Tobacco is the greatest single cause of many non-communicable diseases, including cancer. We calculated the proportion of cancer incidence and mortality in 2015 attributable to tobacco smoking and exposure to secondhand smoke (SHS). Data on the prevalence of active smoking were derived from the 2005 Japanese National Health and Nutrition Survey by age group and gender. For SHS exposure prevalence, data from a nationwide cross-sectional survey from 2004-2005 were used. Based on standard formulas, population attributable fractions (PAFs) for each cancer causally associated with active smoking, namely the oral cavity and pharynx, esophagus, stomach, colon, rectum, liver, pancreas, nasal, larynx, lung, uterine cervix, kidney, renal pelvis and ureter, bladder, and acute myeloid leukemia, were calculated for each sex and age group and aggregated to obtain the PAF among total cancer incidence and mortality. For SHS exposure, PAFs for lung cancer and total cancer were calculated using the same method. For Japan in 2015, 145,765 new cancer cases and 72,520 cancer deaths, corresponding to a PAF of 15.2% for total cancer incidence and 19.6% for total cancer mortality, were attributable to active tobacco smoking. For SHS exposure, 0.5% of total cancer incidence and 0.7% of total cancer mortality in 2015 were attributable. Tobacco is still one of the major causes of cancer in Japan.

Alcohol can cause or contribute to the development of many non-communicable diseases, including cancer. We calculated the proportion of cancer incidence and mortality in 2015 attributable to alcohol consumption in 2005. Data on alcohol consumption, provided in go, a traditional Japanese alcohol measurement unit, was derived from the 2005 Japanese National Health and Nutrition Survey for each sex and age group, then converted into grams of ethanol per day. The optimal consumption of alcohol for the purpose of this study was determined to be none, based on a global assessment derived from previous observational studies that have looked at the association between alcohol consumption and cancer. Using standard formulas, population attributable fractions (PAFs) for all cancers positively associated with alcohol drinking - oral cavity, pharynx, esophagus, stomach, colorectum, liver, larynx, and female breast - were calculated for each sex and age group and aggregated to obtain the PAF among total cancer incidence and mortality. For Japan in 2015, 59,838 cases of cancer incidence and 23,929 cancer deaths were attributable to alcohol consumption. The estimated PAF for cancer incidence and mortality attributable to alcohol consumption was 6.2% and 6.5%, respectively. For both cancer incidence and mortality, the highest percentage of alcohol-attributable cancer sites was esophageal (54.0% for incidence, 52.3% for mortality). Avoidance of alcohol consumption would reduce the burden of alcohol on cancer in Japan.

Overweight and obesity are known contributors to many non-communicable diseases, including cancer, and affect over one-tenth of the global population. One way to maintain a healthy weight and reduce the risk for cancer is through increased physical activity. We estimated the fraction of cancer incidence and mortality in 2015 attributable to excess bodyweight as well as lack of physical activity among the Japanese population. The optimal body-mass index (BMI) for the purposes of this study was determined to be less than 23 kg/m². Mean BMI for each sex and age group was calculated using measured weight and height data extracted from the 2005 Japanese National Health and Nutrition Survey (JNHNS). For the data on physical activity, we extracted the answers from the same survey from a question regarding whether the respondent did regular exercise. Population attributable fractions (PAFs) for each cancer positively associated with excess bodyweight - esophageal adenocarcinoma, stomach (cardia), colorectum, liver, gallbladder, pancreas, female breast (pre- and post- menopausal), ovary, endometrium, advanced prostate and kidney - and for those positively associated with physical inactivity - colorectum, female breast and endometrium - were calculated for each sex and age group and aggregated to obtain the PAF among total cancer incidence and mortality. Excess bodyweight was attributable to 0.7% of cancer incidence and mortality, while lack of regular exercise was attributable to 1.3% of cancer incidence and 0.8% of cancer mortality. Around 1% of cancer incidence and mortality in Japan in 2015 are attributable to excess bodyweight and physical inactivity.

Population attributable fraction (PAF) offers a means to quantify cancer burden that is attributable to a specific etiological factor. To better characterize the current cancer burden due to infection in the Japanese population, we estimated the PAF for cancer incidence and mortality in 2015 that could be attributable to infectious agents, including Helicobacter pylori (H. pylori), Hepatitis B and C (HBV/HCV), Human papillomavirus virus (HPV), Epstein-Barr virus, and human T-lymphotropic virus type 1. We estimated the PAFs for each infectious agent on the basis of representative data on prevalence and risk-outcome associations assuming a latency period of 10 years. Overall, 16.6% of cancer cases in 2015 in Japan were attributable to the infectious agents included in this analysis. The estimated PAF was slightly higher in men (18.1%) than in women (14.7%). The highest proportion of cancer deaths attributable to infectious agents was observed for H. pylori infection, followed by HBV/HCV, and HPV infection. Our findings corroborated with previous estimates that H. pylori and HBV/HCV infections were the two most important infectious agents in the Japanese population. Strategies focusing on eradication of infectious agents among infected individuals or primary prevention through vaccination could decrease the burden of infection-related cancers.

Consumption of vegetables, fruit and dietary fiber is closely associated with cancer incidence and mortality in the population, especially under conditions of insufficient consumption. We estimated the fraction of cancer incidence and mortality in 2015 attributable to insufficient consumption of vegetables, fruit and dietary fiber in the Japanese population. Consumption of vegetables, fruit and dietary fiber in grams per day, by sex and age group, is available for 2005 from the Japanese National Health and Nutrition Survey. Optimal consumption of vegetables and fruits for this study was assumed to be over 350g and 100g/day, respectively. Optimal consumption of dietary fiber was defined by age group according to the Dietary Reference consumption for Japanese. Population attributable fractions (PAFs) were estimated for each sex and age group according to a standard formula, and aggregated to obtain the PAF among total cancer incidence and mortality. Insufficient consumption of vegetables, fruit, and dietary fiber contributed 0.2%, 0.1% and 1.0% of all cancer incidence, and 0.2%, 0.1% and 0.9% of cancer mortality, respectively. The results of this study may provide useful evidence in reducing the cancer burden attributable to insufficient consumption of vegetables, fruit and dietary fiber in Japan.

PM_2.5 is a major environmental health problem and a risk factor for lung cancer. Exposure to PM_2.5 has attracted growing public concern nationwide. Here, we aimed to estimate the cancer in 2015 attributable to PM_2.5 in Japan. Ambient air pollution level due to excess concentration of PM_2.5 was estimated using geophysically based satellite-derived PM_2.5 concentrations in 2005, with a spatial resolution of 0.5° × 0.5° longitude-latitude, and population data presented in a 1 km by 1 km grid. We used the WHO guideline value for PM_2.5 exposure (≤ 10 μg/m³) as the optimal level of PM_2.5 exposure. By using relative risk from a large-scale cohort study in Japan, we estimated the population attributable fraction (PAF) for lung cancer, which is positively associated with PM_2.5, and aggregated the results to obtain the PAF among total cancer incidence and mortality. Population-weighted mean PM_2.5 level in 2005 was 14.9 μg/m³. Approximately 95.7% of the population was exposed to levels above the WHO guideline value. Lung cancer attributable to PM_2.5 exposure corresponded to 11,922 cases and 7,264 deaths, which accounted for 9.7% and 9.8% of total lung cancer incidence and mortality, respectively, and 1.2% and 2.0% of total cancer incidence and mortality, respectively. Substantial geographic variation in PM_2.5-attributable incidence and mortality fractions was found, with cities in western Japan and metropolitan areas having a higher PAF than other municipalities. This study provides useful information to aid policy-makers and public health agencies in the efficient establishment of environmental cancer prevention policies.

Salt consumption is high in most parts of the world, particularly among populations in Asia-Pacific region, including Japan. The recent portion of global deaths attributable to excess salt was largest among dietary exposures. We estimated the cancer in 2015 attributable to highly salted food in the Japanese population. Consumption of highly salted food in grams per day was available by sex and age group for 2005 from the Japanese National Health and Nutrition Survey. The optimal consumption of highly salted food for this study was assumed to be 0 g/day. Population attributable fractions (PAFs) for stomach cancer, which is positively associated with highly salted food intake in Japan, were estimated for respective sex and age groups according to a standard formula, and aggregated to obtain the PAF among total cancer incidence and mortality. In both sexes, 2.4% of cancer incidence and 2.2% of cancer mortality in 2015 were due to intake of highly salted food. Annually at least 22,000 total cancer cases in Japan could have been prevented by avoiding highly salted food.

The International Agency for Research on Cancer has evaluated red meat as probably carcinogenic and processed meat as carcinogenic to humans. The World Cancer Research Fund and American Institute for Cancer Research concluded there is convincing evidence that consumption of processed meat increases the risk of colorectal cancer. We estimated the number and fraction of cancer incidence and mortality in 2015 that could be attributed to excess red and processed meat consumption in 2005 among the Japanese population. Data on the consumption of red and ptocessed meat, in g/day, by sex and age group, is available for 2005 from the Japanese National Health and Nutrition Survey. For the present study, the optimal consumption of red meat in Japan was considered as less than 500 g/week, or 71.4 g/day, and 0 g/day for processed meat. Population attributable fractions (PAFs) were calculated for each sex and age group according to a standard formula, and aggregated to obtain the PAF among total cancer incidence and mortality. We found that 0.01% and 0.4% of cancer incidence was attributable to red and processed meat consumption, respectively, while 0.0002% and 0.3% of cancer mortality was attributable to red meat and to processed meat consumption. Based on the current evidence, monitoring red and processed meat consumption may not contribute to reducing cancer incidence and mortality in Japan.

Exogenous female hormone use has not been as popular in Japan as in western populations. Here, we estimated the population-attributable fraction (PAF) of cancers in Japan in 2015 attributed to exogenous female hormone use. We used the most recent prevalence data for oral contraceptives (OC) and hormone replacement therapy (HRT), available from a large-scale population-based cohort study started in 2011-2016. For the purpose of this study, optimal usage of exogenous hormones was considered to be none. PAF was calculated for each age group using a standard formula. Overall, a negligible fraction, 0.4% of cancer incidence and 0.2% of cancer mortality in Japanese women was attributable to exogenous hormone use (OC use and HRT), and 0.2% of cancer incidence and 0.1% of cancer mortality overall when both sexes combined. The relatively low prevalence of exogenous hormone use in Japan compared to Western countries may explain the low fraction of cancer attributable to exogenous hormones among Japanese women.

We estimated the population attributable fraction (PAF) of cancers in Japan attributed to never breastfeeding in 2015. The data on breastfeeding in Japan were derived from two sources. Data on women aged younger than 40 were obtained from the Longitudinal Survey of Babies in the 21^st Century (LSB21); those for women aged 40 to 69 was derived from the Japan Public Health Center-based Prospective Study for the Next Generation (JPHC-NEXT). For the present study, the optimal frequency of breastfeeding was a history of ever breastfeeding. The PAF was calculated for each age group using a standard formula. Overall, 0.3% of total cancer incidence and 0.1% of total cancer mortality in Japanese women were attributable to never breastfeeding. The high prevalence of women who breastfed children may explain the lower fraction of cancer attributable among Japanese women compared to studies from other parts of the world.