Linda C. Koo

An ecological study of trends in cancer incidence and dietary changes in Hong Kong

Cancer incidence rates from the Hong Kong Cancer Registry show significant increases in lung and colon cancers and decreases in nasopharyngeal cancer in both sexes from 1973 to 1992. Moreover, cervical cancer and male esophageal cancer have declined significantly, and changes in the trends of cancer of the following sites were of borderline significance: decreasing male laryngeal and female esophageal cancers and increasing prostate and female breast cancers. These changes have occurred along with dietary shifts in the population, from a diet predominantly of rice and small portions of meat, vegetables, and fish to one with larger portions of all foods but rice and eggs. The latter data were gathered from six government household surveys from 1963-64 to 1994-95. By combining the two data sets, correlation coefficients were calculated for per capita consumption patterns of eight foods (rice, pork, beef, poultry, saltwater fish, freshwater fish, fresh vegetables, and eggs) and cancer incidence data of the same year or 10 years later. Higher meat intakes were significantly and positively correlated with cancers of the colon, rectum, prostate, and female breast. The correlations also suggested that current diets were more influential than diets a decade before for cancers of the lung, esophagus, rectum, and prostate. Cancers of the nasopharynx and colon were significantly correlated with current and past diets. These results support the hypothesis that intakes of meat and its associated fat are risk factors for colon, rectal, prostate, and female breast cancers.

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 Kongs 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.

Dietary and lifestyle correlates of passive smoking in Hong Kong, Japan, Sweden, and the U.S.A.

From epidemiologic studies in several countries, passive smoking has been associated with increased risk for lung cancer, respiratory diseases, and coronary heart disease. Since the relative risks derived from those studies are weak, i.e. relative risk less than two, we investigated whether poorer diets and less healthy lifestyles might act as confounders and be correlated with having a smoking husband on a cross-cultural basis. Characteristics of never-smoked wives with or without smoking husbands were compared between 530 women from Hong Kong, 13,047 from Japan, 87 from Sweden, and 144 from the U.S. In all four sites, wives with smoking husbands generally ate less healthy diets. They had a tendency to eat more fried food but less fruit than wives with nonsmoking husbands. Other healthy traits, e.g. avoiding obesity, dietary cholesterol and alcohol, or taking vitamins and participating in preventive screening were also less prevalent among wives with smoking husbands. These patterns suggest that never-smoked wives with smoking husbands tend to share the same less healthy dietary traits characteristic of smokers, and to have dietary habits associated with increased risk for lung cancer and heart disease in their societies. These results emphasize the need to take into account the potential confounding effects of diet and lifestyle in studies evaluating the health effects of passive smoking, especially since it is known that the current prevalence rates of smoking among men is indirectly associated with social class and education in affluent urban societies.

Mosquito Coil Smoke and Respiratory Health among Hong Kong Chinese: Results of Three Epidemiological Studies

Mosquito coil smoke is an emission source of indoor air pollution in warm climates. Its contribution to indoor air pollution and possible deleterious effects on the respiratory tract was assessed by utilizing data from three different air pollution and respiratory disease studies in Hong Kong. Among the working class population, current exposure to smoke from burning mosquito coils ranged from 12 to 14%, with 27% ever exposed. Such exposures were not associated with increased nitrogen dioxide gas levels as measured by personal passive samplers, but analysis of airborne particulates in homes indicated increases in some carcinogenic compounds [benz(a)anthracene p = 0.03, benzo(k)fluoranthene p = 0.08]. Prevalence rates at 20% for chronic sputum among exposed primary school children were twice as high as the 10% prevalence rate among unexposed children (p = 0.04). Among the children’s mothers and elderly female controls, such associations were not found. Analysis of the data indicates that although mosquito coil smoke is a source of air pollution which may increase bronchial irritation causing chronic sputum among primary school children, its effect on adults is less obvious, and the symptoms may disappear with age or ceased exposure. Moreover, past mosquito coil smoke exposure was not found to be a risk factor for lung cancer.

Carcinogens in the indoor air of Hong Kong homes: Levels, sources, and ventilation effects on 7 polynuclear aromatic hydrocarbons

Abstract The concentration of carcinogens in the airborne dust of 33 homes in Hong Kong was studied to identify the sources and measure the amounts of 7 polynuclear aromatic hydrocarbons (PAH) including benzo(a)pyrene. The 24 hr samples were collected from kitchens and living rooms of working class homes and analyzed by HPLC. The mean levels of PAH in air and dust were comparatively low, with cooking fires and incense associated with significant increases, and window ventilating fans with significant decreases in PAH concentrations. Perceived pollution sources like water heaters, cigarette smoke, and stir‐fry cooking, led to reduced airborne PAH levels because human responses to these emission sources were to increase natural and mechanical ventilation. The data indicated that compensation behaviours can over‐ride the effects of emission sources, and help explain why measures of increased ventilation from open windows and doors were generally associated with higher PAH levels. The results of this study sh...

Is Chinese Incense Smoke Hazardous to Respiratory Health? Epidemiological Results from Hong Kong

Incense is a common source of indoor air pollution, especially in Asian homes where it is burned for religious reasons. In previous studies in Hong Kong, it was found to be the major source of airborne carcinogens in the home, and a significant contributor to personal exposures to nitrogen dioxide among wom en. To evaluate its effects on respiratory health, data from an air pollution cross-sectional study of 346 primary school children and their 293 non-smok ing mothers, and a lung cancer case-control study of 189 female patients and 197 district matched controls who had ever been married were analysed. No association was found between exposure to incense burning and respiratory symptoms like chronic cough, chronic sputum, chronic bronchitis, runny nose, wheezing, asthma, allergic rhinitis, or pneumonia among the three popu lations studied: i.e. primary school children, their non-smoking mothers, or a group of older non-smoking female controls. Incense burning did not affect lung cancer risk among non-smokers, but it significantly reduced risk among smokers, even after adjusting for lifetime smoking amount. A possible expla nation for this unexpected finding is that incense burning was associated with certain dietary habits, i.e. more fresh fish, more retinol, and less alcohol, which have been associated with lower lung cancer risk in this population. These results indicate that diet can be a significant confounder of epidemiological studies on air pollution and respiratory health.