Risk factors for lung cancer in Singapore Chinese, a population with high female incidence rates

Epidemiology of lung cancer

In the United States, lung cancer remains the leading cause of cancer death in both men and women even though an extensive list of risk factors has been well-characterized. Far and away the most important cause of lung cancer is exposure to tobacco smoke through active or passive smoking. The reductions in smoking prevalence in men that occurred in the late 1960s through the 1980s will continue to drive the lung cancer mortality rates downward in men during the first portion of this century. This favorable trend will not persist unless further reductions in smoking prevalence are achieved.

Characterization of emissions from burning incense

The primary objective of this study was to improve the characterization of particulate matter emissions from burning incense. Emissions of particulate matter were measured for 23 different types of incense using a cyclone/filter method. Emission rates for PM2.5 (particulate matter less than 2.5 microm in aerodynamic diameter) ranged from 7 to 202 mg/h, and PM2.5 emission factors ranged from 5 to 56 mg/g of incense burned. Emission rates were also determined using an electrical low pressure impactor (ELPI) and a small electrostatic precipitator (ESP), and emission rates were compared to those determined using the cyclone/filter method. Emission rates determined by the ELPI method were consistently lower than those determined by the cyclone/filter method, and a linear regression correlation was found between emission rates determined by the two methods. Emission rates determined by the ESP method were consistently higher than those determined by the cyclone/filter method, indicating that the ESP may be a more effective method for measuring semivolatile particle emissions. A linear regression correlation was also found between emission rates determined by the ESP and cyclone/filter methods. Particle size distributions were measured with the ELPI, and distributions were found to be similar for most types of incense that were tested. Size distributions by mass typically ranged from approximately 0.06 to 2.5 microm in aerodynamic diameter, with peak values between 0.26 and 0.65 microm. Results indicated that burning incense emits fine particulate matter in large quantities compared to other indoor sources. An indoor air quality model showed that indoor concentrations of PM25 can far exceed the outdoor concentrations specified by the US EPA's National Ambient Air Quality Standards (NAAQS), so incense smoke can pose a health risk to people due to inhalation exposure of particulate matter. Emissions of carbon monoxide (CO), nitric oxide (NO), and sulfur dioxide (SO2) were also measured for seven types of incense. Emission rates of the gaseous pollutants were sufficient to cause indoor concentrations, estimated using the indoor air quality model, to exceed the outdoor concentrations specified by the NAAQS under certain conditions. However, the incense samples that were tested would fill a room with thick smoke under these conditions.

Cooking oil fumes and risk of lung cancer in women in rural Gansu, China

Cooking oil fumes have been suggested to increase the risk of lung cancer in Chinese women by exposing them to mutagenic substances. We investigated the association between lung cancer and locally made rapeseed and linseed oils in a population-based case-control study in Gansu Province, China. Two hundred and thirty-three incident, female lung cancer cases diagnosed from 1994-98 were identified. A control group of 459 women was selected from census lists and were frequency matched on age and prefecture. Interviewers obtained information on cooking practices and cooking oil use. The odds ratio (OR) for lung cancer associated with ever-use of rapeseed oil, alone or in combination with linseed oil, was 1.67 (95% CI 1.0-2.5), compared to use of linseed oil alone. ORs for stir-frying with either linseed or rapeseed oil 15-29, 30 and > or =31 times per month were 1.96,1.73, and 2.24, respectively (trend, P=0.03), relative to a lower frequency of stir-frying. Lung cancer risks also increased with total number of years cooking (trend, P<0.09). Women exposed to cooking fumes from rapeseed oil appeared to be at increased risk of lung cancer, and there was some evidence that fumes from linseed oil may have also contributed to the risk.

Diet, reproductive factors and lung cancer risk among Chinese women in Singapore: evidence for a protective effect of soy in nonsmokers

The factors associated with risk of lung cancer among nonsmokers have not been fully elucidated, but dietary factors have consistently been shown to play a role. Chinese women are unique in having a high incidence of lung cancer despite a low smoking prevalence. This population is also known to have a high intake of soy, a dietary source of phytoestrogens. We conducted a hospital-based case-control study among Singapore Chinese women, comprising 303 cases and 765 age-matched controls, of whom 176 cases and 663 controls were lifetime nonsmokers. Data on demographic background, reproductive factors and dietary intake of fruit, vegetables and soy foods were obtained by in-person interview. We observed an inverse association between intake of total, cruciferous and non-cruciferous vegetables and risk of lung cancer among smokers. Although smokers in the highest tertile of fruit intake also had a lower risk, this was not statistically significant. Higher intake of soy foods significantly reduced risk of lung cancer among lifetime nonsmokers, but not among smokers. When soy isoflavonoid intake in mg/week was computed based on frequency and portion size of intake of eight common local soy foods, the adjusted OR among nonsmokers for the highest tertile compared to the lowest was 0.56, 95% CI 0.37-0.85 (p for trend <0.01). Fruit intake was also significantly associated with reduced lung cancer risk among nonsmokers, but the effect was not significant after adjustment for soy intake. On the other hand, soy intake remained an independent predictor of risk after controlling for fruit intake. Reproductive effects were also primarily confined to lifetime nonsmokers, among whom having 3 or more livebirths (adjusted OR 0.65, 0.44-0.96) and a menstrual cycle length of more than 30 days (OR 0.46, 0.25-0.84) accorded a significantly reduced risk of lung cancer. Place of birth was significantly associated with risk among nonsmokers (OR 2.6, 1.7-3.9 for China-born vs. local born) but not among smokers. When analysis was restricted to nonsmokers with adenocarcinomas, the dietary effects were consistent or enhanced. On stepwise regression, soy intake and cycle length emerged as the independent dietary and reproductive predictors of lung cancer risk in nonsmokers. These findings are consistent with other evidence suggesting an involvement of estrogen-related pathways in lung cancer among non-smoking women.

Effect of smoking cessation on major histologic types of lung cancer

STUDY OBJECTIVES

It is well-recognized that the risk of lung cancer declines after smoking cessation. However, the degree of decline in different histologic types of lung cancer is not well understood. We conducted a meta-analysis of peer-reviewed studies to assess the effect of smoking cessation on rates of major histologic types of lung cancer.

DESIGN

Studies published in English between 1970 and 1999 were identified through searches of computerized databases (ie, MEDLINE and CANCERLIT). Combined estimates of relative risk and 95% confidence intervals were calculated for 27 studies using fixed and random effects models. Separate analyses were conducted for men and women.

RESULTS

Smoking cessation was associated with a reduction in the risk of all the major histologic types of lung cancer. The highest reduction was in small cell lung carcinoma (SCLC) and squamous cell carcinoma (SQC), and the lowest reduction was seen in large cell cancer and adenocarcinoma. In women, the combined risks for SQC and SCLC were higher than those in men. The dose-response curve for intensity of smoking was steeper in women.

CONCLUSION

The findings of this study suggest that smoking cessation results in the greatest reductions for SCLC and SQC. This effect is most marked in heavy smokers, particularly among women.

Effect of cigarette smoking on major histological types of lung cancer: a meta-analysis

Although cigarette smoking is an established risk factor for lung cancer, the strength of association with different histologic types is not well understood. This meta-analyses of peer-reviewed studies was conducted to assess the effect of cigarette smoking on major histologic types of lung cancer. Studies were identified through MEDLINE and CANCERLIT searches. A total of 48 studies published between 1970 and 1999 were identified. Combined estimates of relative risks (OR) and 95% confidence intervals (CI) were calculated using fixed and random effect models. Separate analyses were conducted by study design and gender. A linear dose-response was fit to studies reporting data on intensity and duration of smoking. All histologic types of lung cancer were significantly associated with cigarette smoking. The association was stronger with squamous cell carcinoma (SQC) and small cell carcinoma (SCLC) than with large cell cancer (LGC) and adenocarcinoma (ADC). The combined OR for heaviest smoking intensity (30+ cigarettes per day) ranged from 4.10 (CI 3.16-5.31) for ADC to 18.3 (CI 9.26-36.4) for SCLC. The combined OR for longest duration of smoking (40+ years) ranged from 3.80 (CI 2.35-6.16) for ADC to 38.6 (CI 11.9-125) for SCLC. In women, the combined OR for SQC and SCLC were higher than those in men. The dose response curve for intensity of smoking was steeper in women. The findings of this study provide additional evidence for a causal relationship between smoking and all histologic types of lung cancer.

Identification of carcinogens in cooking oil fumes

According to earlier studies, fumes from cooking oils were found to be genotoxic in several short-term tests such as the Ames test, sister chromatid exchange, and SOS chromotest. Fume samples from six different commercial cooking oils (safflower, olive, coconut, mustard, vegetable, and corn) frequently used in Taiwan were collected. Polycyclic aromatic hydrocarbons (PAHs) were extracted from the air samples and identified by high-performance liquid chromatography and confirmed by gas chromatography/mass spectrometry. Extracts of fumes from safflower oil, vegetable oil, and corn oil contained benzo[a]pyrene (BaP), dibenz[a,h]anthracene (DBahA), benzo[b]fluoranthene (BbFA), and benzo[a]anthracene (BaA). Concentrations of BaP, DbahA, BbFA, and BaA were 2.1, 2.8, 1.8, and 2.5 microg/m3 in fumes from safflower oil; 2.7, 3.2, 2.6, and 2.1 microg/m3 in vegetable oil; and 2.6, 2.4, 2.0, and 1.9 microg/m3 in corn oil, respectively. The authors constructed models to study the efficacy of table-edged fume extractors used commonly by Taiwanese restaurants. Concentrations of BaP were significantly decreased when the fume extractor was working (P<0.05) and the average reduction in percentage was 75%. The other identified PAHs were undetected. These results indicated that exposure to cooking oil fumes could possibly increase exposure to PAHs, which may be linked to an increased risk of lung cancer. The potential carcinogenic exposure could be reduced by placing table-edged fume extractors near cooking pots.

Genotoxicity of fumes from heated cooking oils produced in Taiwan

Epidemiologic investigations of lung cancer among Taiwanese nonsmoking women have found that exposure to fumes from cooking oils may be an important risk factor. Fume samples from three different commercial cooking oils (lard, soybean, and peanut oils) often used in Taiwan for preparing Chinese meals were collected for genotoxicity analysis in SOS chromotest and sister chromatid exchange (SCE) assays. The induction factors of the SOS chromotest in Escherichia coli PQ 37 were dependent on the concentrations of lard and soybean cooking oil extracts without S9 mix. In addition, when CHO-K1 cells were exposed to condensates of cooking oil fumes for 12 h, SCEs showed a dose-related increase in extracts of lard and soybean oil fumes. This result provides experimental evidence and is in accordance with the findings of epidemiologic studies that women exposed to the emitted fumes of cooking oils are at an increase risk of contracting lung cancer.

Antioxidant vitamins in the prevention of cancer

Cancer is a leading cause of morbidity and mortality in the United States and other developed countries. In searching for preventive strategies against this disease, researchers have postulated that antioxidant vitamins may play a role in preventing cancer since several plausible biological mechanisms exist. This article reviews the epidemiological evidence for a role of antioxidant vitamins (in particular, beta-carotene, vitamin E, and vitamin C) in the development of cancer. Observational studies provide fairly consistent data for an inverse association between high intake of antioxidant vitamins, especially beta-carotene and vitamin C, and cancer risk. However, randomized trials generally have not supported the hypothesis. Several explanations for these inconsistent findings are possible. These include: 1) confounding by other healthy dietary and nondietary habits in observational studies; 2) the protective role of a combination of many different nutrients present in fruits and vegetables, rather than the single nutrient or combination of two nutrients that most trials have tested; 3) inadequate duration of follow-up in most randomized trials; and 4) heterogeneity of the populations studied. Reliable epidemiological evidence regarding whether antioxidant vitamins play a role in preventing cancer will have to come from both observational studies and randomized trials since these different study designs each have unique strengths and limitations. Based on the available evidence, it seems prudent to advocate a diet rich in fruits and vegetables, rather than the consumption of specific antioxidant vitamin supplements, in order to decrease the risk of developing cancer.

Cancer epidemiology in migrant populations

Migrant studies have taken advantage of the wide geographical variation in cancer risk. Cancer rates in migrants, obtained from routinely collected incidence or mortality statistics, are compared with those in the host country and in the country of origin; the rate of change with time since migration (or age at migration) and in subsequent generations is assessed; and the results are interpreted in the light of differences in socio-economic status and the degree of cultural assimilation. Rapid changes in cancer risk following migration imply that life-style or environmental factors are of overriding importance in aetiology. The susceptibility of fair-skinned races to ultraviolet (UV)-associated skin cancers is an example of racial differences based on inherited factors, but the long-term excess or deficit of other cancers in migrants has not yet been attributed definitively to genetic rather than persisting life-style factors. Are there racial differences in metabolism, DNA repair mechanisms or altered expression of oncogenes or tumour suppressor genes? Several genetic polymorphisms affecting the metabolism of known occupational carcinogens or hormonal factors do vary by race. While classical epidemiology has shown that the environment predominates in determining cancer incidence, molecular epidemiology has identified several examples of genetically determined differences between races.

Prevention of exposure to mutagenic fumes produced by hot cooking oil in Taiwanese kitchens

We evaluated the mutagens in fumes produced by heating three different cooking oils used in Taiwan to temperatures of 100 degrees C, 200 degrees C, and 300 degrees C, and constructed models to study the efficacy of fume extractors used commonly by Taiwanese women. Particulates of volatile emissions from lard (at 200 degrees C and 300 degrees C) and soybean oil (at 300 degrees C) were found to be mutagenic in the Salmonella/microsomal test with S9 mix, indicating that exposure of Taiwanese women to cooking oil fumes may be an important risk factor in the etiology of their lung cancer. Mutagenicity of lard and soybean oil fumes collected at 300 degrees C was obtained when a commonly used fume extractor was located at a usual distance of 70 cm above the oil surface, whereas the fume samples were not, or weakly, mutagenic in the Salmonella/ microsomal assay when the distance between fume extractor and oil surface was 60 cm or less. Reduction in mutagenicity was on average 1.2 +/- 0.5 revertants/cm (the percent reduction in mutagenicity was 46%), pointing to a possible cooking practice involving significant reductions in exposure to harmful oil fumes and, consequently, a decreased risk of lung cancer in Taiwanese housewives.

Mutagenicity and polycyclic aromatic hydrocarbon content of fumes from heated cooking oils produced in Taiwan

According to epidemiologic studies, exposure of women to fumes from cooking oils appears to be an important risk factor for lung cancer. Fume samples from three different commercial cooking oils frequently used in Taiwan were collected and analyzed for mutagenicity in the Salmonella/microsome assay. Polycyclic aromatic hydrocarbons were extracted from the samples and identified by HPLC chromatography. Extracts from three cooking oil fumes were found to be mutagenic in the presence of S9 mix. All samples contained dibenz[a,h]anthracene (DB[a,h]A) and benz[a]anthracene (B[a]A). Concentration of DB[a,h]A and B[a]A were 1.9 and 2.2 micrograms/m3 in fumes from lard oil, 2.1 and 2.3 micrograms/m3 in soybean oil, 1.8 and 1.3 micrograms/m3 in peanut oil, respectively. Benzo[a]pyrene (B[a]P) was identified in fume samples of soybean and peanut oil, in concentrations of 19.6 and 18.3 micrograms/m3, in this order. These results provide experimental evidence and support the findings of epidemiologic observations, in which women exposed to the emitted fumes of cooking oils are at increased risk of contracting lung cancer.

Vegetable and fruit intake and the risk of lung cancer in women in Barcelona, Spain

A case-control study on women was carried out in Barcelona, Spain, to investigate the relationship of lung cancer with the intake of vegetables, fruits and some foods of animal origin. The study included 103 cases and 206 controls matched by age and residence. Diet intake was assessed by means of a food frequency questionnaire. A reduction in risk, adjusted for smoking habit, was found for the intake of yellow/orange vegetables (mainly carrots) and tomatoes. The odds ratio (OR) and 95% confidence interval (CI) for the highest versus lowest tertile of intake were 0.37 (0.19-0.74) for yellow/orange vegetables and 0.45 (0.22-0.91) for tomatoes; both had a significant inverse trend. A tendency to a reduction in risk of lung cancer with increased intake was observed for all vegetables, leafy green vegetables, dark green vegetables and cruciferous, but these associations did not reach statistical significance. No association with lung cancer was found for the intake of fruits or foods of animal origin rich in retinol. Similar patterns were observed for women who never smoked and when the analysis was restricted to adenocarcinoma.

Chemoprevention: will it work?

Cancer chemoprevention has been a major area of inquiry in the United States for over a decade. The field originated from the confluence of developments in laboratory carcinogenesis and nutritional epidemiology. Although still owing much to other research disciplines, chemoprevention researchers have developed models and methodologies specific to the topic. Of particular importance has been the search for intermediate endpoints which might provide valid indications of cancer prevention effectiveness. Intermediate endpoints, however, suffer the limitations of the extrapolation required to the prevention of cancer per se. More direct evidence of chemoprevention effectiveness may come from trials that use actual reduction of cancer incidence as the primary endpoint. Several trials of potential chemopreventive agents are underway or have been completed in the United States or elsewhere with U.S. investigator participation. The results to date have been mixed, and unanticipated findings have raised doubts about the probability of success of primary prevention of cancer by chemoprevention. Future prospects for success may depend upon development of a better understanding of biological mechanisms before progressing to large, long-duration human population trials.

Diet and lung cancer 20+ years later: more questions than answers?

A critical review of epidemiological studies on diet and lung cancer over the last 20+ years has not provided overwhelming evidence that higher consumption of vegetables, fruit, low-fat/low-cholesterol foods or such micronutrients as carotenoids, selenium and vitamins A, C or E is associated with reduced lung cancer risk. Results from case-control studies have been more positive, with about one half showing fruit and vegetables or their associated micronutrients to be associated with reduced risk. However, most results from cohort and serum micronutrient studies, which avoid the problems of inaccurate accounting of diet and recall bias, were statistically insignificant. Moreover, although most studies were conducted on white male smokers in North America and Europe, the few studies which found significant contrary trends were among subjects of different backgrounds, i.e., black American males and Chinese women in China. Since male smokers vs. nonsmokers in Europe, North America and Japan have been shown in other studies to be lower consumers of fruit/vegetables, and less likely to pursue "perceived healthier lifestyles," the possibility that some of the epidemiological findings on diet and lung cancer are artifactually due to inadequate adjustment for behavioral correlates of smoking and health seekers in a particular society must be considered. This is especially true with recent chemoprevention trials showing higher lung cancer incidence and deaths among consumers of beta-carotene supplements vs. placebo.

Vegetables, fruit, and cancer prevention: a review

In this review of the scientific literature on the relationship between vegetable and fruit consumption and risk of cancer, results from 206 human epidemiologic studies and 22 animal studies are summarized. The evidence for a protective effect of greater vegetable and fruit consumption is consistent for cancers of the stomach, esophagus, lung, oral cavity and pharynx, endometrium, pancreas, and colon. The types of vegetables or fruit that most often appear to be protective against cancer are raw vegetables, followed by allium vegetables, carrots, green vegetables, cruciferous vegetables, and tomatoes. Substances present in vegetables and fruit that may help protect against cancer, and their mechanisms, are also briefly reviewed; these include dithiolthiones, isothiocyanates, indole-3-carbinol, allium compounds, isoflavones, protease inhibitors, saponins, phytosterols, inositol hexaphosphate, vitamin C, D-limonene, lutein, folic acid, beta carotene, lycopene, selenium, vitamin E, flavonoids, and dietary fiber. Current US vegetable and fruit intake, which averages about 3.4 servings per day, is discussed, as are possible noncancer-related effects of increased vegetable and fruit consumption, including benefits against cardiovascular disease, diabetes, stroke, obesity, diverticulosis, and cataracts. Suggestions for dietitians to use in counseling persons toward increasing vegetable and fruit intake are presented.

Some lifestyle factors in human lung cancer: a case-control study of 792 lung cancer cases

In order to investigate the relationship between some lifestyle factors and lung cancer, a case-control study involving all lung cancer deaths registered in 1986 was performed. The results show that among males, 92.5% of the cases and 75.5% of controls were smokers, implying that cigarette smoking is a primary risk factor for lung cancer in males. By contrast, among females only 60.6% of the cases and 30.8% of the controls were smokers, implying factors other than cigarette smoking must be involved in the development of lung cancer in females. The risk of lung cancer in nonsmoking females was found to be unaffected by exposure to environmental tobacco smoke (ETS). A study of diet and eating habits showed that in males the risk of lung cancer was reduced by the intake of vegetables and fruits, but was significantly increased by a frequent intake of fried foods. The positive association between the intake of fried food and the risk of lung cancer could result from cooking practices and from inappropriate methods used in food preparation. No association can be demonstrated between the consumption of high protein or high fat diets, salty and smoked food items and the incidence of lung cancer. Thus, it is not likely that sufficient lung cancer inducing carcinogens can be generated through the intake of food. In addition, the positive association found to exist between the living index and the risk of lung cancer in females is consistent with the notion that coal smoke or cooking practices may generate sufficient indoor air pollutants to significantly increase the risk of lung cancer in females.

The etiology of lung cancer in nonsmoking females in Harbin, China

A case-control study of female lung adenocarcinoma in Harbin, China involving interviews with 120 cases of nonsmoking females, matched 1:1 with controls, showed that high coal use, indoor air pollution, exposure to coal dust, frequent frying and deep frying food, and a history of lung cancer in the family were statistically significant risk factors for female adenocarcinoma. High personal income, spacious living quarters, and frequent consumption of carrots were protective factors for adenocarcinoma.

Diet as a confounder of the association between air pollution and female lung cancer: Hong Kong studies on exposures to environmental tobacco smoke, incense, and cooking fumes as examples

Chinese females in Hong Kong, where only about a third of the lung cancer cases can be attributed to a history of active smoking, have a world age-standardized lung cancer incidence rate of 32.6 per 100 000, which is among the highest in the world. Trends in Hong Kong's female lung cancer mortality also indicate a tripling in mortality rates from 1961 to 1990. The characteristically high Chinese female lung cancer incidence among nonsmokers is also found among overseas Chinese communities in Singapore and Hawaii. To help elucidate the role of ingested and inhaled substances in the etiology of lung cancer, four epidemiological studies have been conducted in Hong Kong over the last 15 years: (1) a retrospective study of 200 cases and 200 neighbourhood controls, (2) a cross-sectional study measuring personal exposures to nitrogen dioxide among 362 children and their mothers, (3) a site monitoring study of 33 homes measuring airborne carcinogens, and (4) a telephone survey of 500 women on their dietary habits and exposure to air pollutants. Selected data from each study were drawn to evaluate exposures to three major air pollutants (environmental tobacco smoke, incense, and cooking fumes), their relationship with lung cancer risk, and their association with dietary habits. Generally in this population, nutritionally poorer diets were characterized by higher consumption of alcohol and preserved/cured foods, whereas better diets were characterized by higher intakes of fresh fruits, vegetables, and fish. For environmental tobacco smoke, exposure was only moderately high in Hong Kong (36% have current smokers at home), lung cancer risk was equivocal with exposure, and it was associated with poorer diets among wives with smoking husbands. Incense was identified as a major source of exposure to nitrogen dioxide and airborne carcinogens, but it had no effect on lung cancer risk among nonsmokers and significantly reduced risk (trend, P-value = 0.01) among smokers, even after adjusting for smoking. The last finding may be explained by the relatively better diets among smoking women who burned incense versus those who did not. Although about 94% of the Chinese women cook on a regular basis, and the cooking fires were associated with increased airborne carcinogens, nonsmoking women who cooked for more than 25 years had a 60% reduction in lung cancer risk and the trend was highly significant (P < 0.001). Again, this unexpected finding may be due to the confounding effects of diet. Female controls who cooked for more than 25 years had a poorer diet than those who cooked for shorter durations. These three examples were chosen to illustrate the complexities of assessing air pollution exposure, and understanding the behavioral and dietary dynamics underlying lung cancer risk assessments. Our conclusion is that diet can be an important confounding factor affecting lung cancer risk estimates from air pollution exposures among Chinese women living in an affluent urban environment.

Lung cancer, smoking and diet among Swedish men

In a prospective case-control lung cancer study in the west of Sweden, the relationship between lung cancer, smoking and dietary factors was investigated. Suspected cases were collected from pulmonary units at two central hospitals in the area investigated and population controls of the same age and sex were selected from registers. The majority of cases and controls were interviewed by specially trained nurses, using a food frequency questionnaire. The lung cancer diagnosis (ICD 7, 162.1) was made using data from the local cancer register. In an analysis based on 308 cases and 504 controls, a dose-related increase in lung cancer risk for smokers was found, although no significant risk was found for males smoking 1-10 cigarettes/day for less than 20 years. A lower consumption of vegetables was related to a higher risk, both for smokers and nonsmokers. A higher consumption of milk was related to an increased risk.

Nutrition and lung cancer

Epidemiologic evidence on the relationship between nutrition and lung cancer is reviewed. Observational studies of diet and lung cancer, both prospective and retrospective, continue to suggest strongly that increased vegetable and fruit intake is associated with reduced risk in men and women; in various countries; in smokers, ex-smokers, and never-smokers; and for all histologic types of lung cancer. Prospective studies of blood beta-carotene levels, arguably the best available biomarker of vegetable and fruit intake, indicate that low levels are predictive of increased lung cancer incidence. However, in a randomized, placebo-controlled clinical trial in male smokers, lung cancer incidence and total mortality were increased significantly among the men receiving beta-carotene supplements. If beta-carotene can prevent lung carcinogenesis, which the trial cannot rule out, then the dosage, duration of use, method of administration, and/or subpopulation are critical. Ongoing clinical trials, some of which include women, will provide much-needed information. Other carotenoids, other phytochemicals, and associated dietary patterns may explain the beneficial effects of vegetables and fruits and have not been explored adequately in epidemiologic work. Several observational epidemiologic studies, both prospective and retrospective, have indicated that diets high in fat, saturated fat, and cholesterol may increase the risk of lung cancer and that the effect is not mediated through vegetable and fruit intake. The relationship, although not yet established, merits further investigation. Since beta-carotene can function as an antioxidant, other micronutrients with this potential, specifically vitamins E and C and selenium, also have been proposed to reduce lung cancer risk. However, the totality of the epidemiologic evidence is not, at present, persuasive for any one of these micronutrients.

Lung cancer and tobacco smoking

The dominant role of tobacco smoking in the causation of lung cancer has been repeatedly demonstrated over the past 50 years. Current lung cancer rates reflect cigarette smoking habits of men and women in the past decades, but not necessarily current smoking patterns, since there is an interval of several decades between the change in smoking habits in a population and its consequences on lung cancer rates. Over 90% of lung cancer may be avoidable simply through avoidance of cigarette smoking. There is at present a huge premature loss of life world-wide caused by smoking. Rates of lung cancer present in central and eastern Europe at the present time are higher than those ever before recorded elsewhere; lung cancer has increased 10-fold in men and eightfold in women in Japan since 1950. There is a world-wide epidemic of smoking among young women which will be translated into increasing rates of tobacco-related disease, including cancer, in the coming decades. There is another epidemic of lung cancer and tobacco-related deaths building up in China as the cohorts of men in whom tobacco smoking became popular reach ages where cancer is an important hazard. Many solutions have been attempted to reduce cigarette smoking and increasingly many countries are enacting legislation to curb this habit. Cigarette smoking remains the number one target for Public Health action aimed at reducing cancer risk in the general population. General practitioners, hospital physicians and everyone working in oncology have a particularly important exemplary role to play in this process.

Cancer incidence in Asian migrants to New South Wales, Australia

Cancer incidence during 1972-90 in Asian migrants to New South Wales, Australia, is described. Overall cancer incidence was lower than in the Australia born in most migrant groups, and this reached significance in migrants born in China/Taiwan, the Philippines, Vietnam and India/Sri Lanka, and in male migrants born in Indonesia. For the majority of cancers, rates were more similar to those in the Australia born than to those in the countries of birth. For cancers of the breast, colorectum and prostate, rates were relatively low in the countries of birth, but migrants generally exhibited rates nearer those of the Australia born. For cancers of the liver and cervix and, in India/Sri Lanka-born migrants, of the oral cavity, incidence was relatively high in the countries of birth but tended to be lower, nearer Australia-born rates, in the migrants. For these cancers, environmental factors related to the migrant's adopted country, and migrant selection, appeared to have a major effect on the risk of cancer. For certain other cancers, incidence was more similar to that in the countries of birth. Nasopharyngeal cancer, and lung cancer in females, had high rates in both the countries of birth and in migrants to Australia. Nasopharyngeal cancer rates were highest in China/Taiwan and Hong Kong-born migrants, and were also significantly high in migrants from Malaysia/Singapore, Vietnam and the Philippines. Rates of lung cancer were significantly high in women born in China/Taiwan, and the excess was greater for adenocarcinoma than for squamous cell carcinoma. Melanoma had low rates in both the migrants and in the countries of birth. For these cancers, it was probable that genetic factors, or environmental factors acting prior to migration, were important in causation.

Antioxidants and carcinogenesis

It is established beyond doubt that free radicals in tissues and cells can damage DNA, proteins, carbohydrates and lipids. These potentially deleterious reactions are at least partly controlled by antioxidants capable of scavenging free radicals. It is widely believed that a proper balance between free radicals and antioxidants is essential for the health of an organism. A vast body of observational epidemiological studies has suggested that high intake of dietary or supplemental antioxidants protects against ischaemic heart disease, various types of cancer and several other diseases. Final proof for the beneficial effects of antioxidants can, however, be obtained from controlled studies. Conflicting results of the first three major clinical trials force us to postpone conclusions of the usefulness of antioxidant supplements in disease prevention until the other on-going trials have been published.

At least one in seven cases of cancer is caused by smoking. Global estimates for 1985

Tobacco smoking is accepted as a major cause of cancers of the lung, larynx, oral cavity and pharynx, oesophagus, pancreas, kidney and bladder. The proportions of these cancers that are due to smoking were estimated for the year 1985 for 24 areas of the world. Fifteen percent--1.1 million new cases per year--of all cancer cases are attributed to cigarette smoking, 25% in men and 4% in women. In developed countries, the tobacco burden is estimated at 16% of all annual incident cases. In developing countries, the corresponding figure is 10%. In total, 85% of the 676,000 cases of lung cancer in men are attributable to tobacco smoking. The highest attributable fractions (AF: 90-93%) are estimated in areas where the habit of cigarette smoking in men has been longest established: North America, Europe, Australia/New Zealand and the former USSR. Among the other 6 cancer sites considered in this analysis, those with the largest fractions of tobacco-related cases are the larynx, mouth and pharynx (excluding nasopharynx) and oesophagus. In regions where males have smoked for several decades, 30 to 40% of all cancers in this sex are attributable to tobacco. Unless tobacco-control efforts in developing countries are strengthened, the massive rise in cigarette consumption over the last few decades will produce a comparable rise in cancer in these countries within the next 20 to 30 years.

A case-control study of diet and lung cancer in Kerala, south India

A total of 281 male lung-cancer patients were identified from the hospital cancer registry in the Regional Cancer Centre in Trivandrum. The controls were selected from the visitors and patients' bystanders in the hospital. The recruitment of cases and controls started in 1990, and the present study used the cases registered in the first year. The questionnaire administered to cases and controls collected information on tobacco smoking and alcohol habits. Dietary data were collected using a food frequency questionnaire and were analyzed by multiple logistic regression producing odds ratio estimates of the relative risk and deviance chi-squared tests of significance. Analysis was done on the computer package, EGRET. All models included age, education, religion and smoking to adjust for the effect of confounding. Green vegetables and bananas were found to have a protective association with lung cancer. The odds ratio associated with the highest quartile of vegetable consumption compared with the lowest was 0.32 (95% confidence interval 0.13, 0.78). Forward stepwise regression analysis indicated pumpkins and onions as the most consistently significant protective factors. Animal protein foods and dairy products were found to have a predisposing effect on lung cancer in this study. The expected influence of smoking on lung cancer (a considerable increase in risk among smokers) provided evidence of the reliability of the data. In conclusion the results from this study show that diet has a role in lung cancer aetiology, although the association is weak compared to the effects of smoking.

Intake of vegetables, fruits, beta-carotene, vitamin C and vitamin supplements and cancer incidence among the elderly: a prospective study

A cohort of 11,580 residents of a retirement community initially free from cancer were followed from 1981 to 1989. A total of 1,335 incident cancer cases were diagnosed during the period. Relative risks of cancer were calculated for baseline consumption of vegetables, fruits, beta-carotene, dietary vitamin C, and vitamin supplements. After adjustment for age and smoking, no evidence of a protective effect was found for any of the dietary variables in men. However, an inverse association was observed between vitamin C supplement use and bladder cancer risk. In women, reduced cancer risks of all sites combined and of the colon were noted for combined intake of all vegetables and fruits, fruit intake alone, and dietary vitamin C. Supplemental use of vitamins A and C showed a protective effect on colon cancer risk in women. There was some suggestion that beta-carotene intake and supplemental use of vitamin A, C, and E were associated with reduced risk of lung cancer in women, but none of these results were statistically significant. These inverse associations observed in women seem to warrant further investigation, although there was inconsistency in results between the sexes.

Mortality from respiratory system cancer in New South Wales and Sydney

Differential and spatial analyses of respiratory system cancer were undertaken for New South Wales and Sydney for the period 1980-1986. The source of data was death certificate information on the unit list mortality file tapes provided by the Australian Bureau of Statistics. Characteristics of persons dying included age, sex, birthplace, occupational status and cause of death (ICD9 classification). The aim was to identify populations at risk from respiratory system cancer, and where they were located. Deaths were disaggregated for the abovementioned categories by cross-tabulation at the state level and for geographical areas having populations with higher levels of respiratory cancer mortality. Never-married males of lower occupational status had higher rates of respiratory cancer, mainly lung cancer. Divorced men also had higher mortality as did widowers who were in lower occupational status work, while married men in managerial work also had significantly high mortality. The marital status variation was mostly not found with females, although significantly high female mortality was found in several low socioeconomic status areas of Sydney. Mortality of both sexes was significantly higher in metropolitan Sydney than in the rest of New South Wales and associations between older age mortality and some industrial areas were found in Sydney.

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.

Dietary determinants of lung-cancer risk: results from a case-control study in Yunnan Province, China

The relation between diet and lung cancer was studied among male residents of a mining community in Yunnan Province. After obtaining food frequency data from subjects or proxies, we compared diets of 428 cases, aged 35-74 years, and 1,011 age-matched controls. Cases tended to consume slightly more rice, but less protein-rich foods (i.e., bean curd, meat, eggs) and vegetables than did controls. The relative risks of lung cancer across increasing quartiles of meat (i.e., pork) consumption, for example, were 1.00, 0.67, 0.72 and 0.46 (p for trend less than 0.01). The relative risks of lung cancer across increasing quartiles of consumption of dark-green, leafy vegetables were 1.00, 0.62, 0.52 and 0.41 (p for trend less than 0.01). Although specific dietary constituent(s) responsible for the protective effect of vegetable consumption could not be identified, carotenoids other than beta-carotene, or compounds in cruciferous or Allium vegetables, are possibilities.

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.

Vegetables, fruit, and cancer. I. Epidemiology

The epidemiologic literature on the relationship between vegetable and fruit consumption and human cancer at a variety of sites is reviewed systematically. A total of 13 ecologic studies, nine cohort studies, and 115 case-control studies are included. Cancer of all sites, cancers of lung, breast, colon, rectum, esophagus, larynx, oral cavity and pharynx, stomach, pancreas, prostate, bladder, ovary, endometrium, cervix, and thyroid, as well as mesothelioma and gestational trophoblastic disease, are considered. Relevant data from clinical trials, animal, and in vitro studies are included. It is 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. The association is most marked for epithelial cancers--particularly those of the alimentary and respiratory tracts--and, currently, is weak to nonexistent for hormone-related cancers. The association exists for a wide variety of vegetables and fruit with some suggestion that raw forms are associated most consistently with lower risk. Possible mechanisms by which vegetable and fruit intake might alter risk of cancer and possible adverse effects of vegetable and fruit consumption will be considered in Part II of this review.

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 factors in aetiology and prevention of cancer in man

Chemical carcinogenesis, as presently understood, involves a number of carcinogenic factors which act in series of steps. Some industrial carcinogens may pollute the natural environment and penetrate into food. Many substances which are potent carcinogens in experimental animals exist in nature and are present in the human diet. On the other hand, many substances which are known to inhibit experimental carcinogenesis also exist in human diet. The present review discusses experimental and epidemiological data connected with the human cancer and diet. It also postulates that the dietary prevention of human cancer through "prudent" modification of diet and dietary patterns may be of importance; many of the present data are still confusing and conflicting.

Cancer incidence in migrants to New South Wales

Cancer incidence in migrants to New South Wales (NSW) from the British Isles, north-central, eastern and southern Europe, the Middle East and Asia has been compared with that in Australian-born residents using data from the NSW Central Cancer Registry for 1972-84. Indirectly standardized incidence ratios (SIRs) were low in migrants from all 6 regions for melanoma of skin and cancers of lip and, except in men from eastern Europe, colon. Oesophageal, rectal and prostatic cancers also tended to be relatively less common. Cancers which were more common than in the Australian-born were those of the stomach and, for men, bladder (except in the Asian-born). Migrants from different regions showed variations from the cancer pattern of the Australian-born population which, for the most part, were predictable from the known incidence of cancer in the countries within the region of origin. Exceptions were the high relative incidence of nasopharyngeal cancer in migrants from southern Europe and bladder cancer in men from all regions other than Asia.

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.

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.

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.

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.

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.

A case-control study of cervix cancer in Singapore

Cervix cancer is about twice as common in Asia as in the Western world and its incidence varies among different Asian ethnic groups. A study based in Singapore, the population of which comprises Chinese, Indians and Malaysians, offers the opportunity to evaluate whether the same risk factors are important in this part of the world as in the West. A total of 135 cases and an equal number of controls were interviewed and details concerning reproductive and sexual history, smoking, hygiene, socio-economic status and education were collected. Seventy-three cases had invasive cancer while 62 had micro-invasive disease or CIN III. The most important risk factors were parity and number of sexual partners. Smoking was rare in cases and controls and did not appear to be an important determinant of risk. Of the socio-economic factors, education appeared most predictive and lowered the risk. Age at first intercourse was strongly correlated with education (positively) and parity (negatively), but not with number of sexual partners. Biopsies were available for HPV DNA analysis in 38 cases and 37% were positive, mostly for HPV type 16. All these factors gave similar risks in invasive and preinvasive disease.