Impact of Pre-diabetes alone or in combination with Hypertension, Dyslipidemia, or both on Major Adverse Cardiovascular Events


 Background

Whether pre-diabetes in the absence of hypertension (HTN) or dyslipidemia (DLP) is a risk factor for occurrence of major adverse cardiovascular events (MACE) is not fully established. We investigated the effect of impaired fasting glucose (IFG) alone and in combination with HTN, DLP or both on subsequent occurrence of MACE as well as individual MACE components.

Methods

This longitudinal population-based study included 9,831 inhabitants of Northeastern Iran. The participants were free of any cardiovascular disease at baseline and were followed yearly from 2010 to 2017. Cox proportional hazard models were fitted to measure the hazard of IFG alone or in combination with HTN and DLP on occurrence of MACE as the primary endpoint.

Results

297 MACE were recorded during 6.2±0.1 years follow up. IFG alone compared to normal fasting glucose (NFG) was not associated with increased in occurrence of MACE (HR, 1.05; 95% CI, 0.59-1.86; p, 0.8). However, combination of IFG and HTN (HR, 2.75; 95% CI, 1.93-3.90; p, 0.001) or HTN + DLP (HR, 2.85; 95% CI, 1.79-4.54; p, 0.001) significantly increased the hazard of MACE. In contrast, IFG with DLP at baseline did not increase the hazard of MACE compared to normoglycemic- normolipemic individuals (p,0.2). The results also indicated IFG with HTN, DLP, or HTN+DLP were associated with significant higher HRs for some individual components of MACE.

Conclusion

IFG, per se, does not appear to increase hazard of MACE. However, IFG with HTN or HTN + DLP conferred a significant hazard for MACE in an incremental manner.

Pre-diabetes (pre-DM) is often taken as a warning sign. Individuals with pre-DM have a glycemic state that is higher than normal but not high enough to be classified as type 2 diabetes (T2DM). The pre-diabetes state is characterized by impaired fasting glucose (IFG), impaired glucose tolerance (IGT), or HbA1c of 39 mmol/mol ( 5.7% ) to 46 mmol/mol (6.4%). 1 The significance of pre-DM is the associated risk for progression to T2DM which is disproportionately greater at the higher end of the pre-DM range and with the combined presence of IFG and IGT [1]. Pre-DM and T2DM are parts of a continuous spectrum that share in their pathophysiology, and are associated with a common phenotype that includes obesity, hypertension (HTN), and dyslipidemia (DLP) [2]. It is well established that aggregation of the traditional cardiovascular (CV) risk factors such as HTN and DLP in patients with T2DM is associated with the increased risk of cardiovascular disease (CVD) and events [3,4]. Furthermore, insulin resistance per se that is present in the vast majority of individuals with T2DM is associated with the increased risk of CVD independent of other CV risk factors [5,6].
In addition to T2DM, pre-DM is also associated with an increased risk of CVD [7,8].Considering that traditional CV risk factors are frequently present in individuals with pre-diabetes, the question arises that to what extent is the effect of pre-DM on CVD risk mediated by having pre-DM alone or by the associated risk factors [9,10].Since some studies did not fully adjust for concomitant CV risk factors, their findings should be interpreted with caution. Hence, whether pre-DM or IFG alone in the absence of HTN or DLP or their combination carries increased risk for CVD has remained an unanswered issue.
We conducted a prospective cohort study among a population of Iranian people to investigate the impact of IFG alone or in combination with HTN or DLP or both on the primary composite endpoint of major adverse cardiovascular events (MACE) as well as its individual components.

Study design and population
We extracted data from the longitudinal Golestan Cohort Study (GCS) that was launched in Northeastern Iran [11]. The primary aim of GCS is to investigate risk factors of esophageal cancer in this region. Participants in this cohort were also followed for CVD outcomes. In this analysis we examined data from a total number of 11,374 participants that were enrolled from rural and urban areas between April 2010 and March 2012. Participants were followed annually till March 2017. The exclusion criteria of the Golestan cohort were: unwillingness to participate at any stage of the study for any reason, and having a current or previous history of any known CVD events. The study protocol was approved by the ethical review committees of the Digestive Disease Research Institute of Tehran University of Medical Sciences, the US National Cancer Institute, and the International Agency for Research on Cancer. Before interview, the written informed consent was obtained from each participant. They were interviewed by a trained general physician who has recorded demographic and medical information through a questionnaire.
Height, weight, waist and hip circumference were measured at baseline, and body mass index (BMI) was calculated. Blood pressure (BP) was measured twice, with a 10-min interval, from both arms in the sitting position using Richter auscultator sphygmomanometers. Blood samples (10 ml) were collected by a trained technician.
Fasting blood glucose (FBS), triglyceride (TG), cholesterol, and high density lipoprotein (HDL) were measured in all individuals at the time of enrollment.

Follow up
Participants were followed up by annual phone calls from their date of recruitment (2010-2012) until the first occurrence of any of MACE components, death from any cause, or end of the study (March 2017). Each cohort member was also instructed at the time of enrollment to contact the team in case of certain conditions such as hospitalization or development of a new major disease. These contacts were registered and subsequently followed by a staff member. Follow-up assessed at the end of the Golestan study was successful for over 99% of the study participants. If a death was identified, a general practitioner visited the home of the deceased. Causes of death were ascertained through verbal interview and investigation of medical documents [12]. Using the collected documents, two internists independently determined the cause of death with ICD-10 codes. If the two were concordant, a diagnosis was made. Otherwise, the cause of death was determined by a third senior internist.

Definition of IFG, HTN, and DLP
IFG was diagnosed when a participant did not have DM, but had an FBS of 5.6 to <7.0 mmol/L, according to the American Diabetes Association criteria (ADA) [1]. Patients with diagnosed T2DM, defined as a self-reported diagnosis, or being treated with glucose lowering drugs, or those with FBS ≥ 7 mmol/L were excluded from the current analysis.
Normal fasting glucose (NFG) was defined as FBS< 5.6 mmol/L. Hypertension was defined as self-reported hypertension and currently taking antihypertensive drugs, or systolic blood pressure (SBP) ≥140 mm Hg or diastolic blood pressure (DBP) ≥90 mm Hg based on the JNC-7 criteria [13]. DLP was defined as fasting TG ≥1.69 mmol/L, or total cholesterol ≥ 6.20 mmol/L, or HDL<1.29 mmol/L in women and <1.03 mmol/L in men, or receiving lipid lowering medications.

Statistical Analysis:
Data are presented as means (SE) and numbers (percentage). In all cases, final analysis was based on presence or absence of a risk factor (or factors) in both the IFG and NGT groups using fully adjusted models. Student t-test and Pearson χ2 (or Fisher Exact) tests were used to compare continuous and categorical variables, respectively. Risk analysis was conducted in patients with IFG, and Poisson regression model was used to identify predictors of MACE (fatal MI, fatal stroke, non-fatal MI, and non-fatal stroke). Regarding the time to event for MACE and its components, Kaplan-Meyer method was used to estimate the survival probabilities, and Cox proportional hazard models were fitted to measure the hazard ratios. Statistical analyses were performed with Stata software for Windows version 13.0. Values of p <0.05 was considered statistically significant.

Baseline characteristics
The entire prospective cohort included 11,374 participants from the Northern provinces of Iran. Among the cohort 1,543 had DM at baseline and were excluded from this analysis.
Baseline characteristics of the study population are demonstrated in Table 1

IFG and CVD outcomes
Over a mean follow up of 6.2 (± 0.1) years, 297 MACE (199 CVD deaths, 43 non-fatal MI, and 55 non-fatal strokes) were reported. CVD death comprised of 108 fatal MI, 74 fatal strokes, and 17 deaths due to heart failure. Kaplan-Meier analysis with log-rank test shows that addition of IFG to HTN, DLP, or both did not decrease MACE free survival ( Figure 1; p > 0.05 for all comparisons).
We next examined the effect of IFG with HTN, DLP, or both HTN + DLP on the occurrence of individual components of MACE in greater detail. increase the hazard of any of the above cardiovascular events (Table 5).

Discussion
The major findings of the present study on composite CVD outcomes (MACE) in a group of individuals with IFG are that IFG, per se, in the absence of HTN and DLP was not associated with an increase in the hazard for MACE. In contrast, IFG in the presence of Whether pre-DM, per se, is an independent risk factor for CVD has been a matter of debate. In the current study, IFG in the absence of other CV risk factors did not increase the risk of adverse cardiovascular events. Likewise, other longitudinal population-based studies, also did not find an association between pre-DM alone and CVD risk [14,15].
However, other studies have indicated that dysglycemia within pre-diabetic glucose range was associated with an increase in the risk of CVD [6,16,17]. Most studies have suggested that impaired glucose tolerance (IGT) is a stronger predictor than IFG for CVD events [18,19]. However, Barr et al. showed IFG but not IGT is an independent predictor for CVD mortality [20]. Results from a recent review suggested that IGT and HbA1C correlate more with CVD risk than IFG [21]. These inconsistencies might be due to differences in analytical methods, different definitions for pre-diabetes, and ethnic origins of the participants included in the studies.
It is generally agreed that individuals with pre-diabetes or T2DM have higher than normal CV risk factors. This is probably due to the fact that T2DM and pre-DM share common underlying pathophysiologic disturbances such as insulin resistance [2]. In our study, as expected, participants with IFG had significantly higher BMI, WC, SBP, DBP, TG, total cholesterol, and LDL compared to normoglycemic subjects. Moreover, they were more likely to have HTN and DLP than those with NFG. Similar results are frequently reported in previous studies investigating the presence of CV risk factors in individuals with pre-DM [9,10,22].
Aggregation of CV risk factors in individuals with pre-DM is known to place them at higher risk for CV events [10]. In the current study we found that IFG when associated with HTN significantly increased the risk of composite end-point of MACE. This result is in line with the results of some previous studies in which the coexistence of pre-DM and HTN, but not pre-DM without HTN, significantly increased the risk of CVD events [14,15]. Another study showed that pre-DM defined as IFG or IGT even in the presence of prehypertension, DLP, characterized by elevated TG, low concentration of HDL, and an increased number of small dense LDL, plays a critical role in acceleration of atherosclerosis and is reported as an important independent risk factor for CVD [26]. Several studies have demonstrated that individuals with pre-diabetes have deranged lipid profiles compared to normoglycemic subjects. 9,22 The frequent association of DLP with pre-DM, which may reflect the underlying insulin resistance, has led to frequent treatment of DLP in the prediabetes [27,28]. Despite of the importance of screening and treatment of DLP in individuals with pre-diabetes, we have not found studies that combined pre-DM and DLP together in the analysis for predicting CVD risk. Nevertheless, when we compared the impact of IFG plus DLP with that of NFG without DLP, we found that coexistence of DLP and IFG did not confer any additional risk for development of the composite end-point of MACE. One possible explanation for this finding is that individuals with IFG were more likely to use statin compared to normoglycemic individuals. Nowadays, statin therapy is widely recommended for both primary and secondary prevention of CV disease in a wide range of individuals, even in those without hyperlipidemia [29,30]. Statins exert their beneficial effects not only through lowering of LDL, but also by improving endothelial function [31], reducing vascular inflammation [30,32], and exerting antithrombotic

Ethics approval and consent to participate
The study protocol was approved by the ethical review committees of the Digestive Disease Research Institute of Tehran University of Medical Sciences, the US National Cancer Institute, and the International Agency for Research on Cancer. Before interview, the written informed consent was obtained from each participant.

Consent for publication
Not applicable.

Availability of data and material
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
No funding was received for this work.