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F J Kok

Publications and source records attributed to F J Kok.

At least 37 records · Page 2Linked to original sources
PubMed2001

Effect of glutathione S-transferase M1 genotype on progression of atherosclerosis in lifelong male smokers.

We hypothesize that smokers with the null genotype for GSTM1 (GSTM1-0), who thus lack the detoxification enzyme glutathione S-transferase mu-1, develop atherosclerosis at an increased rate compared to smokers with the positive genotype (GSTM1-1). We used data from a 2-year randomized placebo-controlled trial on the effect of vitamin E on atherosclerosis among 189 male smokers. Progression of atherosclerosis was measured by 2-year change of the common carotid intima media thickness (CCA-IMT) as measured by B-mode ultrasonography. The frequency of GSTM1-0 genotype was 0.5 in both the placebo and the vitamin E group. Smokers with GSTM1-0 genotype had a tendency to higher baseline CCA-IMT values than those with GSTM1-1 (0.97 versus 0.92 mm, P=0.09). Within the placebo group, more CCA-IMT progression was found for smokers with the GSTM1-0 than for smokers with the GSTM1-1 genotype after adjustment for baseline IMT and major CVD risk factors (0.050 versus -0.002 mm, P=0.046). In the vitamin E group no effect of GSTM1 genotype on atherosclerosis progression was found. Overall, smokers with GSTM1-0 genotype had a higher mean 2-year progression compared to those with GSTM1-1 as shown by a difference in increase of 0.042 mm (95% CI 0.006; 0.078, P=0.02). In conclusion, our data suggest that smokers lacking the detoxifying enzyme GST mu-1 develop progression of atherosclerosis at an increased rate.

Arteriosclerosis↗
PubMed2001

Peanut butter intake, GSTM1 genotype and hepatocellular carcinoma: a case-control study in Sudan.

OBJECTIVE: Hepatocellular carcinoma (HCC) is one of the major cancers in the world. In Sudan the incidence is thought to be high and increasing. This study aims to assess the association between peanut butter intake, as a source of aflatoxins, and the GSTM1 genotype in the etiology of HCC. METHOD: A case control study was conducted among 150 patients and 205 controls from two regions in Sudan. Food habits with special reference to peanut butter consumption, as well as peanut storage systems, have been investigated, as well as confounders such as hepatitis, drinking and smoking habits, and demographic characteristics. GSTM1 genotype was assessed in DNA extracted from blood samples (110 cases, 189 controls). RESULTS: A positive association was observed for highest vs. lowest quartile of peanut butter intake, humid storage system and HCC, with ORs (95% CI) being 3.0 (1.6-5.5) and 1.6 (1.1-2.5) respectively. The positive association with peanut butter intake was essentially limited to subjects with GSTM1 null genotype with OR for highest vs. lowest quartile 16.7 (2.7-105). CONCLUSION: Peanut butter consumption has been identified as a strong risk factor of HCC in a region with endemic aflatoxin contamination in Sudan and was essentially limited to subjects with the GSTM1 null genotype.

Adult↗
PubMed2001

Fruit and vegetables and cardiovascular risk profile: a diet controlled intervention study.

OBJECTIVE: To evaluate the effect of fruit and vegetables consumption on markers of risk for cardiovascular disease. DESIGN: Randomised, diet controlled, parallel study. SUBJECTS: Forty-eight apparently healthy (40--60 y) volunteers with a low usual consumption of fruit and vegetables. Forty-seven of them completed the study. INTERVENTIONS: During 4 weeks 24 volunteers consumed a standardised meal, consisting of 500 g/day fruit and vegetables and 200 ml/day fruit juice ('high' group) and 23 volunteers consumed 100 g/day fruit and vegetables ('low' group) with an energy and fat controlled diet. RESULTS: Final total cholesterol was 0.2 (95% CI -0.5--0.03) mmol/l lower in the high group than in the low group (P>0.05). Final fibrinogen and systolic blood pressure were 0.1 (-0.1--0.4) g/l and 2.8 (-2.6--8.1) mmHg higher in the high group than in the low group (P>0.05), respectively. Also, other final serum lipid concentrations, diastolic blood pressure and other haemostatic factors did not differ between both groups. CONCLUSIONS: This was a small randomised well-controlled dietary intervention trial of short duration with a considerable contrast in fruit and vegetable consumption. No effects on serum lipids, blood pressure and haemostatic variables were observed.

Adult↗
PubMed2001

Physical exercise and/or enriched foods for functional improvement in frail, independently living elderly: a randomized controlled trial.

OBJECTIVE: To examine the effects of an exercise program and an enriched food regimen on physical functioning of frail elderly persons. DESIGN: A 17-week randomized, placebo-controlled trial. SETTING: Community. PARTICIPANTS: One hundred fifty-seven independently living frail elderly (mean age, 78.7 +/- 5.6yr). INTERVENTION: Thirty-nine subjects participated in a twice weekly group exercise designed to improve daily functioning; 39 subjects daily ate foods enriched with vitamins and minerals (at 25%-100% of the recommended daily allowances); 42 subjects exercised and ate enriched foods; and 37 subjects served as controls. Nonexercising groups followed a social program; nonsupplement groups received the same food products without the micronutrients. MAIN OUTCOME MEASURES: Functional performance based on 6 performance tests, physical fitness based on 7 fitness tests, and disabilities based on the self-reported ability to perform 16 daily activities. RESULTS: Performance sum scores were significantly enhanced in trained (+8%) compared with nontrained subjects (-8%) (difference in change: 1.9 points, p < .001, adjusted for baseline scores). Fitness sum scores were significantly enhanced as well (+3% in trained vs -2% in nontrained) (difference in change: 0.9 points, p = .05, adjusted for baseline scores). No exercise effects on the disability score were observed. Consumption of enriched products did not affect performance, fitness, or disability scores. CONCLUSION: Our comprehensive exercise program, designed for widespread applicability, enhanced physical performance and fitness in a population of frail elderly. Daily consumption of micronutrient enriched foods showed no functional benefits within 17 weeks.

Activities of Daily Living↗
PubMed2001

Nutrient-dense foods and exercise in frail elderly: effects on B vitamins, homocysteine, methylmalonic acid, and neuropsychological functioning.

BACKGROUND: Frail elders are at risk of suboptimal micronutrient status, functional decline, and neurologic disorders. The influence of oral multimicronutrients in physiologic doses and of moderately intense physical exercise on homocysteine (Hcy), methylmalonic acid (MMA), and neurologic functioning have not yet been investigated. OBJECTIVE: Our goal was to determine the effects of enriched foods and exercise on blood vitamins, Hcy, MMA, and neuropsychological functioning in the frail. DESIGN: A 17-wk randomized controlled intervention trial was used to study 1) enriched foods plus a social program, 2) regular foods plus exercise, 3) enriched foods plus exercise, and 4) regular foods plus a social program. Enriched foods contained multiple micronutrients (25-100% of the Dutch recommended dietary allowances); exercises focused on strength, coordination, flexibility, and endurance. Vitamin (cobalamin, red blood cell folate, and pyridoxal 5'-phosphate), Hcy, and MMA concentrations were measured and 2 neuropsychological tests were conducted. RESULTS: Vitamin concentrations were higher in the supplemented groups than in the unsupplemented groups (P < 0.001; total n = 130). Compared with baseline, cobalamin in the supplemented groups was increased by 22%, plasma folate by 101%, red blood cell folate by 87%, and pyridoxal 5'-phosphate by 68%. Concentrations in the unsupplemented groups changed by -2%, -6%, 1%, and -13%, respectively. Hcy decreased by 25% and MMA by 30% in the supplemented groups, compared with a small increase in Hcy (2%) and decrease in MMA (9%) in the unsupplemented groups. Exercise did not significantly affect vitamin, Hcy, or MMA concentrations. No significant effect of either intervention was observed on the neuropsychological tests. CONCLUSIONS: The decrease in Hcy and MMA in frail elders confirms a subclinical metabolic deficiency state. Enriched foods containing physiologic amounts of micronutrients have a beneficial effect on these metabolites. No effects of B vitamins on mental health were identified.

Aged↗
PubMed2001

alpha-Linolenic acid intake is not beneficially associated with 10-y risk of coronary artery disease incidence: the Zutphen Elderly Study.

BACKGROUND: Data on the relation between alpha-linolenic acid intake and coronary artery disease (CAD) are limited. Other dietary components appear to modify the reported relation between alpha-linolenic acid intake and CAD. OBJECTIVE: We examined whether dietary alpha-linolenic acid intake was inversely associated with risk of CAD. DESIGN: We prospectively studied 667 men aged 64-84 y from the Zutphen Elderly Study who were free of CAD at baseline. Dietary intake was assessed by using a cross-check dietary history method. RESULTS: During the 10-y follow-up, we documented 98 cases of CAD. After adjustment for age, standard coronary risk factors, and intake of trans fatty acids and other nutrients, alpha-linolenic acid intake was not significantly associated with CAD risk. The relative risk of CAD for the highest compared with the lowest tertile of alpha-linolenic acid intake was 1.68 (95% CI: 0.86, 3.29). alpha-Linolenic acid intake from sources containing trans fatty acids was also nonsignificantly, yet positively, associated with CAD risk. alpha-Linolenic acid intake from foods that did not contain trans fatty acids was not associated with CAD risk, the relative risk of CAD for the highest compared with the lowest tertile was 1.15 (95% CI: 0.63, 2.11). CONCLUSION: We did not observe a beneficial effect of dietary alpha-linolenic acid intake on the risk of 10-y CAD incidence. Investigating this hypothesis was complicated by the association between intakes of alpha-linolenic acid and trans fatty acids. Given the results of current prospective studies, a protective cardiac effect of alpha-linolenic acid is questionable.

Aged↗
PubMed2001

Serum transferrin receptor concentration indicates increased erythropoiesis in Kenyan children with asymptomatic malaria.

BACKGROUND: Serum transferrin receptor concentrations indicate both erythropoietic activity and the deficit of functional iron in the erythron. In contrast with serum ferritin concentrations, serum transferrin receptor concentrations are not or are only marginally influenced by the inflammatory response to infection. OBJECTIVE: We assessed iron status and examined the relation between serum transferrin receptor concentrations and malaria in children aged 2-36 mo who were asymptomatic for malaria. DESIGN: This was a community-based cluster survey (n = 318). RESULTS: Prevalences of malaria, anemia (hemoglobin concentration <110 g/L), iron deficiency (serum ferritin concentration <12 microg/L), and iron deficiency anemia were 18%, 69%, 53%, and 46%, respectively. Malaria was associated with lower mean hemoglobin concentrations (92.7 compared with 104.1 g/L; P = 0.0001) and higher geometric mean serum concentrations of transferrin receptor (11.4 compared with 7.8 mg/L; P = 0.005), ferritin (21.6 compared with 11.9 microg/L; P = 0.05), and C-reactive protein (12.5 compared with 6.8 mg/L; P = 0.004). There was no evidence for an association between serum concentrations of C-reactive protein and transferrin receptor. Children with malaria had higher serum transferrin receptor concentrations than expected for the degree of anemia, even after adjustment for inflammation indicated by serum C-reactive protein concentration quartiles (P = 0.02). CONCLUSIONS: Our findings are consistent with the notion that malaria-induced hemolysis is accompanied by increased erythropoiesis. Serum transferrin receptor concentration is not useful for detecting iron deficiency in individuals with malaria. Individuals with high concentrations of serum C-reactive protein or similar acute phase reactants should be excluded from analysis if serum ferritin concentrations <12 microg/L are to be used to measure iron deficiency in malaria-endemic areas.

Anemia, Iron-Deficiency↗
PubMed2001

Serum carotenoids, alpha-tocopherol and mortality risk in a prospective study among Dutch elderly.

BACKGROUND: Although beta-carotene has shown inverse associations with chronic diseases involving free radical damage in observational epidemiological studies less attention has been paid to five other major carotenoids also showing antioxidant activity in vitro. METHODS: We studied the associations between 7.2-year mortality and serum levels of six carotenoids, and alpha-tocopherol, measured in stored serum, sampled in 1991/1992 during a health survey among 638 independently living elderly subjects aged 65-85 years. Proportional hazards regression was used to estimate hazard ratios of all-cause mortality for the lowest tertiles of serum vitamins with the highest tertiles, adjusting for possible confounding effects. RESULTS: During a follow-up period of 7.2 years 171 elderly died. The adjusted hazard ratios for all-cause mortality for the lowest tertiles of vitamins compared with the highest tertiles were between 1.02 and 1.73. The strongest increase in mortality risk was seen for beta-cryptoxanthin (1.52, 95% CI : 1.00, 2.32), lutein (1.56, 95% CI : 1.05, 2.31) and zeaxanthin (1.32, 95% CI : 0.89, 1.97) and their sum (oxygenated carotenoids: 1.73, 95% CI : 1.12, 2.67). Tests for trend were significant (P < 0.05) for all-cause mortality risk and serum levels of total carotenoids, oxygenated carotenoids and beta-cryptoxanthin. CONCLUSIONS: Our findings suggest that serum levels of individual carotenoids, particularly the oxygenated species are inversely associated with all-cause mortality and should be considered as candidates for further investigations.

Aged↗
PubMed2001

Changes in frequency of premature complexes and heart rate variability related to shift work.

OBJECTIVES: To investigate whether an increased risk of cardiovascular disease might be caused by increased arrhythmogeneity and by unfavourable changes in autonomic cardiac control the changes in the occurrence of premature complexes (PVCs) and in heart rate variability (HRV) were studied in subjects who started to work in shifts. METHODS: 1 Year changes in frequency of PVCs and HRV were measured in 49 shift workers and 22 control subjects working in daytime. All respondents were starting in a new job in integrated circuit or waste incinerator plants. RESULTS: The incidence of PVC increased significantly in shift workers over the 1 year follow up, compared with daytime workers. The frequency of ventricular extrasystoles increased in 48.9% of the shift workers, and in 27.3% of the daytime workers. The Spearman correlation coefficient between the number of nights worked and the change in PVCs was 0.33 (p=0.004). A small non-significant unfavourable change in HRV was found in both the shift and daytime workers. CONCLUSIONS: A change in arrhythmogeneity, but not in cardiac autonomic control, might explain the increased risk of cardiovascular disease in shift workers.

Adult↗
PubMed2001

Role of genetic polymorphism of glutathione-S-transferase T1 and microsomal epoxide hydrolase in aflatoxin-associated hepatocellular carcinoma.

Exposure to aflatoxins is a risk factor for hepatocellular carcinoma (HCC). Aflatoxins occur in peanut butter and are metabolized by genetically polymorphic enzymes such as glutathione-S-transferases encoded by glutathione-S-transferase mu 1 gene (GSTM1) and glutathione-S-transferase theta 1 gene (GSTT1) and microsomal epoxide hydrolase encoded by epoxide hydrolase gene (EPHX). The rate at which aflatoxins become activated or detoxified may depend on polymorphisms in the encoding genes. GSTM1 homozygous deletion was indeed found to modify the association between peanut butter consumption and HCC. In this study, we investigate possible roles of GSTT1 and EPHX polymorphisms in this relationship. From a Sudanese case-control study on HCC, we analyzed data of 112 incident cases and 194 controls. All participants were interviewed using a standardized questionnaire inquiring about social and demographic factors, peanut butter consumption, and other known HCC risk factors. Univariate analysis showed that GSTT1 polymorphism was not associated with HCC, whereas EPHX 113HH and 139HH genotypes increased the risk of HCC (Odds ratio, 3.10; 95% Confidence interval, 1.18-8.12). Adjustment for age and region of origin slightly attenuated this association (Odds ratio, 2.56; 95% Confidence interval, 0.83-7.95). Interestingly, unlike GSTM1, both GSTT1 and EPHX polymorphism did not modify the association between peanut butter consumption and HCC. In conclusion, these epidemiological findings do not suggest significant roles of GSTT1 and EPHX in aflatoxin metabolism, although EPHX polymorphism is possibly related to the increased risk of HCC. Further studies are needed to investigate mechanisms by which the EPHX polymorphism potentially modifies cancer risk.

Adult↗
PubMed2000

Fish consumption and coronary heart disease mortality in Finland, Italy, and The Netherlands.

Fish consumption seems to protect against death from coronary heart disease (CHD). If this association is due to n-3 polyunsaturated fatty acids, especially fatty fish may be responsible for this protective effect. The association between total, lean, and fatty fish consumption and the risk of CHD mortality was examined in 1,088 Finnish, 1,097 Italian, and 553 Dutch men participants in the Seven Countries Study who were aged 50-69 years and free of CHD around 1970. After 20 years of follow-up, 242 (22.2%) men in Finland, 116 (10.6%) men in Italy, and 105 (19.0%) men in the Netherlands had died of CHD. Cox proportional hazards analysis showed no association between total fish consumption and CHD mortality. After adjustments were made for age, body mass index, smoking, energy intake, and relevant dietary variables, the pooled relative risk for the highest quartile of total fish compared with no fish consumption in the three countries was 1.08 (95% confidence interval: 0.76, 1.53). Lean fish consumption also was not associated with CHD mortality in any country. Fatty fish compared with non-fatty-fish consumption was associated with lower CHD mortality; the adjusted, pooled relative risk for fatty fish consumers was 0.66 (95% confidence interval: 0.49, 0.90). These data suggest that especially fatty fish is protective against CHD mortality.

Adult↗
PubMed2000

Occupational determinants of heart rate variability.

OBJECTIVES: Analysis of HRV has been suggested as a way to study the effects of work-related stresses on cardiovascular autonomic regulation. The aim of this study was to evaluate the use of HRV in the investigation of work-related stressors. METHODS: Cross-sectional data from an ongoing cohort study were used to analyse the relationship of the potential workplace stressors of job-strain, noise and shift work, with HRV. Mean HRV values during sleep and work were calculated in 135 24-h EKG recordings. RESULTS: Shift workers displayed significantly decreased SDNNi levels during sleep, compared with those of the daytime workers (adjusted least square mean values: 69.3 and 85.8 ms, respectively, P < 0.05). Compared with the control group reporting low job demands and high work control (mean: 73.2), we found significantly elevated %LF means during work adjusted for sleep in the low demands, low control group (77.9, P < 0.01), high demands, high control group (77.7, P < 0.05) and high demands, low control group (77.7, P < 0.05). Workers reporting a high noise level compared with a low work noise level also displayed an elevated adjusted mean %LF during work (78.0 and 75.3 respectively, P < 0.06). CONCLUSIONS: The finding of a decreased SDNNi level during sleep in shift workers compared with day workers indicated a less favourable cardiovascular autonomic regulation, which may explain in part the excess cardiovascular disease risk in shift workers. The elevated %LF during work in employees exposed to high job strain or high noise levels indicated a direct shift in the autonomic cardiac balance towards sympathetic dominance. We concluded that the analysis of HRV may provide a useful tool in the study of the physiological effects of work-related stresses.

Adult↗
PubMed2000

Smoking characteristics, antioxidant vitamins, and carotid artery wall thickness among life-long smokers.

We studied the associations between the common carotid-intima-media thickness (IMT), as a marker of atherosclerosis, and smoking characteristics and antioxidant vitamins among 158 male life-long cardiovascular disease (CVD)-free smokers. An "increased" carotid IMT was defined as the upper 25%. The prevalence of increased IMT was 2.5 times (odds ratio (OR) = 2.5; 95% CI: 1.1, 5.6) higher among smokers inhaling smoke deeply into the lungs than among moderate and non-inhalers. This association decreased when adjusted for other CVD risk factors. Smokers with an increased carotid IMT did not differ significantly in mean antioxidant vitamin intake and status with the remaining group. However, classical CVD risk factors contributed importantly to increased carotid IMT. In our study, depth of inhalation was the only smoking characteristic associated with carotid IMT although attenuated after adjustment for traditional risk factors for CVD. Furthermore, in these life-long smokers not using any vitamin supplements, no associations were found for antioxidant vitamins.

Aged↗
PubMed2000

Fruits and vegetables in the prevention of cancer and cardiovascular disease.

OBJECTIVE: We quantified the public health benefit of fruits and vegetables on the prevention of cancer and cardiovascular disease (CVD), using currently available human data. DESIGN: We reviewed over 250 observational studies on cancer and CVD. Relative risks (RRs) for high versus low intake of fruits and vegetables were obtained. The preventable proportion of chronic diseases, i.e. the per cent of cases attributable to low consumption of fruits and vegetables, was estimated using three scenarios: best guess, optimistic (using stronger RRs) and conservative (using weaker RRs and eliminating the contribution of smoking and/or drinking). The preventable proportion was calculated for increasing average intake from the current 250 g day(-1) to the recommended 400 g day(-1) among the general Dutch population. RESULTS: It is estimated that in the Netherlands cancer incidence could be reduced by 19% (12,000 cases annually, best guess), ranging from 6% (conservative) to 28% (optimistic). Cardiovascular deaths could be reduced by 16% (8000 deaths annually, best guess), ranging from 6% to 22%. Evidence is most abundant for gastrointestinal cancers, followed by hormone-related cancers, but limited for other sites and CVD. CONCLUSIONS: Increasing consumption of fruits and vegetables carries a large public health potential. Population trials and biological mechanisms should eventually provide scientific proof of their efficacy. The available evidence is sufficient to justify public health education and promotion aimed at a substantial increase in the consumption of fruits and vegetables.

Cardiovascular Diseases↗
PubMed2000

Fruits and vegetables increase plasma carotenoids and vitamins and decrease homocysteine in humans.

Observational epidemiologic studies have shown that a high consumption of fruits and vegetables is associated with a decreased risk of chronic diseases. Little is known about the bioavailability of constituents from vegetables and fruits and the effect of these constituents on markers for disease risk. Currently, the recommendation is to increase intake of a mix of fruits and vegetables ("five a day"). We investigated the effect of this recommendation on plasma carotenoids, vitamins and homocysteine concentrations in a 4-wk dietary controlled, parallel intervention study. Male and female volunteers (n = 47) were allocated randomly to either a daily 500-g fruit and vegetable ("high") diet or a 100-g fruit and vegetable ("low") diet. Analyzed total carotenoid, vitamin C and folate concentrations of the daily high diet were 13.3 mg, 173 mg and 228.1 microg, respectively. The daily low diet contained 2.9 mg carotenoids, 65 mg vitamin C and 131.1 microg folate. Differences in final plasma levels between the high and low group were as follows: lutein, 46% [95% confidence interval (CI) 28-64]; beta-cryptoxanthin, 128% (98-159); lycopene, 22% (8-37); alpha-carotene, 121% (94-149); beta-carotene, 45% (28-62); and vitamin C, 64% (51-77) (P < 0.05). The high group had an 11% (-18 to -4) lower final plasma homocysteine and a 15% (0.8-30) higher plasma folate concentration compared with the low group (P < 0.05). This is the first trial to show that a mix of fruits and vegetables, with a moderate folate content, decreases plasma homocysteine concentrations in humans.

Adult↗
PubMed2000

Immunity in frail elderly: a randomized controlled trial of exercise and enriched foods.

OBJECTIVE: To examine the effects of 17-wk physical exercise and enriched foods on cellular immune response (CIR) in frail elderly. METHODS: A total of 112 independently living, frail elderly men and women (mean age 79.2 +/- 5.9) received: twice weekly comprehensive, moderate intensity, progressive group exercise (group A, N = 26); daily enriched foods (group B, N = 31); both (group C, N = 29); or neither (group D, N = 26). Exercises focused on skills training. Foods were enriched with micronutrients with a high prevalence of deficiency in older people (at 25-100% the RDA). A social program and identical regular foods were offered as a control. CIR was measured by delayed-type hypersensitivity skin test response (DTH) against seven recall antigens expressed as the total number of positive responses and sum of diameters of all positive responses. RESULTS: No independent or interactive effect of enriched foods was observed. Therefore, exercise (groups A + C) was compared with no exercise (groups B + D). Nonexercising subjects showed an average decline of 0.5 responses compared with an unchanged responsiveness among exercising subjects (difference = 0.5, 95% CI: 0.04-0.89, P = 0.03 adjusted for baseline DTH, activity level, and micronutrient status). Nonexercising subjects had a larger decline in the sum of diameters of all positive responses than exercising subjects but the difference did not reach significance (adjusted difference = 2.1 mm, 95% CI:-1.0-4.8). CONCLUSION: Exercise may prevent or slow the age-related decline in immune response. Micronutrient enriched foods showed no effect. As infectious diseases can have debilitating or even fatal consequences for the elderly, prevention of the age-related decline in CIR could significantly improve their quality of life.

Aged↗