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Evaluation of cancer screening using case-control studies is less valid in comparison to randomized controlled trails, due to the intrusion of a possible self-selection bias in the former. The randomized controlled trial approach, however, may be difficult in developed countries where mass cancer screening programs are already being performed nationally. Accordingly, case-control studies are often performed instead of randomized controlled trials. In case-control studies, no reports could be found in the literature using dietary habit, an important influencing factor in carcinogenesis, as an adjusting item. We surveyed nutrition and food intake status through a nutrition survey using the weighing method, and smoking prevalence and alcohol consumption with questionnaires in the general population in northern Japan, in subjects over 30 years of age. We then compared these results among non-participants and participants in cancer screening programs, and evaluated how any differences between the two groups might affect the results of case-control studies. Non-participants had a significantly lower intake of vegetables, carotene, vitamin C, and dietary fiber, which are thought to be beneficial factors in the prevention of carcinogenesis. Non-participants had a significantly higher cigarette smoking prevalence than participants. In relation to the intake of vegetables, a difference between participants and non-participants was evident, as proper adjustment for vegetable intake led to an odds ratio closer to the null value. The value of the odds ratio will probably not decrease, but it might increase when other dietary factors or smoking are taken into consideration.

The Japanese have the longest lifespan worldwide, but this has been mostly due to reductions in the mortality rates from diseases other than malignant neoplasms. Changes in the age-adjusted mortality rates (AMRs) for malignant neoplasms in Japan from 1950 to 2000 are analyzed to elucidate the overall trend. The overall AMRs for all malignant neoplasms in men increased from 1950 to 2000, and decreased slowly in women during the same period. Changes since 1990 have been small in both genders, but show a hopeful trend towards a decrease in the total AMR since 1995. These trends reflect a balance between the decreased AMR from gastric (both male and female) and uterine cancers and increases in many other malignant neoplasms. However, in the period 1990-2000, the decrease in the AMR from gastric and uterine cancers has shown a trend towards leveling off. Therefore, improving the trend towards reductions in cancer incidence and mortality in the 21st century and beyond will depend on achieving changes in other cancer sites, which can only be realized through the twofold approach of preventative medicine and research as well as improvements in the levels of diagnosis and therapy. Much more emphasis must therefore be placed on primary prevention, in particular on anti-smoking campaigns, as well as stepping-up research into the etiology of, and novel treatments for other malignant neoplasms, especially colorectal and breast cancers.

Background: It is well recognized that the season of the year exerts an influence on some diseases and causes of death such as coronary heart diseases, stroke, infectious diseases and so on., Methods: We evaluated the influence of seasonal changes on diseases and causes of death in Japan using the Japan Vital Statistics from 1970 to 1999 and recorded weather data (mean temperature), by a Fourier decomposition in a log linear regression model., Results: Major influences of seasonal change with the highest rates in winter were seen on the following: the overall causes of death; infectious and parasitic diseases including tuberculosis; respiratory disease, including pneumonia and influenza; heart and cerebrovascular diseases; diabetes; and digestive diseases and accidents. Two peaks were seen in suicides, a large peak in April and a small peak in autumn. Cancer and homicides were little or not at all influenced by seasonality. There was no major difference in changes between the years studied, except for respiratory disease and tuberculosis, which showed a clear reduction in the seasonality effect from 1970 to 1999., Conclusions: To reduce the overall mortality rate and to prolong life expectancy in Japan, measures must be taken to reduce those mortality rates associated with seasonal differences, especially those causes of death which show a strong correlation with seasonal change: respiratory, heart, cerebrovascular, diabetes and infectious diseases.