In the context of previous literature
Our results are consistent with the observation that men are prone to abdominal fat deposition, particularly in the abdominal cavity, a condition described as visceral obesity . Notably, despite known differences in body fat distribution between individuals of African and European ancestry [21, 22], we found similar gender interactions with VAT and adiponectin levels as in previous studies . Similarly, gender proved to be an effect modifier of the association between SAT and serum adiponectin . Nevertheless, opposite to previous studies that indicated an inverse association between SAT and adiponectin , our investigation suggested a direct association between these two variables, confirming a series of previous investigations [24, 25]. Among men, the nonsignificant association between VAT and adiponectin provides insight which might explain why when compared with other races/ethnicities African American men have lower adiponectin levels despite smaller VAT compartments.
Waist circumference cannot differentiate between VAT and SAT compartments despite the fact that WC appears as a good predictor of VAT . This is particularly important, as VAT and SAT may be differently associated with inflammatory cytokines secretion and with differential metabolic risk profiles . The negative correlation between adiponectin and VAT is stronger than with SAT [28, 29]. In 69 non-diabetic African Americans, adiponectin negatively correlated with VAT (r = −0.41) in men and with VAT (r = −0.55) and SAT (r = −0.35) in women . In findings similar to our own, Considine and colleagues found that SAT was not significantly associated with adiponectin in the models that adjusted concomitantly for VAT .
Recent Jackson Heart Study (JHS) data suggest that abdominal obesity is particularly profound among African Americans as indicated by the fact that nearly two-thirds of the JHS sample has an elevated WC . Whether compared with whites, African Americans with elevated WC experience a higher risk for cardiovascular events due to greater abdominal adiposity is uncertain because whites have greater VAT than African Americans  and, in nationwide samples, higher WC . At similar degrees of obesity as defined by BMI, African Americans have a lower quantity of VAT compared with whites and Asian populations, despite higher rates of insulin resistance, diabetes and hypertension .
VAT secretes less adiponectin than SAT . Low levels of adiponectin, high levels of leptin and chronic low-grade inflammatory state are generally observed in the obese status and have been associated with insulin resistance and metabolic syndrome . Preliminary clinical evidence has linked these adipose tissue-derived hormones to measures of atherosclerosis and to development of future cardiovascular events , suggesting that adiponectin, leptin and C-reactive protein (CRP) may play an important role for increased risk of cardiovascular mortality in individuals with the metabolic syndrome. In the few studies conducted so far, higher WC was associated with lower total adiponectin after controlling for the effect of total fat mass, indicating that these associations are driven mainly by central fat accumulation, as indicated by the WC level rather than by total body adiposity [36, 37]. As shown by Steffes and colleagues in the CARDIA cohort (3,355 study participants), central obesity, as measured by WC, is a primary factor affecting levels of circulating adiponectin . Similarly with our investigation, both SAT and VAT were strongly correlated with insulin resistance (but with gender differences) in an investigation conducted among 78 nondiabetic African Americans . Moreover, as shown by Tulloch-Reid and colleagues , among African American women SAT have a greater effect on insulin resistance, in agreement with our findings.
Few previous studies have assessed the association of adiponectin with abdominal adipose tissue compartments as measured by CT scan. In a study conducted in nondiabetic women, adiponectin was more strongly determined by VAT, whereas leptin was more strongly influenced by SAT . In an investigation conducted in a Japanese male population, adiponectin levels were inversely associated with VAT and directly associated with SAT when these two measures of abdominal adiposity were both in a regression model . In this study from Japan, the negative regression slope of the association between VAT and adiponectin (the steepness of the association) was four times larger compared with that in our African American population. Considering also the lower VAT volumes (about 75% lower than those in the white participants in the Framingham Heart Study) and lower adiponectin values in African Americans compared with white and Asian populations, this suggests that the VAT – adiponectin relationship is less strong in African Americans men compared with other populations. In the same direction, in a sample of participants selected from the IRAS Family Study, sample that included 522 African-Americans, adiponectin was significantly associated with age, gender, HDL-cholesterol, VAT and SAT . The slope of the association between adiponectin and VAT was more than twice compared with the value that we detected within our investigation. It is worthy to note that the mean values of adiponectin within our sample were lower compared with the IRAS Family sample as well as with those from the Health ABC study that reported an association between adiponectin and risk of coronary heart disease . Our results showing in women a higher slope of the association between VAT and adiponectin (when contrasted with that between SAT and adiponectin) are in agreement with a series human adiposity tissues studies that indicated a lower adiponectin secretion in omental fat versus subcutaneous fat .
Although traditionally regarded as a silent organ that passively stores excess energy, the adipose tissue is now considered an endocrine organ not only contributing to the management of energy flux within the body but also interacting with the inflammatory system and the vascular wall. Several studies have demonstrated that adipose tissue actively produces a variety of locally and systemically functioning bioactive molecules that interact in various obesity-related diseases, e.g., leptin , adiponectin , tumor necrosis factor-α (TNF-α) , plasminogen-activator inhibitor type-1 (PAI-1)  and resistin . Adiponectin was discovered to be the most abundant adipose-specific transcript . Furthermore, recent studies have underlined that there are intricate interplays among adipocytes, the sympathetic nervous system and the renin-angiotensin system, which participate in the obesity-associated dysmetabolic state . The possible explanation for differences between VAT and SAT may be related to differences in their anatomic location and cytokine secretion profiles. SAT may preferentially release more leptin, whereas VAT may mainly release tumor-necrosis factor-α, known to influence the secretion of adiponectin . In addition, a series of studies showed that androgens reduce plasma adiponectin , providing insights into the gender differences of the association between VAT and adiponectin. Additionally, adiponectin’s compensatory effects of metabolic disorders’ improvements seem to entail massive expansion of subcutaneous adipose tissue depot .