Dietary vitamin A and risk of cancer in the Western Electric study

Dietary beta-carotene, cigarette smoking, and lung cancer in men

A cohort of 5,080 men living in a retirement community in California (United States) and initially free from lung cancer were followed from June 1981 to December 1989. At recruitment, each study participant completed a mailed questionnaire which requested information on the subject's medical history, use of cigarettes, and usual consumption frequencies during the preceding 12 months of 44 vegetable and fruit items. Men who had never smoked had the highest mean daily intake of beta-carotene (8,505 micrograms), followed by past smokers (7,761 micrograms) and then by current smokers (6,178 micrograms). beta-Carotene intake of the subject's wife was correlated significantly with that of the husband in the 4,018 spouse pairs (r = 0.46; P = 0.0001). Among men with similar smoking habits, dietary beta-carotene intake significantly decreased with the spouse's smoking habit: never, past, and current smokers (P = 0.004; test for linear trend). During 31,477 person-years of follow-up, 125 incident cases of lung cancer were observed among the cohort of 5,080 men. Age-adjusted relative risks for lung cancer were below unity (i.e., demonstrating a reduced risk) for higher relative to lower consumption of beta-carotene, of all vegetables and fruits, and of yellow vegetables alone. However, these relative risks approached or crossed the null value when adjusted for personal smoking.

Ecologic study of lung cancer risk factors in the U.S. and Japan, with special reference to smoking and diet

Lung cancer mortality rates among United States and Japanese males were compared and related to smoking and dietary data. Mortality rates increased from 1950 to 1985 in both countries, but the absolute values are consistently lower in Japan (38.2 deaths/100,000 in 1985) than in the U.S. (72.2/100,000). The proportion of smokers is higher in Japan than in the U.S. since 1955. Japanese males start smoking considerably later than U.S. males, but smoke a higher quantity of cigarettes per day. Available information on inhalation practices and yield and type of cigarettes smoked showed no differences among the two countries large enough to account for the differences in mortality rates. Further data in this regard should be obtained. Dietary data show that fat consumption (as percentage of calories) is consistently higher in the U.S. than in Japan from 1950 (40% vs. 7.9%) through 1985 (43.5% vs. 24.5%). A linear relationship is observed between lung cancer mortality and fat intake. Our data support the hypothesis that dietary habits may modulate the carcinogenic effects of tobacco smoking.

Diet in the epidemiology of bladder cancer in western New York

We present the dietary epidemiology of bladder cancer while controlling for a number of lifestyle and environmental risk factors in a study of 351 white male cases with histologically confirmed transitional cell carcinoma of the bladder and 855 white male controls selected from Erie, Niagara, and Monroe counties of western New York from 1979 to 1985. Usual diet was estimated by comprehensive interviews with use of a detailed food frequency questionnaire. An increased risk of bladder cancer was associated with higher kilocalorie intake, but only among those under 65 years of age, with the strongest pattern associated with fat intake. Further analyses of fat, carbohydrates, and protein, with adjustment for total kilocalories, resulted in a positive association of risk with fat intake and a decreasing risk with higher protein intake. Of the vitamins, carotenoid consumption appeared to decrease risk with increased consumption for those under 65 years of age. No significant differences between cases and controls were seen for intake of calcium, retinol, thiamin, riboflavin, niacin, vitamin C, vitamin D, and vitamin E. After adjustment for kilocalories and other confounders, higher intake of dietary sodium was associated with increased risk among both age groups, and the trends were statistically significant. The importance of diet in the etiology of bladder cancer is suggested by our findings.

Fruit, vegetables, and cancer prevention: a review of the epidemiological evidence

Approximately 200 studies that examined the relationship between fruit and vegetable intake and cancers of the lung, colon, breast, cervix, esophagus, oral cavity, stomach, bladder, pancreas, and ovary are reviewed. A statistically significant protective effect of fruit and vegetable consumption was found in 128 of 156 dietary studies in which results were expressed in terms of relative risk. For most cancer sites, persons with low fruit and vegetable intake (at least the lower one-fourth of the population) experience about twice the risk of cancer compared with those with high intake, even after control for potentially confounding factors. For lung cancer, significant protection was found in 24 of 25 studies after control for smoking in most instances. Fruits, in particular, were significantly protective in cancers of the esophagus, oral cavity, and larynx, for which 28 of 29 studies were significant. Strong evidence of a protective effect of fruit and vegetable consumption was seen in cancers of the pancreas and stomach (26 of 30 studies), as well as in colorectal and bladder cancers (23 of 38 studies). For cancers of the cervix, ovary, and endometrium, a significant protective effect was shown in 11 of 13 studies, and for breast cancer a protective effect was found to be strong and consistent in a meta analysis. It would appear that major public health benefits could be achieved by substantially increasing consumption of these foods.

Carotenoids and retinoids in human nutrition

Since the discovery of vitamin A as a fat-soluble growth factor in the early part of the century, research into carotenoids and retinoids has attracted the attention of many scientists. These two groups of compounds are still being actively studied all over the world since many gaps in knowledge exist and new frontiers are being pursued. Recent developments in studies into the possible roles of carotenoids and retinoids beyond their classical functions in vision have created a great deal of excitement in the biomedical community. This review covers a wide range of topics pertaining to these two closely related compounds. Particular emphasis is given to the functions of these compounds and their roles in human nutrition. Various aspects of vitamin A deficiency and studies on carotenoids and retinoids in cancer development and prevention are reviewed in some detail.

Physiological and clinical aspects of vitamin A and its metabolites

Retinoids, including retinol and retinoic acid (RA), are a group of naturally occurring and synthetic compounds that exhibit vitamin A-like biological activity. They achieve their effects by binding to intracellular proteins. Important sites of action are the nuclear retinoic acid receptors (RAR). These receptors, namely, RAR alpha, RAR beta, and RAR gamma, function as transcription factors by binding to RA-responsive elements (RARE) of multiple genes. Retinoids play a role in vision, embryogenesis, immune modulation, growth and differentiation of normal, premalignant and malignant tissues, the suppression of carcinogenesis, and the inhibition of tumor growth in experimental systems and humans. Reports of the significant antitumor effect of all-trans-RA in acute promyelocytic leukemia and the synthesis of new, less toxic, and more potent retinoids has generated renewed interest in these compounds. Retinoids may have an important role to play in the chemoprevention and therapy of cancer.

Antioxidant status (selenium, vitamins A and E) and aging

Antioxidant status can be evaluated by blood selenium, vitamins A and E. The level of selenium was determined in whole blood, erythrocytes and plasma of 170 French people (70-95 years old) healthy and with intercurrent illness, by using PIXE (proton-induced X-ray emission analysis). These results are discussed with other values from the literature. Plasma levels of vitamins A and E have been measured by HPLC. All data were compared with those obtained for younger subjects. Healthy elderly people residing in a geriatric home received selenium supplements during 1 month. The influence of this supplementation brought to light a deficiency for this trace element. The correlation of aging and nutritional requirements with immune function, heart and cancer death rate is presented and discussed.

Dietary intake and risk of lung cancer in women who never smoked

A case-control study was conducted to examine the influence of dietary factors on the risk of developing lung cancer among women who have never smoked cigarettes. This study included 124 cases of histologically confirmed carcinoma of the lung and 263 community-based controls. Dietary data were collected utilizing the reduced version of the National Cancer Institute (Block) food frequency questionnaire. The results of this analysis, adjusted for age, education, and total calories, indicated a strong protective effect associated with total vegetable consumption and intake of carotene. Individuals in the highest quartile of vegetable consumption experienced the greatest decreased risk with an odds ratio (OR) of 0.2, [confidence interval (CI) 0.1-0.5]. The effect of all vegetables combined was greater than that of green and yellow vegetables alone (highest quartile OR 0.4, CI 0.2-0.7). Similarly, the protective effect of total carotene (highest quartile OR 0.3, CI 0.1-0.6) was somewhat greater than that of beta-carotene alone (highest quartile OR 0.4, CI 0.2-0.8). Retinol intake was not associated with a decreased risk of lung cancer in our population. There was an inverse association between lung cancer risk and vitamin C intake, which was not significant, although a statistically significant trend was noted.

Inverse correlation between essential antioxidants in plasma and subsequent risk to develop cancer, ischemic heart disease and stroke respectively: 12-year follow-up of the Prospective Basel Study

There is accumulating evidence that free radicals may contribute to various diseases such as cancer or cardiovascular disease. Possible health hazards can to some extent be prevented by the body's multilevel defense system against free radicals, which comprises, besides others, antioxidant vitamins. The 12-year mortality follow-up of 2,974 participants of the Basal Study allowed to test the hypothesis that low antioxidant vitamin plasma concentrations (vitamin A, C, E and carotene) were associated with increased death from cancer of various sites and death from atherosclerosis such as ischemic heart disease and stroke, respectively. For the analysis 204 cancer cases, 132 fatalities from ischemic heart disease (IHD) and 31 deaths from cerebral vascular disease were available. Cancer mortality. Overall mortality from cancer was associated with low mean plasma levels of carotene adjusted for cholesterol (p less than 0.01) and of vitamin C (p less than 0.01). Bronchus and stomach cancers were associated with a low mean plasma carotene level (p less than 0.01). Subjects with subsequent stomach cancer had also lower mean vitamin C and lipid-adjusted vitamin A levels than survivors (p less than 0.05). Calculating the relative risk with exclusion of mortality during the first two years of follow-up, low plasma carotene was associated with an increased risk for bronchus cancer (RR 1.8, p less than 0.05), and the small number of stomach cancer cases (RR 2.95, p less than 0.05) low plasma levels of carotene and vitamin A with all cancer types (RR 2.47, p less than 0.01), and low plasma retinol in older subjects (greater than 60 years) with lung cancer (RR 2.17, p less than 0.05). Studies in other cohorts with a poor vitamin E status revealed an increased risk of subsequent cancer at low vitamin E levels as well. It is concluded that low plasma levels of all major essential antioxidants are associated with an increased risk of subsequent cancer mortality. Cardio-vascular mortality. Plasma carotene concentration below quartile 1 was associated with an increased risk for IHD (RR 1.53, p = 0.02). The same was true for low levels of both carotene and vitamin C (RR = 1.96, p = 0.022). The risk of cerebrovascular death was elevated in subjects with low carotene in the presence of low vitamin C plasma concentration (RR 4.17, p less than 0.01). These data confirm and extend recent findings on an inverse correlation of beta-carotene and vitamin C respectively to CVD.(ABSTRACT TRUNCATED AT 400 WORDS)

Vegetables, fruit, and cancer. II. Mechanisms

The epidemiologic literature on the relationship between vegetable and fruit consumption and human cancer at a variety of sites was reviewed systematically in Part I. It was concluded that consumption of higher levels of vegetables and fruit is associated consistently, although not universally, with a reduced risk of cancer at most sites, and particularly with epithelial cancers of the alimentary and respiratory tracts. Possible mechanisms by which vegetable and fruit intake might alter risk of cancer are addressed here. A large number of potentially anticarcinogenic agents are found in these food sources, including carotenoids, vitamins C and E, selenium, dietary fiber, dithiolthiones, glucosinolates and indoles, isothiocyanates, flavonoids, phenols, protease inhibitors, plant sterols, allium compounds, and limonene. These agents have both complementary and overlapping mechanisms of action, including the induction of detoxification enzymes, inhibition of nitrosamine formation, provision of substrate for formation of antineoplastic agents, dilution and binding of carcinogens in the digestive tract, alteration of hormone metabolism, antioxidant effects, and others. It appears extremely unlikely that any one substance is responsible for all the associations seen. Possible adverse effects of vegetable and fruit consumption are also examined. One way to consider the relationships reviewed here is to hypothesize that humans are adapted to a high intake of plant foods that supply substances crucial to the maintenance of the organism, but only some of which are currently called 'essential nutrients.' Cancer may be the result of reducing the level of intake of foods that are metabolically necessary--it may be a disease of maladaptation.

Free radicals as carcinogens and their quenchers as anticarcinogens

An oxygen dependent signal was detected, late in the 1950s by electron spin resonance (ESR) in a saline solution of hematoporphyrin (Hp) excited by light. This signal expressed a free radical consisting of 'some kind of an association between Hp and oxygen', that Smaller et al. called 'oxyradical' (HpOO.). It soon opened a new level of understanding in carcinogenesis triggered by photodynamic substances, including Hp itself, polycyclic hydrocarbons (PCHs), as well as any carcinogen involving molecular species activated by radiation and/or metabolic reaction. Early in the 1960s, this prompted the discovery of benzo(a)pyrene (BP) photocarcinogenic enhancement (BP-PCE) in mice, probably due to an increase in free oxygen radical generation following correct light exposure. This assumption was confirmed in 1980 by the fact that mice orally loaded with antioxidants and radical quenchers, such as beta-carotene (BC) and cantaxanthin (CX), were protected against BP-PCE at 100% and against total BP carcinogenicity at more than 60%. These achievements were presented as the bases of the current explosion of interest in biology and medicine in building up the new field of chemoprevention against cancer and other chronic diseases by supplementation with antioxidant vitamins, retinoids and especially carotenoids and their synergistic association. The relevant findings of this research obtained in the last decade in in vitro and in vivo experiments as well as human interventions are reported and discussed with personal contributions.

Dietary factors in cancer of the lower urinary tract

This dietary study was based on 195 male and 66 female cases of lower urinary tract cancer, identified in Hawaii between 1977 and 1986. Each case was matched for sex, age, and ethnic group (Caucasian or Japanese) to 2 population-based controls. There was a decrease in risk with increasing levels of consumption of vitamin C in women (p = 0.03) and dark green vegetables in men (p = 0.02). When examined by quartile, the odds ratios for the highest quartile of intake compared to the lowest quartile were 0.4 for women and 0.6 for men, respectively. Although dark green vegetables are a source of carotenoids, the intake of total carotenoids, retinol and total vitamin A was weakly and inconsistently related to risk in both sexes. Among women only, there was also an inverse association with the consumption of regular ground coffee (p = 0.02) but not with other types of coffee. Finally, there were no statistically significant or consistent differences between cases and controls in the intake of artificial sweeteners and tea.

Dietary cholesterol, fatty acids, and the risk of lung cancer among men

The relation between dietary cholesterol and fatty acids and the incidence of lung cancer was studied among 4,538 Finnish men aged 20-69 years and initially free of cancer. During 20 years of follow-up, 117 lung cancer cases were diagnosed. Cholesterol intake was not associated with lung cancer risk, the age-, smoking-, and energy-adjusted relative risk between the lowest and highest tertiles being 1.0 [95% confidence interval (CI) = 0.6-1.9]. The intake of saturated fatty acids was nonsignificantly related with lung cancer incidence, the relative risk for the lowest compared with the highest tertile being 1.6 (CI = 0.8-3.2). The association was stronger among smokers than among nonsmokers, the relative risks being 2.1 (CI = 1.0-4.3) and 1.3 (CI = 0.4-4.1), respectively. The relative risk among smokers, however, decreased to 1.5 after adjustment for the amount they smoked. In the total cohort, there was a significantly elevated risk of lung cancer among men with a high intake of butter, one of the main sources of saturated fatty acids, the relative risk being 1.9 (CI = 1.1-3.2). The present data do not confirm previous results suggesting that dietary cholesterol predicts the occurrence of lung cancer among men. The association between intake of saturated fatty acids and lung cancer observed in the present study may be partly due to heavy smoking among high consumers of saturated fat.

The effects of postharvest treatment and chemical interactions on the bioavailability of ascorbic acid, thiamin, vitamin A, carotenoids, and minerals

All recent health recommendations include admonitions to reduce calories, maintain desirable weight, reduce fat, increase complex carbohydrates, and ensure an adequate intake of nutrients. Such recommendations require that we know not only nutrient composition of foods, but also potential losses and decreased bioavailability due to postharvest treatment and chemical interactions. This article discusses in some detail the reactions of concern that cause such changes and their potential alleviation with several key nutrients. The nutrients discussed were chosen as a result of the conclusions of the Joint Nutrition Monitoring Report of the Department of Health and Human Services and the U.S. Department of Agriculture. Obviously other choices could have been made, but the authors felt that the nutrients chosen--ascorbic acid, thiamin, vitamin A, carotenoids, calcium, and iron--were representative of a key profile of nutrients whose reactivity makes them vulnerable to losses in bioavailability, as well as being noted in the Joint Nutrition Monitoring Report.

Food and nutrient intake differences between smokers and non-smokers in the US

Data from the Second National Health and Nutrition Examination Survey were analyzed to determine food and nutrient intake differences between current smokers (also categorized as light, moderate, and heavy smokers) and non-smokers. Smokers in several age-race-sex categories have lower intakes of vitamin C, folate, fiber, and vitamin A than non-smokers, and intake tended to decrease as cigarette consumption increased, particularly for vitamin C, fiber, and folate. Smokers were less likely to have consumed vegetables, fruits (particularly fruits and vegetables high in vitamins C and A), high fiber grains, low fat milk, and vitamin and mineral supplements than non-smokers. A negative linear trend was found between smoking intensity and intake of several categories of fruits and vegetables. These data suggest that the high cancer risk associated with smoking is compounded by somewhat lower intake of nutrients and foods which are thought to be cancer protective.

Dietary vitamin A, beta carotene and risk of epidermoid lung cancer in south-western France

This hospital-based case-control study was designed to investigate the association of low dietary vitamin A and beta carotene consumption with epidermoid lung cancer. Cases were patients with histologically confirmed epidermoid lung cancer diagnosed in six selected hospitals of southwestern France in 1983-84. Controls were selected from patients admitted to the same hospitals during the same period with diagnoses other than cancer. Cases and controls were matched for sex, age, place of residence, occupation, professional exposure to carcinogens, tobacco and alcohol consumption. A total of 106 cases of epidermoid lung cancer and 212 controls were interviewed on their typical weekly intake of 80 food items rich in preformed vitamin A and beta carotene. Index measures of the vitamin A and beta carotene daily intakes were computed for each individual patient and expressed in retinol equivalent (RE). A statistically significant odds ratio (OR) was found for preformed vitamin A (OR = 4.3; 95% CI: 2.5-7.3) with the threshold of 1,000 RE. A similar result was found for beta carotene with the same threshold (OR = 4.1; 95% CI: 2.3-7.4). Using the conditional logistic regression, consumption of preformed vitamin A and consumption of beta carotene were significantly and independently associated with epidermoid lung cancer. While confirming the protective role of beta carotene against epidermoid lung cancer, this study also shows that preformed vitamin A might have a distinct and important protective effect.

Cancer chemoprevention by supplemental carotenoids and synergism with retinol in mastodynia treatment

Cancer chemoprevention with beta-carotene (BC), canthaxanthin (CX) and retinol-BC is reported with respect to skin, breast, gastric, colon carcinogeneses induced by benzo(a)pyrene (BP) with or without ultra violet radiation (UV-A, UV-B), dimethylbenzathracene (DMBA) +/- UVB, P-UVA, N-methyl-N'-N-nitro-nitrosoguanidine (MNNG), dimethylhydrazine (DMH), and with respect to transplanted tumours. When animals were loaded with carotenoid supplementation one month before the carcinogenic induction (continued throughout the experiment), cancer prevention was observed up to 60-100%. The absence of provitamin A-activity in CX shows the carotenoid antioxidant property. Fifteen patients given BC + CX to prevent recurrences after radical removal of the primary neoplasia in organs like lung, breast, colon, urinary bladder, head and neck were studied in 1980-89. A longer than expected disease-free interval was preliminarily found. Supplementation of BC +/- retinol was also reported to prevent and treat oral leucoplakia. Supplementation and intermittent retinol administration was also tested in benign cyclical mastalgia with clear cut side effect free therapeutic results.

Strategies for cancer prevention through diet modification

Diet and cancer research at the National Cancer Institute has grown from a budget of $2.5 million in 1974 to $55 million in 1988. The emphasis is partially on demonstrations of prevention strategies and chemoprevention trials. Studies to disseminate dietary goals in practical ways are undertaken with the aid of the food industry.

Experimental approaches to nutrition and cancer: fats, calories, vitamins and minerals

Chronic energy intake restriction (CEIR) inhibits lymphoproliferative disease, autoimmune-based renal disease and mammary adenocarcinoma in mice of numerous short-lived strains (MRL/lpr, C3H/Bi, C3H/Ou). Doubling and tripling of life span and health span and inhibition of development of diseases associated with aging could be attributed to restriction of calories but not to restriction of dietary fat in the absence of calorie restriction. In mice of both long- and short-lived strains, CEIR dramatically prevents the waning of immunologic vigor that commonly occurs with aging, delays thymic involution, impairs formation of circulating immune complexes, prevents the renal injury that accompanies autoimmune disease, and significantly forestalls development of genetically determined lymphoproliferative or neoplastic disease. Evidence suggests that CEIR may exert these beneficial influences in part through regulation of cellular proliferation. Trace elements, particularly zinc, as well as vitamins may play important roles in maintaining immunocompetence and also appear to be of significance in the dietary prevention of certain experimental cancers.

Vitamin A and lung cancer

In a dozen case-control and cohort studies, high intake of fruits and vegetables containing carotenoids has been associated with a reduced risk of lung cancer. In contrast, little relation has been found between intake of preformed vitamin A and this disease. Although initial studies suggested that persons with lower levels of serum retinol have higher future rates of lung cancer, this idea was not confirmed in subsequent investigations. Prediagnostic levels of beta-carotene in blood, however, have been inversely related with risk of lung cancer. Available data thus strongly support the hypothesis that dietary carotenoids reduce the risk of lung cancer, but the data are also compatible with the possibility that some other factor in these foods is responsible for the lower risk. Even if ultimately shown to be casual, the relation between diet and lung cancer is modest compared with the deleterious effect of cigarette smoking.

Changes in serum concentrations of beta-carotene and changes in the dietary intake frequency of green-yellow vegetables among healthy male inhabitants of Japan

Serum levels of beta-carotene among 147 healthy male inhabitants were measured twice with an interval of one year in order to determine the relationship between changes in serum beta-carotene levels and changes in the dietary intake of green-yellow vegetables. A positive association was found to exist between changes in the intake frequency of green-yellow vegetables and changes in serum beta-carotene levels, whereas changes in alcohol intake and smoking were discovered to be negatively associated with changes in serum beta-carotene levels. The positive association between changes in the intake frequency of green-yellow vegetables and changes in serum beta-carotene levels was preserved after adjustment for these negative factors.

Concepts in cancer chemoprevention research

Cancer prevention through the use of chemical intervention regimens (chemoprevention) is an emerging field with broad potential for impacting on cancer incidence rates in defined high-risk groups and the general population. Information from cancer epidemiologic studies coupled with that from basic research on cancer biology have combined to reveal several categories of agents with potential for clinical application, including natural and synthetic tumor suppressive retinoids and antioxidants. Chemopreventive agents may inhibit the development of cancer by limiting exposure to initiators or promoters through stimulation of inactivation or excretion mechanisms. Biological consequences of exposure to carcinogens may also be interfered with, e.g., by inhibiting the activation of proto-oncogenes or by antagonizing the effects of oncogene expression. Hundreds of compounds with chemopreventive efficacy in vitro have been isolated from foods and plant products. The testing and development of candidate chemopreventives proceeds through a series of preclinical efficacy screens, followed by controlled clinical trials.

Dietary factors and risk of lung cancer: results from a case-control study, Toronto, 1981-1985

Associations between dietary factors and risk of lung cancer are reported from a study of 839 cases and 772 population-based controls interviewed in metropolitan Toronto between 1981 and 1985. Increased consumption of vegetables is associated with a decreased relative risk of 0.60 (95% confidence limits = 0.40 to 0.88) for those in the highest compared with the lowest quartile. Cholesterol intake is associated with increased risk, but this is restricted to those in the highest quartile for whom the relative risk is 1.58 (95% confidence limits = 1.05 to 2.38) compared with those in the lowest quartile. The results of this study suggest that dietary factors may affect the risk of lung cancer, but identification of the specific constituents involved will require further research.

A case-control study of serum vitamins A, E, and C in lung cancer patients

In a case-control study, serum levels of vitamins E, C, and A, carotenoids, total cholesterol, and retinol-binding protein along with smoking levels were studied on 59 persons newly diagnosed with lung cancer and also on matched hospitalized controls. The relative risk for smoking increased with the number of pack years of cigarettes smoked. Cases had significantly lower serum levels of carotenoids, vitamin E, and total cholesterol. Adjustment for serum cholesterol levels diminished the case-control difference for serum carotenoid levels and reduced the case-control difference for serum vitamin E levels. The results indicate that serum vitamin E may also be associated with lung cancer, possibly to a greater degree than serum retinol (vitamin A) is associated with lung cancer.

Effects of beta-carotene repletion on beta-carotene absorption, lipid peroxidation, and neutrophil superoxide formation in young men

The chemopreventive effects of beta-carotene are usually attributed to its antioxidant properties. To determine the effects of beta-carotene supplementation on different parameters of oxidative metabolism, 15 normal young male subjects (18-30 yrs) were placed on a carotenoid-free liquid diet for two weeks prior to entry into the study. Blood was then measured for five carotenoids, retinol, retinyl palmitate, retinol-binding protein, alpha-tocopherol, vitamin C, zinc, lipid peroxides, and neutrophil superoxide production. Absorption tests were performed with 15 mg of beta-carotene to determine absorption curves for each subject. Subjects were then divided into two groups and given either 15 (n = 7) or 120 (n = 8) mg of beta-carotene daily for four weeks along with the same carotenoid-free liquid diet. The absorption test and the blood measurements were repeated. After repletion with beta-carotene, serum lipid peroxide levels decreased in both groups (p less than 0.05), but no other changes were noted in either the neutrophil superoxide production or in the levels of any of the vitamins measured. In contrast to vitamin E, the superoxide scavenging ability of beta-carotene apparently does not contribute to its effects in lowering serum lipid peroxide levels.

Diet and cancer. A review

Diet is one of the major causes of cancer. The epidemiologic data on which this conclusion is based has been derived from analytic epidemiologic studies, buttressed by descriptive (ecologic) epidemiology and studies in experimental animals. Although the evidence is not entirely consistent, high dietary fat intake appears to be a major cause of breast cancer, and more consistently, of colorectal cancer, and probably prostate cancer as well. Obesity is an important cause of endometrial cancer, and increases the risk of breast cancer in postmenopausal women, though increasingly there is evidence that suggests that obesity is protective for breast cancer in premenopausal women. There is inconsistent evidence that dietary fibre is protective for colorectal cancer, though good evidence that vegetable consumption is protective. Several studies have pointed to a protective effect of betacarotene for lung cancer, but betacarotene may be acting as an indicator of other protective factors in diet. Recommendations for dietary modification, congruent with recommendations for the prevention of cardiovascular and other chronic diseases, are now appropriate.

Normal serum response to oral beta-carotene in humans

This study was performed to determine (1) the normal serum response to a single oral dose of beta-carotene (BC), (2) the effect of meal timing and serum response to meal lipids on serum BC, (3) the effect of administered BC on other serum carotenoids and retinoids, and (4) the relationship of body composition to serum BC response. Subjects consumed one BC dose with a liquid 500 kcal BC-free diet; fasting and hourly venous blood was collected for 8 hours and again at 24 hours. A second liquid BC-free meal was consumed 4 hours post-dosing; this midday meal was omitted in some subjects. Serum BC levels rose and peaked initially at 5 hours, but continued to be absorbed in most subjects, remaining significantly elevated at 24 hours as compared to baseline values (p less than 0.001), independent of BC dose. The area under the BC absorption curve (8-hr AUC) increased linearly with BC dose and correlated positively with peak serum triglycerides (TG) after a meal (n = 26 tests, r = 0.56, p less than 0.003). Omission of the midday meal significantly delayed the initial BC peak to 7 hours (p less than 0.0004). Serum levels of retinol, alpha-carotene, cryptoxanthin, lycopene, and lutein remained unchanged. Serum retinyl esters did not rise in all subjects following BC intake; when it did, retinyl esters rose and peaked concomitantly with BC, but declined within 8 hours. There was no correlation between the initial serum BC, peak BC, 24-hr BC, 8-hr AUC, or peak serum TG and the percentage of body fat. We conclude that: (1) the timing of the serum response to oral BC is independent of dose, (2) the serum BC response is greater in those with a greater serum triglyceride response to meal lipids, (3) BC at the doses given does not alter the levels of other serum carotenoids, and (4) there is no correlation between the serum BC parameters measured and adiposity.

Investigation of the relationships between plasma levels of ascorbate, vitamin E and beta-carotene and the frequency of sister-chromatid exchanges and release of reactive oxidants by blood leucocytes from cigarette smokers

In this study the frequencies of sister-chromatid exchanges (SCEs) were correlated with measurements of the release of reactive oxidants by phagocytes, as determined by luminol-enhanced chemiluminescence (LECL), and levels of the anti-oxidants ascorbate, beta-carotene and vitamin E in blood specimens taken from 65 young asymptomatic cigarette smokers. Increased SCE frequencies correlated with LECL responses (p less than 0.0075) of activated blood phagocytes. Anti-oxidant levels did not correlate with either LECL or SCEs. These findings indicate that increased generation of reactive oxidants by circulating phagocytes from cigarette smokers are associated with cytogenetic changes.

Cancer chemoprevention by supplemental carotenoids in animals and humans

Experiments were carried out in mice demonstrating that dietary carotenoids (beta-carotene or canthaxanthin), starting before cancer initiation and continuing throughout the experiment, have a protective effect against indirect skin carcinogenesis induced by benzo[a]pyrene +/- UVA and breast cancer induced by 8-methoxypsoralen + UVA. Experiments in rats demonstrated that carotenoids also prevent the direct gastric carcinogenesis induced by N-methyl-N'-nitro-nitroso-guanidine. Recently, prevention by beta-carotene against colon cancer induced in mice by dimethylhydrazine, another indirect carcinogen, was confirmed by others. The prospects for carotenoid intervention with humans were based on their antitumorigenic effect, which is quite independent of pro-vitamin A activity, their lack of toxicity even after prolonged administration, and their immunostimulating activity. These facts helped to build up a rationale predicting that any epithelial cancer, after radical surgery, can be chemoprevented with supplemental carotenoids. Thus, it is expected that the remaining initiated epithelial tissue will be protected by quenching oxygen radical formation, against the onset of a second primary malignancy. This type of prevention can be envisaged in organs like the lung, urinary bladder, breast, stomach, and colon-rectum. At present, human intervention protocols with a randomized drug/placebo method are underway under the supervision of the Centro Tumori of Pavia to chemoprevent with beta-carotene second primary lung or bladder cancer after radical surgery. Preliminary observations regarding findings in humans without randomization (1980-1988) in Pavia are also reported here. This consisted of chemoprevention with beta-carotene plus canthaxanthin against recurrence of different epithelial malignancies after radical treatment (surgery +/- chemoradiotherapy). None of the 11 cases recruited, on the basis of radical nature of treatment and patient adherence, have shown any recurrence beyond their expected disease-free intervals.

Strategies for analyzing nutritional data for epidemiological purposes--conceptual framework

The relation between nutritional factors and health investigated in epidemiological studies are often inconsistent. One of the reasons for such findings can be the improper addressing of the multitude of nutritional dimensions in the specific study situation such as physiological individuality of human beings, different living conditions, or numerous interdependencies between nutritional variables. Epidemiological research in nutrition and health should recognize such facts and work with appropriate study models and adequate data analyses. Instead of investigating heterogeneous populations it is advisable to concentrate on specific "types" of people. Under consideration of the study goals such "types" can be compiled according to physiological properties, e.g., cholesterol sensitivity, or biological-constitutional factors such as body build, life-style entities, or other factors. The variety of nutrition factors far beyond the commonly applied nutrient values can be expressed in integrated indices of "food patterns". Such "food patterns" can be derived in many ways. They can be deduced from theories by using specific criteria, but also explored by modern multivariate statistical analyses. The ways leading to "food patterns" are discussed. The ideas presented and discussed in this paper lead to an improved model for research in the field of nutrition and health with integrated indices of "food patterns" as the critical point. It is assumed that using this approach will generate new insight in the relation of nutrition and health, a currently still diffuse research area.

Relationship between carotenoids and cancer. The Multiple Risk Factor Intervention Trial (MRFIT) Study

We evaluated the baseline serum levels of beta carotene, total carotenoids, vitamin A and E, and retinol-binding protein among 156 initially healthy men who participated in the Multiple Risk Factor Intervention Trial (MRFIT) and who subsequently died of cancer and 311 controls individually matched for age, smoking status, randomization group, date of randomization, and clinical center. Both total carotenoids and beta carotene levels were lower in the 66 lung cancer cases than in their matched controls. For all cancer deaths combined, there were no significant differences in total carotenoids or beta carotene between cases and controls. The relationship between lower serum carotenoid levels and lung cancer persisted after adjusting for the number of cigarettes, alcohol intake, serum thiocyanate levels, and cholesterol levels in the blood. Serum levels of retinol, alpha tocopherol, and retinol-binding protein were not related to any cancer site. The results of this study provide further evidence for a possible protective effect of beta carotene against lung cancer among cigarette smokers.

Serum levels of beta-carotene, vitamin A, and zinc in male lung cancer cases and controls

The mean serum levels of beta-carotene and vitamin A in a multivariate analysis of data from 64 histologically confirmed male lung cancer cases were statistically significantly lower than those from 63 randomly selected male hospital controls, who were admitted for small surgical operations (p values for both beta-carotene and vitamin A less than 0.001). The mean serum levels of zinc were not statistically significantly different between cases and controls (p = 0.10). The levels of beta-carotene, vitamin A, or zinc were not statistically significantly influenced by either the extent of the cancer (p = 0.45) or the cancer cell type (p = 0.06). The possible biological significance of these findings is discussed briefly.

Dietary and alcohol intake, smoking pattern, occupational risk, and family history in lung cancer patients: results of a case-control study in males

In a case-control study of 71 consecutive new male cases of lung cancer and 71 male hospital control patients, previous dietary and alcohol intake, smoking pattern, occupation, dust exposure, and family history of lung cancer were investigated. The cases and controls were similar in age, country of origin, area of residence, and marital status. Using a frequency-based assessment of previous dietary intake, broad food groups were similar for cases and controls. Cases had a significantly lower intake of fish than controls did (odds ratio = 0.5, confidence interval = 0.2-1.0, p = 0.05). A protective effect for fish consumption in lung cancer has not been previously reported. The dietary intake of foods containing retinol and beta-carotene and the intake of alcohol were not significantly different between cases and controls. For cases, smoking duration was longer and the time since cessation for exsmokers was shorter, cigarette pack years were longer, and the number of cigarettes smoked per day was greater. The factors of occupation, dust exposure, and family history of cancer (including lung cancer) were similarly distributed between cases and controls.

Vaginal hydrolysis of retinyl acetate: increase in plasma retinol and retinol binding protein in women with cervical dysplasias

We previously reported the clinical feasibility of a Phase I trial involving the topical administration of a RA gel applied cervicovaginally in women with mild or moderate cervical dysplasia. Now, we report hydrolysis and systemic absorption of the RA gel from the vagina. HPLC analysis of samples of residual gel obtained from the cervical canal after topical bolus application indicate that the RA undergoes prompt in vivo hydrolysis yielding retinol as a major metabolite. Venous blood samples of 41 subjects, who self-administered a RA gel, were analyzed for plasma retinol and RBP concentrations prior to and upon completion of a 7-day treatment course and upon return for follow-up examinations. An increase in both the concentrations of plasma retinol and RBP were detected after topical application of the RA gel. These elevated values receded after the gel administration was discontinued. No significant changes were observed in plasma retinol or RBP concentrations in placebo-treated subjects. The efficacy of RA as a chemopreventive agent in treating cervical dysplasias remains to be determined.