The present cohort study examined how lifestyle, household environment, and caries activity test score of Japanese children at age 1.5 years affected their dental caries incidence at age 3. Inclusion criteria were 1.5-year-old children with no dental caries. Dental examinations were performed for 33,655 children who participated in routine dental examinations at 1.5 years of age, and the exam was repeated approximately 21 months later (at age 3) at the Kobe City Public Health Center in Japan. After excluding 622 children who had caries at age 1.5 and 1831 children with missing lifestyle and household environment data in the questionnaires, the final data analysis was performed on a total of 31,202 children (16,052 boys, 15,150 girls).The multivariate logistic regression analysis indicated a strong association of the consumption of sugar-sweetened beverages/snacks, less frequent tooth brushing by the parents, lack of fluoride varnish, family history of smoking, with the risk of developing dental caries. A child’s late bedtime is also one of the major risk factors for dental caries development. Further investigation is needed to examine whether the short duration or the irregularity of the sleep-wake cycle would affect early childhood oral health and whether there is a relationship between late bedtime and late night snack intake.

A few studies in Japan have demonstrated positive attitudes, self-efficacy, social support, and perceived barrier were associated with fruit and vegetable (F&V) intake in adults; however, limited evidence addresses the association of psychosocial factors with F&V intake in adolescents. A cross-sectional study through a questionnaire survey was conducted at junior and senior high schools, and 933 students completed the questionnaire. Data were analyzed by X² test and Student t-test. The findings demonstrated 2.7% of participants were aware of the current recommendations for vegetable and 2.0% for fruit. Only 4% and 8.1% of participants reported they consumed recommended amount of vegetables and fruits. In comparison with males, females showed higher scores of attitude (p < 0.01), responsibility (p < 0.01), and social support (p < 0.01). The barriers to vegetable intake were “I’m eating enough now”, “not always available when eating away from home”; the barriers to fruit intake were “don’t have a habit of having 100% juice or fruit in the morning”, and “cost too much”. The findings suggest the change of adolescents’ knowledge about what they should eat is needed in boosting F&V consumption. The development of an intervention program for adolescents needs to target socio-environmental factors such as family support, and nutritional education for early healthy habit formation.

There is limited evidence in Japan regarding the psychosocial determinants of fruit/vegetable intake. We performed a cross-sectional study of people aged 18 years or older in four regions of Japan; 2308 (men: 1012, women: 1296) individuals who completed the questionnaires were included. We found that 24.8% of people were aware of the current recommendations for vegetables and 13.2% for fruit and that “ability to design meals” and “availability when eating outside of the home” were the most important factors related to self-efficacy and barriers to fruit and vegetable intake, respectively. People with high self-efficacy (OR: 3.16; 95% CI: 2.17, 4.60 for fruit; OR: 4.52; 95% CI: 3.08, 6.64 for vegetables) were more likely to consume more fruit and vegetables. People with high scores on attitude (OR: 1.54; 95% CI: 1.06, 2.24) and social support (OR: 1.59; 95% CI: 1.11, 2.27) were more likely to consume more fruit. People with high perceived barriers (OR: 0.69; 95% CI: 0.48, 0.98) were less likely to consume fruit. This study suggests a need to increase the general population’s awareness of the fruit and vegetable intake recommendations; facilitating positive attitudes, self-efficacy, and social support for individuals and strengthening the ability of individuals to design meals with more vegetables and fruit might be useful intervention programs.

Some studies have shown that exposure to forests has positive effects on human health, although the mechanisms underlying the health benefits of a forest environment have not been elucidated yet. The current study was aimed at examining how the levels of urinary hydrogen peroxide (H₂O₂) and 8-hydroxy-2’deoxyguanosine (8-OHdG) change after a forest or urban walk in healthy subjects. Twenty-eight volunteers (19 men and 9 women) participated in the study. The forest walks were carried out in a forest in Okayama Prefecture, Japan, and the urban walks (15 men and 7 women) were carried out in the downtown area of Okayama city, each for two hours. Spot urine samples were collected before the walk, the next day and one week after the forest or urban walk. Compared with pre-forest walk levels, urinary H₂O₂ (p < 0.1) and 8-OHdG (p < 0.1) concentrations significantly decreased in the participants the day after the forest walk; furthermore, urinary 8-OHdG remained at a low level even at one week after the forest walk (p < 0.05). However, there were no significant changes in the concentrations of these oxidative biomarkers after the urban walk. These findings suggest the possibility that exposure to forests may alleviate oxidative stress in the body.

A few studies indicate exposure to forests may alleviate oxidative stress in the body. However, more evidence is needed to support this potentiality. The purpose of the current study aimed at examining whether there is any difference in urinary levels of oxidatively modified proteins or lipids—dityrosine (DT) and hexanoyl-lysine (HEL), respectively, after a forest or urban walk. The study was performed on 29 university students who took part in forest walks (Shinjo Village) in Okayama Prefecture of Japan and on 42 university students who took part in urban walks in the downtown area of Okayama City. Urine samples before and after the walks were analyzed for DT and HEL excretion. Air phytoncides during the walks were also measured. We found a decreased tendency in urinary DT and HEL (p < 0.05) in most participants after the forest walks, but not after the urban walks. We further found the total levels of air phytoncides in the forest field were 1.50 times higher compared with those in the urban field. This study suggests the possibility that regular immersion in a forest environment might contribute toward weakening of the oxidative modifications of proteins or lipids in the body.

Hexanoyl-lysine (HEL), 8-hydroxy-2′deoxyguanosine (8-OHdG), and dityrosine (DT) have served as potential biomarkers for detecting oxidative modified lipids, DNA, and proteins in biological samples, respectively. Whether regular higher levels of consumption of vegetables/fruit (V/F) would decrease oxidative modification of these biomolecules in the body remain unelucidated. To examine the association of regular V/F consumption with the generation of these reactive oxygen species-induced biomarkers, this study evaluated V/F consumption in a school-based sample of teenaged girls (mean age 15.6 ± 1.7 years, n = 103), and quantified the formation of oxidative stress biomarkers in their urine. Only 19.4% and 23.3% of participants reported that they consumed the recommended daily amount of vegetables and fruits, respectively. Individuals who consumed lower levels of fruit (<100g/day) or vegetables (<250g/day) had significantly higher HEL excretion in their urine than those who consumed higher levels of fruit (≥100g/day) (p < 0.05) or vegetables (≥250g/day) (p = 0.057). The results of a multiple regression analysis showed that vegetable consumption was an important inhibiting factor of early lipid peroxidation measured as HEL in urine, independent of various confounders (β = − 0.332, p < 0.05). The findings suggest that relatively higher consumption of vegetables would help in the prevention of early lipid peroxidation in adolescents.