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F J Kok

Publications and source records attributed to F J Kok.

At least 91 records · Page 5Linked to original sources
PubMed1994

Fermented dairy products, dietary calcium and colon cancer: a case-control study in The Netherlands.

To examine whether the consumption of fermented dairy products or the dietary intake of calcium decreases colon cancer risk, a case-control study was conducted in the The Netherlands. Dietary patterns were assessed in detail (for cases before diagnosis or symptoms occurred) using a structured dietary history questionnaire. After adjustment for potential confounding variables, consumption of fermented dairy products, hard cheese and unfermented dairy products was not significantly associated with risk of colon cancer: an odds ratio (OR) of 1.1 was found for individuals consuming more than one serving of fermented dairy products per day as compared to those consuming less than 10% of one serving a day. Adjustment for dietary calcium attenuated the associations. Total dietary calcium was positively but non-significantly associated with colon cancer risk after adjustment for age, gender, urbanization level and total energy intake. Additional adjustment for a positive family history of colorectal cancer, cholecystectomy and energy-adjusted intake of total fat, dietary fibre, vitamin C and alcohol increased the association. No differences were observed between calcium from fermented and from unfermented dairy sources. The observed associations for fermented dairy products and dietary calcium differed between men and women: positive significant associations were observed in men, while in women non-significant inverse associations were found. Our results do not support the hypothesis that an increased intake of commercially available, commonly used fermented dairy products or dietary calcium decreases the risk of colon cancer.

Aged↗
PubMed1994

Calcium, vitamin D, dairy foods, and the occurrence of colorectal adenomas among men and women in two prospective studies.

A high intake of calcium, vitamin D, or specific dairy products is thought to reduce the incidence of colorectal cancer. The association of these nutrients and foods with the occurrence of colorectal adenomas, precursors of cancer, was studied in two large US cohort studies. Cases were patients with a diagnosis of adenomatous polyps of the left colon or rectum (331 men, 1986-1990; 350 women, 1980-1988), and controls were persons with endoscopic findings negative for adenoma (9,159 men and 8,585 women). After adjustment for age, total energy, family history of colorectal cancer, body mass index, alcohol consumption, folate, intake of saturated fat and fiber, indications for endoscopy, and previous endoscopy, total calcium intake was not associated with the risk for adenoma (relative risk (RR), highest vs. lowest quintile of intake: men, 1.13, 95% confidence interval (CI) 0.76-1.66; women, 1.17, 95% CI 0.81-1.69). Total vitamin D intake was unrelated to the risk for adenoma in men (RR = 1.29, 95% CI 0.87-1.93). An inverse nonsignificant association was observed in women in the 1980-1988 analyses (RR = 0.68, 95% CI 0.41-1.13, trend p = 0.09), mainly attributable to the intake of multivitamin supplements, but an analysis of 4-year data (1984-1988) using a more detailed dietary assessment showed no association with vitamin D (RR = 1.04, 95% CI 0.65-1.67). Milk consumption and intake of total fermented dairy products were not related to adenoma risk. In conclusion, the occurrence of colorectal adenoma was neither related to calcium intake nor to milk consumption, whereas vitamin D from supplements but not diet was slightly, but not significantly, inversely associated with risk among women only.

Adenoma↗
PubMed1994

Cardiac Infarction Injury Score predicts cardiovascular mortality in apparently healthy men and women.

OBJECTIVE: The Cardiac Infarction Injury Score (CIIS) is an electrocardiogram classification system that was developed to identify ischaemic heart disease. As well as being of diagnostic value, the CIIS may also be of prognostic value. DESIGN: The prognostic value of the CIIS for mortality of coronary heart disease and cardiovascular disease was assessed in a 28 year follow up study of 3091 apparently healthy middle aged men and women (Dutch Civil Servants Study). RESULTS: The rates of coronary heart disease and cardiovascular disease mortality during the first 15 years of follow up were significantly higher in men and women with a CIIS of > 10 than in those with a CIIS of < or = 0 (rate ratio of coronary heart disease mortality 2.9 (95% confidence interval 1.5 to 5.8) for men and 5.6 (2.0 to 15.5) for women). Coronary heart disease mortality was also higher in men with a CIIS of 1-10 than in men with CIIS of < or = 0. When individuals with major Minnesota code items were excluded, the associations were weaker and no longer statistically significant. CONCLUSION: These results indicate that a high CIIS is a risk indicator for coronary heart disease mortality in the general population. Classification of electrocardiograms by means of the CIIS seems to be equivalent to classification by a combination of Minnesota code items. Because CIIS coding is simpler and can be performed by computer it may be more efficient than the Minnesota code for classifying cardiac injury in epidemiological studies.

Adult↗
PubMed1994

A prospective study of plasma homocyst(e)ine and risk of ischemic stroke.

BACKGROUND AND PURPOSE: Several studies have reported elevated circulating homocyst(e)ine levels in subjects with cerebral atherosclerosis. We assessed prospectively whether high plasma levels of homocyst(e)ine affect risk of ischemic stroke and evaluated whether high blood pressure modifies any such effect. METHODS: The study sample was drawn from the Physicians' Health Study, a randomized, double-blind, placebo-controlled trial of aspirin and beta-carotene in 22,071 US male physicians. A total of 14,916 subjects 40 to 84 years old with no prior history of stroke, transient ischemic attack, or myocardial infarction provided blood samples at baseline and were followed for 5 years, with 99.7% morbidity and 100% mortality follow-up. Using a nested case-control design, we assayed homocyst(e)ine in samples from 109 subjects who subsequently developed ischemic stroke and 427 control subjects. RESULTS: The mean plasma concentration of homocyst(e)ine was slightly higher in subjects with stroke (11.1 +/- 4.0 [+/- SD] nmol/mL) than in control subjects (10.6 +/- 3.4 nmol/mL), but the difference was not statistically significant (P = .12). The crude odds ratio of ischemic stroke for subjects in the upper 20% (> 12.7 nmol/mL) compared with those in the bottom 80% of homocyst(e)ine levels was 1.4 (95% confidence interval, 0.8 to 2.2). The odds ratio was 1.2 (95% confidence interval, 0.7 to 2.0) after controlling for several risk factors and other potential confounders. In subgroup analyses, elevated homocyst(e)ine levels appeared to be more strongly predictive of ischemic stroke in normotensive subjects and in men 60 years or younger. Although not statistically significant, in these subgroups increases in risks of 100% and 70%, respectively, were observed for men in the upper 20% of homocyst(e)ine values. CONCLUSIONS: In this study, the data were compatible with a small but nonsignificant association between elevated plasma homocyst(e)ine and risk of ischemic stroke. However, since the sample size is small and the confidence intervals are wide, either no association or a moderate increase in risk cannot be excluded, particularly in subgroups otherwise at low risk, eg, younger men and those with normal blood pressure.

Adult↗
PubMed1994

Antioxidants and coronary heart disease.

This review briefly summarizes the scientific evidence for a possible role of antioxidants in the prevention of coronary heart disease (CHD). Antioxidants in our diet include vitamins E, C, and beta-carotene, whereas selenium is an integral part of the antioxidant enzyme glutathione peroxidase (GSHPx). Experimental evidence suggests that free-radical damage and antioxidant defence may play an important role in the development of coronary heart disease. Epidemiological studies have produced some intriguing results, but have not indicated unequivocally that a high intake of antioxidants leads to a decreased cardiovascular disease risk. We conclude that the antioxidant atherosclerosis hypothesis is promising, but that the results of long-term intervention studies are still to be awaited. Preventive action based on antioxidant supplementation is therefore not justifiable as yet. Nevertheless, the findings so far certainly do support the recommendations for a varied diet rich in vegetables and fruit.

Animals↗
PubMed1993

Antioxidants in adipose tissue and risk of myocardial infarction: the EURAMIC Study.

Laboratory and epidemiological studies suggest that the antioxidants, vitamin E and beta-carotene, protect against coronary heart disease. In a European multicentre case-control study alpha-tocopherol and beta-carotene concentrations were measured in adipose-tissue samples collected in 1991-92 from 683 people with acute myocardial infarction and 727 controls. Mean adipose-tissue beta-carotene concentration was 0.35 microgram/g in cases and 0.42 in controls, with age-adjusted and centre-adjusted mean difference 0.07 microgram/g (95% confidence interval [CI] 0.04-0.10). Mean alpha-tocopherol concentrations were 193 micrograms/g and 192 micrograms/g for cases and controls, respectively. The age-adjusted and centre-adjusted odds ratio for risk of myocardial infarction in the lowest quintile of beta-carotene as compared with the highest was 2.62 (95% CI 1.79-3.83). Additional control for body-mass index and smoking reduced the odds ratio to 1.78 (95% CI 1.17-2.71); other established risk factors did not substantially alter this ratio. The increased risk was mainly confined to current smokers: the multivariate odds ratio in the lowest beta-carotene quintile in smokers was 2.39 (95% CI 1.35-4.25), whereas it was 1.07 for people who had never smoked. A low alpha-tocopherol concentration was not associated with risk of myocardial infarction. Our results support the hypothesis that high beta-carotene concentrations within the normal range reduce the risk of a first myocardial infarction. The findings for alpha-tocopherol are compatible with previous observations of reduced risk among vitamin E supplement users only. The consumption of beta-carotene-rich foods such as carrots and green-leaf vegetables may reduce the risk of myocardial infarction.

Adipose Tissue↗
PubMed1993

Risk ratio and rate ratio estimation in case-cohort designs: hypertension and cardiovascular mortality.

Multivariate analysis in case-base designs depends on approximate methods. In the present study, new pseudo-likelihood methods are developed for this design. With these methods, the case-cohort risk ratio and rate ratio as well as their standard errors are easily estimated using logistic regression and Poisson regression, respectively. This is illustrated by the association between hypertension and cardiovascular mortality in a cohort, estimated by case-cohort analysis, using samples of several sizes. The estimates are compared with those obtaining in full-cohort and nested case-control designs. The results indicate that these methods, which require nothing but widely available computer software, are valid. The case-cohort design, therefore, is a good, sometimes even advantageous alternative to the nested case-control design, in studying a disease that is not very rare. Application of the risk ratio method to the full cohort, using a 'sample' of 100 per cent follows logically; whenever the true risk ratio is desired instead of the odds ratio, a multivariate model for its estimation is therefore available.

Adult↗
PubMed1993

Inverse association between serum total cholesterol and cancer mortality in Dutch civil servants.

The association between serum total cholesterol and cancer mortality was investigated in a 28-year follow-up study of 3,091 Dutch civil servants aged 40-65 years and their spouses. After adjustment for age, body mass index, and smoking, an inverse association between serum total cholesterol and all-cancer mortality was observed in men during the first 15 years of follow-up, excluding the first 2 years: The multivariate rate ratio of those in the lowest cholesterol quintile compared with those in the highest quintile was 2.1 (95% confidence interval (Cl) 1.1-4.0); this association was accounted for mainly by gastrointestinal cancers (RR = 4.2, 95% Cl 1.4-12.9). For follow-up years 16-28, the multivariate rate ratio for all-cancer mortality was 0.8 (95% Cl 0.5-1.40. In women, no consistent association between serum total cholesterol and cancer was observed. After the first 5 years of follow-up were excluded, the significant inverse association in men still persisted. These results suggest that in this study population, low serum cholesterol seems not to be attributable to undetected cancer, but might be a risk factor for cancer mortality in men.

Adult↗
PubMed1993

Calcium intake and 28-year gastro-intestinal cancer mortality in Dutch civil servants.

The association between calcium intake and gastrointestinal cancer mortality was investigated in a 28-year follow-up study. Data were obtained from a general health examination in 1953-1954 among Dutch civil servants and their spouses, aged 40 to 65 years. Information from 2,591 participants was used for this study. Risk analyses were performed using logistic regression models with the highest quintile of calcium intake as reference. No statistically significant relation between calcium intake and gastrointestinal cancer mortality is observed, although the risk estimate for women with the lowest calcium intake is substantial. Odds ratios (OR) were adjusted for age, energy intake and dietary fiber. After inclusion of other potential confounders to the models (body-mass index and smoking habits), the results hardly differed. Both men and women who died of colorectal cancer had a lower mean calcium intake compared to the rest of the population. For women this was statistically significant. Our results suggest that a low calcium intake may be related to gastrointestinal cancer mortality among women of this study population.

Adult↗
PubMed1993

Perimenopausal increase in serum cholesterol: a 10-year longitudinal study.

The relative contribution of menopause to the age-related increase in serum total cholesterol concentration in women is not exactly known. Cross-sectional studies suggest a considerable contribution of menopause, whereas in short-term longitudinal studies, only a small increase was observed around menopause. In a 10-year follow-up study (1979-1989), serum total cholesterol concentration and dietary intake were measured annually in 167 healthy perimenopausal women (initially aged 49-56 years) who lived in the mixed rural/industrial community of Ede, the Netherlands. The longitudinal design enabled us to study the "natural course" of serum total cholesterol concentration and the influence of dietary fat intake during and after cessation of ovulation. For data analysis, three menopausal cohorts were created based on years relative to menopause: 2 years before ("perimenopausal"), 2 years after ("early postmenopausal"), and 6 years after ("late postmenopausal"). In each cohort, the analysis was conducted on data from 4 years of follow-up. The results show that from 2 years before to 6 years after menopause, serum total cholesterol concentration increased on average by at least 1.1 mmol/liter (19%). Thereafter, only a minor increase was observed. The rise was significantly lower in women who increased their intake of polyunsaturated fatty acids as compared with women who reduced their intake during that period. It is concluded that cessation of ovulation appears to be associated with a major increase of 19% in serum total cholesterol concentration during an 8-year period around menopause. This increase may be reduced by increasing the intake of polyunsaturated fatty acids.

Cholesterol↗
PubMed1992

Passive smoking and sister-chromatid exchanges in lymphocytes.

The object of this study was to determine whether exposure to environmental tobacco smoke is associated with DNA damage reflected by the frequency of sister-chromatid exchange (SCE) in lymphocytes. Within a cross-sectional design, 106 male non-smoking adults, employees of two administrative companies, were divided on the basis of self-reported exposure into high and low passive smoking groups. The high exposed subjects (passive smokers, n = 50) lived with smokers, worked with smokers and were exposed to tobacco smoke for an average of 70 h/week. The low exposed non-smokers (n = 56) were exposed for an average of 5 h/week. Plasma cotinine levels for the passive smokers ranged between 0.4 and 9.0 ng/ml (median 1.4 ng/ml), and for the low exposed group between 0.0 and 1.9 ng/ml (median 0.4 ng/ml) (p less than 0.0001; Mann-Whitney test). No difference was observed between the two groups in the frequency of SCEs in lymphocytes: 4.66 +/- 0.05 for passive smokers and 4.68 +/- 0.04 for low exposed non-smokers (mean +/- SEM) (p = 0.80; t-test). Reclassification of subjects on the basis of plasma cotinine levels did not change the results substantially. These results are in accordance with observations that the increase in cancer risk due to passive smoking is small in comparison with the increase due to active smoking. The SCE test may be too insensitive to be useful for the evaluation of possible cytogenetic effects related to passive smoking.

Adult↗
PubMed1992

No influence of beta-carotene on smoking-induced DNA damage as reflected by sister chromatid exchanges.

The putative cancer-preventive potential of beta-carotene may be explained by its anti-oxidant capacity to prevent free-radical-induced DNA damage. To evaluate this hypothesis, we studied the effect of 14 weeks of beta-carotene supplementation on the frequency of sister chromatid exchanges (SCE) in lymphocytes in 143 heavy smokers in a randomized, double-blind, placebo-controlled intervention trial. Age, smoking habits and pretreatment blood levels of cotinine, beta-carotene, retinol and vitamins C and E were similar in the placebo group (n = 73) and the treatment group (n = 70). Plasma beta-carotene levels increased 13-fold in the treatment group during intervention, whereas the other parameters remained stable in both groups. Initial SCE levels were similar in the treatment and placebo groups (5.10 +/- 0.98 vs. 5.00 +/- 0.99 SCE/lymphocyte). During the intervention, both groups showed an almost identical decrease, and at the end of the intervention period there was no difference in SCE levels between the treatment and the placebo groups (4.37 +/- 0.38 vs. 4.24 +/- 0.37 SCE/lymphocyte). This study shows no protective effect of beta-carotene on DNA damage as reflected by sister chromatid exchanges in lymphocytes. Our results thus do not yield support for a cancer-preventive mechanism of beta-carotene involving this form of DNA damage. It cannot be excluded, however, that beta-carotene prevents other forms of smoking-induced DNA damage, affects other tissues, or is preventive in later stages of carcinogenesis.

Carotenoids↗
PubMed1992

Well shaped ST segment and risk of cardiovascular mortality.

OBJECTIVE: To investigate the prognostic value of frequently occurring slight variations in the ST segment for cardiovascular mortality in healthy subjects. DESIGN: Follow up study of mortality in relation to variations in ST segment level in a cohort over the 28 years from 1953 to 1981. A case-cohort sampling design was applied to limit the number of electrocardiograms that had to be coded by hand. SETTING: General health examination carried out in 1953 of civil servants in Amsterdam and assessment of subsequent mortality. SUBJECTS: Apparently healthy civil servants aged 40 to 65 years: 1583 men and 1508 women. MAIN OUTCOME MEASURES: Relative risk of variations in ST segment level for mortality from all causes, cardiovascular disease, and coronary heart disease. RESULTS: In men the multivariate relative risks of 15 year mortality from cardiovascular disease and coronary heart disease of slight ST elevation at 80 ms past the J point (compared with isoelectric ST segment) were 0.5 (95% confidence interval 0.3 to 0.9) and 0.4 (0.2 to 0.8), respectively. As expected, ST segment depression (greater than 0.25 mm) was associated with increased risk: 1.9 (1.1 to 3.0) and 2.2 (1.2 to 3.9), respectively. In women associations were weaker. The full 28 year period showed a similar pattern of somewhat weaker associations for men; among women, however, no predictive value was apparent. CONCLUSION: These results are empirical evidence for the intuitive opinion among doctors that a curved, upward sloping ST segment, resulting in slight ST elevation at 80 ms, indicates low risk compared with the isoelectric flat, stretched ST segment.

Adult↗
PubMed1992

Decreased excretion of thioethers in urine of smokers after the use of beta-carotene.

Epidemiologic studies have demonstrated an inverse relation between vitamin A intake and lung cancer rate. There is strong evidence that the provitamin A, beta-carotene, plays a more important role in the protective effect than vitamin A itself. The anticarcinogenic properties of beta-carotene have so far been attributed to its scavenger properties in deactivating or trapping reactive chemical species such as singlet oxygen and certain organic free radicals. Smoking results in increased excretion of detoxification products of electrophilic agents (mercapturic acids) in urine. Since reactive electrophilic intermediates are involved in carcinogenesis, we performed a double-blind, placebo-controlled intervention trial to investigate whether the intake of beta-carotene by smokers would affect urinary thioether excretion. Before the intervention the beta-carotene group (n = 62) and the placebo group (n = 61) had similar thioether excretion levels in urine (4.2 vs 4.3 mmolSH/mol creatinine). During the intervention (20 mg beta-carotene daily for 14 weeks) the placebo group showed a 12% increase, whereas the beta-carotene group showed a 5% decrease (P = 0.004). After the intervention the beta-carotene group had a 15% lower thioether excretion level than the placebo group (4.1 vs 4.7 mmolSH/mol creatinine; P = 0.0017). Our study shows that urinary thioether excretion varies considerably over time, and that smokers have a decreased excretion of thioethers in urine after the use of beta-carotene.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Beta-carotene supplementation in smokers reduces the frequency of micronuclei in sputum.

beta-carotene has been hypothesised to reduce lung cancer risk. We studied the effect of 14 weeks of beta-carotene supplementation (20 mg d-1) on the frequency of micronuclei in sputum in 114 heavy smokers in a double-blind trial. Micronuclei reflect DNA damage in exfoliated cells and may thus provide a marker of early-stage carcinogenesis. Pre-treatment blood levels of cotinine, beta-carotene, retinol and vitamins C and E were similar in the placebo group (n = 61) and the treatment group (n = 53). Plasma beta-carotene levels increased 13-fold in the treatment group during intervention. Initial micronuclei counts (per 3,000 cells) were higher in the treatment group than in the placebo group (5.0 vs 4.0, P < 0.05). During intervention, the treatment group showed a 47% decrease, whereas the placebo group showed a non-significant decrease (16%). After adjustment for the initial levels, the treatment group had 27% lower micronuclei counts than the placebo group at the end of the trial (95% CI: 9-41%). These results indicate that beta-carotene may reduce lung cancer risk in man by preventing DNA damage in early-stage carcinogenesis.

Adult↗