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.

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.