging longitudinal PCOS cohort would also afford the opportunity to observe the fluctuations of androgens and potential metabolic disturbances in the menopausal transition. A well-characterized, phenotyped PCOS cohort with detailed race/ethnicity data is necessary to determine how these variables impact subclinical CVD and future cardiometabolic risk.

In conclusion, there appear to be alterations of the vascular endothelium in women with PCOS. The role of these alterations must be further studied in long-term prospective studies to determine their impact on overt CVD and CVD mortality.