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

Dietary vitamins A and C and lung cancer risk in Louisiana

The authors describe the results of a hospital-based incident case-control study of lung cancer conducted in a high-risk region of southern Louisiana from January 1979 through April 1982. Dietary intake of carotene, retinol, and vitamin C was estimated from food frequency questionnaires administered to 1253 cases and 1274 controls. An inverse association was found between level of carotene intake and lung cancer risk, and this protective effect was specific for squamous and small cell carcinoma (odds ratio [OR] = 0.84, 95% confidence interval: 0.64-1.09, high intake). A stronger protective effect for these tumors was associated with dietary vitamin C intake (OR = 0.65, 0.50-0.87, high intake). A significant inverse gradient in risk with retinol intake was limited to adenocarcinoma (OR = 0.64, 0.44-0.94, high intake) and more pronounced among blacks.

Hypocarotenemia in patients fed enterally with commercial liquid diets

We have found that 12 patients requiring permanent enteral feeding secondary to cerebrovascular accident with adequate Vitamin A nutritional status had serum concentrations of various carotenoids which were only 8-17% of sex- and age-matched healthy controls. Their serum retinol levels were normal, but only 61% of their controls despite receiving two to three times the recommended daily allowance (RDA) in retinol equivalents. Commercial enteral formulas were found to contain only negligible quantities of the carotenoids and were the cause of the hypocarotenemia. To assess the ability of these patients to absorb beta-carotene, nine tube-fed patients were given 15 mg of beta-carotene (2.5 times the RDA) in a single dose. Serum concentration time curves showed that only four patients absorbed significant quantities of the beta-carotene and absorption was delayed compared to previously studied subjects taking enteral formulas as meals. These studies suggest that the efficiency of absorption of the fat soluble vitamins may be lower in tube-fed patients and that patients receiving long-term tube feeding are denied the possible protective effects of the carotenoids normally contained in the American diet.

Displacement of nutritional receptors on cell membrane as an initiation factor in carcinogenesis

Carcinogenesis is a multi-step process, and initiation is the first step. The cell membrane may hold the key to the entry of carcinogens. According to our hypothesis, the cell membrane may have receptors for nutrients including the essential vitamins, in addition to hormones, immune modulators, prostaglandins and neurotransmitters. In addition, there may be cytoplasmic counter receptors to the above. Carcinogens after prolonged contact with cell membrane may displace nutritional receptors to gain an abnormal foothold on cell membrane before entering the cytoplasm and cell nucleus and activating the oncogenes. If this is proven to be correct, there is a possibility of cancer prevention at the cellular level. A possible experimental approach is also described.

Chemoprevention of indirect and direct chemical carcinogenesis by carotenoids as oxygen radical quenchers

Beta-carotene (BC) and canthaxanthine (CX), two carotenoids with and without pro-vitamin A activity, respectively, were found to help to prevent benzo[a]pyrene (BP)-induced skin carcinogenesis in the dark and BP photocarcinogenesis (UV 300-400 nm) when given as an oral supplement to female Swiss albino mice. The same experimental procedure was adapted to 8-methoxypsoralen (8-MOP) photoinduction of mammary carcinomas in mice. Here also, the two carotenoids were strongly antitumorigenic. Indeed, 8-MOP photomutagenesis, tested in S. typhimurium TA 102, appeared to depend on a two-step reaction, namely an oxygen-independent DNA-8-MOP photoadduct, followed by an oxygen-dependent second step, sensitive to carotenoids. This result suggests that dietary carotenoids (powerful antioxidant molecules) might prevent the carcinogenic risk caused by substances that are transformed into ultimate carcinogens by oxidative processes which are indirectly carcinogenic. Finally, to verify whether supplemental carotenoids can affect carcinogenesis where neither light excitation nor oxidative metabolic processes are involved, an experimental attempt was made on gastric carcinogenesis induced in rats by the direct carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The results demonstrate that supplemental carotenoids do not affect initiation and progression stages, but do prevent the progression stage of dysplasias to infiltrating gastric carcinomas. Thus, this provides strong presumptive evidence for oxygen radical involvement in the later stages of this neoplastic development, as recently reported in the literature. As far as mutagenicity in S. typhimurium is concerned, carotenoids do not exert, as expected, any protective effect on MNNG mutagenic activity. The above experimental data suggest that supplemental carotenoids, instead of sunscreen preparations, can be adopted by outdoor workers to prevent skin cancer. Accordingly, such natural antioxidants may be useful in human chemoprevention against neoplasias of the lung, breast, urinary bladder, and colon and rectum even after radical surgery.

Serum beta-carotene and subsequent risk of cancer: results from the BUPA Study

In the BUPA Study, a prospective study of 22,000 men attending a screening centre in London, serum samples were collected and stored. The concentration of beta-carotene was measured in the stored serum samples from 271 men who were subsequently notified as having cancer and from 533 unaffected controls, matched for age, smoking history and duration of storage of the serum samples. The mean beta-carotene level of the cancer subjects was significantly lower than that of their matched controls (198 and 221 micrograms l-1 respectively, P = 0.007). The difference was apparent in subjects from whom blood was collected several years before the diagnosis of the cancer, indicating that the low beta-carotene levels in the cancer subjects were unlikely to have been simply a consequence of pre-clinical disease. Men in the top two quintiles of serum beta-carotene had only about 60% of the risk of developing cancer compared with men in the bottom quintile. The study was not large enough to be able to indicate with confidence the sites of cancer for which the inverse association between serum beta-carotene and risk of cancer applied, though the association was strongest for lung cancer. The association may be due to beta-carotene affecting the risk directly or it may reflect an indirect association of cancer risk with some other component of vegetables or with a nonvegetable component of diet that is itself related to vegetable consumption.

Plasma carotenoid profiles in normals and patients with cancer

Most human cancers arise in epithelial tissues, which are critically dependent on vitamin A for normal differentiation and proliferation. Dietary carotenoids consist of individual retinoids--pro-vitamin A precursors and non-pro-vitamin A precursors-displaying different biological activity. Although epidemiological data suggest that low serum vitamin A levels were associated with an increased risk of cancer, it is not known whether one specific or all vitamin A carotenoids are involved. To assess whether the plasma carotenoids are related to the nutritional or cancer-bearing state, a study was conducted to measure total and individual carotenoids in four groups: cancer-bearing, malnourished; cancer-bearing, well-nourished; non-cancer, malnourished; and well-nourished volunteers of comparable age and sex. There was no difference in total carotenoids and pro-vitamin A precursors between the well-nourished--both normal volunteers and cancer patients. Malnourished cancer and non-cancer patients had significantly (p less than 0.05) lower value of both. Most of the circulating carotenoids in all groups were the non-pro-vitamin A precursors. Both malnourished cancer and non-cancer patients had lower values than well-nourished (p less than 0.05). Differences were related to nutritional state, rather than presence of cancer.

The relationship of dietary intake and serum levels of retinol and beta-carotene with breast cancer. Results of a case-control study

The possible association between the risk of breast cancer, blood level, and dietary intake of preformed Vitamin A (retinol) and beta-carotene was investigated in a case-control study carried out from May 1982 to June 1985. The patients studied were 214 previously untreated individuals with T1-2, N0-1, M0 breast cancer admitted to the National Cancer Institute of Milan and 215 controls admitted for conditions other than neoplastic or metabolic disorders. Both cases and controls were selected from an age group ranging from 30 to 65 years old. Plasma levels of retinol and beta-carotene were tested from blood samples drawn during the first day after admission to the hospital. A questionnaire about diet was used to estimate the mean intake of 69 food items from which a daily dietary index of retinol and beta-carotene intake was computed. Information relating to the woman's history, socioeconomic status, and known risk factors for breast cancer was also collected. No association was found between beta-carotene (in the diet or blood) or dietary retinol and the risk of breast cancer. As for blood retinol, our data show a significant trend of increasing risk with higher levels; multivariate relative risk for subsequent serum levels based on the control quintiles, are 1, 1.5, 1.8, 1.7; (test for linear trend: chi-square = 8.26). Thus, these findings, together with the results of other studies, suggest that retinol and beta-carotene are unlikely to be related to the risk of breast cancer.

Dietary habits and lung cancer risk among Chinese females in Hong Kong who never smoked

This describes a retrospective study in which 88 lung cancer patients and 137 district-matched controls were interviewed concerning the effects of diet on lung cancer risk among Hong Kong Chinese women who never smoked tobacco. Those in the lowest tertile of consuming fresh fruit or fresh fish had statistically significant adjusted relative risks (RRs) of 2.4 and 2.8, respectively. The protective effects of diet, i.e., higher consumption of leafy green vegetables, carrots, tofu, fresh fruit, and fresh fish, were confined mostly to those with adenocarcinoma or large cell tumors. Only fresh fruit was found to positively, and smoked meats to negatively, affect the risk of squamous or small cell tumors. Foods high in vitamin C, retinol, and calcium seemed to exert larger effects. Subjects from larger households were shown to be more frequent consumers of fresh vegetables, fruit, and fish. Because the lifetime weighted household size could be used as a surrogate index of past dietary quality, when it was combined with current dietary intakes of fresh fruit, the RR increased as either factor decreased in a dose-response manner. The adjusted RR was 5.8 at the lowest level. Further testing of the validity of the lifetime weighted household size as an index of past dietary quality is needed.

Epidemiologic patterns in lung cancer by histologic type

Three thousand and ninety-seven lung cancer patients interviewed in different U.S. hospitals in 1977-1984 were classified into Kreyberg I and Kreyberg II categories. In both sexes, Kreyberg II patients were found to be younger and more frequently Jewish; among the male patients only, Kreyberg II cases were higher in educational and occupational level. These differences remained when the effect of cigarette smoking was controlled. Study data showed an increase in the frequency of Kreyberg II cases over time, and significantly, a decrease with younger age of the Kreyberg I:Kreyberg II ratio in both sexes. It is concluded that the observed secular increase in Kreyberg II is real and not merely due to changes in diagnostic methodology. On the basis of demographic differences noted, possible etiologic factors that may have contributed to the recent changes in lung cancer distribution by cell type are suggested.

Effects of vitamin A and E supplementation to diets containing two different fat levels on methylnitrosourea-induced mammary carcinogenesis in female SD-rats

The aim of this study was to elucidate the effects of dietary vitamin A and E supplementation on tumorigenesis in correlation to the fat content of the respective diet in an animal model. One hundred and twenty female SD rats were initiated intravenously with 25 mg MNU kg-1 on day 50 of life. For a period of 6 months, beginning after the day of initiation, all animals received a semisynthetic diet containing 25% or 45% of the energy as fat, supplemented either with a 10-fold higher amount of naturally occurring vitamins A and E than in rat standard diets or, with a normal level of these vitamins. The experiment showed: (1) Vitamin A and E supplementation showed no significant chemopreventive effect against mammary tumour development. (2) This result was independent from the supplied fat level of the respective diet. (3) The fat content per se did not significantly influence mammary tumorigenesis.

Purification of prealbumin from human serum

A method is presented by which prealbumin (thyroxine-binding prealbumin; tryptophan-rich prealbumin) may be purified to homogeneity from human serum. The method involves precipitation of contaminating proteins with dilute aqueous phenol, ion-exchange chromatography on DEAE-Sephacel, and gel permeation chromatography on Sephadex G-100. The yield is 25-30%, and the prealbumin is homogeneous by polyacrylamide gel electrophoresis at pH 8.9 and pH 3.6.

Optical automation for sputum cytology

The use of high-resolution image analysis in the detection and classification of cellular atypias has been demonstrated in many instances. We have applied this technique to the classification of bronchial epithelial atypias from sputum. Our research indicates that, in classifying cells into one of five atypia stages, 90% of the cell classifications were within one category of the criterion stage, while 88.6% of the subjects were correctly diagnosed. These results indicate the feasibility of using high-resolution cell image analysis to monitor the progression of squamous cell carcinoma of the lung and, it is to be hoped, to permit the reversal of that process.

Separation of plasma carotenoids and quantitation of beta-carotene using HPLC

A method was developed for the extraction and separation of human plasma carotenoids and quantitation of beta-carotene. Carotenoids were extracted from plasma with ethanol: hexane and separated by C18 reversed phase HPLC using spherical 3 micron packing. beta-Carotene was identified and quantitated using an external standard. The within-run precision of three different plasma pools ranged from 3.53-5.72% relative standard deviation (RSD). The between-run precision was 7.34% RSD. The method was linear to 500 micrograms/l with a statistical detection limit of 3.80 micrograms/l. Recovery of added beta-carotene was from 90.41-100.37%. This method was compared to a spectrophotometric 'total carotene' method. The mean plasma concentrations of 25 male and 25 female human volunteers for the 'total carotene' were 1,549 micrograms/l for all samples, 1,487 micrograms/l for males and 1,611 micrograms/l for females. The corresponding true beta-carotene concentrations obtained by HPLC analysis were 134.8, 115.9 and 153.7 micrograms/l, respectively. The true beta-carotene concentrations were on the average only 8.76% (8.07% for males and 9.46% for females) of the concentrations obtained by the spectrophotometric 'total carotene' method. Correlation between the methods had an r = 0.6107. The poor correlation is due to the difference in the measured components. Total carotene methods measure all solvent extractable moieties having absorbance in the 430-460 nm region, while the HPLC method quantitates true beta-carotene after chromatographic separation from other carotenoids. Reference intervals were established for plasma beta-carotene using REFVAL, an IFCC computer program for determining statistical reference intervals. The reference interval for all samples is 40 to 344 micrograms/l.

Esophageal cancer: vitamin and lipotrope deficiencies in an at-risk South African population

The nutritional status of individuals from areas of South Africa that are known for having a high incidence of esophageal cancer was investigated. Our results show that individuals living in high-risk areas differ significantly from those in low-risk areas with respect to vitamins A, E, and B12 in addition to folate. These results suggest that deficiencies in these nutrients may play a significant role in the etiology of esophageal cancer.

Legume carotenoids

In recent years, the results of research studies have suggested a positive beneficial relationship between a vegetarian-based diet and low incidence of diseases, including coronary heart disease, cancer, obesity, dental caries, and osteoporosis. beta-Carotene has specifically been suggested as a nutrient with antitumorigenic properties. In this regard there is a need to evaluate the carotenoid content of foods. Legumes are one of the staple components of a vegetarian diet. This review specifically surveys the prevalence of carotenoids in food and forage legumes. In addition, the methods available for carotenoid analysis are discussed; factors affecting the determination of carotenoid content during maturation, germination, processing and storage are identified; research areas which have been inadequately explored are identified; and suggestions are made for future lines of investigation.

The effect of beta-carotene on BP-induced respiratory tract tumors in hamsters

The modifying effect of beta-carotene on benzo[a]pyrene (BP)-induced tumors of the respiratory tract was investigated in Syrian hamsters. Groups of hamsters were fed a semisynthetic diet supplemented with either no or 56 mg/kg beta-carotene. Respiratory tract tumors were induced by intratracheal instillation of BP attached to ferric oxide. The beta-carotene and vitamin A contents of the liver were increased in the high beta-carotene group, but the serum beta-carotene levels were very low when compared with those commonly observed in humans. beta-Carotene supplementation did not affect the tumor response of the respiratory tract. Neither the incidence and severity of preneoplastic changes were influenced. However, there was a statistically significant inverse relationship between serum retinol content and the presence of respiratory tract tumors in survivors, regardless of the dietary treatment.

Vitamin A and female lung cancer: a case-control study on plasma and diet

Plasma and dietary levels of retinol and beta-carotene were evaluated in a consecutive series of 47 females with histologically proven primary lung cancer and 159 nonneoplastic hospital controls. The dietary questionnaire included 69 different items: special care was given to foods rich in vitamin A and seasonal foods (e.g., vegetables and fruits), whereas serum analysis was focused on retinol and beta-carotene. Age-adjusted mean values for cases and controls were, respectively, 458.3 vs. 551.3 mg for plasma retinol, 276.1 vs. 390.1 mg for plasma carotene; 598.1 vs 820.6 mg for daily retinol, and 628.0 vs. 882.5 mg for dietary carotene. The odds ratios for low vs. high tertile, adjusted for age, smoking, retinol or carotene, cholesterol, and triglycerides by multivariate analysis were, respectively, 1.13 for plasma retinol, 5.04 for plasma carotene, 3.27 for dietary retinol, and 2.93 for dietary carotene. For all the examined items, there was a trend of increased risk for the second and third tertile, and statistical significance was reached for plasma beta-carotene (p less than 0.05). The hypothesis that a higher risk of lung cancer is related to a low vitamin A consumption is supported by these data.

Dietary vitamin A and lung cancer: results of a case-control study among chemical workers

A nested case-control study conducted among a cohort of chemical manufacturing employees provided an opportunity to test the hypothesis that lung cancer risk is inversely related to dietary intake of vitamin A. Eligible for study were 308 former male employees who had died of lung cancer between 1940 and 1980. Two control groups, one a decedent and the other a "living" series, were individually matched to the cases one-for-one. Interviews were completed with 734 subjects or their next-of-kin and included a food frequency list. A vitamin A index was developed for each subject based on the frequency of consumption of 29 food items. After adjustment for a number of potentially confounding variables (e.g., smoking, educational level, and use of vitamin supplements), there was evidence that vitamin A intake was inversely associated with lung cancer risk. The effect was most pronounced in the comparisons with the "living" controls and appeared strongest among cigarette smokers. Subjects in the lowest tertile of vitamin A intake had approximately twice the risk of lung cancer as those in the highest. Analyses of an index of carotenoids and of individual food items suggested that plant sources of vitamin A may play a more important role in producing the effect than do animal sources.

Vitamin A, carotenoids, and retinoids

One promising area of current research in chemoprevention is the possibility that micronutrients, including vitamin A analogues, may decrease cancer incidence. The term "vitamin A" refers either to retinol (preformed vitamin A) and its synthetic analogues, or to certain carotenoids (provitamin A), which are converted to retinol in the body, as needed. Retinol and the other retinoids are integrally involved in cell growth and differentiation, which may affect carcinogenesis. Such a role has been supported by a large number of in vitro and animal experiments. Data from studies among humans are sparse, in part because most dietary studies have been conducted in populations in which the vast majority of vitamin A intake is actually beta-carotene and other carotenoids, found in carrots and other vegetables and fruits. Although the carotenoids do not have the hormone-like properties of retinol, they do have a potent antioxidant effect and could thus reduce cancer risk by preventing tissue damage due to oxidation. This possibility is supported by data from a large number of observational epidemiologic studies, most of which have consistently found an inverse relation between consumption of carotene-rich vegetables and cancer risk. However, the only direct way to determine whether carotenoids have a beneficial effect is through large, carefully conducted randomized trials. Several such studies are currently underway and should provide sound evidence on which future medical policy and practice can be based.

Dietary factors for cancer of specific sites

Even though the issues have been greatly simplified in this article by citing of only the most salient data, when a number of different cancers are examined, a diverse range of dietary factors is implicated. For a number of cancers, very little is known, and for others, competing hypotheses are supported by conflicting data. Despite these obvious limits, some generalizations regarding common patterns of risk at different cancer sites may be possible. For example, although the nutrients and mechanisms may vary by site, lack of consumption of fruits and vegetables has been linked repeatedly to cancers of the mouth, larynx, esophagus, and lung. A similar association is suggested for cancers of the cervix and bladder. Another commonality is the association of dietary fat with cancers of the breast, ovary, prostate, and, possibly, colon. Alcohol is associated with cancers of the mouth, larynx, and, possibly, rectum. Coffee has been studied in association with cancers of the pancreas, ovaries, and lungs, but few of these studies have been replicated and the role of this common dietary exposure remains in question. In most other instances, unique cancers are linked to unique dietary exposures, for example, fiber and colorectal cancer or nitrates and stomach cancer. Given that both common and unique sources of dietary risk may be identified for different cancers, future research may benefit from a two-pronged research strategy. Basic nutrients need to be examined for multiple cancers, and specific aspects of diet require in-depth study for specific cancers. From such an approach, it may be possible to resolve some of the questions and issues reviewed herein.

Beta-carotene therapy for erythropoietic protoporphyria and other photosensitivity diseases

This paper describes the development of the use of carotenoid pigments in the treatment of light-sensitive skin diseases. It also discusses the animal and human studies involved in determining whether carotenoids have any anti-cancer activity. The possible mechanisms of carotenoid photoprotective and anti-cancer actions are briefly discussed.

Cancer of the cervix uteri and vitamin A

The concentrations of retinol and beta carotene were measured in serum samples taken from 113 women with cervical cancer, 32 with invasive and 81 with pre-invasive disease, and compared with those from 226 age-matched control women. There was little difference in serum retinol levels between women with cancer of the cervix, at any stage, and the control women, after adjusting for potential confounding factors. Serum beta carotene concentrations were likewise similar in women with invasive disease and the controls. However mean beta carotene levels were significantly reduced in women with pre-invasive disease compared to the controls (221.3 cf. 291.6 micrograms l-1, P less than 0.05). This reduction was more evident amongst women with a diagnosis of carcinoma-in-situ (mean 213.1 micrograms l-1 than amongst those with severe dysplasia (mean 228.7 micrograms l-1. There is a negative trend between beta carotene and risk of pre-invasive disease which is of borderline significance. These data have also been used to investigate the effects of smoking and oral contraceptive usage on the serum levels of retinol and beta carotene. Both habits tend to increase retinol and decrease beta carotene concentrations.

Lipoprotein cholesterol, vitamin A, and vitamin E in an alcoholic population

Elevated alcohol consumption is associated with an increased risk of cancer. Reasons for this association are not well established but may relate to alterations in cholesterol, vitamin A (carotene and retinol), and vitamin E metabolism, since low levels of these factors have been linked to risk of cancer. Blood levels of cholesterol, carotene, retinol, and vitamin E were determined in 192 male alcoholics entering into an alcohol detoxification program. Compared to nonalcoholic populations, their cholesterol (187 mg/dl) and carotene (94 micrograms/dl) concentrations were markedly reduced at entrance; however, abstinence of 33 days returned both to normal levels. In contrast, the retinol and vitamin E levels were within the normal range at baseline and remained relatively stable throughout rehabilitation. Of particular interest was that the low density lipoprotein cholesterol was highly correlated with carotene (r = +0.40, whites, r = +0.54, blacks). The results suggest that alterations in the metabolism of cholesterol and carotene, due to alcohol intake, may partially account for the relationship of alcohol to increased cancer risk.

Application of cell-image analysis to the diagnosis of cellular atypias in sputum: a review

The incidence of carcinoma of the lung continues to steadily rise, and attempts at early diagnosis to improve prognosis have not yet been rewarding. The goal of our research is to decrease the incidence of lung cancer by detecting premalignant bronchial dysplasias in individuals in whom development of lung cancer is potentially preventable. To achieve this, we have developed an atypia status index (ASI)--the assignment of numerical values to the various stages of atypical bronchial epithelial cells in sputum, and a cell atypia profile (CAP)--an ASI-generated scale of 200 such atypical bronchial epithelial cells in a single sputum specimen. Computerized cell-image analysis techniques and statistical data analysis are used to generate the ASIs and CAPs for each subject. This study is a step toward the development of an automated cell-image analysis system for mass screening of premalignant atypias in sputum of those considered at high risk for lung cancer (i.e., men and women of 40 yr of age and older, with more than 20 pack-yr of cigarette smoking).

Inhibition of hamster tongue carcinogenesis by selenium and retinoic acid

The inhibitory effect of selenium, 13-cis-retinoic acid, and their combination was studied in an animal model in which squamous cell carcinoma of the tongue was induced by 0.5% 9,10 dimethyl-1,2 benzanthracene (DMBA). A controlled, blinded experiment was carried out using 60 Syrian hamsters divided into four groups of 15 each. When compared to controls, the mean day of carcinoma onset was delayed 3 weeks for animals given selenium, 6 weeks for animals given retinoic acid, and 5.5 weeks for animals given selenium plus retinoic acid. The differences between each experimental group and the control group are statistically significant. We conclude that both selenium and retinoic acid inhibit the development of DMBA-induced squamous cell carcinoma of the tongue in hamsters. The dose of retinoic acid used produces a stronger inhibitory effect, but is associated with significant toxicity. At the doses used, combined inhibitory effect is no greater than that for retinoic acid alone.

Epidemiologic studies of vitamins and cancer of the lung, esophagus, and cervix

Epidemiologic studies of the relationships between vitamins and 3 types of cancer are reviewed. First, the widely reported association between vitamin A and beta-carotene and risk of lung cancer is considered. In a large population-based case-control study of lung cancer among white males in New Jersey, increased intake of vegetables, dark green vegetables, dark yellow-orange vegetables, and carotenoids were each associated with reduced risk, but intake of retinol or total vitamin A was not related. The protective effect of vegetables was limited to current and recent cigarette smokers, which suggests that vegetable intake prevents a late-stage event in carcinogenesis. Consumption of dark yellow-orange vegetables was consistently more predictive of reduced risk than either the total carotenoid index or consumption of any other food group, possible because of the high content of beta-carotene in this food group. The results and limitations of other epidemiologic studies of diet and lung cancer are reviewed. Second, the evolving relationship between multiple micronutrient deficiencies and esophageal cancer is discussed. In a death certificate-based case-control study of esophageal cancer in black males in Washington, D.C., several indicators of general nutritional status, including consumption of fresh or frozen meat and fish, dairy products and eggs, and fruit and vegetables, and the number of meals eaten per day, were inversely and independently correlated with the risk of esophageal cancer. Estimates of intake of micronutrients, such as carotenoids, vitamin C, thiamin, and riboflavin, were less strongly associated with reduced risk than were the broad food groups that provide most of each micronutrient. Thus no single micronutrient deficiency was identified. Other studies suggest that generally poor nutrition may partially explain the susceptibility of urban black men to esophageal cancer. Finally, the postulated association between low folacin levels and risk of cervical cancer is examined. Among women who use oral contraceptives, serum and red blood cell folacin levels were reported to be lower among those with cervical dysplasia. In a clinical trial involving oral contraceptive users, cervical dysplasia gradually decreased in the group supplemented with oral folate but remained unchanged in the group given the placebo. Other epidemiologic studies of diet and cervical cancer are discussed.

Dietary vitamin A and cancer--a multisite case-control study

The relationship between an index of dietary vitamin A and cancer risk at 25 sites was assessed in retrospective case-control studies. Common control groups for males and females were used in all analyses. Relative risk estimates were derived from multiple logistic regression analyses that controlled for age, alcohol consumption, and smoking exposure. We found that among males, dietary vitamin A is associated with lower risk for cancers of the tongue, floor and other mouth, pharynx, larynx, esophagus, and lung but higher risk for Hodgkin's disease and leukemia. Among females, we found that dietary vitamin A had less effect on risk generally but was associated with lower risk for bladder cancer. These findings are consistent with previous research that showed dietary vitamin A to be associated with decreased risk of squamous epithelial cancers. The association of dietary vitamin A and increased risk of Hodgkin's disease and leukemia among males in addition to the disparity in effect of dietary vitamin A on risk between males and females are areas worthy of further research.

Biological antioxidants

The mechanism of lipid peroxidation and the ways in which the rate of this reaction can be reduced by small quantities of certain specific chemicals, called antioxidants, are described. The types and roles of the different antioxidants found in living systems are considered. Vitamin E (alpha-tocopherol) has long been recognized as an important lipid-soluble, chain-breaking antioxidant. It has an unexpectedly high reactivity towards peroxyl radicals, which can be understood only after detailed consideration of its structure. It is the major antioxidant of its class in human blood and its effectiveness in plasma is greatly improved by a synergistic interaction with water-soluble reducing agents such as ascorbic acid. Experiments designed to locate vitamin E within phospholipid bilayers and to discover the origin of the different biopotencies of stereoisomers of alpha-tocopherol are also described.

Decapreno-beta-carotene as an internal standard for the quantification of the hydrocarbon carotenoids by high-performance liquid chromatography

The application of decapreno-beta-carotene as an internal standard in quantification of the hydrocarbon carotenoids extracted from raw carrots has been thoroughly examined. Decapreno-beta-carotene is a C50 beta-carotene that has most of the requirements of an internal standard and it can be commercially synthesized in high purity. An isocratic high-performance liquid chromatographic (HPLC) system has been developed that separated all-trans-alpha-carotene, all-trans-beta-carotene, and its 15,15'-cis-isomer from this internal standard. Quantitative determination of the hydrocarbon carotenoids in carrots by HPLC using the internal standard technique gave values for alpha- and beta-carotene similar to those obtained from alpha- and beta-carotene standards alone.

Serum micronutrient levels in relation to gastric pathology

As part of an ongoing cohort study of gastric cancer precursors in Nariño, Colombia, blood levels of ascorbic acid, vitamin E, retinol, pre-albumin, retinol binding protein and carotenoids were measured and correlated with histopathologic findings of gastric biopsies. Carotene levels in both sexes and vitamin E levels in males were significantly lower in subjects with gastric dysplasia than in subjects with normal mucosa and subjects with less advanced gastric lesions (chronic atrophic gastritis and intestinal metaplasia). No other significant correlations were found.

Serum and plasma beta-carotene levels measured with an improved method of high-performance liquid chromatography

An isocratic high-performance liquid chromatographic method specifically developed to allow simple and rapid determination of beta-carotene concentrations in serum and plasma is reported. Using a method modified from a previously published technique, serum and plasma proteins are denatured by exposure to perchloric acid, and beta-carotene is subsequently extracted into an organic matrix consisting of ethyl acetate-tetrahydrofuran (1:1); no evaporation step is required. Separation is achieved using isocratic elution from a reversed-phase C18 column with UV detection at 436 nm. Recovery of beta-carotene from water and plasma was greater than 98.1%; beta-carotene was stable in the extraction matrix for at least 4 h. Three anticoagulants (oxalate, citrate, and EDTA) caused losses of beta-carotene; perchloric acid and tetrahydrofuran could also destroy beta-carotene under certain conditions. Each run required less than 15 min; within-day coefficient of variation for identical samples averaged 2.3%, between-day coefficient of variation was 4.4% and sensitivity was better than 10 ng/ml. Stability of beta-carotene in plasma was also examined. This method permits a simple, rapid, sensitive, precise, and accurate determination of beta-carotene using 0.5 ml of serum or heparinized plasma.