Generalizability of Relative Risk Estimates from a Well-defined Population to a General Population

Secular changes in bone mineral density of adult Japanese women from 1995 to 2013

INTRODUCTION

Secular changes in hip fracture incidence have been reported in the last few decades in Japan, but whether long-term bone mineral density (BMD) is also changing is unclear. This study aimed to determine whether BMD of Japanese women has changed over time.

METHODS

Subjects were 10,649 adult women who underwent BMD measurement in a health check-up population in Niigata, Japan, between 1995 and 2013. BMD of the distal, non-dominant forearm was measured by dual-energy X-ray absorptiometry. Demographic information and BMI were also obtained. Secular trends were determined by linear regression analysis.

RESULTS

BMD of subjects in their 40's decreased significantly in the age-adjusted model (P for trend=0.0162), but not in the age- and BMI-adjusted model (P for trend=0.2171). BMD of subjects in their 50's decreased marginally in the age-adjusted model (P for trend=0.0535), but not in the age- and BMI-adjusted model (P for trend=0.6601). BMDs of subjects in their 30's and 60's did not significantly change, while BMIs of subjects in their 40's-60's decreased significantly.

CONCLUSIONS

A secular decrease in BMD, partly attributed to decreases in BMI, was observed in middle-aged Japanese women from 1995 to 2013. Measures to help maintain suitable BMI will be necessary to prevent a decrease in BMD among women.

Fat mass and obesity-associated gene polymorphisms, pre-diagnostic plasma adipokine levels and the risk of colorectal cancer: The Japan Public Health Center-based Prospective Study

Although their functional outcomes remain largely unknown, single nucleotide polymorphisms (SNPs) in the fat mass and obesity-associated gene (FTO) may interact with adipokines, especially leptin and adiponectin, to modify the risk of colorectal cancer. We conducted a prospective study of 375 colorectal cancer cases and 750 matched controls to examine the effects of SNPs in the FTO, either alone or in interaction with pre-diagnostic plasma adipokine levels. Using a conditional logistic regression model, we obtained odds ratios (ORs) and their 95% confidence intervals (CIs) of colorectal cancer. Seven SNPs in strong linkage disequilibrium demonstrated a similarly positive association with colorectal cancer, and most evidently for rs1558902, rs8050136, rs3751812, and rs9939609 (Ptrend = 0.02). Of interest, we observed a statistically significant interaction of rs8050136 with plasma total adiponectin levels (Pinteraction = 0.03). Compared to non-carriers in the lowest quintile of plasma total adiponectin, A allele carriers in the same quintile showed a considerably elevated risk of colorectal cancer, with a body mass index-adjusted OR of 2.54 (95% CI, 1.36-4.75). This investigation of the interaction between SNPs in the FTO and pre-diagnostic plasma adipokine levels has revealed the importance of both genetic and hormonal factors associated with adiposity in colorectal carcinogenesis.

Effect heterogeneity and variable selection for standardizing causal effects to a target population

The participants in randomized trials and other studies used for causal inference are often not representative of the populations seen by clinical decision-makers. To account for differences between populations, researchers may consider standardizing results to a target population. We discuss several different types of homogeneity conditions that are relevant for standardization: Homogeneity of effect measures, homogeneity of counterfactual outcome state transition parameters, and homogeneity of counterfactual distributions. Each of these conditions can be used to show that a particular standardization procedure will result in an unbiased estimate of the effect in the target population, given assumptions about the relevant scientific context. We compare and contrast the homogeneity conditions, in particular their implications for selection of covariates for standardization and their implications for how to compute the standardized causal effect in the target population. While some of the recently developed counterfactual approaches to generalizability rely upon homogeneity conditions that avoid many of the problems associated with traditional approaches, they often require adjustment for a large (and possibly unfeasible) set of covariates.

Association between serum liver enzymes and all-cause mortality: The Japan Public Health Center-based Prospective Study

BACKGROUND & AIMS

The association of serum liver enzyme levels with all-cause mortality in individuals without hepatitis B virus or hepatitis C virus infection is inconsistent. We aimed to investigate all-cause and non-liver disease mortality according to levels of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyltransferase (GGT) stratified by hepatitis virus infection status in a Japanese cohort.

METHODS

Participants were 7243 men and 13 513 women aged 40-69 years at the baseline survey in 1993-1994. Multivariate-adjusted hazard ratios of death from the baseline health check-up to December 2012 were calculated with a Cox proportional hazards model controlling for potential confounding factors.

RESULTS

During follow-up, 2235 deaths in men and 1901 deaths in women were identified. All serum liver enzymes were associated with all-cause mortality in each sex and hepatitis virus infection status. In participants without infection, those with more than twice the upper level of normal (ULN), which was defined as 30 IU/L for AST and ALT and 50 IU/L for GGT, had a higher risk of non-liver disease mortality compared to those below the ULN (HR 1.69; 95% confidence interval 1.13-2.53, 1.49; 1.02-2.18, 1.39; 1.11-1.73, 1.72; 1.08-2.74 and 1.72; 1.10-2.69 for AST, ALT, and GGT in men and AST and GGT in women, respectively), except for ALT in women.

CONCLUSIONS

In participants without hepatitis virus infection, serum liver enzyme levels were positively associated with all-cause mortality. Similar associations were also found for non-liver disease mortality.

Plasma tea catechins and risk of cardiovascular disease in middle-aged Japanese subjects: The JPHC study

BACKGROUND AND AIMS

Although a potential benefit of drinking green tea has been suggested to reduce the development of cardiovascular disease, no study has investigated the relationship between plasma tea catechin and risk of cardiovascular disease.

METHODS

A prospective, nested case-control study was conducted to examine the association between plasma tea catechin and risk of stroke and coronary heart disease (CHD) in a cohort of 29,876 men and women aged 40-69 years without history of heart disease, stroke or cancer. Participants completed a survey and donated blood samples between 1990 and 1994, and were followed-up through 2008. A total of 1132 stroke cases and 209 CHD cases, matched 1:1 to controls (n = 1132) for stroke and 1:2 to controls (n = 418) for CHD, were included in the analysis.

RESULTS

We found no significant association between plasma tea catechin and the incidence of stroke or CHD in either men or women. However, we found that high plasma levels of epigallocatechin gallate (EGCG) were associated with reduced risk of stroke in non-smoking men; the adjusted odds ratio (95% CI) for the highest vs. non-detectable levels was 0.53 (0.29-0.98). The respective OR in male smokers was 1.23 (0.75-2.16). A significant interaction by smoking status was found for the highest vs. non-detected plasma EGCG in relation to stroke (p-for-interaction: p = 0.09).

CONCLUSIONS

Plasma tea catechin was not associated with reduced risks of either stroke or CHD, while a protective effect of certain tea catechin on stroke risk is suggested for male non-smokers.

An Out-of-Pocket Cost Removal Intervention on Fecal Occult Blood Test Attendance

INTRODUCTION

To date, no comparative study has assessed the impact of a cost-removal intervention on fecal occult blood testing (FOBT). In 2012, the Japanese government introduced a nationwide project to remove out-of-pocket costs for FOBT. The study objective was to evaluate the differential impact of the intervention on FOBT attendance in the total population and various subgroups.

METHODS

This study analyzed 309,103 people in national, repeated cross-sectional studies, observed pre- and post-intervention (2010 and 2013), using covariate-adjusted difference-in-differences estimates to compare intervention and no-intervention groups. The outcome measure was uptake of FOBT attendance resulting from the intervention. Stratified analyses were conducted according to sociodemographic and health-related characteristics.

RESULTS

The intervention was associated with significantly positive uptake of FOBT in both genders, but the impact was greater in women than men: 6.7% (95% CI=5.2, 8.1) for women and 2.7% (95% CI=1.1, 4.3) for men in the covariate-adjusted models. Post-intervention, attendance increased in almost all subgroups in women. However, among men, some socially advantaged subgroups, such as high expenditure, high education, and public officers, showed no effect. Some subgroups such as current smokers and less than high school education were identified as hard-to-reach populations that may be less sensitive to the intervention, irrespective of gender.

CONCLUSIONS

This is the first comparative study of cost-removal intervention for uptake of FOBT. The intervention may increase FOBT attendance. However, the size of the effect is not great, especially in men, and differential effects occurred across subgroups including gender and socioeconomic differences.

Generalizing results of randomized trials to clinical practice: reliability and cautions

BackgroundWell designed randomized controlled trials provide reliable evidence of treatment effects, but there is no consensus on how best to apply these results to clinical practice. The main concerns are that populations enrolled in trials are more selected than those treated in a clinical setting, and whether the treatment effects observed in trials will also be observed in clinical practice.

MethodsAn informal literature review was undertaken to find studies analysing the issue of generalizing trial results (external validity) to clinical practice.

ResultsMost of the studies focused on differences in patients characteristics (age, gender, severity of disease, concomitant treatments and so on) between the clinical trial population and a ‘real world’ clinical population. None provided good evidence of a reduction in the treatment effect in the trial compared to what might happen in clinical practice for simple pharmacological treatments. However complex treatments like surgery or percutaneous interventional procedures, had a greater potential for variation. Extrapolating treatments to different health care settings from the trial can result in important variations in treatment effects.

ConclusionsComplex therapies need careful consideration before they can be applied routinely from trials into practice, and applying results from one health care environment to a different one should be carried out with caution. Generalizing results from well conducted trials to clinical practice can mostly be carried out with confidence, especially for simple therapies with good evidence of benefit.

Prediction of the 10-year probability of gastric cancer occurrence in the Japanese population: the JPHC study cohort II

Gastric cancer is a particularly important issue in Japan, where incidence rates are among the highest observed. In this work, we provide a risk prediction model allowing the estimation of the 10-year cumulative probability of gastric cancer occurrence. The study population consisted of 19,028 individuals from the Japanese Public Health Center cohort II who were followed-up from 1993 to 2009. A parametric survival model was used to assess the impact on the probability of gastric cancer of clinical and lifestyle-related risk factors in combination with serum anti-Helicobacter pylori antibody titres and pepsinogen I and pepsinogen II levels. Based on the resulting model, cumulative probability estimates were calculated and a simple risk scoring system was developed. A total of 412 cases of gastric cancer occurred during 270,854 person-years of follow-up. The final model included (besides the biological markers) age, gender, smoking status, family history of gastric cancer and consumption of highly salted food. The developed prediction model showed good predictive performance in terms of discrimination (optimism-corrected c-index: 0.768) and calibration (Nam and d'Agostino's χ(2) test: 14.78; p values = 0.06). Estimates of the 10-year probability of gastric cancer occurrence ranged from 0.04% (0.02, 0.1) to 14.87% (8.96, 24.14) for men and from 0.03% (0.02, 0.07) to 4.91% (2.71, 8.81) for women. In conclusion, we developed a risk prediction model for gastric cancer that combines clinical and biological markers. It might prompt individuals to modify their lifestyle habits, attend regular check-up visits or participate in screening programmes.

Plasma isoflavones and risk of primary liver cancer in Japanese women and men with hepatitis virus infection: a nested case-control study

BACKGROUND

Evidence suggests that estrogen plays a preventive role in primary liver cancer development, and it might be thought that isoflavones, which are structurally similar to estrogens and bind to estrogen receptors, are associated with the risk of liver cancer. We investigated this suspected association by measuring plasma concentrations of isoflavones in a nested case-control study of a population-based prospective cohort in Japan.

METHODS

From 18,628 target participants ages 40 to 69 years who returned the baseline questionnaire and provided blood samples, we selected those with either hepatitis B or hepatitis C virus infection at baseline (n = 1,544). Among these, 90 (28 women and 62 men) were newly diagnosed with primary liver cancer from 1993 through 2006; they were matched with 175 controls (54 women and 121 men). Plasma concentrations of isoflavones (genistein, daidzein, glycitein, and equol) were measured using triple quadrupole tandem liquid chromatography-mass spectrometry. The ORs of liver cancer development based on plasma concentrations were estimated with a conditional logistic regression model.

RESULTS

Basically, distributions of plasma isoflavone concentrations did not differ between the cases and controls. No statistically significant associations of genistein, daidzein, glycitein, and equol with primary liver cancer risk were found in either women or men.

CONCLUSIONS

In middle-aged Japanese women and men with hepatitis virus infection, plasma isoflavones were unassociated with the occurrence of primary liver cancer.

IMPACT

The role of isoflavones in liver carcinogenesis merits further study using both biomarkers and data on dietary intake of isoflavones. Cancer Epidemiol Biomarkers Prev; 24(3); 532-7. ©2014 AACR.

Diabetes mellitus defined by hemoglobin A1c value: Risk characterization for incidence among Japanese subjects in the JPHC Diabetes Study

Aims/Introduction:  Although several risk factors for type 2 diabetes have been identified, most of them have been identified in studies on Western populations, and they should be evaluated in a Japanese population. In 2010, new diagnostic criteria for diabetes mellitus using hemoglobin A1c (HbA1c) were released and its use in epidemiological studies has many advantages. The aim of the present study was to evaluate risk factors for type 2 diabetes defined based on HbA1c values in a Japanese population.

MATERIALS AND METHODS

  A total of 9223 subjects (3076 men and 6147 women) were followed up for 5 years. Diabetes was defined based on self-report or HbA1c value. Risk factors for diabetes were evaluated as odds ratios adjusted for potential confounding factors by logistic regression.

RESULTS

  During the 5-year follow-up period, we documented 518 incident cases of diabetes (232 men and 286 women). Of the 518 incident cases, 310 cases were diagnosed by HbA1c alone. Among the men, age, smoking (both past smoking and current smoking) and family history of diabetes significantly increased the risk of diabetes. Among the women, body mass index, family history of diabetes and hypertension significantly increased the risk of diabetes. These results did not change markedly after adjustment for the baseline HbA1c values, and the baseline HbA1c value itself was a significant risk factor for diabetes mellitus.

CONCLUSIONS

  Known risk factors for diabetes established in Western populations also increased the risk of diabetes in a Japanese population defined on the basis of HbA1c values. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00119.x, 2011).

Effect modification of body mass index and body fat percentage on fatty liver disease in a Japanese population

BACKGROUND AND AIM

No previous study has performed multivariate analysis of the risk factors of fatty liver disease (FL), focusing on the effect of weight gain of ≥ 10 kg since the age of 20, and no analysis model exists that simultaneously evaluates body mass index (BMI) and body fat percentage (BFP) as adjustment variables.

METHODS

To investigate these, we collected anthropometric data from health checkups, and conducted a cross-sectional study (targeting 1851 males and 1259 females aged 30 years or over).

RESULTS

Regardless of sex, weight gain of ≥10 kg since the age of 20 was positively associated with FL. Our stratified analysis of BFP into two categories, to evaluate the interaction between BMI and BFP in FL, indicated an approximately fivefold increase in the odds ratio in the male group with high BMI and BFP values compared to those with low BMI and BFP values, with a synergy index of 1.77 > 1. On the other hand, females demonstrated no significant additive interaction, with a synergy index of 0.49 < 1.

CONCLUSIONS

We revealed that weight gain ≥ 10 kg since the age of 20 is significantly associated with FL regardless of sex. In addition, by performing a synergy index (S), we showed that the additive interaction between BMI and BFP in FL differs according to gender.

Plasma levels of adiponectin and primary liver cancer risk in middle-aged Japanese adults with hepatitis virus infection: a nested case-control study

BACKGROUND

Excess body weight is an independent risk factor for primary liver cancer, and the role of adiponectin in the pathogenesis of obesity-related malignancies is a focus of research interest. Few prospective studies have examined the association between circulating adiponectin and liver cancer risk, so we investigated this association in a nested case-control study of a population-based prospective cohort in Japan.

METHODS

From 18,628 target participants of ages 40 to 69 years who returned the baseline questionnaire and provided blood samples, we selected those with either hepatitis B or C virus infection at baseline (n = 1,544). Among these, 90 were newly diagnosed with primary liver cancer from 1993 through 2006, and matched to 177 controls. The ORs of liver cancer development based on plasma levels of adiponectin were estimated with a conditional logistic regression model.

RESULTS

Median values of total and high-molecular-weight (HMW) adiponectin tended to be higher in the patients with liver cancer, and plasma levels of adiponectin were positively associated with liver cancer risk. Body mass index- and diabetes-adjusted ORs for the highest tertile of total and HMW adiponectin levels versus the lowest were 3.30 [95% confidence interval (CI), 1.45-7.53; Ptrend < 0.01] and 3.41 (95% CI, 1.50-7.73; Ptrend < 0.01), respectively. There was no effect modification by body mass index and diabetes.

CONCLUSIONS

Higher plasma adiponectin levels were associated with an increased risk of primary liver cancer in middle-aged Japanese adults with hepatitis virus infection.

IMPACT

Circulating adiponectin levels may be a risk marker for primary liver cancer.

The combination of Helicobacter pylori- and cytotoxin-associated gene-A seropositivity in relation to the risk of myocardial infarction in middle-aged Japanese: The Japan Public Health Center-based study

BACKGROUND

Limited evidence is available concerning the impact of the combination of Helicobacter pylori- (H. pylori) and cytotoxin-associated gene-A (CagA)-positivity on the risk of myocardial infarction (MI) and stroke, particularly in Asian populations, in which the prevalence of H. pylori infection is high.

METHODS

A prospective, nested case-control study was conducted to examine the association between H. pylori and CagA and risk of MI and stroke within a cohort of 29,876 men and women aged 40-69 years with no history of heart disease, stroke or cancer. Participants completed a risk factor survey and donated blood samples between 1990 and 1994. Systematic cardiovascular surveillance was performed through 2002. One control for each stroke case and two controls for each MI case were matched by sex, age, date of blood sampling, time since last meal and study location.

RESULTS

During the follow-up period, there were 600 strokes and 106 MIs. H. pylori-IgG positivity was not associated with the risk of MI, while CagA positivity tended to be associated with it (OR = 1.72, 95%CI: 0.91-3.26, p = 0.10). We found no association between H. pylori or CagA and risk of stroke.

CONCLUSIONS

H. pylori infection was not significantly associated with risk of MI and stroke among middle-aged Japanese. However, CagA positivity tended to be associated with MI.

Plasma testosterone and sex hormone-binding globulin concentrations and the risk of prostate cancer among Japanese men: a nested case-control study

Sex hormones, particularly androgens, have been implicated in prostate carcinogenesis. Overall, however, prospective studies have reported no association between circulating levels of sex hormones and the risk of prostate cancer. However, despite the possible difference in the effects of hormones on prostate cancer risk by stage, age, body mass index (BMI) and isoflavones, evidence for these is sparse. Moreover, few studies have been conducted in Asian populations, who are relatively lean and have high isoflavone consumption. We examined the hypothesis that plasma concentrations of circulating testosterone and sex hormone-binding globulin (SHBG) are associated with the risk of prostate cancer in a case-control study nested in the Japan Public Health Center-based Prospective Study. Concentrations of total testosterone and SHBG were measured in plasma samples from 201 patients with prostate cancer and 402 matched control participants, and concentrations of free testosterone were calculated. No overall association between the plasma levels of any hormone and total prostate cancer was observed. Odds ratios (95% confidence interval [CI]) in the highest versus lowest group were 0.71 (95% CI = 0.36-1.41, Ptrend = 0.43) for total testosterone, 0.70 (95% CI = 0.39-1.27, Ptrend = 0.08) for free testosterone and 1.38 (95% CI = 0.69-2.77, Ptrend = 0.23) for SHBG. When stratified by cancer stage, age, BMI and plasma isoflavone level, free testosterone was inversely associated with localized cancers and equol producers, while SHBG was associated with an increased risk of prostate cancer in younger men. In conclusion, in this nested case-control study, concentrations of circulating total testosterone, free testosterone or SHBG were not strongly associated with a risk for total prostate cancer.

Participation in health check-ups and mortality using propensity score matched cohort analyses

OBJECTIVE

All Japanese aged ≥40 years are eligible for free annual health check-ups including blood pressure and cholesterol measurements. It is well known that health check-up screenees are more likely to have healthy lifestyles and better health conditions than non-screenees. Therefore, controlling these factors is required to investigate whether screenees have a lower mortality risk than non-screenees independent of their lifestyles or health conditions.

METHODS

We followed 48,775 Japanese National Health Insurance beneficiaries aged 40-79 years since 1994 for 11 years. We used Cox proportional hazard models adjusted for possible confounding factors. We also performed propensity for use of the health check-up matched cohort analyses.

RESULTS

Compared to non-screenees, multiple-adjusted hazard ratios (95% confidence intervals) for all-cause and cardiovascular disease mortality among screenees were 0.74 (0.62-0.88) and 0.65 (0.44-0.95) for men and 0.69 (0.52-0.91) and 0.61 (0.36-1.04) for women, respectively. These relations were also observed when we used propensity matched cohort analyses.

CONCLUSION

This is the first study to show that mortality rates are lower among screenees than non-screenees in Japanese health check-ups when propensity matched cohort analyses were used for adjusting confounding factors. Further prospective studies, including randomized controlled trials, are required to confirm whether screening lowers mortality.

Plasma organochlorines and subsequent risk of prostate cancer in Japanese men: a nested case-control study

BACKGROUND

Although accumulating evidence suggests that exposure to organochlorine pesticides and polychlorinated biphenyls (PCBs) may contribute to the development of prostate cancer, few investigations have used biological samples to classify exposure to specific organochlorines. To our knowledge, this is the first prospective study to investigate the association between blood levels of organochlorines and prostate cancer risk.

METHODS

We conducted a nested case-control study using data from the Japan Public Health Center-based Prospective (JPHC) Study. A total of 14,203 men 40-69 years old who returned the baseline questionnaire and who provided blood samples were followed from 1990 to 2005. Using a mean follow-up period of 12.8 years, we identified 201 participants who were newly diagnosed with prostate cancer. Two matched controls for each case were selected from the cohort. We used a conditional logistic regression model to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for prostate cancer in relation to plasma levels of nine organochlorines: PCBs, dichlorodiphenyltrichloroethane (DDT), hexachlorobenzene (HCB), beta-hexachlorocyclohexane (beta-HCH), trans- and cis-nonachlor, oxychlordane, and mirex.

RESULTS

No statistically significant association with total prostate cancer was seen for any plasma organochlorine, although we did observe an insignificant inverse association for plasma HCB and beta-HCH. Total PCB in plasma was also inversely associated with advanced prostate cancer but without statistical significance.

CONCLUSION

Our results suggest that no overall association exists between prostate cancer and organochlorines at the levels measured in our study population.

Impact of metabolic factors on subsequent cancer risk: results from a large-scale population-based cohort study in Japan

The impact of metabolic factors, which are major risk factors for cardiovascular disease, on total cancer risk has not been clarified. We prospectively examined whether metabolic factors and their aggregates predict the subsequent occurrence of total and major sites of cancer in the Japan Public Health Center-based Prospective Study. A total of 27 724 participants (9548 men and 18 176 women) aged 40-69 years participating in a questionnaire and health checkup survey in 1993-1995 were followed for total cancer incidence through 2004. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated for metabolic factors and for two criteria of their aggregates (three or more than three factors and two or more than two additional factors in addition to being overweight) with a Cox proportional hazards model to control for potential confounding factors. In both sexes, the presence of metabolic factors in the aggregate did not predict subsequent occurrence of cancer as a whole. By site, a significant increase in risk was observed for male liver cancer [HR = 1.73, CI = 1.03-2.91 (three or more than three factors); HR = 1.99, CI = 1.11-3.58 (two or more than two additional factors in addition to being overweight)], and female pancreatic cancer [HR = 1.99, CI = 1.00-3.96 (two or more than two additional factors in addition to being overweight)]. For other sites, positive associations were observed only for specific metabolic factors, that is, high triglycerides and male colon cancer (HR = 1.71, CI = 1.11-2.62), and obesity and female breast cancer (HR = 1.75, CI = 1.21-2.55). Metabolic factors in the aggregate may have little impact on total cancer risk in the Japanese population, although the association between specific components and specific cancers suggests an etiologic link between them.

Isoflavone consumption and subsequent risk of hepatocellular carcinoma in a population-based prospective cohort of Japanese men and women

The incidence of hepatocellular carcinoma (HCC) is much higher in men than in women. Several experiment and epidemiological studies have suggested that estrogen might play an inhibitory role in the development of HCC. Because isoflavones have a similar structure as 17beta-estradiol and appear to have an anti-estrogenic effect in women and estrogenic effect in men, we hypothesized that the effect of isoflavones on HCC differs by sex. We investigated the association between isoflavones (genistein and daidzein) and soy products and HCC in Japan in a population-based prospective study in 19,998 Japanese (7,215 men and 12,783 women) aged 40-69 years. During 11.8 years of follow-up, 101 subjects (69 men and 32 women) were newly diagnosed with HCC. Case patients were grouped according to consumption of isoflavones and soy products and stratified by hepatitis virus infection. Hazard ratios (HRs) and 95% confidence intervals (CIs) for HCC were calculated by Cox proportional-hazards modeling. In women, genistein and daidzein were dose-dependently associated with an increased risk of HCC, with multivariable HRs for the highest versus lowest tertile of 3.19 (95%CI = 1.13-9.00, p(trend) = 0.03) and 3.90 (95% CI = 1.30-11.69, p(trend) = 0.01), respectively. No association between isoflavones and HCC was observed in men. These results persisted when analysis was restricted to subjects positive for either or both hepatitis C and B virus. In conclusion, isoflavone consumption may be associated with an increased risk of HCC in women. Women with hepatitis virus infection may be advised to abstain from isoflavone consumption. Further studies are warranted to confirm these findings.

Blood pressure and the risk of stroke, cardiovascular disease, and all-cause mortality among Japanese: the JPHC Study

BACKGROUND

Little is known about the influence of blood pressure (BP) on cardiovascular disease (CVD) outcomes among Asian populations.

METHODS

We examined population attributable fractions (PAFs) and hazard ratios (HRs) associated with BP in relation to stroke and coronary heart disease (CHD) incident and mortality within a cohort of 33,372 Japanese men and women aged 40-69 years, free of prior diagnosis of cancer and CVD. The BP was classified based on modified criteria of the 2003 European Society of Hypertension-European Society of Cardiology guidelines. A total of 943 stroke events, 182 CHD events, 262 stroke deaths, and 120 CHD deaths occurred between the baseline questionnaire (1990-1994) and the end of follow-up in 31 December 2003.

RESULTS

BP levels were linearly associated with incidence and mortality of CVD in men and women. According to the PAF estimation, the elimination of normal to severe hypertension would prevent 64% of stroke incidence in men and 50% in women; 67% of stroke mortality in men and 29% in women; and 38% of total CVD mortality in men and 36% in women. The PAF estimate for total stroke incidence was the highest for mild hypertension, and lower for moderate to severe hypertension in both sexes.

CONCLUSIONS

The contributions of normal BP, high normal BP, and mild hypertension to the occurrence of stroke events were greater than those made by moderate and severe hypertension, highlighting the importance of primary prevention and of treatment for low-to-moderate degrees of hypertension.

Metabolic factors and subsequent risk of hepatocellular carcinoma by hepatitis virus infection status: a large-scale population-based cohort study of Japanese men and women (JPHC Study Cohort II)

OBJECTIVE

The association between metabolic factors and hepatocellular carcinoma (HCC) has not been well clarified. We prospectively examined whether metabolic factors predicts the subsequent risk of HCC in the Japan Public Health Center-based Prospective Study Cohort II, in consideration of hepatitis virus infection status.

METHODS

A total of 17,590 subjects aged 40-69 participating in a questionnaire and health checkup survey during 1993-1994 were followed for incidence of HCC through 2006. A total of 102 cases of HCC were newly documented. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated for metabolic factors controlling for potential confounding factors.

RESULTS

The presence of metabolic factors in the aggregate was associated with a significantly increased risk of HCC, especially with hepatitis virus infection. HCC was positively associated particularly with high glucose (HR = 1.75, CI = 1.11-2.74) and overweight (HR = 2.22, CI = 1.42-3.48). Results were similar when analyses were limited to subjects with HCV infection.

CONCLUSIONS

Although metabolic factors in the aggregate may be associated with an increased risk of HCC, the main contributors to this association under HCV infection appear to be overweight and high glucose. Improvement of these factors may be a crucial target in preventing progression to HCC in those with HCV infection.

Population attributable fraction of mortality associated with tobacco smoking in Japan: a pooled analysis of three large-scale cohort studies

BACKGROUND

Quantitative measures of the burden of tobacco smoking in Asian countries are limited. We estimated the population attributable fraction (PAF) of mortality associated with smoking in Japan, using pooled data from three large-scale cohort studies.

METHODS

In total, 296,836 participants (140,026 males and 156,810 females) aged 40-79 years underwent baseline surveys during the 1980s and early 1990s. The average follow-up period was 9.6 years. PAFs for all-cause mortality and individual tobacco-related diseases were estimated from smoking prevalence and relative risks.

RESULTS

The prevalence of current and former smokers was 54.4% and 25.1% for males, and 8.1% and 2.4% for females. The PAF of all-cause mortality was 27.8% [95% confidence interval (CI): 25.2-30.4] for males and 6.7% (95% CI: 5.9-7.5) for females. The PAF of all-cause mortality calculated by summing the disease-specific PAFs was 19.1% (95% CI: 16.0-22.2) for males and 3.6% (95% CI: 3.0-4.2) for females. The estimated number of deaths attributable to smoking in Japan in 2005 was 163,000 for males and 33,000 for females based on the former set of PAFs, and 112,000 for males and 19,000 for females based on the latter set. The leading causes of smoking-attributable deaths were cancer (61% for males and 31% for females), ischemic heart diseases and stroke (23% for males and 51% for females), and chronic obstructive pulmonary diseases and pneumonia (11% for males and 13% for females).

CONCLUSION

The health burden due to smoking remains heavy among Japanese males. Considering the high prevalence of male current smokers and increasing prevalence of young female current smokers, effective tobacco controls and quantitative assessments of the health burden of smoking need to be continuously implemented in Japan.

Plasma isoflavones and subsequent risk of prostate cancer in a nested case-control study: the Japan Public Health Center

PURPOSE

The incidence of prostate cancer is much lower in Japanese than Western populations. Given the preventive effects of isoflavones on carcinogenesis in the prostate in many nonhuman studies and the high consumption of isoflavones in Japanese, this low incidence may be partly due to the effects of soy.

PATIENTS AND METHODS

We conducted a nested case-control study within the Japan Public Health Center-based Prospective Study. A total of 14,203 men aged 40 to 69 years who had returned the baseline questionnaire and provided blood samples were observed from 1990 to 2005. During a mean of 12.8 years of follow-up, 201 newly diagnosed prostate cancers were identified. Two matched controls for each case were selected from the cohort. Conditional logistic regression model was used to estimate the odds ratios (ORs) and 95% CIs for prostate cancer in relation to plasma levels of isoflavone.

RESULTS

Plasma genistein level tended to be inversely associated with the risk of total prostate cancer. Although plasma daidzein showed no association, the highest tertile for plasma equol, a metabolite of daidzein, was significantly associated with a decreased risk of total prostate cancer (OR = 0.60; 95% CI, 0.36 to 0.99; P(trend) = .04). These inverse associations were strengthened after analysis was confined to localized cases, with ORs in the highest group of plasma genistein and equol compared with the lowest of 0.54 (95% CI, 0.29 to 1.01; P(trend) = .03) and 0.43 (95% CI, 0.22 to 0.82; P(trend) = .02), respectively. Plasma isoflavone levels were not statistically significantly associated with the risk of advanced prostate cancer.

CONCLUSION

Isoflavones may prevent the development of prostate cancer.

Plasma Isoflavone Level and Subsequent Risk of Breast Cancer Among Japanese Women: A Nested Case-Control Study From the Japan Public Health Center-Based Prospective Study Group

Purpose

Because they have large variations in consumption, Asian countries are suitable settings for studies of the effect of relatively high-dose isoflavone intake on breast cancer risk. Nevertheless, no prospective study from Asia has assessed blood or urine levels as biomarkers of isoflavone intake.

Patients and Methods

A total of 24,226 women ages 40 to 69 years in the Japan Public Health Center–based prospective study who responded to the baseline questionnaire and provided blood in 1990 to 1995 were observed to December 2002. During a mean 10.6 years of follow-up, 144 patients newly diagnosed with breast cancer were identified. Two matched controls for each patient were selected from the cohort. Isoflavone levels were assessed by plasma level and food frequency questionnaire, and the odds ratio of breast cancer according to isoflavone level was estimated using a conditional logistic regression model.

Results

We found a statistically significant inverse association between plasma genistein and risk of breast cancer, but no association for plasma daidzein. Adjusted odds ratios for the highest versus lowest quartile of plasma level were 0.34 for genistein (95% CI, 0.16 to 0.74; P for trend, .02) and 0.71 for daidzein (95% CI, 0.35 to 1.44; P for trend, .54). Median plasma genistein values in the control group were 31.9 ng/mL for the lowest and 353.9 ng/mL for the highest quartile groups. Regarding dietary intake of isoflavones, nonsignificant inverse associations were observed for both genistein and daidzein.

Conclusion

This nested case-control study found an inverse association between plasma genistein and the risk of breast cancer in Japan.