Apolipoprotein B and Insulin Resistance in Hypertensive Compared With Normotensive Patients: An Epidemiological Study.

Abstract

To the Editor: Cross-sectional studies performed recently have suggested that the prevalence of type 2 diabetes in persons with familial hypercholesterolemia might be lower than unaffected individuals (1.75% vs 2.93%, respectively; P<.01). Moreover, statin therapy might increase the risk of type 2 diabetes by 46% with substantial decreases in insulin secretion and resistance as reported by the researchers in the Metabolic Syndrome in Men (METSIM) cohort. The exact relationship between cholesterol and insulin resistance remains unclear in persons with hypertension. We have attempted to evaluate the relationship between Apolipoprotein B (Apo B) and insulin resistance in hypertensive patients. We performed an analysis of the cross-sectional data from the National Health and Nutrition Examination Survey1 for the period 2008–2012 to evaluate the relationship between Apo B and insulin resistance in both a normotensive and hypertensive population. We stratified the serum Apo B levels into low (<100 mg/dL) and high (≥100 mg/dL) groups. Data on variables including age at screening, body mass index (kg/m), waist circumference (cm), mean systolic blood pressure (mm Hg), and cholesterol (mg/dL) were tabulated. We excluded persons 18 years or younger from our analysis. Blood pressure (BP) was categorized as normotensive (systolic BP <140 mm Hg) and hypertensive (systolic BP ≥140 mm Hg). The homeostasis model assessment of insulin resistance (HOMA-IR) was calculated using the formula (–fasting insulin (lU/mL)9fasting blood glucose (mg/dL)/405). We performed the independent sample t test comparing variables between the two groups. Additionally, we performed nonparametric (spearman) correlation between Apo B and HOMA-IR, Apo B and fasting serum insulin level(s) (lU/mL), and Apo B and fasting blood glucose (mg/dL) in both normotensive and hypertensive patients. SPSS version 21 (IBM, Armonk, NY) was used for statistical analysis. There were 3557 persons with normal BP and 497 with hypertension in the study population. Persons with low Apo B and high Apo B levels were equally distributed between normotensive and hypertensive patients (chi-square, 0.89). There was no difference in the mean Apo B level between normotensives and hypertensive patients (87.8 [ 25.1] vs 87.5 [ 25.3], P=.80). The results of the comparison (Student t test) between the low Apo B group and the high Apo B group in persons with hypertension is summarized in the Table. The high Apo B group had significantly higher fasting insulin, insulin resistance (HOMA-IR), and fasting blood glucose levels (P=.04, P<.01, and P<.01, respectively). There was a significant positive correlation between Apo B, fasting insulin, and fasting blood glucose levels, as well as HOMA-IR in both the normotensive and hypertensive groups. However, the relationship between Apo B and fasting insulin levels was stronger in hypertensive patients (Spearman correlation coefficient (q)=0.198, P<.01) as compared with persons without hypertension (Spearman correlation coefficient (q)=0.148, P<.01). This greater correlation was also seen in the relationship between Apo and HOMA-IR (q=0.214, P<.01 vs q=0.180, P<.01). Recently, higher insulin resistance was associated with lower lipoprotein (a) levels in persons with hypertension. The results of our cross-sectional study show that higher Apo B levels are associated with increased insulin resistance. A meta-analysis published last year showed that statin-induced cardiovascular risk reduction is more closely associated with Apo B levels than lowdensity lipoprotein cholesterol. Prospective studies may be needed to better describe the underlying relationship.