Influence of Prefecture-Level Yield of Not-for-Sale Vegetables on Vegetable Intake in Japan: A Natural Experiment

Increased vegetable intake contributes to better health for people. The distribution of not-for-sale vegetables is an important source of vegetable intake in Japan. This study examined the impact of prefecture-level yield of not-for-sale vegetables on vegetable intake in Japan. This study regarded the increase in yield of not-for-sale Chinese cabbage in Nagano Prefecture in 2012 as a natural experiment. The years 2012 and 2016 were the large-scale survey years of the Japanese National Health and Nutrition Survey. Therefore, the effect of the change in prefecture-level yield of not-for-sale vegetables on vegetable intake was evaluated by comparing the changes in Chinese cabbage intake in Nagano between 2012 and 2016 with those of other prefectures classified in the same regional block as Nagano. Statistical analysis was performed using general linear models to examine the interaction of year and prefecture with Chinese cabbage intake. Consequently, the regression coefficient for the interaction term was −3.38 (95% CI, −9.59–2.83), that of the model adjusted for basic characteristics and energy intake was −2.99 (95% CI, −9.22–3.24), and that of the model adding health-related variables was −5.03 (95% CI, −12.40–2.34). The prefecture-level yield of not-for-sale vegetables typically had a minor effect on vegetable intake.