Demographic, behavioral, biochemical, and dietary correlates of plasma triglycerides. Lipid Research Clinics Program Prevalence Study

Meta-analysis of the effects of smoking and smoking cessation on triglyceride levels

Smoking increases lipid levels, including triglycerides, leading to increased cardiovascular disease risk. We performed a meta-analysis to quantify the effects of smoking and smoking cessation on triglyceride levels. The PubMed and Scopus databases were searched to identify studies reporting either triglyceride levels in smokers and non-smokers or the effects of smoking cessation on triglyceride levels. Fixed- and random-effects models were used to perform the analyses when three or more studies/comparisons were available. We identified 169 and 21 studies evaluating the effects of smoking and smoking cessation, respectively, on triglyceride levels. Triglyceride levels were 0.50 mmol/L (95% confidence interval: 0.49-0.50 mmol/L) higher in smokers than non-smokers, but the effect differed widely across studies. No statistically significant effect was observed on triglyceride levels between baseline and 6 weeks (mean difference [MD] = 0.02 [-0.09, 0.12] mmol/L), 2 months (MD = 0.03 [-0.21, 0.27] mmol/L), 3 months (MD = 0.08 [-0.03, 0.21] mmol/L), or 1 year (MD = 0.04 [-0.06, 0.14] mmol/L) after quitting. However, a slightly significant decrease in triglyceride levels was observed at 1 month after cessation (MD = -0.15 [-0.15, -0.01] mmol/L). The results of this meta-analysis provide a basis for understanding the effects of smoking and smoking cessation on triglyceride levels, which could have important implications for public health.

Triglycerides and coronary risk

Despite extensive research, it has not yet been determined whether triglycerides represent an independent risk factor for coronary heart disease (CHD). The association has been obscured by imprecision in triglyceride measurements, individual variability, and complex interactions between triglycerides and other lipid-nonlipid parameters. Recent large-scale epidemiologic data indicate that elevated fasting triglycerides represent a useful marker for risk of coronary heart disease. The strong interrelationships of triglyceride level, high-density lipoprotein (HDL) level, and low-density lipoprotein (LDL) particle size with CHD risk suggest a metabolic interaction between the triglyceride-rich and cholesterol ester-rich lipoproteins in increasing risk of myocardial infarction. Limited data from clinical trials suggest that intervention with agents that lower triglycerides and raise HDL tend to reduce event rates among those with elevated and normal LDL levels. Many important issues defining the role of triglycerides in the primary and secondary prevention of CHD need further evaluation. These issues include the degree of risk associated with high triglyceride levels in various age, gender, racial, and ethnic subgroups, and the prognostic significance of postprandial versus fasting triglyceride levels. Further, primary and secondary intervention trials that more specifically address the clinical benefit of reducing triglyceride levels are warranted. Ultimately, screening and treatment guidelines may have to be modified to allow greater focus on fasting-triglyceride levels. Although current guidelines do not mandate screening for elevated triglyceride levels in the general population, obtaining triglyceride levels in those with known CHD or with other risk factors can provide valuable prognostic information and therefore be of aid in therapeutic decisions.

Fasting triglycerides, high-density lipoprotein, and risk of myocardial infarction

BACKGROUND

Recent data suggest that triglyceride-rich lipoproteins may play a role in atherogenesis. However, whether triglycerides, as a marker for these lipoproteins, represent an independent risk factor for coronary heart disease remains unclear, despite extensive research. Several methodological issues have limited the interpretability of the existing data.

METHODS AND RESULTS

We examined the interrelationships of fasting triglycerides, other lipid parameters, and nonlipid risk factors with risk of myocardial infarction among 340 cases and an equal number of age-, sex-, and community-matched control subjects. Cases were men or women of <76 years of age with no prior history of coronary disease who were discharged from one of six Boston area hospitals with the diagnosis of a confirmed myocardial infarction. In crude analyses, we observed a significant association of elevated fasting triglycerides with risk of myocardial infarction (relative risk [RR] in the highest compared with the lowest quartile=6.8; 95% confidence interval [CI]=3.8 to 12.1; P for trend <.001). Results were not materially altered after control for nonlipid coronary risk factors. As expected, the relationship was attenuated after adjustment for HDL but remained statistically significant (RR in the highest quartile=2.7; 95% confidence interval [CI]=1.4 to 5.5; P for trend=.016). Furthermore, the ratio of triglycerides to HDL was a strong predictor of myocardial infarction (RR in the highest compared with the lowest quartile=16.0; 95% CI=7.7 to 33.1; P for trend <.001).

CONCLUSIONS

Our data indicate that fasting triglycerides, as a marker for triglyceride-rich lipoproteins, may provide valuable information about the atherogenic potential of the lipoprotein profile, particularly when considered in context of HDL levels.

Blood pressure, lipids and other risk factors for cardiovascular disease in Aborigines and persons of European descent of southeastern Australia

Based on a survey in two country towns of southeastern Australia, cardiovascular risk-factor prevalence data from Aborigines and persons of European descent are presented. The mean diastolic blood pressure in 123 Aboriginal males was 83.2 mmHg, compared with 79.2 mmHg in 272 European males (P = 0.005). In 178 Aboriginal females, mean diastolic pressure was 79.2 mmHg, compared with 76.3 mmHg in 281 European females (P = 0.006). Mean plasma total cholesterol was higher in Europeans (both males and females: 5.7 mmol/L) than in Aborigines (in males 5.2 and females 5.0 mmol/L) (male comparison, P = 0.02, female comparison, P < 0.001). The prevalence in participants aged 25 to 64 years of at least one major risk factor (diastolic blood pressure 95 mmHg or higher, plasma cholesterol 6.5 mmol/L or higher, or smoking more than one cigarette daily) was higher in both these samples of Aborigines (94 per cent in males, 89 per cent in females) and Europeans (70 per cent in males, 59 per cent in females) than in the 1989 urban sample of the National Heart Foundation (47 per cent in males, 36 per cent in females). Multivariate analyses showed statistically significant independent contributions of body mass index and the variable 'ethnicity' (unidentified genetic and environmental differences between the groups) to blood pressure and other risk factors. The higher cardiovascular mortality of Aborigines may be explained partly by the higher prevalence of risk factors in this group compared with other Australians. Further, the risk-factor profile may be worse among rural compared with urban Europeans.

Metabolic and behavioral covariates of high-density lipoprotein cholesterol and triglyceride concentrations in postmenopausal women

OBJECTIVE

To determine predictors of high-density lipoprotein cholesterol (HDL) and triglyceride (TG) concentrations in postmenopausal women.

DESIGN

Cross-sectional study.

SETTING

Clinical research facility.

PARTICIPANTS

One hundred twenty-seven healthy, relatively sedentary, postmenopausal women not on estrogen replacement, mean age 57 years.

MEASUREMENTS

Alcohol intake, cigarette smoking, aerobic fitness (VO2max), body mass index (BMI), percent body fat, waist-hip ratio, lipids and lipoproteins, fasting plasma glucose (FPG), and insulin (FPI) concentrations.

RESULTS

In univariate analyses, HDL was significantly (P < 0.05) inversely related to BMI, waist-hip ratio, smoking, FPG, and FPI, and directly related to VO2max and alcohol intake. Triglycerides were related directly to BMI, waist-hip ratio, percent body fat, FPG, and FPI, and inversely to VO2max. In stepwise multiple regressions, BMI, waist-hip ratio, alcohol, smoking, and FPG were significantly associated with HDL (R2 for the model = 0.43). Addition of TG to these models reduced relations of BMI and waist-hip ratio, but not the other variables, to insignificance. For triglycerides, waist-hip ratio, alcohol, smoking, FPG, and FPI were significant predictors (R2 = 0.33). VO2max and percent body fat did not contribute to any model.

CONCLUSIONS

Obesity, abdominal obesity, smoking, alcohol intake, and measures of carbohydrate metabolism predict HDL and triglyceride concentrations in postmenopausal women.

Serum lipid profile and its association with some cardiovascular risk factors in an urban Chinese population

The lipid profile of a Chinese population, which has a lower prevalence of coronary heart disease compared with Caucasians, is studied to determine whether lipid-modifying disease prevention programs are necessary. The study population consisted of 910 men (mean age 36.7 +/- 9.2 yrs) and 603 women (mean age 38.6 +/- 9.1 yrs), who were employees of a public utility company and non-medical staff of a district hospital. Indices of obesity, fasting cholesterol (TC), and its various subfraction, triglycerides (TG), apolipoprotein A-I (Apo A-I), and apolipoprotein B (Apo B) concentrations were measured. Glucose tolerance was also estimated by measuring fasting and 2 h glucose after a 75 g oral glucose load. The lipid profile was similar to that of the North American population, with an overall prevalence of low density lipoprotein cholesterol (LDL-C) > or = 4.1 mmol/L of 21% and 11% in men and women respectively. Similar variations with age, sex, smoking and glucose tolerance compared with Caucasian populations were observed. The high prevalence of subjects with "undesirable" lipid values in this Chinese population, which at present has a coronary artery disease prevalence of one-eighth to one-quarter compared with that in Caucasians, suggests that the incidence of the disease may well rise in the future to pose a similar problem to that in Caucasian populations. Cut off values of lipids conferring increased cardiovascular risks need to be determined in this population, so that public health strategies may be formulated.

Plasma triglyceride level and mortality from coronary heart disease

BACKGROUND

Whether the plasma triglyceride level is a risk factor for coronary heart disease has been controversial, and evaluation of the triglyceride level as a risk factor is fraught with methodologic difficulties.

METHODS

We studied the association between plasma triglyceride levels and the 12-year incidence of death from coronary heart disease in 10 North American populations participating in the Lipid Research Clinics Follow-up Study, while adjusting for the potential confounding effects of other risk factors for cardiovascular disease, including the level of high-density lipoprotein (HDL) cholesterol. All analyses were sex-specific, and separate analyses were performed in high and low strata of HDL cholesterol, low-density lipoprotein (LDL) cholesterol, fasting plasma glucose, and age.

RESULTS

The rates of coronary death in both men and women increased with the triglyceride level. In Cox proportional-hazards models adjusted for age, in which the natural log of the triglyceride levels was used to give a normal distribution, the relative risk per natural-log unit of triglyceride (e.g., a triglyceride level of 150 mg per deciliter vs. a level of 55 mg per deciliter) was 1.54 (95 percent confidence interval, 1.19 to 1.98; P < 0.001) in men and 1.88 (95 percent confidence interval, 1.19 to 2.98; P < 0.007) in women. After an adjustment for potential covariates, however, these relative risks were not statistically significant. Analyses based on lipoprotein cholesterol levels revealed a positive association between the triglyceride level and coronary mortality in the lower stratum of both HDL and LDL cholesterol, but not in the higher stratum. Conversely, the HDL cholesterol level was unrelated to coronary mortality in the lower stratum of LDL cholesterol, but was strongly inversely associated with coronary death in the higher stratum of LDL cholesterol. The relative risk of coronary death associated with triglyceride level was higher at younger ages. The associations between the triglyceride level and coronary mortality in the lower HDL cholesterol, LDL cholesterol, and age strata were small and were further reduced by an adjustment for the fasting plasma glucose level.

CONCLUSIONS

Overall, the plasma triglyceride level showed no independent association with coronary mortality. However, in subgroups of subjects with lower HDL and LDL cholesterol levels and in younger subjects, defined a priori, an association between the triglyceride level and coronary mortality was observed, although this association was small and was not statistically significant after an adjustment for the plasma glucose level.

The effects of generation and gender on the joint distributions of lipid and apolipoprotein phenotypes in the population at large

The generation and gender effects on the joint distributions of total plasma cholesterol (Total-C), ln triglycerides (lnTrig), HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), apolipoproteins AI (Apo AI), AII (Apo AII), and E (lnApo E) were studied in 184 male grandparents (MGP), 242 female grandparents (FGP), 237 male parents (MP), 235 female parents (FP), 202 male children (MC), and 200 female children (FC). Homogeneity of variance tests revealed that lipid variances were gender and/or generation specific while apolipoprotein variances were homogeneous across strata. In the absence of heterogeneity of variance, significant heterogeneity in LDL:lnTrig and lnTrig:Apo AII covariation was found between genders in the parental generation. In the presence of heterogeneity of variance, significant heterogeneity of correlation between genders and/or across generations was found for the HDL-C:LDL-C, Total-C:LDL-C, Total-C:lnTrig, lnTrig:LDL-C, Total-C:lnApo E and HDL-C:lnApo E bivariate distributions. Analyses of principal components revealed that the generation and gender specific cohorts have similar eigenvalues but distinct eigenvectors for the first two principal components underlying the seven dimensional lipid and apolipoprotein distribution. We conclude that the amount of variability explained by the first two principal components is the same across cohorts but how the interindividual variability is distributed among the lipid and apolipoprotein traits is generation and gender specific. This study documents the role that variance and covariance might play in determining risk of disease for special subgroups of the population at large. It also demonstrates how variances and covariances between risk factors traits characterize life processes of aging and sexual dimorphism. This study argues that future biometrical genetic and epidemiological studies of coronary artery disease must take into account age and gender effects on interindividual variability and covariability of risk factors.

Treatment of nephrotic hyperlipoproteinemia with gemfibrozil

Hypercholesterolemia is a known complication of the nephrotic syndrome. Patients with persistent proteinuria and prolonged hypercholesterolemia are probably at increased risk for cardiovascular disease. Until recently there has been no safe and effective treatment for this disorder. The effects of gemfibrozil on plasma lipids and lipoproteins in hypercholesterolemic patients with the nephrotic syndrome were therefore studied. Eleven patients with the nephrotic syndrome were studied in a randomized, double-blind placebo-controlled trial with six-week treatment periods. Gemfibrozil 600 mg or placebo was administered twice a day. There was a third unblinded period in which seven patients received gemfibrozil plus the bile acid-binding resin, colestipol, 10 grams twice a day. Gemfibrozil treatment produced a marked reduction in plasma triglyceride (51%, P = 0.001) and a 15% decrease in plasma total cholesterol (P = 0.003). Low density lipoprotein cholesterol decreased 13% (P greater than 0.05), high density lipoprotein cholesterol increased 18% (P = 0.006) and the ratio of low density lipoprotein to high density lipoprotein cholesterol fell 26% (P = 0.01). Apolipoprotein A-l was unchanged while apolipoprotein B decreased 26% (P = 0.006). Four patients were unable to complete period 3 because of gastrointestinal symptoms. The remaining patients had further improvement in plasma lipids and lipoproteins with the combined therapy: total cholesterol further decreased 26%, triglycerides decreased 17%, low-density lipoprotein cholesterol decreased 36%, high-density lipoprotein to high-density lipoprotein cholesterol fell 33%. Gemfibrozil improved lipid and lipoprotein cardiovascular risk factors without major toxicity. Persistent elevations in total plasma and low-density lipoprotein cholesterol during gemfibrozil treatment, however, indicate the need for individualized drug therapy.

The association of increased levels of intermediate-density lipoproteins with smoking and with coronary artery disease

Studies were undertaken to determine whether there is an association between elevated levels of intermediate-density lipoproteins (IDL) (Sf 12-60 lipoproteins) and coronary artery disease. Forty-five to sixty-five-year-old men with objectively documented coronary artery disease (n = 58) who were free of known risk factors (diabetes, hypertension, obesity, hyperuricemia, and hypercholesterolemia) were compared with similar men who were free of coronary artery disease (n = 52). Smokers could not be excluded. The coronary artery disease group had a higher rate of cigarette smoking (NS, due to large variations); higher concentrations of triglycerides in their plasma (p = .003) and higher levels of very low-density lipoproteins (VLDL) (p = .007), IDL (p = .016), and low-density lipoproteins (LDL) (p = .04); as well as somewhat lower levels of high-density lipoprotein (HDL) cholesterol (p = .04). Chi-squared analysis demonstrated a strong association between coronary artery disease and IDL apolipoprotein (apo) B (p = .006), coronary artery disease and IDL triglyceride (p = .032), and coronary artery disease and IDL apo B times IDL triglyceride (p = .006) when the top quintile of the population was compared with the bottom quintile for each of these variables. Stepwise logistic regression analysis resulted in rejection of an association between coronary artery disease and HDL cholesterol, plasma triglyceride, VLDL triglyceride, or LDL triglyceride. However, it did show that coronary artery disease was most strongly associated with smoking and that the second strongest association was with IDL.(ABSTRACT TRUNCATED AT 250 WORDS)