Abdominal obesity phenotypes and risk of cardiovascular disease in a decade of follow-up: The Tehran Lipid and Glucose Study
Introduction
Along with the epidemic of obesity and abdominal obesity, concomitant metabolic derangements pose obese individuals at greater risk for future morbidity and mortality [1], [2]. A combination of obesity and metabolic components leads to evolvement of different obesity phenotypes that may have different risks for future health outcomes such as cardiovascular disease (CVD), type-2 diabetes, and all-cause mortality [3], [4]. In this regard, “metabolically healthy obesity” (MHO) is in the center of attention and inconsistencies exist on the benign nature of this obesity phenotype [5]. While many studies suggest that MHO is a relatively benign condition in comparison to metabolically unhealthy phenotypes [1], [2], [6], other studies show that this might not be the case and in longer follow-ups the so-called “benign obesity” is not that benign after all, when compared to metabolically healthy non-obese subjects [4], [7], [8], [9].
Although no uniform definition for MHO exists, about one-fifth to one-third of obese individuals are estimated to have MHO-like phenotypes highlighting the importance of this condition [5]. Using different criteria for defining both obesity and metabolic health may be a source of inconsistency in different studies, as well as the length of follow-ups, and also the specific outcomes of interest [4], [10]. The choice of an appropriate anthropometric index for defining obesity is one obstacle in characterizing MHO individuals; although most studies in this field use body mass index (BMI), recently some have also used abdominal obesity measures like waist circumference (WC) for this purpose [11], [12]. In fact, increased health risks in the “metabolically healthy obese” and also the “metabolically unhealthy non-obese” observed in some studies, may be in part due to increased waist circumference or higher abdominal obesity rates in these groups. Evidence shows that increased BMI and WC are both strongly associated with morbidity and mortality in the long-term, but some suggest that abdominal obesity measures may better predict CVD and other health outcomes in comparison with BMI [13], [14], [15]. On the other hand, visceral adiposity and insulin resistance may be the driving force for other metabolic derangements and may precede the evolvement of metabolic syndrome [16]; hence using abdominal obesity measures (e.g. WC) is a reasonable approach that provides deeper insight into the nature of different obesity phenotypes.
Given the aforementioned inconsistencies, we used WC and metabolic syndrome components, and also insulin resistance, to categorize abdominal obesity phenotypes in a population-based prospective cohort study in Iran and compared incident CVD in the “healthy” and “unhealthy” abdominal obesity phenotypes over a 10-year follow-up.
Section snippets
Participants
The Tehran Lipid and Glucose Study (TLGS) is an ongoing prospective, population-based study being conducted to determine the risk factors for non-communicable diseases among a representative Tehranian urban population [17]. In the TLGS, 15,005 Participants, aged ≥3 years, were selected by a multistage cluster random sampling method. Details of the study protocol are available elsewhere [17]. For the current study, 9754 participants, aged ≥30 years, which entered the study during phases I and II
Results
Of the 7122 participants enrolled in this study, 42.7% were men and the mean age was 47.4 (12.4) years. Of this population, 692 (9.7%) participants lacked the additional follow-up data for the outcome and were lost to follow-up, leaving us with 6430 for final outcome analysis. The baseline characteristics of those who were lost to follow-up were not significantly different from those who remained in the study regarding age, BMI, WC, and metabolic indices (data not shown).
Table 1 shows the
Discussion
In this large population-based study, we evaluated the risk of cardiovascular disease (CVD) in different obesity phenotypes based on abdominal obesity and metabolic health during a 10-year follow-up. About half of the initial population were abdominal obese and of these, 23.5% were categorized as “metabolically healthy” or MHAO phenotype. When compared to the reference group (MHNAO), all other phenotypes (including MHAO and MUNAO) had an increased risk for CVD.
The prevalence of “healthy
Conflicts of interests
The authors declare no conflicts of interests.
Acknowledgment
FH and SK designed the study. FH, MB, and SS performed the data collection, analysis and interpretation of data. FH, SD, and SK participated in literature review and writing the manuscript. FA, SK and FH did the final review of the work.
We would like to acknowledge Ms. Niloofar Shiva for critical editing of English grammar and syntax of the manuscript, and also the staff and participants in the TLGS Study for their important contribution.
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