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G van Poppel

Publications and source records attributed to G van Poppel.

At least 37 records · Page 2Linked to original sources
PubMed1997

Lipoprotein oxidation, antioxidants and cardiovascular risk: epidemiologic evidence.

This review summarizes the scientific evidence for a possible role of antioxidants in the prevention of coronary heart disease (CHD). Dietary antioxidants include vitamin E, vitamin C and beta-carotene, whereas selenium is an integral part of the antioxidant enzyme glutathione peroxidase. Experimental studies suggest that the oxidation of low-density lipoproteins (LDL) in the vessel wall plays an important role in the development of atherosclerotic lesions. The resistance of LDL to oxidation is increased by antioxidant supplementation, at least in vitro. Epidemiological studies have not demonstrated unequivocally that a high intake of antioxidants leads to a decreased risk of CHD. Studies on dietary intake and serum levels of antioxidants do point in the direction of a preventive effect of antioxidants, whereas the results of intervention studies are less conclusive. Beta-carotene supplementation is not associated with any decrease in CHD; high doses of vitamin E may be beneficial, but results from large trials are to be awaited. General preventive measures based on antioxidant supplementation are not yet justifiable.

Animals↗
PubMed1997

The effect of beta-carotene on sputum cytology in smokers: a preliminary study.

The use of biomarkers is a promising approach to the study of human cancer risk. Bronchial metaplasia in sputum cytology may be a marker for potential premalignancy that can be used for population studies. We recently performed a randomized, controlled trial in smokers on the effect of 14 weeks beta-carotene (20mg/day) on markers for DNA damage. We now have evaluated the application of sputum cytology in this study and performed a preliminary evaluation of the effect of beta-carotene. Of the 150 potential participants in this trial 75 were not eligible because they failed to produce sputum samples (n = 29), or because samples were unsatisfactory (n = 46). The eligible group was older (41 vs 37 years) and had smoked longer (23 vs 19 years), but had similar cigarette consumption (mean 21/day) and plasma cotinine levels. Metaplasia was graded in seven categories. Only 11 subjects (15%) showed minor or mild atypia on study entry. Agreement within and between observers was 95% within the same or an adjacent category. We observed no significant correlation between before and after treatment final metaplasia scores in either the beta-carotene (Spearman R = 0.18, P = 0.3) or placebo group (Spearman R = 0.17, P = 0.3). Initial metaplasia scores were somewhat higher in the beta-carotene group (n = 33) than in the placebo group (n = 42) (P = 0.06). Final metaplasia scores were similar in both groups (P = 0.69), and there was no decrease in metaplasia scores in the beta-carotene group (P = 0.75). This study indicates that sputum cytology may not yet be a readily applicable marker in studies of a healthy asymptomatic population, because many smokers do not spontaneously produce sputum, more severe lesions are rare, and variation over time in the minor lesions in large. Therefore, the preliminary evidence that beta-carotene has no influence should be interpreted with care.

Adult↗
PubMed1996

Trans unsaturated fatty acids in plasma phospholipids and coronary heart disease: a case-control study.

A high intake of trans fatty acids (TFAs) has been shown to have an undesirable effect on serum lipid profiles and lipoprotein(a) (Lpa)) levels and may thereby increase the risk for coronary heart disease (CHD). We performed a study in CHD patients, and measured the TFA concentration of the plasma phospholipid fraction. Comparison was made between a case group with angiographically documented severe CHD (> 80% stenosis in one coronary vessel, n = 83) and a control group of patients who had just minor stenosis on the coronary angiography (< 50% stenosis in all three major vessels, n = 78): All subjects were under 68 years of age and were prestratified on age, gender and smoking habits. The two groups were comparable according to the prestratification criteria, body mass index, blood pressure, number of cigarettes smoked and total fat intake. Controls had higher plasma HDL levels (P < 0.001) and lower, albeit not significantly lower, (P = 0.07) plasma LDL levels. No significant correlations were found between percentages of TFAs in plasma phospholipids and plasma LDL or HDL cholesterol levels. Of the major fatty acid classes, only the percentage of saturated fatty acids was significantly higher in cases (46.2 +/- 0.92%) than in controls (45.8 +/- 1.07% (means +/- S.D.)). The difference in total TFA content between cases and controls (0.32 +/- 0.02% versus 0.35 +/- 0.02%) was -0.03% (P = 0.2). For the specific TFAs C16:1n-7tr, C18:1n-9tr and C18: 2n-6tr, just minor differences were found. Adjusted odds ratios for tertiles of TFA percentages were 0.56 (0.25-1.23) and 0.76 (0.36-1.61) for the highest middle tertile compared to the lowest. These findings do not support an association between TFA intake and risk for coronary heart disease.

Aged↗
PubMed1996

Consumption of black tea and cancer risk: a prospective cohort study.

BACKGROUND: Tea is one of the most frequently consumed beverages in the world. Antioxidant polyphenol compounds (such as catechins and flavonols) are abundantly present in both green and black teas and have been observed to have anticarcinogenic properties in cell and animal model studies. In black tea, however, most of the catechins have been oxidized to forms that may have reduced anticarcinogenic properties. Despite indications from experimental studies that tea may protect against cancer, epidemiologic evidence has been inconclusive. PURPOSE: The association between black tea consumption and the subsequent risk of stomach, colorectal, lung, and breast cancers was investigated in The Netherlands Cohort Study on Diet and Cancer among 58,279 men and 62,573 women aged 55-69 years. METHODS: Subjects in the cohort completed a self-administered questionnaire on dietary habits and other risk factors for cancer at base line in 1986. Follow-up for cancer was done by means of computerized record linkage with all nine regional cancer registries in The Netherlands and the national pathology database. During 4.3 years of follow-up, 200, 650, 764, and 650 cases of stomach, colorectal, lung, and breast cancers were diagnosed, respectively. The questionnaire data of case subjects and those of a random subcohort (n = 3500) were used to calculate rate ratios (RRs) of cancer in categories of consumers of black tea compared with nonconsumers. RESULTS: Tea was not used by 13% of the subjects in the cohort, whereas 37%, 34%, and 16% consumed one to two, three to four, and five or more cups of tea per day, respectively. No association was observed between tea consumption and risk of colorectal cancer: The risk among tea drinkers in each consumption category was similar to that among nondrinkers. The RR of breast cancer among consumers of five or more cups of tea per day was 1.3 (95% confidence interval = 0.9-2.0); no dose-response association was observed. In age- and sex-adjusted analyses, consumption of tea was inversely associated with stomach (two-sided P for trend = .147) and lung (two-sided P for trend < .001) cancers. However, tea drinkers appeared to smoke less and to eat more vegetables and fruits than nondrinkers. When smoking and dietary factors were taken into account, tea in itself did not appear to protect against stomach and lung cancers: The RRs in all consumption categories were close to unity. Analysis of the tea and cancer relationship in a subgroup that included subjects in the lowest two quintiles of consumption of vegetables and fruits also failed to reveal a protective effect of tea consumption on the risk of three cancer types studied (colorectal, lung, and breast cancers). CONCLUSIONS: This investigation does not support the hypothesis that consumption of black tea protects against four of the major cancers in humans; a cancer-enhancing effect was not evident, either.

Aged↗
PubMed1996

Autoantibodies against MDA-LDL in subjects with severe and minor atherosclerosis and healthy population controls.

Autoantibodies against oxidized low-density lipoprotein (LDL) have been reported to be associated with atherosclerosis. However, data are not consistent. We compared the titres of autoantibodies to malondialdehyde-modified LDL in three groups, a case group with angiographically documented severe coronary stenosis (> 80% stenosis in at least 1 vessel, n = 47), a hospital control group with minor stenosis on the coronary angiography (< 50% stenosis in all three major vessels, n = 47) and a healthy population control group with no history of coronary heart disease (n = 49). Age ranged from 26 to 68 years. Subjects were frequency-matched for gender distribution and storage time of the blood samples. No relevant differences in autoantibody titre between case and control groups were found. The mean autoantibody titres (+/- S.D.) were 1.44 +/- 1.82, 1.46 +/- 1.40 and 1.62 +/- 1.95 for cases, hospital controls and population controls, respectively. No correlations were found between autoantibody titre and age, number of cigarettes smoked and LDL or total cholesterol. Autoantibody titres were correlated with body mass index (r = 0.2) and high-density lipoprotein (HDL) (r = -0.2). Odds ratios (OR) were calculated by tertiles of autoantibody titres for the hospital control group and the population control group, respectively. Age-adjusted OR (95% confidence interval) for medium and high compared to low autoantibody titre were 0.76 (0.27-2.14) and 1.09 (0.39-2.95) for the comparison between cases and hospital controls and 1.09 (0.39-3.07) and 0.90 (0.32-2.56) for the comparison between cases and population controls. Adjustment for gender, body mass index, smoking habits and HDL yielded essentially the same results. This study does not support an association between autoantibody titres to oxidized LDL and the extent of coronary stenosis.

Adult↗
PubMed1996

Do dietary phytochemicals with cytochrome P-450 enzyme-inducing activity increase high-density-lipoprotein concentrations in humans?

Low plasma concentrations of high-density lipoprotein (HDL) are associated with increased risk of coronary heart disease. Several drugs that induce the microsomal cytochrome P-450-dependent enzyme system in liver and intestine, the sites of HDL apolipoprotein (apo) A-I and A-II synthesis, raise plasma HDL concentrations in humans. To test the hypothesis that phytochemicals with cytochrome P-450-inducing activity may also increase plasma HDL concentrations, two controlled dietary trials were undertaken in healthy nonsmoking males aged 20-28 y. One study examined the effect of replacing 300 g glucosinolate-free vegetables with 300 g Brussels sprouts/d for 3 wk. The other study examined the effects of 150 mg eugenol/d in capsule form, using a double-blind, placebo-controlled crossover design. There were no significant increases in plasma apo A-I, apo A-II, HDL cholesterol, or HDL phospholipids. These results suggest that dietary phytochemicals that induce members of the cytochrome P-450 system do not necessarily raise plasma HDL concentrations in humans, but do not exclude the possibility that some phytochemicals may have such an effect.

Adult↗
PubMed1996

Epidemiological evidence for beta-carotene in prevention of cancer and cardiovascular disease.

OBJECTIVE AND CONCLUSIONS: This article gives an overview of observational and experimental epidemiological studies relating beta-carotene to risk of cancer and cardiovascular disease. Observational epidemiological studies have consistently shown that a diet rich in beta-carotene-rich fruits and vegetables or high blood levels of beta-carotene are associated with a reduced risk of cancer at a number of common sites, such as lung and stomach. For other cancer sites, such as prostate and breast, the observational evidence is not very consistent or absent altogether. For cardiovascular disease, observational studies are less numerous but do point to a protective effect of high beta-carotene intake. The associations from observational epidemiology may indeed be ascribed to beta-carotene, since a number of plausible preventive mechanisms have been demonstrated for cancer as well as cardiovascular disease. However, observational epidemiology cannot resolve the question whether other constituents from fruits and vegetables or other factors may explain the findings from the case-control and cohort studies. The results of intervention studies undertaken so far are disappointing and do not indicate a preventive potential for beta-carotene. Further intervention trials with longer follow-up may be needed to elucidate whether beta-carotene is protective against certain forms of cancer and against cardiovascular disease.

Cardiovascular Diseases↗
PubMed1996

Epidemiological studies on brassica vegetables and cancer risk.

This paper gives an overview of the epidemiological data concerning the cancer-preventive effect of brassica vegetables, including cabbage, kale, broccoli, Brussels sprouts, and cauliflower. The protective effect of brassicas against cancer may be due to their relatively high content of glucosinolates. Certain hydrolysis products of glucosinolates have shown anticarcinogenic properties. The results of 7 cohort studies and 87 case-control studies on the association between brassica consumption and cancer risk are summarized. The cohort studies showed inverse associations between the consumption of cabbage, cauliflower, and broccoli and risk of lung cancer; between the consumption of brassicas and risk of stomach cancer; between broccoli consumption and risk of all cancers taken together; and between brassica consumption and the occurrence of second primary cancers. Of the case-control studies, 67% showed an inverse association between consumption of total brassica vegetables and risk of cancer at various sites. For cabbage, broccoli, cauliflower, and Brussels sprouts, these percentages were 70, 56, 67, and 29%, respectively. Although the measured effects might have been distorted by various types of bias, it is concluded that a high consumption of brassica vegetables is associated with a decreased risk of cancer. This association appears to be most consistent for lung, stomach, colon, and rectal cancer and least consistent for prostatic, endometrial, and ovarian cancer. It is not yet possible to resolve whether associations are to be attributed to brassica vegetables per se or to vegetables in general. Further epidemiological research should separate the anticarcinogenic effect of brassica vegetables from the effect of vegetables in general.

Anticarcinogenic Agents↗
PubMed1995

Epidemiologic evidence for beta-carotene and cancer prevention.

In 1981 it was hypothesized that a high dietary intake of beta-carotene might reduce human cancer rates. Since then, several observational epidemiologic studies have addressed this topic. The results of both case-control and cohort studies show a remarkable consistency for the association of increased lung cancer risk with low amounts of dietary beta-carotene or low plasma beta-carotene concentrations. For stomach cancer, the evidence is also consistent, although the number of studies is more modest. For breast and prostate cancer, the studies indicate no consistent association of plasma or dietary beta-carotene and reduced cancer risk. For colorectal cancer, the effect will be moderate, if existent. For several other cancer sites, the numbers of cases in prospective studies are often small, implying that only strong associations can be detected. For some of these sites, results from retrospective studies are promising. The epidemiologic studies should be carefully interpreted because dietary habits may be misclassified and smoking may reduce plasma beta-carotene concentrations. Observational epidemiology cannot definitively resolve whether associations are indeed due to beta-carotene, or to other components of fruit and vegetables that are rich in beta-carotene. However, overall results are promising and several plausible cancer preventive mechanisms have been reported for beta-carotene. The ongoing human intervention studies will provide more answers regarding cancer prevention by beta-carotene but may need long follow-ups to be conclusive.

Antioxidants↗
PubMed1995

Effects of consumption of brussels sprouts on plasma and urinary glutathione S-transferase class-alpha and -pi in humans.

The effects of consumption of glucosinolate-containing Brussels sprouts on plasma and urinary glutathione S-transferase (GST) class-alpha and -pi were investigated. Five male and five female non-smoking volunteers were randomly assigned to two groups in a crossover design. Five persons started on a glucosinolate-free diet (control period), while the other five consumed 300 g of cooked Brussels sprouts per day, at the expense of 300 g of glucosinolate-free vegetables (sprouts period). Dietary regimes were reversed after 1 week. GST levels were measured by enzyme-linked immunoabsorbent assay. At the end of the sprouts period, a significant increase (1.5-fold) in plasma class-alpha GST levels was observed in males but not in females (control versus sprouts, paired t-test; P-values 0.031 and 0.317 respectively), while plasma GST class-pi levels as well as secretion of urinary GST class-alpha and -pi levels remained unchanged. We conclude that (i) increased plasma GST class-alpha levels in males originate probably solely from the liver and not from stomach, intestine or kidney; (ii) males are more susceptible for induction of hepatic GSTs than females; and (iii) urinary GST concentration seems less useful as a biomarker for hepatic GST induction.

Adult↗
PubMed1995

Reduction of oxidative DNA-damage in humans by brussels sprouts.

The effect of consumption of Brussels sprouts on levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in human urine was investigated in 10 healthy, male, non-smoking volunteers. Following a 3 week run-in period, five volunteers continued on a diet free of cruciferous vegetables for a subsequent 3 week intervention period (control group), while the other five (sprouts group) consumed 300 g of cooked Brussels sprouts per day, at the expense of 300 g of a glucosinolate-free vegetable. Levels of 8-oxodG in 24 h urine samples were measured by HPLC. In the control group there was no difference between the two periods in levels of 8-oxodG (P = 0.72). In contrast, in the sprouts group the levels of 8-oxodG were decreased by 28% during the intervention period (P = 0.039). The present findings support the results of epidemiologic studies that consumption of cruciferous vegetables may result in a decreased cancer risk.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

Effects of consumption of Brussels sprouts on intestinal and lymphocytic glutathione S-transferases in humans.

A high intake of glucosinolate-containing cruciferous vegetables, such as Brussels sprouts (Brassica oleraceae), has been linked to a decreased cancer risk, but the underlying mechanism is still unclear. The aim of this study was to reveal possible modulating effects of consumption of Brussels sprouts on duodenal, rectal and lymphocytic (i) glutathione S-transferase (GST) enzyme activity, (ii) GST isozyme levels and (iii) glutathione (GSH) content. Ten healthy non-smoking volunteers were randomly assigned to two groups in a cross-over design. Five persons started on a glucosinolate-free diet (control period), while the other five consumed 300 g/day cooked Brussels sprouts, at the expense of 300 g glucosinolate-free vegetables (sprouts period). After 7 days the regimen was changed for a further week. At the end of both periods blood samples and duodenal and rectal biopsies were taken. Mean GST activity showed marked differences between duodenal, rectal and lymphocytic cytosols (737 +/- 54, 321 +/- 29 and 154 +/- 14 nmol/min/mg protein respectively), but was uninfluenced by the dietary regimen. Isozyme distribution varied greatly between the tissues. In duodenum GST-alpha, -pi, and -mu isozymes were expressed in considerable amounts (8441 +/- 1365, 3002 +/- 223 and 536 +/- 248 ng/mg protein respectively). Rectal biopsies also contained above three GST classes, but here GST-pi was the most pronounced expressed isozyme (2849 +/- 246) followed by GST-mu (495 +/- 242), while GST-alpha was only present in minor quantities (149 +/- 31). In lymphocytes only GST-pi (755 +/- 96) and GST-mu (83 +/- 54) could be detected. As a result of the dietary regimen rectal GST-alpha and -pi levels were slightly increased at the end of the sprouts period, by 30 and 15% respectively. GSH contents were uninfluenced by the dietary regimen. In conclusion, consumption of glucosinolate-containing Brussels sprouts for 1 week results in increased rectal GST-alpha and -pi isozyme levels. We hypothesize that these enhanced detoxification enzyme levels may partly explain the epidemiological association between a high intake of glucosinolates (cruciferous vegetables) and a decreased risk of colorectal cancer.

Adult↗
PubMed1995

No influence of beta-carotene on haemostatic balance in healthy male smokers.

A high intake of beta-carotene has been associated with a decreased risk for cardiovascular disease. To evaluate whether beta-carotene may exert a protective effect through an impact on haemostasis a randomized, placebo-controlled trial was conducted in male smokers (n = 149) using 20 mg/day beta-carotene for 14 weeks. For comparisons, haemostatic indicators were also evaluated in a group of non-smokers (n = 54). Smokers compared with non-smokers had higher fibrinogen (3.5 vs. 3.1 mg/ml, P < 0.01), higher tissue-type plasminogen activator antigen (t-PA; 8.03 vs. 6.60 ng/ml, P < 0.05), lower levels of soluble fibrin (3.40 vs. 5.16 micrograms/ml, P < 0.01) and slightly higher plasma levels of total degradation products of fibrin and fibrinogen (TDP; 47.0 vs. 41.3 ng/ml, P = 0.21). Within the group of smokers, there were no initial differences in the four haemostatic indicators between the placebo (n = 77) and beta-carotene (n = 72) groups, and in both groups there was virtually no change in the indicators during the 14 weeks treatment. It is concluded that the different haemostatic profile in smokers may partly explain their increased risk for cardiovascular disease. beta-Carotene has no influence on the measured haemostatic indicators, and cardiovascular protection for beta-carotene via a beneficial effect on haemostasis seems improbable.

Adult↗
PubMed1995

Supplementation with low doses of vitamin E protects LDL from lipid peroxidation in men and women.

There is accumulating evidence that oxidative modification of LDL is an important step in the process of atherogenesis and that antioxidants may protect LDL from oxidation. We and others have previously shown that ingestion of pharmacological doses of the antioxidant D,L-alpha-tocopherol (vitamin E), far above the recommended daily intake (ie, 12 to 15 IU/d for adults), increases the oxidation resistance of LDL. In this study, we ascertained the minimal supplementary dose of vitamin E necessary to protect LDL against oxidation in vitro. Twenty healthy volunteers (10 men and 10 women, aged 21 to 31 years) ingested consecutively 25, 50, 100, 200, 400, and 800 IU/d, D,L-alpha-tocopherol acetate during six 2-week periods. No changes were observed in LDL triglyceride content, fatty acid composition of LDL, or LDL size during the intervention. Concentrations of alpha-tocopherol in plasma and LDL were both 1.2 times the baseline values after the first period (25 IU/d) and 2.6 and 2.2 times, respectively, after the last period (800 IU/d). There was a linear increase in LDL alpha-tocopherol levels up to an intake of 800 IU/d (r = .79, P < .0001) and a good correlation between alpha-tocopherol in plasma and LDL (r = .66, P < .0001). Simultaneously, the resistance of LDL to oxidation was elevated dose-dependently (+28% after the last period) and differed significantly from the baseline resistance time even after ingestion of only 25 IU/d.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Plasma cotinine: stability in smokers and validation of self-reported smoke exposure in nonsmokers.

The stability of plasma cotinine was studied in smokers and the validity of a brief questionnaire on environmental tobacco smoke (ETS) exposure was assessed in nonsmokers. The correlation between two cotinine levels measured 14 weeks apart was 0.81 in smokers (n = 148). A single measurement will classify 95% of all subjects within 30% of their habitual plasma cotinine level. Plasma cotinine was higher in ETS-exposed nonsmokers (n = 50) than in ETS-unexposed nonsmokers (n = 55; 1.6 ng/ml vs 0.6 ng/ml; P < 0.0001), but there was a substantial part of intersubject overlap. The sensitivity and specificity with respect to self-reported smoke exposure were 56 and 89%, respectively. This study shows that a single plasma cotinine determination gives a good impression of cotinine levels. It is dubious if a brief questionnaire about hours of passive smoke exposure in nonsmokers is valid to distinguish ETS-exposed from ETS-unexposed nonsmokers.

Adult↗
PubMed1994

No effect of beta-carotene supplementation on plasma lipoproteins in healthy smokers.

A high intake of beta-carotene has been associated with a decreased risk for cardiovascular disease. To evaluate whether beta-carotene intake may exert a protective effect through an impact on lipoprotein metabolism, we conducted a randomized, double-blind trial in healthy, male cigarette smokers. Total cholesterol, high-density-lipoprotein (HDL) cholesterol, apolipoprotein A-I (apo) A-I, apo B-100, and lipoprotein(a) were measured before and after 14 wk of treatment with beta-carotene (20 mg/d, n = 25) or placebo (n = 25). The beta-carotene and placebo groups were comparable with respect to all initial characteristics, but initial apo B-100 was significantly higher in the beta-carotene group (1.23 vs 1.44 g/L). During the intervention, plasma concentrations of beta-carotene increased 15-fold in the treatment group. Mean concentrations of total and HDL cholesterol, lipoprotein(a), apo A-I, and apo B-100 did not change significantly in either group. We conclude that a 20 mg beta-carotene supplement/d does not influence plasma lipoproteins in healthy male smokers.

Adult↗
PubMed1994

Consumption of Brussels sprouts results in elevated alpha-class glutathione S-transferase levels in human blood plasma.

The effect of consumption of glucosinolate-containing Brussels sprouts on alpha-class glutathione S-transferase levels in human blood plasma was investigated in 10 healthy, male, non-smoking volunteers. Following a 3-week run-in period, five volunteers continued on a glucosinolate-free diet during a subsequent 3-week intervention period (control group), while the other five (sprouts group) consumed 300 g of cooked Brussels sprouts per day, at the expense of 300 g of a glucosinolate-free vegetable. alpha-Class glutathione S-transferases were measured by radioimmunoassay. In the control group, similar alpha-class glutathione S-transferase levels were observed in both periods (P = 0.814), while in the sprouts group the alpha-class glutathione S-transferase levels were elevated by a factor of 1.4 (P = 0.002). We hypothesize that the elevated alpha-class GST levels in plasma reflect GST-alpha induction in tissues such as liver and small intestine under non-toxic conditions. The present findings indicate that alpha-class GST levels in plasma may be used as a biomarker for alpha-class GST levels in tissues. In addition, they support the results of epidemiologic studies that consumption of cruciferous vegetables may result in a decreased cancer risk.

Adult↗