Differential patterns of reproductive and lifestyle risk factors for breast cancer according to birth cohorts among women in China, Japan and Korea.

BACKGROUND: The birth cohort effect has been suggested to influence the rate of breast cancer incidence and the trends of associated reproductive and lifestyle factors. We conducted a cohort study to determine whether a differential pattern of associations exists between certain factors and breast cancer risk based on birth cohorts. METHODS: This was a cohort study using pooled data from 12 cohort studies. We analysed associations between reproductive (menarche age, menopause age, parity and age at first delivery) and lifestyle (smoking and alcohol consumption) factors and breast cancer risk. We obtained hazard ratios (HRs) with 95% confidence intervals (CIs) using the Cox proportional hazard regression analysis on the 1920s, 1930s, 1940s and 1950s birth cohorts. RESULTS: Parity was found to lower the risk of breast cancer in the older but not in the younger birth cohort, whereas lifestyle factors showed associations with breast cancer risk only among the participants born in the 1950s. In the younger birth cohort group, the effect size was lower for parous women compared to the other cohort groups (HR [95% CI] 0.86 [0.66-1.13] compared to 0.60 [0.49-0.73], 0.46 [0.38-0.56] and 0.62 [0.51-0.77]). Meanwhile, a higher effect size was found for smoking (1.45 [1.14-1.84] compared to 1.25 [0.99-1.58], 1.06 [0.85-1.32] and 0.86 [0.69-1.08]) and alcohol consumption (1.22 [1.01-1.48] compared to 1.10 [0.90-1.33], 1.15 [0.96-1.38], and 1.07 [0.91-1.26]). CONCLUSION: We observed different associations of parity, smoking and alcohol consumption with breast cancer risk across various birth cohorts.

Association between reproductive factors with lung cancer incidence and mortality: A pooled analysis of over 308,000 females in the Asia cohort consortium.

Previous studies have investigated the association between reproductive factors and lung cancer risk; however, findings have been inconsistent. In order to assess this association among Asian women, a total of 308,949 female participants from 11 prospective cohorts and four Asian countries (Japan, Korea, China, and Singapore) were included. Cox proportional hazards regression models were used to estimate the hazard ratios (HR) and 95% confidence intervals (CIs). A total of 3,119 primary lung cancer cases and 2247 lung cancer deaths were identified with a mean follow-up of 16.4 years. Parous women had a lower risk of lung cancer incidence and mortality as compared with nulliparous women, with HRs of 0.82 (95% CI = 0.70-0.96) and 0.78 (95% CI = 0.65-0.94). The protective association of parity and lung cancer incidence was greater among ever-smokers (HR = 0.66, 95% CI = 0.49-0.87) than in never-smokers (HR = 0.90, 95% CI = 0.74-1.09) (P-interaction = 0.029). Compared with age at first delivery ≤20 years, older age at first delivery (21-25, ≥26 years) was associated with a lower risk of lung cancer incidence and mortality. Women who ever used hormone replacements had a higher likelihood of developing non-small cell lung cancer (HR = 1.31, 95% CI = 1.02-1.68), compared to those who never used hormone replacements. Future studies are needed to assess the underlying mechanisms, the relationships within these female reproductive factors, and the potential changes in smoking habits over time.

Association of female reproductive and hormonal factors with gallbladder cancer risk in Asia: A pooled analysis of the Asia Cohort Consortium.

The female predominance of gallbladder cancer (GBC) has led to a hypothesis regarding the hormone-related aetiology of GBC. We aimed to investigate the association between female reproductive factors and GBC risk, considering birth cohorts of Asian women. We conducted a pooled analysis of 331,323 women from 12 cohorts across 4 countries (China, Japan, Korea, and Singapore) in the Asia Cohort Consortium. Cox proportional hazard models were used to estimate the hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) to assess the association between reproductive factors (age at menarche, parity, age at first delivery, breastfeeding, and age at menopause) and GBC risk. We observed that a later age at menarche was associated with an increased risk of GBC (HR 1.4, 95% CI 1.16-1.70 for 17 years and older vs. 13-14 years), especially among the cohort born in 1940 and later (HR 2.5, 95% CI 1.50-4.35). Among the cohort born before 1940, women with a later age at first delivery showed an increased risk of GBC (HR 1.56, 95% CI 1.08-2.24 for 31 years of age and older vs. 20 years of age and younger). Other reproductive factors did not show a clear association with GBC risk. Later ages at menarche and at first delivery were associated with a higher risk of GBC, and these associations varied by birth cohort.

Plasma Albumin, Bilirubin, and Uric Acid and the Subsequent Risk of Cancer: A Case-Cohort Study in the Japan Public Health Center-based Prospective Study.

Several epidemiological studies have investigated the circulating levels of albumin, bilirubin, and uric acid (UA) in relation to cancer risk; however, they have provided equivocal evidence. In this prospective case-cohort study, we aimed to explore the association of plasma albumin, bilirubin, and UA levels with cancer incidence. We measured the plasma levels of albumin, bilirubin, and UA and investigated their association with cancer incidence in 3,584 cases and 4,270 randomly selected participants with a median follow-up of 15.8 years. The adjusted hazard ratios (HR) and 95% confidence intervals (CI) of total cancer for the highest (Q4) versus lowest quartile (Q1) was 0.77 (95% CI: 0.67-0.90, P for trend: <0.001) for albumin. This association was attenuated after excluding liver cancer cases with lower plasma albumin levels. Plasma bilirubin levels were positively related to liver cancer but inversely to total cancer after excluding liver cancer with adjusted HR Q4 vs. Q1 of 0.86 (95% CI: 0.74-0.99, P for trend = 0.015). Plasma UA levels were not dose-responsively associated with total cancer risk. Higher plasma bilirubin levels were associated with a decreased risk of total cancer after excluding liver cancer, which is likely attributed to the antioxidant properties of bilirubin.

Sex difference in the association of dietary fiber intake with visceral fat volume in Japanese adults.

PURPOSE: Dietary fiber is a possible nutritional component which aids in the prevention of visceral fat accumulation. We examined the association between dietary fiber intake and visceral fat volume (VFV) by sex, and further analysed the association by major food sources of dietary fiber. METHODS: In this cross-sectional study, we measured VFV in 2779 Japanese (1564 men and 1215 women) aged 40-89 who underwent positron emission tomography/computed tomography for cancer screening between 2004 and 2005. Dietary fiber intake was calculated based on a validated semi-quantitative food frequency questionnaire. The association between dietary fiber intake and VFV was investigated using multivariate linear regression models after adjustment for potential confounders. RESULTS: Total, soluble, and insoluble fiber intakes were inversely associated with VFV in men (Q1: 3740 cm3, Q4: 3517 cm3, Ptrend: 0.0006 for total fiber), but not in women (Q1: 2207 cm3, Q4: 2193 cm3,Ptrend: 0.88 for total fiber). Statistically significant sex difference was observed (Pinteraction = 0.001 for total fiber). Subgroup analyses by major food sources revealed that dietary fiber intakes from beans, vegetables and fruits showed an inverse association with VFV in men, while cereal fiber intake showed a tendency toward a positive association in both sexes (Q1: 3520 cm3, Q4: 3671 cm3, Ptrend: 0.05 in men, Q1: 2147 cm3, Q4: 2227 cm3, Ptrend: 0.10 in women). CONCLUSION: We observed a sex-specific association between dietary fiber intake and VFV in Japanese adults. This study suggests that efforts against visceral fat accumulation should take account of the source of dietary fiber.

[Actual usage of Dietary Reference Intakes for Japanese among individuals engaged in work related to food and nutrition: Comparison between workplaces].

Objective　The aim of this study was to compare how Dietary Reference Intakes for the Japanese (DRIs), which are dietary guidelines proposing reference values for the intake of energy and nutrients by healthy Japanese people, are used by personnel whose work involves diet, food, or nutrition.Methods　A web-based questionnaire survey was conducted in July 2023 among those involved in work closely related to diet, food and/or nutrition. The frequency of the use of DRIs in daily work and the details of use, including the chapter used, difficulty of use, information source for revisions, and interest in a revised version, were compared among workplaces (e.g., medical institutions; school and welfare facilities; government institutions; dietitian training schools; companies; and freelancer in community and others).Results　Among 1,030 participants, 58% (n=597) used DRIs "very often" or "often" in their daily work. For example, DRIs were used to prepare institutional meals and facilitate nutrition management and guidance in medical institutions; prepare institutional meals in schools and welfare facilities; ensure nutrition management and guidance for citizens and prepare courses/materials for government institutions; and prepare courses/materials for dietitian training schools. Regarding the main parts of the DRIs used, most respondents chose the chapters entitled "Energy" (66%) and "Macronutrients" (72%). For all participants (n=1,030), the main difficulties in the use of DRIs were "a large number of sentences in the DRIs and an insufficient time to read" (stated by 54% of all respondents; the proportion did not significantly differ among workplaces). The main source of information on revised DRIs was "seminars and workshops by the Japan Dietetic Association" (70% of all respondents). However, many respondents in the government and dietitian training institutions also identified "workshops or public information by the Ministry of Health, Labour and Welfare" as major sources. Regarding participants' main interest in the revised version of the DRIs, general policy (77%) and revised reference values (74%) generated the highest levels of interest. Those working at dietitian training schools had a greater interest in change related to scientific evidence for each reference value than those working elsewhere.Conclusions　DRIs are frequently used by those involved in work related to food and nutrition. In this study, DRI use and related interests differed based on the workplaces surveyed. In future revisions of DRIs, the addition of further descriptions or appendices in line with their use in workplaces may be needed.

Sugar intake and colorectal cancer risk: A prospective Japanese cohort study.

The influence of sugar consumption on the risk of colorectal cancer (CRC) remains controversial. Prospective cohort studies focusing on total and specific types of sugar intake among the Asian population who have different patterns of sugar intake sources than American and European populations are scarce. We intended to examine the association of sugar intake with CRC risk among middle-aged adults in a Japanese large-scale population-based cohort study. The participants (42,405 men and 48,600 women) who were 45-74 years old and answered the questionnaire in 1995-1999 in the Japan Public Health Center-based Prospective Study were followed up until December 2013. Total sugars, total fructose, and specific types of sugar intake were estimated using a validated 147-item food frequency questionnaire and divided into quintiles (Q1-Q5). We used Cox proportional hazard regression models adjusted for potential confounders to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). During the follow-up, 2118 CRC cases (1226 men and 892 women) were identified. We did not observe any clear association between all types of sugar intake and an increased risk of CRC. Analyses by tumor sites yielded a positive association of total sugar consumption with rectal cancer in women (1.75 [1.07-2.87] for Q1 vs. Q5; p linear trend  = 0.03), but no statistically significant trend was detected among men. Sugar intake was not associated with CRC risk in middle-aged Japanese adults. However, for rectal cancer, the probability of an increased risk among women with a higher total sugar intake cannot be excluded.

Association of chronic kidney disease with total and site-specific cancer incidence in participants of the Japan Public Health Center-based Prospective Study.

BACKGROUND: Although studies have found an association between chronic kidney disease (CKD) and cancer incidence, the results are inconsistent. METHODS: This study included participants in the Japan Public Health Center-based Prospective Study who had data on serum creatinine measurements. We assessed the association between estimated glomerular filtration rate (eGFR) and the risk of total and site-specific cancer incidence using a systematic survey in Japan. We estimated hazard ratios (HRs) and 95% confidence intervals (CIs) with adjustment for participant demographics and lifestyle factors. RESULTS: A total of 21 978 participants who met the inclusion criteria were followed up for a mean period of 12.9 years, during which a total of 2997 incident cancer cases were reported. In the multivariable adjusted models, an eGFR of <45 mL/min/1.73 m2 was not significantly associated with total cancer incidence (adjusted HR 1.22, 95% CI 0.94-1.60), compared with an eGFR of 60-89 mL/min/1.73 m2 (reference). The HR among those with eGFRs of ≥90 mL/min/1.73 m2 was 1.10 (95% CI 1.00-1.22). CONCLUSIONS: In this large prospective study, a low eGFR was not significantly associated with an increased risk of total cancer incidence in patients with CKD, which may be partly due to an underpowered sample size. This finding may be due to the many shared risk factors between CKD and cancer.

p53 Arg72Pro polymorphism, adiposity status, and cancer risk: Two case-cohorts within a Japanese prospective study.

The tumor suppressor protein, p53, is a critical molecule involved in cancer development. However, the association between p53 Arg72Pro polymorphism and cancer risk remains unclear, possibly due to the pro-tumor potential of p53 under metabolic stress. Here, we hypothesized that the p53 Arg72Pro polymorphism plays different roles during tumorigenesis by adiposity status. We measured baseline body mass index (BMI) and p53 Arg72Pro polymorphism for two case-cohorts, which included 4264 cancers with up to 20 years of follow-up. Multivariable-adjusted hazard ratios (HRs) and confidence intervals (CIs) were estimated using weighted Cox proportional-hazards method. Without consideration of adiposity status, p53 Arg72Pro polymorphism was not associated with cancer risk. However, proline (Pro) homozygous genotype conferred an increased cancer risk for individuals with a BMI <25 kg/m2 (HR [95% CI]: 1.12 [1.00-1.26] for total cancer and 1.19 [1.02-1.38] for obesity-related cancer), but not for those with a BMI ≥ 25 kg/m2 . The heterogeneous effect of p53 Arg72Pro polymorphism on cancer risk according to adiposity status was indicated (pheterogeneity : 0.07 for total cancer and 0.03 for obesity-related cancer). Furthermore, the association between overweight and cancer risk was only observed in arginine (Arg) carriers, but not in Pro homozygous carriers (pheterogeneity : 0.07 for total cancer and 0.02 for obesity-related cancer). Pro homozygous carriers were more likely to be predisposed to cancer than Arg carriers with normal-weight conditions. In addition, overweight was related to a higher cancer risk in Arg carriers than Pro homozygous carriers. Our findings may suggest the adiposity-dependent dual effects of p53 Arg72Pro polymorphism during tumorigenesis.

Association of Escherichia coli containing polyketide synthase in the gut microbiota with colorectal neoplasia in Japan.

Escherichia coli containing polyketide synthase in the gut microbiota (pks+ E coli) produce a polyketide-peptide genotoxin, colibactin, and are suspected to play a role in the development of colorectal neoplasia. To clarify the role of pks+ E coli in the early stage of tumorigenesis, we investigated whether the pks status of E coli was associated with the prevalence of colorectal neoplasia. This cross-sectional analysis of data from a prospective cohort in Izu Oshima, Japan included asymptomatic residents aged 40-79 years who underwent screening colonoscopy and provided a stool sample. We identified 543 participants with colorectal neoplasia (22 colorectal cancer and 521 adenoma) as cases and 425 participants with normal colon as controls. The pks status of E coli was assayed using stool DNA and specific primers that detected pks+ E coli. The proportion of pks+ E coli was 32.6% among cases and 30.8% among controls. Compared with those with pks- E coli, the odds ratio (OR) (95% confidence interval) for participants with pks+ E coli was 1.04 (0.77-1.41) after adjusting for potential confounders. No statistically significant associations were observed regardless of tumor site or number of colorectal adenoma lesions. However, stratified analyses revealed increased ORs among participants who consumed cereals over the median intake or vegetables under the median intake. Overall, we found no statistically significant association between pks+ E coli and the prevalence of colorectal adenoma lesions among this Japanese cohort. However, positive associations were suggested under certain intake levels of cereals or vegetables.

Association between C-reactive protein and risk of overall and 18 site-specific cancers in a Japanese case-cohort.

BACKGROUND: Evidence of the association between chronic low-grade inflammation, as reflected by C-reactive protein (CRP) measurements, and cancer risk is equivocal. Specifically, few studies have examined this in uncommon cancers and Asian populations. METHODS: We utilised a case-cohort design consisting of multi-types of cancer (N = 3608), and a random subcohort (N = 4432) in a Japanese large population-based study, with a median follow-up time of 15.6 years, and measured baseline plasma CRP using high sensitivity assay. The hazard ratios (HRs) were estimated using weighted Cox proportional hazards methods. RESULTS: The multivariable-adjusted HR (95% confidence interval) for the top quartile of CRP was 1.28 (1.11‒1.48) (Ptrend < 0.001) for overall cancer compared to the bottom quartile of CRP. Among site-specific cancers, higher CRP levels were associated with an increased risk of colorectal, lung, breast, biliary tract, and kidney cancer, and leukaemia. These positive associations remained among participants after >3 years' follow-up. Furthermore, subgroup analyses for overall cancer robustly showed a positive association with CRP levels, regardless of sex and obesity. CONCLUSION: Our consistent findings suggested that chronic low-grade inflammation measured by CRP is associated with the risk of cancer.

Dietary fiber intake and risk of gastric cancer: The Japan Public Health Center-based prospective study.

Evidence of the association between dietary fiber intake and gastric cancer (GC) risk from prospective studies is limited. We examined the association between dietary fiber intake and GC risk in a large prospective study. A total of 91 946 eligible Japanese aged 45 to 74 years (42 773 men and 49 173 women) participated in a population-based cohort study (Japan Public Health Center-based prospective study). From a validated food frequency questionnaire with 138 food items, total and food source-specific dietary fiber intake was calculated as exposure. The hazard ratio (HR) and the 95% confidence interval (CI) of GC incidence according to quintile of dietary fiber intake were examined after adjusting for confounding factors. In total, 2228 GC cases (1559 men and 669 women) were observed during the 15.0 years follow-up. Total dietary fiber intake was not associated with GC risk; however, a marginally increased risk trend because of high HR in the highest quintile of total fiber intake was found in women (HR [95% CI] in Q5 vs Q1: 0.95 [0.79-1.14], P for trend .30 in men, HR [95% CI] 1.25 [0.98-1.61], P for trend .05 in women). Stratification by tumor location did not change the results. A marginal but not significant inverse trend was observed regarding cereal fiber intake and GC risk in men. Total dietary fiber intake was not associated with GC risk. Further studies are warranted to confirm this association.

Dietary intake of branched-chain amino acids and survival after colorectal cancer diagnosis.

Branched-chain amino acids (BCAAs), including leucine, isoleucine and valine, may potentially influence cancer progression by various mechanisms including its role in insulin resistance. However, the association of BCAAs with survival among patients with established colorectal cancer (CRC) remains unclear. We evaluated the associations between postdiagnostic BCAA intake with CRC-specific mortality and overall mortality among 1674 patients with nonmetastatic CRC in the Nurses' Health Study and the Health Professionals Follow-up Study. Patients completed a validated food frequency questionnaire. Multivariable hazard ratios (HRs) were calculated using Cox proportional-hazards regression model after adjustment for tumor characteristics and potential confounding factors. Comparing the highest with the lowest quartile intake of postdiagnostic total BCAA, the multivariable HRs were 1.18 (95% confidence interval [CI], 0.75-1.85, P for trend = .46 across quartiles) for CRC-specific mortality and 1.30 (95% CI, 1.01-1.69, P for trend = .04) for all-cause mortality. The multivariable HRs (the highest vs the lowest quartile) for all-cause mortality were 1.33 (95% CI, 1.03-1.73, Ptrend = .02) for valine, 1.28 (95% CI, 0.99-1.66, P for trend = .05) for leucine and 1.25 (95% CI, 0.96-1.61, P for trend = .06) for isoleucine. No statistically significant associations with each of the BCAA intake were observed for CRC-specific mortality (all P for trend > .30). Our findings suggest positive associations between higher intake of dietary BCAAs and risk of all-cause mortality in CRC patients. These findings need to be confirmed and potential mechanisms underlying this association need to be elucidated.

Dietary glycemic index, glycemic load, and endometrial cancer risk: The Japan Public Health Center-based Prospective Study.

Evidence supporting the association of glycemic index (GI) and glycemic load (GL) with the risk of endometrial cancer is controversial and reports from Asia were limited. Therefore, we aimed to investigate the association in Japanese women. We evaluated 52 460 women in the Japan Public Health Center-based Prospective Study aged 45-74 years who responded to the 5-year follow-up survey. GI and GL were calculated from a validated food frequency questionnaire, and the participants were divided into three groups by GI and GL. The hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated with the Cox proportional hazard model adjusted for potential confounding factors. As a result, within 15.5 years of follow-up, 166 new cases of endometrial cancer were identified. Compared with the lowest GI and GL tertile groups, the HR of the risk of endometrial cancer in the highest GI tertile group was 0.80 (95% CI, 0.53-1.20; Ptrend  = .33), and that of the highest GL tertile group was 0.79 (95% CI, 0.52-1.19; Ptrend  = .82). The results were unchanged after stratification by body mass index, coffee consumption, and history of diabetes. In conclusion, we did not find any significant association between GI and GL with the risk of endometrial cancer. Further research is required to clarify the association.

Body mass index and colorectal cancer risk: A Mendelian randomization study.

Traditional observational studies have reported a positive association between higher body mass index (BMI) and the risk of colorectal cancer (CRC). However, evidence from other approaches to pursue the causal relationship between BMI and CRC is sparse. A two-sample Mendelian randomization (MR) study was undertaken using 68 single nucleotide polymorphisms (SNPs) from the Japanese genome-wide association study (GWAS) and 654 SNPs from the GWAS catalogue for BMI as sets of instrumental variables. For the analysis of SNP-BMI associations, we undertook a meta-analysis with 36 303 participants in the Japanese Consortium of Genetic Epidemiology studies (J-CGE), comprising normal populations. For the analysis of SNP-CRC associations, we utilized 7636 CRC cases and 37 141 controls from five studies in Japan, and undertook a meta-analysis. Mendelian randomization analysis of inverse-variance weighted method indicated that a one-unit (kg/m2 ) increase in genetically predicted BMI was associated with an odds ratio of 1.13 (95% confidence interval, 1.06-1.20; P value <.001) for CRC using the set of 68 SNPs, and an odds ratio of 1.07 (1.03-1.11, 0.001) for CRC using the set of 654 SNPs. Sensitivity analyses robustly showed increased odds ratios for CRC for every one-unit increase in genetically predicted BMI. Our MR analyses strongly support the evidence that higher BMI influences the risk of CRC. Although Asians are generally leaner than Europeans and North Americans, avoiding higher BMI seems to be important for the prevention of CRC in Asian populations.

Increased Levels of Branched-Chain Amino Acid Associated With Increased Risk of Pancreatic Cancer in a Prospective Case-Control Study of a Large Cohort.

BACKGROUND & AIMS: A marker is needed to identify individuals at risk for pancreatic cancer. Increases in branched-chain amino acids (BCAAs) have been associated with pancreatic cancer. We performed a prospective case-control study to study the association between plasma BCAA levels and risk of pancreatic cancer in a large cohort. METHODS: We conducted a nested case-control study selected from 30,239 eligible participants 40-69 years old within the Japan Public Health Center-based prospective study. Over 16.4 years, 170 newly diagnosed pancreatic cancer cases were identified. Each case was matched to 2 controls by age, gender, geographic area, and fasting time at blood collection. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for pancreatic cancer were calculated using conditional logistic regression models with adjustment for potential confounding factors. RESULTS: Increased plasma BCAA levels at baseline were associated with an increased risk of pancreatic cancer. Compared with the lowest quartile of BCAA levels, the OR in the highest quartile was 2.43 (95% CI 1.21-4.90), and the OR per 1 SD increase in BCAA levels was 1.32 (95% CI 1.05-1.67). The association was especially strong for cases with blood samples collected at least 10 years before cancer diagnosis (OR per SD 1.60, 95% CI 1.10-2.32) compared with those detected less than 10 years before diagnosis (OR per SD 1.16, 95% CI 0.86-1.57). CONCLUSIONS: In an analysis of data from the Japan Public Health Center-based prospective study, we found an association between increased plasma BCAA level and increased risk of pancreatic cancer-particularly when the increase in BCAAs was observed at least 10 years before diagnosis. These findings add to the growing body of evidence for the association between BCAA levels and pancreatic cancer risk.

Iodine Excretion in 24-hour Urine Collection and Its Dietary Determinants in Healthy Japanese Adults.

BACKGROUND: Since seaweed is a common component of the Japanese diet, iodine intake in Japanese is expected to be high. However, urinary iodine excretion, measured using 24-hour urine samples, and its dietary determinants are not known. METHODS: Apparently healthy adults aged 20 to 69 years living in 20 areas throughout Japan were recruited in February and March, 2013. Urinary iodine excretion was evaluated using 24-hour urine collected from 713 subjects (362 men and 351 women), and the difference among age groups was assessed. The association between dietary intake of food groups and urinary iodine excretion was assessed among 358 subjects who completed a semi-weighed 4-day diet record (DR) and urine collection. The correlations between iodine intake and iodine excretion were also evaluated, and correlation coefficients were calculated for iodine intake in the DR of the overlapping day or the DR 1 day before and after urine collection. RESULTS: Median iodine excretion in 24-hour urine was 365 µg, and excretion was significantly higher in older subjects. Iodine intake estimated by the DRs was significantly correlated with urinary iodine excretion when DRs and urine collection were obtained on the same day (r = 0.37). After adjustment for confounding factors, iodine excretion was significantly associated with intakes of kelp and soup stock from kelp and fish. CONCLUSIONS: Although multiple measurements for urinary iodine are required to confirm our results, this study showed the current iodine status of healthy Japanese adults. The results suggest that kelp and fish are the main contributors to Japanese iodine status measured by 24-hour urine.

Estimation of habitual iodine intake in Japanese adults using 16 d diet records over four seasons with a newly developed food composition database for iodine.

Although habitual seaweed consumption in Japan would suggest that iodine intake in Japanese is exceptionally high, intake data from diet records are limited. In the present study, we developed a composition database of iodine and estimated the habitual intake of iodine among Japanese adults. Missing values for iodine content in the existing composition table were imputed based on established criteria. 16 d diet records (4 d over four seasons) from adults (120 women aged 30-69 years and 120 men aged 30-76 years) living in Japan were collected, and iodine intake was estimated. Habitual intake was estimated with the Best-power method. Totally, 995 food items were imputed. The distribution of iodine intake in 24 h was highly skewed, and approximately 55 % of 24 h values were < 300 µg/d. The median iodine intake in 24 h was 229 µg/d for women and 273 µg/d for men. All subjects consumed iodine-rich foods (kelp or soup stock) on one or more days of the sixteen survey days. The mean (median) habitual iodine intake was 1414 (857) µg/d for women and 1572 (1031) µg/d for men. Older participants had higher intake than younger participants. The major contributors to iodine intake were kelp (60 %) and soup stock (30 %). Habitual iodine intake among Japanese was sufficient or higher than the tolerable upper intake level, particularly in older generations. The association between high iodine intake as that observed in the present study and thyroid disease requires further study.

Adequacy of iodine intake in three different Japanese adult dietary patterns: a nationwide study.

BACKGROUND: Iodine intake is considered to be high in Japan due to regular seaweed consumption. Subgroups that do not have a traditional Japanese-style diet may consume insufficient amounts of iodine. METHOD: Three hundred and ninety apparently healthy adults (195 men and 195 women) aged 20 to 69 years from 20 areas throughout Japan completed four-day diet records and collected a 24-h urine sample. Dietary patterns were extracted from 31 food groups by cluster analysis. The iodine adequacy of each dietary pattern was examined using reference values from the Dietary Reference Intakes for Japanese. RESULTS: Three dietary patterns, labelled "Cluster I (Rice and vegetables)" (n = 101), "Cluster II (Meat, non-Japanese noodles, and sugar-sweetened beverages)" (n = 34), and "Cluster III (Fish, Japanese noodles, and alcohol)" (n = 60), were identified in male subjects. Another set of three patterns, "Cluster I (Rice and vegetables)" (n = 22), "Cluster II (Fish and Japanese noodles)" (n = 33), and "Cluster III (Bread and non-Japanese noodles)" (n = 140), was found in female subjects. Although the habitual iodine intake of almost all participants was above the estimated average requirement (EAR), iodine intake was statistically significantly lowest in Cluster II in men and Cluster III in women. Moreover, the mean participant age was the youngest in these clusters. CONCLUSION: Although Japan is known as a high iodine-consuming country, some Japanese individuals who do not eat a traditional Japanese-style diet consume low amounts of iodine. Since younger people tend to have modern, Westernized dietary patterns, iodine deficiency might be given additional consideration hereafter in Japan.