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In an international comparison of recent mortality statistics among G7 countries, Japan had the longest average life expectancy, primarily due to remarkably low mortality rates from ischemic heart disease and cancer (particularly breast and prostate). As recently as the 1960s, life expectancy in Japan was the shortest among the G7 countries, owing to relatively high mortality from cerebrovascular disease—particularly intracerebral hemorrhage—and stomach cancer. Mortality rates for these diseases subsequently decreased significantly while the already low rates for ischemic heart disease and cancer also decreased, resulting in Japanese life expectancy becoming the longest. The low mortality rates from ischemic heart disease and cancer are thought to reflect the low prevalence of obesity in Japan; low intake of red meat, specifically saturated fatty acids; and high intakes of fish, specifically n-3 polyunsaturated fatty acids, plant foods such as soybeans, and nonsugar-sweetened beverages such as green tea. The decreasing mortality rates from cerebrovascular disease are thought to reflect the increases in animal foods, milk, and dairy products and consequently in saturated fatty acids and calcium, together with a decrease in salt intake which may have led to a decrease in blood pressure. This decrease in salt and highly salted foods also seems to account for the decrease in stomach cancer. The typical Japanese diet as characterized by plant food and fish as well as modest Westernized diet such as meat, milk and dairy products might be associated with longevity in Japan.

Because gastric cancer is still the most common cancer, its prevention is one of the most important aspects of Japan's cancer control strategy. Observations among Japanese immigrants in the USA and Brazil based on the geographic differences, the trend in cancer incidence with time, and the change in incidence patterns indicate that gastric cancer is closely associated with dietary factors, such as the intake of salt and salted food. In international and intra‐Japanese ecological studies, the average salt excretion level, estimated using randomly selected 24‐h urine samples in each population, was closely correlated with gastric cancer mortality. Several case–control and cohort studies, including the author's recent works, have shown that a higher intake of some traditional salt‐preserved food and salt per se, which was estimated using a validated food‐frequency questionnaire, was associated with a risk of gastric cancer. While salted food intake may increase the risk of Helicobacter pylori infection, it can also act synergistically to promote the development of gastric cancer. Based on substantial evidence about the association between salt and salted food intake and the risk of gastric cancer from ecological, case–control, and cohort studies conducted in Japan and other countries, as well as mechanistic plausibility, dietary modification involving less salt and salted food intake is a practical strategy with which to prevent gastric cancer. (Cancer Sci 2005; 96: 1–6)

Over the last 60 years, Japanese people have experienced a rapid and drastic change in lifestyle, including diet. Suspicions have been raised that so‐called ‘Westernization’, characterized by a high‐calorie diet and physical inactivity, is associated with increasing trends in the incidence of cancer of the colon, liver, pancreas, prostate, and breast, as well as type 2 diabetes. Epidemiological evidence from our prospective study, the Japan Public Health Center‐based Prospective (JPHC) study, and systematic literature reviews generally support the idea that factors related to diabetes or insulin resistance are associated with an increased risk of colon (mostly in men), liver, and pancreatic cancers. These cancers are inversely associated with physical activity and coffee consumption, which are known to decrease the risk of type 2 diabetes. The suggested mechanism of these effects is that insulin resistance and the resulting chronic hyperinsulinemia and increase in bioavailable insulin‐like growth factor 1 (IGF1) stimulate tumor growth. In contrast, associations with diabetes are less clear for cancer of the colon in women, and breast and prostate, which are known to be related to sex hormones. The effect of insulin resistance or body fat on sex‐hormone production and bioavailability may modify their carcinogenic effect differently from cancers of the colon in men, and liver and pancreas. In conclusion, there is substantial evidence to show that cancers of the colon, liver, and pancreas are associated with insulin resistance, and that these cancers can be prevented by increasing physical activity, and possibly coffee consumption. (Cancer Sci 2010; 101: 1073–1079)

Purpose The present study aimed to examine the association between adherence to the Japanese diet and the subsequent risk of all-cause and cause-specific mortality using a large-scale cohort from settings all over Japan. Methods We analyzed data from a cohort study of 92,969 Japanese adults aged 45–74 years, covering 11 public health center areas nationwide. We collected dietary information using a validated 147-item food frequency questionnaire. Adherence to the Japanese diet consisting of eight components (high intake of rice, miso soup, seaweeds, pickles, green and yellow vegetables, fish, and green tea; low intake of beef and pork) was assessed using 8-item Japanese Diet Index (JDI8) score, with scores ranging from 0 to 8. The Cox proportional hazards model was used to estimate the hazard ratio (HR) and 95% confidence interval (CI) for all-cause and cause-specific mortality. Results During a median follow-up of 18.9 years, we documented 20,596 deaths. A higher JDI8 score was significantly associated with a lower risk for all-cause and cardiovascular disease (CVD) mortality. The multivariable-adjusted HR of all-cause and CVD mortality for the highest JDI8 score group (score of 6–8) versus the lowest JDI8 score group (score of 0–2) were 0.86 (95% CI 0.81–0.90, P trend < 0.001), and 0.89 (95% CI 0.80–0.99, P trend = 0.007), respectively. Conclusions Adhering to the Japanese diet, as assessed by the JDI8, was associated with a decreased risk of all-cause and CVD mortality among adults living in multiple areas across Japan.

There are geographic and ethnic differences in the incidence of gastric cancer around the world as well as with its trends for each population over time. The incidence patterns observed among immigrants change according to where they live. All of these factors serve to indicate the close association of gastric cancer with modifiable factors such as diet. This review presents epidemiological evidence on the association between dietary factors and gastric cancer based on previous systematic reviews and subsequent updates. Infection with Helicobacter pylori is a strong and established risk factor of gastric cancer but is not a sufficient cause for its development. Substantial evidence from ecological, case-control, and cohort studies strongly suggests that the risk may be increased with a high intake of various traditional salt-preserved foods and salt per se and decreased with a high intake of fruit and vegetables, particularly fruit. However, it remains unclear which constituents in fruit and vegetables play a significant role in gastric cancer prevention. Among them, vitamin C is a plausible candidate supported by a relatively large body of epidemiological evidence. Consumption of green tea is possibly associated with a decreased risk of gastric cancer, although the protective effects have been, for the most part, identified in Japanese women, most of whom are nonsmokers. In contrast, processed meat and N-nitroso compounds may be positively associated with the risk of gastric cancer. In conclusion, dietary modification by reducing salt and salted food intake, as well as by increasing intake of fruit and vitamin C, represents a practical strategy to prevent gastric cancer.

Exposure to certain chemicals in the environment may contribute to the risk of developing cancer. Although cancer risk from environmental chemical exposure among general populations is considered low compared to that in occupational settings, many people may nevertheless be chronically exposed to relatively low levels of environmental chemicals which vary by such various factors as residential area, lifestyle, and dietary habits. It is therefore necessary to assess population-specific exposure levels and examine their association with cancer risk. Here, we reviewed epidemiological evidence on cancer risk and exposure to dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), polychlorinated biphenyls (PCBs), per- and polyfluoroalkyl substances (PFASs), cadmium, arsenic, and acrylamide. Japanese are widely exposed to these chemicals, mainly through the diet, and an association with increased cancer risk is suspected. Epidemiological evidence from Japanese studies to date does not support a positive association between blood concentrations of DDT, HCH, PCBs, and PFASs and risk of breast or prostate cancer. We established assessment methods for dietary intake of cadmium, arsenic, and acrylamide using a food frequency questionnaire. Overall, dietary intakes of cadmium, arsenic, and acrylamide were not significantly associated with increased risk of total cancer and major cancer sites in the Japan Public Health Center-based Prospective Study. However, statistically significant positive associations were observed between dietary cadmium intake and risk of estrogen receptor-positive breast cancer among postmenopausal women, and dietary arsenic intake and risk of lung cancer among male smokers. In addition, studies using biomarkers as exposure assessment revealed statistically significant positive associations between urinary cadmium concentration and risk of breast cancer, and between ratio of hemoglobin adducts of acrylamide and glycidamide and risk of breast cancer. Epidemiological studies of general populations in Japan are limited and further evidence is required. In particular, studies of the association of organochlorine and organofluorine compounds with risk of cancer sites other than breast and prostate cancer are warranted, as are large prospective studies of the association between biomarkers of exposure and risk of cancer.

Although our understanding of the etiology of breast cancer has improved, many well‐known risk factors are not modifiable and present knowledge has proved insufficient to allow the disease to be overcome. Indeed, incidence and mortality among Japanese women have increased over the past three decades. Here, we review epidemiological evidence from our cohort and case–control studies among Japanese women in comparison with other published findings. Our studies confirm the important role of established factors derived primarily from Western populations, such as menstrual and reproductive factors, anthropometric factors, physical activity, and alcohol intake, in the development of breast cancer. In addition, we provide further evidence to better understand the role of traditional Japanese foods in the etiology of breast cancer. Our cohort study found that a higher intake of isoflavone and higher levels of plasma genistein, but not daidzein, were associated with a decreased risk of breast cancer. Our case–control studies reveal a dose–response pattern for these compounds; specifically, decreased risk as women move from “no” to “moderate” intake and leveling off thereafter. In addition, gene–environment interactions have been revealed in the effects of isoflavones. The evidence reviewed suggests that isoflavone has a protective effect against breast cancer in Asian populations. Conversely, our cohort study did not observe an inverse association between breast cancer risk and the intake of green tea and/or the plasma level of tea polyphenols, but we did find an association between increased risk and active and passive smoking. In conclusion, based on current knowledge, primary prevention according to individual lifestyle modification should focus on alcohol intake, weight control, physical activity, and tobacco smoking. (Cancer Sci 2011; 102: 1607–1614)

A third of dementia cases could be attributable to modifiable risk-factors. Midlife high-density lipoprotein cholesterol (HDL-C) is a measure which could help identify individuals at reduced risk of developing age-related cognitive decline. The Japan Public Health Centre-based prospective (JPHC) Study is a large population-based cohort which started in 1990. This study included 1299 participants from Saku area in Nagano prefecture. Participants had HDL-C measured in 1995–1996, and underwent a mental health screening in 2014–2015. Of these, 1114 participants were included in MCI analyses, and 781 participants were included in dementia analyses. Logistic regression models were used to determine odds ratios (OR) and 95% confidence intervals (CI) for the association between HDL-C quartiles and MCI and dementia, respectively. For dementia analysis, quartiles 2–4 were collapsed due to low number of cases. Missing data was addressed through multiple imputations. There were 386 cases of MCI and 53 cases of dementia. Compared to the lowest HDL-C quartile, the highest HDL-C quartile was significantly inversely associated with MCI (OR = 0.47, 95% CI, 0.28–0.79) in the multivariable analysis. High HDL-C (quartiles 2–4) was inversely associated with dementia compared to low HDL-C (quartile 1) (OR = 0.37, 95% CI, 0.16–0.88). This study has found that high midlife HDL-C levels are inversely associated with both late-life MCI and dementia in a Japanese population.

Changing trends in the prevalence of H . pylori infection in the general population over time are thought to be the main driving force behind the declining gastric cancer mortality in Japan. However, whether the prevalence of H . pylori infection itself shows a birth-cohort pattern needs to be corroborated. We performed a systematic review of studies that reported the prevalence of H . pylori infection among Japanese individuals. Meta-regression was conducted in the framework of a generalized additive mixed model (GAMM) to account for heterogeneity in the prevalence of H . pylori infection as a function of birth year. The prevalence of H . pylori infection confirmed a clear birth cohort pattern: the predicted prevalence (%, 95% CI) was 60.9 (56.3–65.4), 65.9 (63.9–67.9), 67.4 (66.0–68.7), 64.1 (63.1–65.1), 59.1 (58.2–60.0), 49.1 (49.0–49.2), 34.9 (34.0–35.8), 24.6 (23.5–25.8), 15.6 (14.0–17.3), and 6.6 (4.8–8.9) among those who were born in the year 1910, 1920, 1930, 1940, 1950, 1960, 1970, 1980, 1990, and 2000, respectively. The present study demonstrated a clear birth-cohort pattern of H . pylori infection in the Japanese population. The decreased prevalence of H . pylori infection in successive generations should be weighed in future gastric cancer control programs.