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There has been much interest in the potential role of soy in reducing the risk of chronic diseases. Soy foods are uniquely rich in isoflavones, a fact that has triggered much research including intervention studies. However, there have been few long-term prospective observational studies that include disease itself as an outcome. High intake of soy foods is intrinsic to the Japanese diet, which can be advantageous for conducting such studies in Japan. The present report reviews the findings from Japanese prospective cohort studies on soy intake and the risk of cardiovascular diseases, cancer, type 2 diabetes, osteoporosis, menopausal symptoms, and dementia. The results suggest a beneficial role of soy in several chronic diseases, but they are not without controversy. Discrepancies have been observed in the findings of studies of Japanese or other Asians as compared to those of non Asians. This review discusses the issues to be explored in future studies.

It has been suggested that soy isoflavones have protective effects against breast cancer. However, data from epidemiological studies are not conclusive. A recent meta-analysis showed that soy intake was inversely associated with breast cancer risk in Asian but not Western populations, which indicates that protection against breast cancer may require that women consume levels of soy typical in Asian diets. In addition to the amount of soy isoflavones consumed, the form and food source of isoflavones, timing of isoflavone exposure, estrogen receptor status of tumors, and equol-producer status and hormonal profile of individuals may modify the association between soy isoflavone intake and the risk of breast cancer. These factors might explain the heterogeneity of results from studies. This present report contrasts background data from Japanese and Western women to identify the potential modifying of these factors.

Background: The association between the number of teeth and mortality among community-dwelling people has been examined in many epidemiological studies. However, few Japanese studies have included cancer mortality as an endpoint. We prospectively investigated the association between number of remaining teeth and all-cause and cancer mortality in a Japanese community. Methods: This study included participants in the Takayama Study who were aged 35–70 years old at baseline in 1992. Information on the number of remaining teeth was obtained from 11,273 participants via questionnaire at the second survey in 2002. The response rate was 66.9%. Deaths and their causes were ascertained during 11.8 years of follow-up. Results: A total of 1,098 deaths (435 cancer-related and 235 cardiovascular-related) were identified during the follow-up period. After adjusting for covariates, participants with 0 to 9 teeth were at moderate but significantly increased risk of all-cause mortality (hazard ratio [HR] 1.19; 95% confidence interval [CI], 1.03–1.39) and cancer mortality (HR 1.31; 95% CI, 1.03–1.67) compared to those with 20 or more teeth. With regard to cancer site, a significant association was observed for lung cancer (HR for 0–9 teeth vs. 20 or more teeth, 1.75; 95% CI, 1.08–2.83). This association was somewhat strengthened among never-smokers (HR 3.56; 95% CI, 1.02–12.45). Conclusions: We observed that a lower number of remaining teeth was significantly associated with increased risk from all-cause and lung cancer mortality. Further studies on the number of teeth and lung and other types of cancer are needed.

Few large epidemiological studies have evaluated the association between dietary advanced glycation end products (AGEs) and cancer risk. We evaluated the relationship between dietary AGE intake and the incidence of total cancer and site‐specific cancers in a population‐based prospective study in Japan. Participants were 14,173 men and 16,549 women who were 35 years of age or older in 1992. Dietary intake was assessed via a validated food frequency questionnaire. Intake of the AGE Nε‐carboxymethyl‐lysine (CML) was estimated using databases of CML content in foods determined using ultraperformance liquid chromatography–tandem mass spectrometry. Cancer incidence was confirmed through regional population‐based cancer registries. During a mean follow‐up period of 13.3 years, 1954 men and 1477 women developed cancer. We did not observe a significant association between CML intake and the risk of total cancer in men or women. In men, compared with the lowest quartile of CML intake, the hazard ratios of liver cancer for the second, third, and highest quartiles were 1.69 (95% CI: 0.92–3.10), 1.48 (95% CI: 0.77–2.84), and 2.10 (95% CI: 1.10–3.98; trend p = 0.04). Conversely, a decreased relative risk of male stomach cancer was observed for the second and highest quartiles of CML intake versus the lowest quartile, with hazard ratios of 0.73 and 0.67, respectively (trend p = 0.08). Our finding on the potential harmfulness of consuming AGEs on liver cancer risk is intriguing and warrants further study. A high intake of advanced glycation end products Nε‐carboxymethyl‐lysine was associated with an increased risk of liver cancer in Japanese men. Our finding suggests the potential harmfulness of consuming advanced glycation end products on liver cancer risk.

Introduction and hypothesisLittle is known about the prevalence of pelvic organ prolapse (POP). We aimed to evaluate the prevalence of POP and identify its risk factors in Japan.MethodsThis was a single-centre, cross-sectional study. We recruited Japanese women seen for a Pap smear from July 2018 through May 2019. After providing their informed consent, subjects were asked to complete questionnaires. Pelvic organ support was assessed using the POP quantification (POP-Q) system by an examiner. Logistic regression analyses were conducted to identify risk factors for POP.ResultsThere were 1032 women aged 21 to 84 years. The distribution of POP-Q stage was stage 0, 38.0%; stage I, 45.0%; stage II, 16.4%; stage III, 0.6%; and stage IV, 0%. Rates (95% confidence interval [CI]) of stage II or greater in each age group were 6.6% (2.4–10.8) in 20 s–30 s; 17.6% (13.3–21.9) in 40 s; 17.1% (12.9–21.3) in 50 s; 18.0% (12.6–23.4) in 60 s; and 28.7% (19.6–37.9) in 70 s and over. Multivariate analysis revealed the following risk factors for POP, with odds ratio (95% CI): body mass index [BMI] ≥ 25 kg/m2, 1.63 (1.05–2.51); BMI < 18.5 kg/m2, 0.40 (0.17–0.94); hysterectomy, 4.09 (1.55–10.80); ≥ 3 vaginal deliveries, 2.26 (1.19–4.28); and ≥ 1 cup of coffee per day, 0.63 (0.43–0.92).ConclusionAmong Japanese women undergoing routine gynaecological examinations, 17.1% (14.7–19.5) had POP-Q stage II or greater. Overweight, hysterectomy and ≥ 3 vaginal deliveries increased the risk for POP, whereas underweight and daily coffee consumption decreased it.

Despite an increasing number of students studying abroad worldwide, evidence about health risks while they are abroad is limited. Diarrhea is considered the most common travelers’ illness, which would also apply to students studying abroad. We examined diarrhea and related personal characteristics among Japanese students studying abroad. Japanese university students who participated in short-term study abroad programs between summer 2016 and spring 2018 were targeted (n = 825, 6–38 travel days). Based on a 2-week-risk of diarrhea (passing three or more loose or liquid stools per day) among travelers by country, the destination was separated into intermediate- and low-risk countries. After this stratification, the associations between personal characteristics and diarrhea during the first two weeks of their stay were evaluated using logistic regression models. Among participants in intermediate-risk countries, teenagers, males and those with overseas travel experience were associated with an elevated risk of diarrhea; the odds ratios (95% confidence intervals) were 2.42 (1.08–5.43) for teenagers (vs. twenties), 1.93 (1.08–3.45) for males (vs. females) and 2.37 (1.29–4.33) for those with overseas experience (vs. none). Even restricting an outcome to diarrhea during the first week did not change the results substantially. The same tendency was not observed for those in the low-risk countries. Teenage students, males and those with overseas travel experience should be cautious about diarrhea while studying abroad, specifically in intermediate-risk countries.

Background: Few studies have examined the association between seaweed intake and blood pressure in children. We conducted an intervention study to investigate whether seaweed intake affects blood pressure. Methods: Subjects were children aged 4 to 5 years attending a preschool in Aichi Prefecture, Japan, in 2010. Among 99 students, 89 (89.9%) were enrolled in our study. Nori (dried laver), an edible seaweed widely consumed in Japan, was used as a dietary intervention. Children in the intervention group were asked to consume 1.76 grams per day of roasted nori in addition to standard meals for 10 weeks. Children in the control group consumed their usual diet. Before the intervention and at the 10th week of the intervention, children’s blood pressure was measured three times successively using an automated sphygmomanometer with subjects in a sitting position. Changes in systolic (SBP) and diastolic blood pressure (DBP) were compared between 55 children in the intervention group and 26 in the control group after adjustment for SBP and DBP before the intervention. Results: Changes in SBP were −8.29 mm Hg in the intervention group and +0.50 mm Hg in the control group (P for difference in change = 0.051). Changes in DBP were −6.77 mm Hg in the intervention group and −0.05 mm Hg in the control group (P = 0.031). In girls, no difference in blood pressure changes was found between the intervention and control groups. Conclusion: Nori intake lowered DBP level in boys. Seaweed intake might have preventive effects on elevated blood pressure in childhood.

There is some biological plausibility that exogenous melatonin plays a role in preventing liver carcinogenesis. There has been little research on the association between melatonin intake in a normal diet and health outcomes. We evaluated the association between dietary melatonin intake and the incidence of liver cancer in a population‐based prospective study in Japan. This study included 30,824 residents of Takayama city who were 35 years of age or older in 1992 and had participated in the Takayama study, Japan. Dietary intake was assessed using a validated food frequency questionnaire at the baseline. Melatonin content in foods was measured by liquid chromatography–tandem mass spectrometry. Cancer incidence was confirmed through regional population‐based cancer registries in Gifu. Liver cancer was defined as code C22 according to the International Classification of Diseases and Related Health Problems, 10th Revision. Hazard ratios for liver cancer were estimated for the tertile groups of melatonin intake using a Cox proportional hazards model. During the mean follow‐up period of 13.6 years, 189 individuals developed liver cancer. Compared with subjects in the lowest tertile of melatonin intake, those in the middle and highest tertiles had decreased risks of liver cancer, with a significant linear trend after multivariate adjustments (hazard ratios: 0.64 and 0.65, respectively, trend p  = 0.023). There was no significant interaction by sex (interaction p  = 0.54). This initial finding, which needs to be confirmed by further studies, suggests that consuming melatonin‐containing foods might play a role in the prevention of liver cancer.

The effect of body mass index (BMI) on esophageal and gastric carcinogenesis might be heterogeneous, depending on subtype or subsite. However, findings from prospective evaluations of BMI associated with these cancers among Asian populations have been inconsistent and limited, especially for esophageal adenocarcinoma and gastric cardia cancer. We performed a pooled analysis of 10 population‐based cohort studies to examine this association in 394,247 Japanese individuals. We used Cox proportional hazards regression to estimate study‐specific hazard ratios (HRs) and 95% confidence intervals (CIs), then pooled these estimates to calculate summary HRs with a random effects model. During 5,750,107 person‐years of follow‐up, 1569 esophageal cancer (1038 squamous cell carcinoma and 86 adenocarcinoma) and 11,095 gastric (728 cardia and 5620 noncardia) cancer incident cases were identified. An inverse association was observed between BMI and esophageal squamous cell carcinoma (HR per 5‐kg/m2 increase 0.57, 95% CI 0.50–0.65), whereas a positive association was seen in gastric cardia cancer (HR 1.15, 95% CI 1.00–1.32). A nonsignificant and significant positive association for overweight or obese (BMI ≥25 kg/m2) relative to BMI <25 kg/m2 was observed with esophageal adenocarcinoma (HR 1.32, 95% CI 0.80–2.17) and gastric cardia cancer (HR 1.24, 95% CI 1.05–1.46), respectively. No clear association with BMI was found for gastric noncardia cancer. This prospective study—the largest in an Asian country—provides a comprehensive quantitative estimate of the association of BMI with upper gastrointestinal cancer and confirms the subtype‐ or subsite‐specific carcinogenic impact of BMI in a Japanese population. The impact of BMI on upper gastrointestinal cancer by subtype or subsite among Asians is inconclusive. Using data from 10 large‐scale population‐based cohort studies, we evaluated the association between BMI and upper gastrointestinal cancers for 394,247 Japanese individuals. With 1038 esophageal squamous cell carcinoma, 86 esophageal adenocarcinoma, 728 gastric cardia cancer, and 5620 gastric noncardia cancer cases, we confirmed the subtype‐ or subsite‐specific carcinogenic impact of BMI in an Asian population.

Purpose Several epidemiological studies have demonstrated the health benefits of polyphenols, but the associations between polyphenol intake and mortality including total and major causes of death remain unclear. We investigated the associations between subjects’ total polyphenol intake and their mortality from all causes, cardiovascular disease (CVD), cancer, and other causes of death in a population-based cohort study in Japan. Methods A total of 29,079 residents of Takayama City, Japan were analyzed. Their dietary intake was assessed using a validated semi-quantitative food-frequency questionnaire (FFQ) in 1992. Mortality was ascertained over the subsequent 16 years. The dietary polyphenol intake was calculated by matching the subjects’ food consumption data with our original polyphenol content database. Results A total of 5339 deaths occurred during the follow-up. After multivariable adjustment, the highest quartile of total polyphenol intake compared with the lowest quartile was significantly associated with a lower risk of all-cause mortality (HR: 0.93, 95% CI: 0.82–0.99, p trend = 0.003). The subjects in the highest quartile showed significantly lower CVD mortality compared to those in the lowest quartile, and among the types of CVD mortality, a strong inverse association was observed for stroke mortality. Inverse associations were also observed for mortality from other causes, specifically digestive disease. The total polyphenol intake was not significantly associated with the risk of cancer mortality. Conclusions The results of this prospective study indicate that dietary total polyphenol intake in Japanese is inversely associated with all-cause mortality and mortality from cardiovascular and digestive diseases.