Effects of smoking on oral fat tolerance and high density lipoprotein cholesterol

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.

HDL and lifestyle interventions

The main lifestyle interventions to modify serum HDL cholesterol include physical exercise, weight loss with either caloric restriction or specific dietary approaches, and smoking cessation. Moderate alcohol consumption can be permitted in some cases. However, as these interventions exert multiple effects, it is often difficult to discern which is responsible for improvement in HDL outcomes. It is particularly noteworthy that recent data questions the use of HDL cholesterol as a risk factor and therapeutic target since randomised interventions and Mendelian randomisation studies failed to provide evidence for such an approach. Therefore, these current data should be considered when reading and interpreting this review. Further studies are needed to document the effect of lifestyle changes on HDL structure-function and health.

The changes of blood glucose control and lipid profiles after short-term smoking cessation in healthy males

OBJECTIVE

Our aim was to evaluate the changes in blood glucose control and lipid profiles after 2-months of smoking cessation in healthy males.

METHODS

Smoking abstinence was evaluated through self-report and urine cotinine levels. 12 individuals who succeeded in quitting smoking were analyzed. Fasting values of glucose and insulin were used to estimate the β-cell activity and insulin resistance was evaluated using the Homeostasis Model Assessment (HOMA) and Quantitative Insulin Sensitivity Check Index (QUICKI).

RESULTS

The data showed that the subjects had a significant increase in weight, body mass index and fasting plasma glucose levels after smoking cessation. The HOMA-Insulin Resistance and the HOMA β-cell function increased significantly (p=0.005, p=0.047 respectively). The QUICKI showed a significant decrease (p=0.005). In addition, the low-density lipoprotein cholesterol levels decreased significantly (p=0.028); however, changes in the high-density lipoprotein cholesterol, the triglyceride and total cholesterol levels were not significant (p=0.284, p=0.445 respectively).

CONCLUSION

During the initial stage of smoking abstinence, insulin resistance increased and insulin sensitivity decreased due to elevated body weight and fat composition. Therefore, it is important to educate individuals that stop smoking about the necessity of weight control during smoking cessation programs.

Smoking and smoking cessation -- the relationship between cardiovascular disease and lipoprotein metabolism: a review

Cigarette smoking is generally accepted as the most preventable cause of death in the United States today. Individuals who smoke experience a wide range of physiologic side effects that increase the risk of cardiovascular disease (CVD), including insulin resistance, elevated catecholamine levels which contribute to an elevated heart rate and blood pressure, and hypercholesterolemia. The link between hypercholesterolemia and cardiovascular disease has been extensively researched and is undeniable. What is more, this link is strengthened in smokers as cigarette smoking is known to increase total cholesterol (TC), triglycerides (TG), and low-density lipoprotein (LDL), while acting to decrease the cardio-protective high-density lipoprotein (HDL). Alterations in the enzymes that control lipid transport may be a key underlying mechanism contributing to these health destroying effects. This review examines the current literature related to: (1) smoking, lipoproteins, and lipid-related enzymes; (2) the impact of nicotine, carbon monoxide and free radicals on physiologic parameters related to health; and (3) metabolic issues involving smoking cessation and nicotine replacement therapy.

Acute in vivo chylomicron metabolism and postalimentary lipoprotein alterations in normolipidemic male smokers

Increased postprandial lipemia has been stated as one of the mechanisms responsible for atherogenesis in smokers. We measured the postalimentary lipid response and the in vivo intravascular delipidation index of an artificial chylomicron emulsion in healthy adult smokers and controls. The blood was collected in the fasting state immediately after the smokers smoked one cigarette. The lipemia was measured 2, 4, 6 and 8 h postalimentarily in smokers (S, n = 8) and in non-smoking controls (C, n = 8) and the chylomicron metabolism rate was measured 2, 4, 6, 8, 12, 16, 20, 24 and 30 min after the injection of an artificial emulsion to S (n = 10) and to C (n = 10). The lipoproteins were isolated in the fasting period and 4 h after the fatty meal and their chemical composition in cholesterol, triglycerides, phospholipids and protein was determined. Smokers showed an increased lipolysis percentage value (mean +/- S.E.M.) of the artificial chylomicron (39.1 +/- 3.1) compared to controls (26.5 +/- 3.3) and higher levels of HDL(2)-PL: 28.4 +/- 4.3 (S) versus 16.2 +/- 2.0 (C) mg/dl (mean +/- S.E.M.). In conclusion, the oral fat tolerance was not altered in smokers but an upregulation of the rate of metabolism of the TG-rich lipoproteins was elicited immediately after smoking one cigarette.

The effect of smoking on post-heparin lipoprotein and hepatic lipase, cholesteryl ester transfer protein and lecithin:cholesterol acyl transferase activities in human plasma

INTRODUCTION

Smoking is associated with dyslipidaemia, particularly raised plasma triglycerides and reduced high-density lipoprotein (HDL)-cholesterol and a delayed clearance of triglyceride in fat tolerance tests. The aim of this study was to investigate whether these phenomena could be explained by a reduced lipoprotein lipase activity in smokers.

METHODS

A group of 40 healthy individuals [plasma cholesterol 5.07 (SD 0.90) mmol L-1, plasma triglyceride 1.02 (SD 0.39) mmol L-1)] was studied to examine the effects of smoking on plasma enzyme activities, particularly post-heparin lipase activities. The group comprised 20 smokers and 20 non-smokers, who were matched for age, gender and body mass index (BMI).

RESULTS

Post-heparin lipoprotein lipase (LPL) activity [3.89 (SD 1.58) vs. 5.85 (SD 2.30) mumol free fatty acids (FFA) mL-1 h-1, P < 0.005], but not post-heparin hepatic lipase (HL) activity, was reduced in smokers. Plasma cholesteryl ester transfer protein (CETP) activity and lecithin: cholesterol acyl transferase (LCAT) activity were measured in a subgroup of 18 individuals, comprising nine smokers with nine matched non-smokers. There was no difference in CETP activities between two groups, but smokers had a significantly reduced plasma LCAT activity [112 (SD 23) vs. 152 (SD 24) nmol cholesterol mL-1 h-1, P < 0.005]. In both smokers (r=-0.53, P < 0.05) and non-smokers (r=-0.54, P < 0.05), HDL2 concentration was negatively associated with HL activity. In non-smokers, HDL3 concentration was negatively associated with CETP activity (r= -0.77, P < 0.05), whereas in smokers HDL3 concentration was negatively associated with LCAT activity (r= -0.78, P < 0.050).

CONCLUSION

It was shown by direct measurement that the activity of plasma post-heparin LPL is reduced in smokers, independently of age, gender and BMI. It is concluded that this enzyme perturbation associated with smoking may contribute to the development of the atherogenic lipoprotein phenotype seen in smokers.

Poland and United States Collaborative Study on Cardiovascular Epidemiology. A comparison of HDL cholesterol and its subfractions in populations covered by the United States Atherosclerosis Risk in Communities Study and the Pol-MONICA Project

HDL cholesterol (HDL-C) levels are inversely related to coronary heart disease (CHD) risk, and HDL-C distributions vary among countries. Poland is one of the few developed countries in which CHD rates are increasing at the same time that US rates have been falling, but whether these differences are explained by differences in risk factors such as HDL-C has not been determined. To examine this possibility, levels of HDL-C and its subfractions were compared in US and Polish urban and rural men and women aged 45 to 64 years. Age-adjusted HDL-C means were 0.20 mmol/L higher in urban Polish men and 0.37 mmol/L higher in rural Polish men than in their US counterparts (P < .0001); means in urban Polish women were 0.06 mmol/L higher (P < .05) and in rural Polish women 0.09 mmol/L higher (P < .001) than in their US counterparts. Adjustment for age, education, alcohol intake, smoking, BMI, heart rate, and menopause status (in women) had little effect on differences. Means of HDL2 and HDL3 levels showed similar between-country differences, although differences were minimal for HDL2 in urban men and women, and HDL3 means did not differ between rural women. BMI was inversely related to HDL-C and both subfractions in all gender-country-site strata (P < .001), and alcohol was directly related to HDL-C (P < .001) in all strata except Polish women. Cigarette smoking was negatively related to HDL-C and both subfractions in all US samples except HDL2 in urban men, whereas in Polish samples, significant associations were found only in urban women for HDL-C and in rural and urban women for HDL3. Age, heart rate, and education showed inconsistent or no association with HDL-C and its subfractions in either country. This profile of HDL-C and its subfractions in Polish samples contrasts sharply with the opposite trend in CHD mortality rates, which suggests either that other risk factors may account for the trends or that the relationship between HDL-C and CHD may differ between the two countries.

Increased level of hemoglobin A1c, but not impaired insulin sensitivity, found in hypertensive and normotensive smokers

Smoking is associated with an abnormal plasma lipoprotein pattern. Recently, both insulin resistance and normal insulin action have been reported in smokers. In a total of 191 hypertensive and normotensive subjects recruited from a health survey, serum lipoprotein lipids, glucose tolerance (by intravenous glucose tolerance test (IVGTT), insulin secretion, and insulin sensitivity (euglycemic insulin clamp) were compared in the 41 smokers and 150 nonsmokers. Subjects were examined in the morning during a fasting state and after abstinence from smoking for 10 to 12 hours. Smokers showed a higher level of hemoglobin A1c (HbA1c) as compared with nonsmokers, 4.9% versus 4.7% (P < .05). There were no significant differences in fasting glucose, insulin, or insulin-mediated glucose disposal. However, a number of indices of insulin sensitivity tended to show enhanced insulin action among smokers. Only lower glucose and insulin values during the late phase (40 to 90 minutes) of the IVGTT reached statistical significance. Compared with nonsmokers, smokers had an expected higher level of serum triglycerides (2.1 v 1.8 mmol/L, P < .05) and an increased low-density lipoprotein (LDL) to high-density lipoprotein (HDL) cholesterol ratio (4.5 v 3.9, P < .05). These differences between smokers and nonsmokers were similar in both hypertensives and normotensives. In conclusion, smokers examined in the abstinence phase showed no signs of impaired insulin action. Lipoprotein abnormalities and elevated HbA1c may be caused in part by the insulin resistance induced during acute smoking and therefore may be quantitatively related to the time exposed to smoking. The effect on insulin sensitivity appears to be reversible over 10 to 12 hours.

Smoking and plasma lipoproteins in man: effects on low density lipoprotein cholesterol levels and high density lipoprotein subfraction distribution

In a survey of a healthy population (n = 197), LDL cholesterol, plasma triglycerides and VLDL triglycerides were found to be substantially increased and plasma HDL cholesterol decreased in smokers. The lipid-associated atherogenic risk in smokers as assessed by the LDL/HDL ratio was significantly higher [2.89 (SD 1.18, n = 63)] than in non-smokers [2.38 (SD 0.98, n = 86) P < 0.01]. The lower HDL level found in smokers was explained by a lower HDL-2 subfraction as determined by analytical ultracentrifugation. HDL 2b, 2a and 3a, measured by gradient gel electrophoresis, were all lower in the smokers but this was only significant for HDL 2a. Smoking had no effect on Lp(a) levels. HDL cholesterol and HDL-2 were strongly negatively correlated whereas LDL cholesterol and LDL/HDL ratio were strongly positively correlated with the plasma triglyceride concentration. There was a small but significant reduction in plasma CETP activity [non-smokers 49% t/microliter (SD 17, n = 90), smokers 43% t/microliter (SD 17, n = 66) P < 0.05] but CETP activity was not correlated with any measure of HDL in this population. Smoking was found to be an important independent contributor to the variation in plasma triglyceride, HDL, HDL-2 and LDL/HDL ratio. After correcting for sex, age, BMI, alcohol consumption, oral contraceptive use and plasma triglycerides smoking was still found to be significantly associated with HDL and the LDL/HDL ratio. Upon adjustment for covariant factors the mean differences between smokers and non-smokers for HDL cholesterol, HDL-2 and LDL/HDL were 0.15 mM, 16 mg dl-1 and 0.39 respectively. There appeared to be important sex differences in the influence of smoking on plasma lipoproteins. In women the main impact of smoking was on triglyceride levels and they in turn affected LDL and HDL. In contrast, in men, smoking had little impact on triglycerides and affected HDL more directly. We conclude that smoking cigarettes has an important effect on plasma lipoprotein metabolism through multiple mechanisms.

Cigarette smoking and plasma cholesterol

Plasma cholesterol levels were determined for 51,723 participants of community-based cholesterol screenings in 10 United States cities during 1988. Among white adult men and women under the age of 60 without other cardiovascular disease risk factors, a dose-response relationship was found between the number of cigarettes smoked per day and increasing levels of plasma cholesterol. In men aged 18 to 60 years, average plasma cholesterol increased by 0.33 mg/dl for each cigarette smoked (p less than 0.001); in women aged 31 to 50 years, average plasma cholesterol increased by 0.48 mg/dl for each cigarette smoked (p less than 0.001). Plasma cholesterol levels among ex-smokers were found to be similar to those of nonsmokers. No association between cigarette smoking and levels of plasma cholesterol was observed in men and women over age 60. Possible mechanisms for this observed relationship include an antiestrogenic effect of cigarette smoking that makes the observation more noticeable in younger female cohorts, enhanced lipolysis that increases levels of plasma free fatty acids, or differences in dietary intake between smokers and nonsmokers.

Effects of acute smoking and exercise on high-density lipoprotein-cholesterol and subfractions in black female smokers

This study investigated the effects of acute bouts of both exercise and smoking on high-density lipoprotein-cholesterol subfractions, HDL2-C and HDL3-C in black females. During two testing trials, seven subjects were exposed to either acute exercise or smoking. Treadmill exercise was performed at 70% of heart rate reserve for 15 minutes. Blood samples were taken before, immediately after, and 10 minutes after exercise. The smoking trial consisted of subjects smoking two cigarettes followed by 30 minutes of nonsmoking. Blood samples were taken before smoking, after each cigarette, and after two 15-minute intervals of nonsmoking. The exercise protocol resulted in a 10.8% increase in total HDL-C, primarily through an increase in the HDL2-C subfraction. The values returned to baseline within 10 minutes after exercise. Smoking one cigarette decreased total HDL-C by 10%. Neither subfraction was significantly effected by smoking; however, the HDL3-C subfraction was decreased 11% and HDL2-C subfraction was decreased 14.7% from resting values. The maximum reduction in HDL3-C subfraction occurred after the smoking of the first cigarette, while the maximum reduction in the HDL2-C subfraction occurred after the first 15-minute nonsmoking period. Acute cigarette smoking was associated with a decrease in total HDL-C that was maintained through 15 minutes of nonsmoking. It is suggested that the adverse effect on HDL-C by acute smoking is a significant contributor to coronary heart disease (CHD) risk in black females. Results further indicate that low-intensity exercise is capable of transiently increasing the total HDL-C via an increase in the anti-atherogenic HDL2-C subfraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of smokeless tobacco, cigarette smoking, and hypercholesterolemia

The primary purpose of this study was to determine the extent to which regular use of smokeless tobacco is associated with hypercholesterolemia (greater than or equal to 6.2 mmol/L) among 2,840 adult males. The confounding effects of age, education, physical fitness, body fatness, and other tobacco use were also examined. After adjustment, smokeless tobacco users were 2.5 times, heavy smokers were 2 times and mild/moderate smokers were 1.5 times more likely to have hypercholesterolemia than non-users of tobacco. Cigarette smokers did not differ significantly from users of smokeless tobacco regarding hypercholesterolemia. Users of smokeless tobacco were younger and less educated compared to non-users of tobacco, while smokers were less educated and less physically fit.

Cigarette smoking and serum lipid and lipoprotein concentrations: an analysis of published data

To examine the association between cigarette smoking in adults and serum lipid and lipoprotein concentrations the results of 54 published studies were analysed. Overall, smokers had significantly higher serum concentrations of cholesterol (3.0%), triglycerides (9.1%), very low density lipoprotein cholesterol (10.4%), and low density lipoprotein cholesterol (1.7%) and lower serum concentrations of high density lipoprotein cholesterol (-5.7%) and apolipoprotein AI (-4.2%) compared with nonsmokers. Among non-smokers and light, moderate, and heavy smokers a significant dose response effect was present for cholesterol (0, 1.8, 4.3, and 4.5% respectively), triglycerides (0, 10.7, 11.5, and 18.0%), very low density lipoprotein cholesterol (0, 7.2, 44.4, and 39.0%), low density lipoprotein cholesterol (0, -1.1, 1.4, and 11.0%), high density lipoprotein cholesterol (0, -4.6, -6.3, and -8.9%), and apolipoprotein AI (0, -3.7 and -5.7% in non-smokers and light and heavy smokers). These dose response effects may provide new evidence for a causal relation between exposure to cigarette smoke and changes in serum lipid and lipoprotein concentrations whether as a direct result of physiological changes or of dietary changes induced by smoking. Adequate prospective data to estimate the excess risk of coronary artery disease existed only for cholesterol concentration. When that information was combined with data from the present study, and given that smokers as a group face an average overall excess risk of coronary artery disease of 70%, it was estimated that the observed increased serum cholesterol concentration in smokers may account for at least 9% of that excess risk. Furthermore, the dose response effect of smoking on serum cholesterol concentration suggests a gradient of increased absolute risk of coronary artery disease between light and heavy smokers.

Assessment of the effects of alpha- and beta-blockade in hypertensive patients who smoke cigarettes

A 24-week, crossover, comparison study was conducted to observe the effects of alpha-blockade with prazosin and beta-blockade with propranolol on blood pressure and plasma lipoprotein levels in 15 hypertensive cigarette smokers. Before treatment, mean sitting blood pressure was 140/100 mm Hg and rose to 147/105 mm Hg after the patients smoked two cigarettes. Treatment with prazosin and propranolol lowered sitting blood pressure to 127/89 mm Hg and 129/91 mm Hg, respectively (not significant), and did not alter the pressor response to smoking. The total cholesterol level at baseline was 207.3 +/- 11.0 mg/dl. This increased to 210.5 +/- 10.2 mg/dl with propranolol treatment and decreased to 201.0 +/- 11.1 mg/dl with prazosin treatment. The low-density lipoprotein cholesterol level was 132.5 +/- 8.1 mg/dl at baseline, 136.9 +/- 8.3 mg/dl with propranolol treatment, and 129.4 +/- 9.0 mg/dl with prazosin treatment (0.05 less than p less than 0.10 between-group comparison). The data indicated that whereas prazosin and propranolol are equally effective in controlling blood pressure in hypertensive cigarette smokers, effects on plasma lipoproteins also may need to be considered when selecting a first-step antihypertensive agent in this coronary-prone population.

Variation in serum lipid and lipoprotein levels associated with changes in smoking behaviour in non-obese Caucasian males

A population of healthy male caucasians was analysed with respect to lipid and lipoprotein parameters, according to differences in current and previous smoking patterns. High density lipoprotein (HDL) cholesterol, and the HDL2 subfraction were significantly higher in non-smokers compared to current smokers. In ex-smokers, the levels of these 2 parameters increased with the length of time since giving up the habit, until levels were no longer distinguishable from non-smokers. A similar increase was observed for weight, although both triglyceride and very low density lipoprotein (VLDL) levels decreased. Low density lipoprotein (LDL) levels showed no significant variation in any of the comparisons. Lower alcohol consumption in both the ex-smokers, and in the non-smokers may account partially for the changes in triglyceride and VLDL, although the same observation is contrary to the effects observed in both HDL and HDL2.

Effects of short term beta adrenoreceptor blockade on serum lipids and lipoproteins in patients with hypertension or coronary artery disease

The effects of beta adrenoceptor blockade with propranolol or pindolol on serum total cholesterol, low density lipoprotein cholesterol (LDL), high density lipoprotein cholesterol (HDL), and its subfractions HDL2 and HDL3, serum triglyceride, and Intralipid clearance were studied in 17 normolipidaemic, non-diabetic patients with hypertension or angina pectoris. Both pindolol and propranolol had similar effects on fasting serum total and lipoprotein cholesterol concentrations. HDL2 cholesterol concentrations were reduced by 9 +/- 29% and HDL3 cholesterol increased by 11 +/- 16%, but there were no significant changes in total or LDL cholesterol in the combined groups after six weeks' treatment. After 12 weeks' treatment total cholesterol concentrations were reduced by 7 +/- 10% mainly owing to a reduction in the LDL fraction of 9 +/- 15%. Concentrations of HDL2 remained low, 8% less than control values. Serum triglyceride concentrations were increased by both drugs at six weeks but had returned to base values in the pindolol group by the twelfth week. Pindolol, but not propranolol, enhanced the rate of clearance of intravenous Intralipid.