Obesity and serum lipids: an evaluation of the relative contribution of body fat and fat distribution to lipid levels

The association of obesity and hyperlipidemia does not mean that fatness per se is the primary determinant of the lipid abnormality. To evaluate the contribution of fatness to fasting levels of serum triglycerides (TG), LDL cholesterol (LDL-C), and HDL cholesterol (HDL-C), we analyzed data on 368 caucasian adults (286 women, 82 men) consecutively entering a weight control program. Although most subjects were overweight, the population represented a wide spectrum of body weights and lipid levels. Study variables included body fat mass (by total body water), fat free mass (FFM), body build (chest to height ratio), fat cell size and number (from bilateral buttock biopsy specimens), upper-lower body fat pattern by arm to thigh circumference ratio, central-peripheral fat pattern by subcapsular to triceps skinfold ratio, waist to hip ratio, and the presence or absence of diabetes. Our results concurred with previously noted correlations of body weight with TG (r = 0.29, P less than 0.0001) and with HDL-C (r = -0.28, P less than 0.0001) at least in the larger sample of women, but there was no significant correlation with LDL-C (r = -0.06). In order to evaluate the relative contribution of the various components of body composition and fat distribution to lipid levels, stepwise regression analyses were performed on the subgroups of women and men. Among women: TG level was predicted best by FFM, upper body fat pattern, age, and diabetes (explaining 30 percent of TG variance); LDL-C level was predicted by age only (explaining 12 percent of variance); and HDL-C level was predicted by body build only (8 percent). Among men: TG level was predicted best by central and upper body fat patterns and diabetes (31 percent of variance); LDL-C and HDL-C levels were not significantly predicted by any of the 11 study variables. These results, obtained from cross-sectional analysis of a predominantly obese sample, suggest that lipid levels may be more directly related to body fat pattern, fat free mass and body build than to body fatness itself.     

The relative contribution of androgens and insulin in determining abdominal body fat distribution in premenopausal women.

To investigate the relative contribution of insulin and sex hormones in determining the abdominal pattern of fat distribution in premenopausal women, five groups of age-matched subjects were examined: Group 1 consisted of 14 normal weight eumenorrheic women (NO); Group 2 of 9 obese eumenorrheic women (OB); Group 3 of 14 normal weight hyperandrogenic women with polycystic ovary syndrome (NO-HA); Group 4 of 10 obese hyperandrogenic women with polycystic ovary syndrome (OB-HA) and, finally, Group 5 of 10 obese hyperandrogenic women with polycystic ovary syndrome and acanthosis nigricans (OB-HA-AN). Both the two normal weight groups and the three obese groups were matched for body mass index values. Sex hormone pattern showed significantly higher LH and testosterone levels in hyperandrogenic women with respect to NO and OB women but obese hyperandrogenic groups (OB-HA and OB-HA-AN) presented significantly lower LH concentrations than NO-HA. Fasting and glucose-stimulated insulin levels were significantly higher in OB than NO, in OB-HA and OB-HA-AN than in OB and NO-HA, and in OB-HA-AN than in OB-HA, without any significant difference between OB and NO-HA. Body fat distribution, expressed by the waist to hip ratio (WHR), showed progressively higher values (p less than 0.01) from NO to OB, NO-HA, OB-HA and, particularly, OB-HA-AN women. Determination coefficients r2 obtained from simple regression analysis showed that the sum of insulin values during the glucose tolerance test and testosterone levels had a more significant power in determining WHR variability.(ABSTRACT TRUNCATED AT 250 WORDS)     

Both lean and fat body mass associate with blood pressure

High body mass index (BMI) is known to be associated with elevated blood pressure (BP). The present study aims to determine the relative importance of the two components of BMI, fat mass and lean body mass index, on BP levels.We assessed body composition with bioimpedance and performed 24 hour ambulatory BP measurements in 534 individuals (mean age 61 ± 3 years) who had no cardiovascular medication. Fat mass index and lean mass index were calculated analogously to BMI as fat mass or lean body mass (kg) divided by the square of height (m²).Both fat mass index and lean mass index showed a positive, small to moderate relationship with all 24 hour BP components independently of age, sex, smoking, and leisure-time physical activity. There were no interaction effects between fat mass index and lean mass index on the mean BP levels.Adult lean body mass is a significant determinant of BP levels with an equal, albeit small to moderate magnitude as fat mass. Relatively high amount of muscle mass may not be beneficial to cardiovascular health.     

The contribution of genes, environment and of body mass to blood pressure variance in young adult males

OBJECTIVE: (1) To determine by means of multivariate genetic modelling whether the covariation of blood pressure (BP) and body mass index (BMI) is compatible with a direct effect of BMI on BP, or rather with pleiotropy or environmental association, and (2) to quantify the contribution of such an effect and of heritability and environmental factors to BP variance. DESIGN AND METHODS: Fifty monozygous and 41 dizygous male twin pairs (ages: 17-38 years) were studied. BMI was calculated as weight/height. Blood pressure was the mean of three conventional measurements in the supine position. Estimates for the path coefficients of the three hypothesised models were obtained using Maximum Likelihood Estimation and were used to calculate the predicted covariance matrices for these models. A chi2 goodness-of-fit index of P>0.05 indicated an adequate fit. Likelihood ratio chi2 statistics and the Akaike Information Criterion (AIC) were used to choose the best model among the fitting models. The path coefficients of the best model were used to estimate the variance decomposition of BP. RESULTS: All hypothesised models fitted the data. The AIC was lowest for the model representing an influence of BMI on BP, for both systolic (AIC = -22.3) and diastolic (AIC = -22.2) BP. The estimated percentages of the total phenotypic variance of BP, which could be explained by the influence of BMI on BP, were 11.4% and 12.9% for systolic and diastolic pressure respectively. The remaining variances were associated with variation in genetic and environmental factors. CONCLUSIONS: A direct influence of BMI on BP constitutes the most likely explanation of the BP-BMI-covariation and it accounts for about 12% of the BP-variance in young healthy men.     

The relationship of body fat distribution to blood pressure in normotensive men: the normative aging study

Body fat distribution may be a more specific marker than obesity for risk of cardiovascular disease and diabetes. The relationship between body fat distribution and sitting systolic and diastolic blood pressure was examined in a cross-sectional analysis of 1936 normotensive men aged 21 to 80 years. In this analysis body fat distribution was represented by the ratio of abdomen circumference to hip breadth (denoted as WHbR). Pearson product-moment correlations adjusted for age revealed a positive correlation between WHbR and both systolic and diastolic blood pressure (r = 0.13 and r = 0.14, respectively). In a multiple linear regression model controlling for age, smoking status and body mass index (BMI), WHbR was associated with systolic blood pressure [regression coefficient (standard error) = 3.58 (1.8), P = 0.048)], but had much less of an association with diastolic blood pressure [regression coefficient (standard error) = 1.90 (1.3), P = 0.141]. Further adjustment for alcohol intake decreased the association between WHbR and systolic blood pressure [regression coefficient (standard error) = 2.90 (1.81), P = 0.110]. Body fat distribution, as represented by WHbR was associated with level of systolic blood pressure independently of overall level of obesity (BMI) in normotensive men; adjustment for alcohol intake attenuated the relationship. These data suggest that dietary factors, notably alcohol intake, may influence the effect of body fat distribution on blood pressure.     

Sex differences in the contributions of visceral and total body fat to blood pressure in adolescence

Excess body fat deposited viscerally rather than elsewhere in the body is associated with higher risk for hypertension; this relationship is stronger in men than in women. Here we investigated whether similar sex dimorphism exists already in adolescence. A population-based sample of adolescent boys (n=237) and girls (n=262), age 12 to 18 years, was studied. Total body fat (TBF) was assessed with multifrequency bioelectrical impedance, and visceral fat (VF) was quantified with MRI. Blood pressure (BP) was measured beat by beat during an hour-long protocol, including supine, standing, sitting, mental stress, and poststress sections. Multivariate mixed-model analysis was used to assess the relative contributions of TBF and VF to BP during these sections. In boys, BP was strongly positively associated with VF (P<0.0001), whereas it was less strongly and negatively associated with TBF (P=0.004); these relationships did not substantially vary during the protocol. In contrast, in girls, BP was strongly positively associated with TBF (P=0.0006), whereas it was not associated with VF (P=0.08); the relationship with TBF varied during the protocol and was most apparent during mental stress (TBF*section interaction: P=0.002). Furthermore, when waist circumference was included in multivariate models instead of VF, it was not associated with BP in either sex; this indicates that waist circumference may not be an appropriate surrogate for VF. Thus, in adolescence, adiposity-related BP elevation is driven mainly by visceral fat in males and by fat deposited elsewhere in females. This dimorphism suggests sex-specific mechanisms of obesity-induced hypertension and the need for sex-specific criteria of its prevention.     

The structural arteriolar changes in diabetes mellitus and essential hypertension: The relative contribution of ageing and high blood pressure

AIM: To evaluate the relative contribution of blood pressure, non-insulindependent diabetes mellitus and ageing on arteriolar structuralchanges in essential hypertension and diabetes mellitus. POPULATION AND METHODS: One hundred subjects, 25 with hypertension (A), 25 with hypertensionand diabetes (B), 25 with diabetes (C) and 25 healthy subjects(D). Blood pressure average values, obtained with non-invasivemonitoring, and minimal vascular resistance, calculated withstrain-gauge plethysmography, were statistically correlated.Multiple regression analysis was performed to assess the contributionof blood pressure and age. RESULTS: Minimal vascular resistance was higher in A, B and C than inD, and higher in B than in A and C. The coefficient of bloodpressure in the multiple regression analysis was significantfor all the parameters in A and B but not in C and D; that ofage was significant only in A and only for the average valuesof mean and diastolic blood pressure. CONCLUSION: Hypertension and diabetes show arteriolar structural changesof similar gravity. Age does play a role in hypertension buta smaller one than that played by blood pressure. In hypertensionand diabetes the lack of significance of the contribution ofage to the correlation between minimal vascular resistance andpressure could be ascribed to other neurohumoral factors. Thesefactors play a much more important role in diabetes, where neitherblood pressure nor age show any correlation with high vascularresistance.     

Autonomic contribution to blood pressure and metabolism in obesity

Obesity is associated with alterations in the autonomic nervous system that may contribute to the increase in blood pressure and resting energy expenditure present in this condition. To test this hypothesis, we induced autonomic withdrawal with the ganglionic blocker trimethaphan in 10 lean (32+/-3 years) and 10 obese (35+/-3 years) subjects. Systolic blood pressure fell more in obese compared with lean subjects (-17+/-3 versus -11+/-1 mm Hg; P=0.019) because of a greater decrease in total peripheral resistance (-310+/-41 versus 33+/-78 dynes/sec/cm(-5); P=0.002). In contrast, resting energy expenditure decreased less in obese than in lean subjects, (-26+/-21 versus -86+/-15 kcal per day adjusted by fat-free mass; P=0.035). We confirmed that the autonomic contribution to blood pressure was greater in obesity after including additional subjects with a wider range of blood pressures. Systolic blood pressure decreased -28+/-4 mm Hg (95% CI: -38 to -18.0; n=8) in obese hypertensive subjects compared with lean (-9+/-1 mm Hg; 95% CI: -11 to -6; n=22) or obese normotensive subjects (-14+/-2 mm Hg; 95% CI: -18 to -10; n=20). After removal of autonomic influences, systolic blood pressure remained higher in obese hypertensive subjects (109+/-3 versus 98+/-2 mm Hg in lean and 103+/-2 mm Hg in obese normotensive subjects; P=0.004) suggesting a role for additional factors in obesity-associated hypertension. In conclusion, sympathetic activation induced by obesity is an important determinant to the blood pressure elevation associated with this condition but is not effective in increasing resting energy expenditure. These results suggest that the sympathetic nervous system could be targeted in the treatment of obesity-associated hypertension.     

Genetic and environmental influences on body fat and blood pressure in African-American adult twins

OBJECTIVE: African Americans have a particularly high prevalence of excessive body fat and high blood pressure. Genetic and environmental influences may be implicated for both of these risk factors. We investigated the potential for common genetic and environmental influences on body fat (waist circumference (WC), body mass index (BMI)) and blood pressure measures (systolic and diastolic pressure (SBP, DBP)) among African-American male and female subjects. RESEARCH METHODS AND PROCEDURES: Measurements were taken as part of the Carolina African-American Twin Study of Aging (CAATSA). The CAATSA sample contains 217 same-sex African-American male and female twins with average age of 47 years. This analysis included 39 monozygotic male pairs (MZ), 43 dizygotic male pairs (DZ); 63 MZ female pairs, and 72 DZ female pairs. Maximum likelihood quantitative genetic analyses were used. RESULTS: The total genetic variance for SBP was 22% in male subjects and 40.1% in female subjects. Of this total variance, 3.1% was in common with BMI in male subjects and 6% was in common with BMI in female subjects. After controlling for the effects of BMI, WC had less than 1% of its variance in common with SBP in male and female subjects. For DBP, the total genetic variance was 16.9% in male and 38.7% in female subjects. Of this total variance 6.1% was in common with BMI in male subjects and 3.7% was in common in female subjects. Again, WC had less than 1% of its genetic variance in common with DBP in both male and female subjects. The environmental variance common among these measures was also very small. The remaining variance was primarily accounted for by genetic and environmental effects unique to each measure as well as age. DISCUSSION: Based on the very small common genetic variance for BMI, SBP, and DBP as well as WC and the blood pressure measures, our results suggest that searching for common genes among these measures may be inconclusive.     

The relationship between body weight and blood pressure

In adults of Western societies the positive relationship between blood pressure and body weight has often been demonstrated, both cross-sectionally and longitudinally. This correlation is even stronger in children and early adulthood. In most studies in children, the association between age and blood pressure disappears after controlling for weight. Association must be differentiated from causation. It has however been shown in several intervention studies that treatment of obesity by weight loss decreases blood pressure substantially both in hypertensive and normotensive subjects. Although combining results from several intervention trials is difficult this is the only practical way to get an overall estimate of the hypotensive response to be expected from weight reduction. In the randomised controlled intervention studies, conducted in obese hypertensive patients and reviewed in the present meta-analysis, a decrease in body weight by 1 kg resulted in a reduction of systolic and diastolic pressure by 1.2 and 1.0 mmHg, respectively. Blood pressure generally decreased before normal weight was achieved and remained reduced as long as there was no marked regain in body weight. Although a decrease in salt intake during dieting may contribute to the blood pressure lowering effect of weight reduction, also other mechanisms, such as a reduction in plasma renin activity and a decrease in sympathetic tone may also be involved.     

血压水平与颈动脉血流速度的关系

目的探讨血压水平和高血压类型与颈动脉血流速度的关系。方法选择脑卒中队列研究人群中55~65岁年龄段,无脑卒中、心脏病和糖尿病史者1 084例,依据基线调查时的收缩压、舒张压水平和高血压类型进行分组,其中收缩压按每增加10 mm Hg(1 mm Hg=0.133 kPa)分为9组,舒张压按每增加5 mm Hg分为8组,根据血压水平分为4种类型,比较和分析各组间颈动脉血流速度指标的差异。结果当收缩压≥120 mm Hg或舒张压≥80 mm Hg时,脑血管最大血流速度(Vmax)、最小血流速度(Vmin)和平均血流速度(Vmean)均开始呈逐渐下降趋势;当收缩压≥160 mm Hg或舒张压≥100 mm Hg时,脑血流速度下降的趋势更加明显。不同类型高血压组间的流速差异主要表现为左侧Vmin和右侧Vmax,各组的流速均显著低于血压正常患者(P<0.01)。结论从脑供血角度,理想的血压水平应<120/80 mm Hg,当血压水平≥160/100 mm Hg时,颈动脉血流速度明显减慢。     

The relationship of percent body fat by bioelectrical impedance analysis with blood pressure, and glucose and lipid parameters

The objective of this study was to clarify the clinical significance and usefulness of measuring percent body fat (PBF) when compared with body mass index (BMI) in the Japanese population. A total of 2,483 Japanese individuals (1,380 men and 1,103 women) who underwent a medical checkup from 1999-2002 were employed. PBF was determined using bioelectrical impedance analysis (BIA). Relationships of age, BMI and PBF with several metabolic parameters, including blood pressure, lipids and plasma glucose levels were assessed in both genders separately. In men, PBF was a stronger determinant of total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C) and triglycerides (TG) compared with age and BMI, whereas in women, age was the strongest determinant of TC and LDL-C. In both genders, BMI was the strongest determinant of serum HDL-C among age, PBF and BMI. Based on these data, we suggest that measuring PBF by BIA is superior to BMI for predicting TC, LDL-C and TG in Japanese men.     

The contribution of environmental temperature and humidity to geographic variations in blood pressure.

The pattern of geographic blood pressure variations in Britain has raised the possibility that temperature or other climatic factors may be of importance. Data from two population studies have been examined: the British Regional Heart Study (BRHS), which involved 7735 mean aged 40-59 years, and the Nine Towns Study (NTS), concerning blood pressure among 2596 men and women aged 25-59 years. In the BRHS, significant negative associations were found between daily maximum outdoor temperature and systolic blood pressure (-0.38 mmHg/degrees C; P less than 0.001) and diastolic blood pressure (-0.18 mmHg/degrees C; P less than 0.001). There were similar, although non-significant, associations in the NTS. No significant associations were found between blood pressure and room temperature in either study after taking account of town blood pressure differences, nor between blood pressure and outdoor humidity in the NTS. In the NTS, skin temperature was negatively associated with blood pressure after the adjustment for body mass index, significantly so for male diastolic (-0.62 mmHg/degrees C; P less than 0.05). The BRHS estimates suggest that, in Britain, geographic differences in outdoor temperature may contribute no more than 2 mmHg systolic and 1 mmHg diastolic to regional blood pressure variations. This represents a relatively small proportion of the town differences in blood pressure observed in both the BRHS and NTS. Furthermore, international comparisons suggest that environmental temperature is not an important determinant of population blood pressure levels.     

Differential rates of fat change relative to weight change at different body sites

As shown in 620 adults followed over a 5-year period, rates of change in outer fat differ from skinfold to skinfold and, to a lesser extent, between the sexes. At each of four sites and for men and women respectively fatness change rates per kilogram of weight change are much the same for heavier and lighter individuals, for fatter and leaner subjects, and during weight gain as compared with weight loss. In both sexes the abdominal and iliac sites are more sensitive to overall changes in weight and fatness.     

The contribution of fat and fat-free tissue to body mass index in contemporary children and the reference child

BACKGROUND: Body mass index (BMI) is widely used to assess the prevalence of childhood obesity in populations, and to infer risk of subsequent obesity-related disease. However, BMI does not measure fat directly, and its relationship with body fatness is not necessarily stable over time. OBJECTIVE: To test the hypothesis that contemporary children have different fatness for a given BMI value compared to the reference child of two decades ago. DESIGN: Comparison of children from Cambridge, UK with the reference child of Fomon and colleagues (Am J Clin Nutr 1982; 35: 1169-1175). SUBJECTS: A total of 212 children aged 1-10.99 y. MEASUREMENTS: Body composition was assessed by deuterium dilution. Fat-free mass and fat mass were both adjusted for height to give fat-free mass index and fat mass index. RESULTS: Contemporary Cambridge children have similar mean BMI values to the reference child. However, both boys and girls have significantly greater mean fatness and significantly lower mean fat-free mass than the reference child after taking height into account. Contemporary Cambridge children have greater fatness for a given BMI value than the reference child. CONCLUSION: BMI-based assessments of nutritional status may be under-estimating the increase in children's fatness. Any change over time in the relationship between BMI and body fatness will create a mismatch between (1) current estimates of childhood obesity and (2) predicted risk of future adult illness, calculated on the basis of longitudinal cohorts recruited in childhood several decades ago. However, an alternative interpretation is that the reference data are inappropriate. Caution should therefore be used in generalizing from this study, and further investigations of the issue are required.     

The contribution of vasopressin and angiotensin to the maintenance of blood pressure after autonomic blockade

The contribution of vasopressin and angiotensin II to the maintenance of blood pressure after short-term autonomic blockade was investigated in conscious Long-Evans and Brattleboro (vasopressin-deficient; hereditary diabetes insipidus) rats. After short-term autonomic blockade by atropine (1 mg/kg), propranolol (5 mg/kg), and pentolinium (5 mg/kg and 10 mg/kg/hr), the fall in blood pressure was significantly greater in Brattleboro rats than in Long-Evans rats (48 +/- 3 vs 32 +/- 2 mm Hg; p less than 0.01). Administration of the vasopressin vascular receptor antagonist D(CH2)5Tyr-(Me)AVP (2 micrograms/kg) caused further blood pressure decreases only in Long-Evans rats, so that the final blood pressure in both groups was identical. Administration of enalaprilat (10 mg/kg), an angiotensin converting enzyme inhibitor, further reduced blood pressure in both strains. When enalaprilat was given first after autonomic blockade, it reduced blood pressure in Brattleboro rats but not in Long-Evans rats. Administration of the vasopressin antagonist after enalaprilat further reduced blood pressure only in Long-Evans rats. The fall in blood pressure following vasopressin blockade was greater than that occurring after angiotensin converting enzyme inhibition (14 +/- 1 vs 6 +/- 1 mm Hg; p less than 0.05) in autonomic blockade Long-Evans rats. Plasma levels of vasopressin in Long-Evans rats increased markedly after short-term autonomic blockade, whereas plasma renin and angiotensin II levels were unchanged. Plasma angiotensin II levels were increased by the vasopressin antagonist and decreased by enalaprilat. We conclude that, due to sympathetic nervous system blockade and consequent blunting of renal renin release, vasopressin has a greater capacity than the renin-angiotensin system for maintaining blood pressure after short-term autonomic blockade.