The Epidemiology and Prevention Division has planned and conducted independent and collaborative studies on cancer etiology and prevention, with a special focus on dietary, environmental and genetic factors. Several epidemiological projects are currently in progress.

Diet has been implicated in the etiology of cancer and in the unique patterns of cancer incidence in Japan. However, the epidemiological evidence for this contention has been limited. The division therefore initiated a cohort study, the Japan Public Health Center-based Prospective Study (JPHC Study), in 1990, in collaboration with 11 public health centers and other institutes, in which approximately 140,000 individuals from 11 areas were scheduled to be followed up for at least 20 years. A total of 16,252 deaths, 13,559 cases of cancers and 5,767 cases of cardiovascular diseases had been documented as of October, 2008. Lifestyle factors that were assessed in the baseline or 5 year follow up questionnaire were examined in relation to the subsequent risk of cancer and other lifestyle-related diseases. On passive smoking, compared with women married to never smokers, the hazard ratio (HR) for incidence of adenocarcinoma of the lung in women who lived with a smoking husband was 2.03 ⁽¹⁴⁸⁾. As for drinking alcohol, compared with occasional drinkers, the HR for lung cancer incidence in the highest category (450 g ethanol/week) was 1.69 among current smokers ⁽¹⁴⁹⁾ A higher level of daily total physical activity may be of benefit in preventing premature deaths ⁽¹⁵⁰⁾ and total cancer ⁽¹⁵¹⁾. Fruit and vegetable intake was not associated with decreased risk of total cancer ⁽¹⁵²⁾ but was in the case of esophageal cancer ⁽¹⁵³⁾, while fruit intake reduced the risk of cardiovascular disease. Other analyses were performed to investigate the association between body mass index, smoking, cholelithiasis and risk of biliary tract cancer ⁽¹⁵⁴⁾, dairy products, saturated fatty acid and calcium intake and prostate cancer risk ⁽¹⁵⁵⁾, green tea and prostate cancer risk ⁽¹⁵⁶⁾, coffee and endometrial cancer risk ⁽¹⁵⁷⁾, soy and isoflavone intake and colorectal cancer risk ⁽¹⁵⁸⁾, calcium, vitamin D and colorectal cancer risk ⁽¹⁵⁹⁾, female reproductive factors and gastric cancer ⁽¹⁶⁰⁾ and colorectal cancer risk ⁽¹⁶¹⁾.

Seven nested case-control studies using cryopreserved blood samples were performed, which investigated associations between isoflavone and breast cancer ⁽¹⁶²⁾ and prostate cancer risk ⁽¹⁶³⁾, folate and colorectal cancer risk ⁽¹⁶⁴⁾, polyphenols and gastric cancer risk ⁽¹⁶⁵⁾, Helicobacter pylori infection and gastric cancer risk by histologic type ⁽¹⁶⁶⁾, organochlorine and breast cancer risk ⁽¹⁶⁷⁾, and carotenoids, retinol and tocopherol and gastric cancer risk ⁽¹⁶⁸⁾. Other studies on cardiovascular diseases ^(169-175), overweight and obesity trends ⁽¹⁷⁶⁾, by the diabetes study group ⁽¹⁷⁷⁾ and a reply ⁽¹⁷⁸⁾ were also published.

To develop an evidence-based cancer prevention strategy in terms of lifestyle intervention suitable for the Japanese population, a systematic literature review project and some interventional studies are in progress. The association between drinking alcohol and gastric ⁽¹⁷⁹⁾ and liver cancer risk ⁽¹⁸⁰⁾ was evaluated. A pooled analysis on alcohol and colorectal cancer risk from five cohort studies in Japan was performed ⁽¹⁸¹⁾. Evidence on foods and infectious diseases as risk factors of the main cancers in Japan was reviewed to make final judgments in addition to smoking, alcohol, anthropometry, fruit and vegetables, each of which has been made public or updated on the WEB.

An analysis from a randomized controlled trial to assess the effectiveness of vitamin C supplementation for individuals with chronic atrophic gastritis to prevent gastric cancer in the high-risk area of Hiraka, Akita prefecture, showed a protective effect of vitamin C on oxidative stress ⁽¹⁸²⁾. A community-based randomized cross-over trial designed to develop an effective dietary modification tool and system was held in the same area between 1998-2000, and the follow-up survey was completed in 2003. The collected data are under analysis. SNPs in 44 candidate cancer susceptibility genes were screened in a case-control study on gastric and colorectal cancers ⁽¹⁸⁹⁾.

The ethnic differences in the incidence of cancer suggest an interaction between environmental and genetic factors. Several epidemiologic studies in Brazil, a multi-ethnic nation with 1.2 million people of Japanese ancestry, are in progress. Updated information to 2001 of secular trends in cancer mortality among Japanese immigrants in the state of Sao Paulo was summarized ⁽¹⁸³⁾. A case-control study for breast cancer has been completed and data analysis is in progress. A case-control study for colonic adenoma is in progress.

A project to evaluate the risk of endocrine- disrupting chemicals (EDC) on human health has been completed and is under analysis. A cross-sectional study among Japanese women consulting doctors for infertility suggested no association between urinary cadmium and endometriosis⁽¹⁸⁴⁾. Long-time follow up of urinary bisphenol A in elementary school children showed average levels which were rather low and declining ⁽¹⁸⁵⁾.

Specialized assistance was given for analysis of the clinical data^{(186-188, 190)}. Pooled analyses were performed using data from the JPHC Study.