Although vitamin deficiency is primarily considered to be overcome in Japan, vitamin insufficiency, milder than deficiency, still increases the risk of various diseases. Biomarkers play an important role in the nutritional assessment of vitamins and must be understood based on their roles: status and function. Two reference values must be discriminated: the reference range and cut-off value. This review addresses the basic issues, underlying pathophysiology, associated disease risk, and recent evidences. However, clinical and epidemiological studies are limited in Japan and are therefore urgently required.

 Attention must be given to the difference between evidence-based nutrition (EBN) and evidence-based medicine (EBM). In addition, the discrepancy in results between observational and intervention studies is of great importance. Unlike drugs, vitamins are present in the body prior to intervention. Therefore, the intervention effects are significant in deficient subjects, but small in sufficient subjects, and most subjects in the large-scale intervention studies are those with vitamin sufficiency. Overall, more significant intervention effects and higher disease incidence are associated with fewer individuals required.

 Nutrient interventions, including vitamins, have a smaller effect than drug treatments. Although nutritional therapy is suitable for primary prevention in patients with low-to-moderate disease risk, the disease incidence is low in such populations, and numerous individuals are required for significant intervention effects. These issues have not been discussed in Japan, and issues such as the evaluation of EBN and observational studies should be addressed.

Objective: Estrogen and progesterone may affect taste sensitivity, which is associated with food intake and appetite. However, the relationship between these factors remains unclear. This study aimed to investigate whether the menstrual cycle induces changes in sweet taste sensitivity and evaluate its impact on appetite, food preference, food intake, and body weight.

Methods: Seventeen young women with regular menstrual cycles were studied for a total of 3 days over the menstrual, ovulatory, and luteal phases. Body weight and body fat percentage were measured, and body mass index (BMI) was calculated using self-reported height. Taste sensitivity was measured using the whole-mouth tasting method, and chocolate preference was evaluated. The participants also completed questionnaires on appetite and menstrual symptoms. The diet was assessed photographically during the days of the experiment and for 2 days thereafter.

Results: The sweet taste recognition threshold was significantly lower during the luteal phase than during the ovulatory phase. However, no differences in appetite, chocolate preference, energy intake, energy-producing nutrient intake, body weight, or body fat percentage were observed among the three menstrual cycle phases. The sweet taste recognition threshold positively correlated with BMI, regardless of the menstrual cycle phase, whereas it positively correlated with body weight and body fat percentage, and negatively correlated with appetite during the luteal phase.

Conclusions: Our results suggest that sensitivity to sweet taste is relatively higher during the luteal phase. Furthermore, increased sweet taste sensitivity in the luteal phase was associated with lower body weight, BMI, body fat percentage, and higher appetite.

Objective: This study examined the association between the frequency of energy drink intake and insomnia tendencies among Japanese high school students.

Methods: We recruited 826 students from a high school in Hokkaido, Japan, and conducted a survey from September to October 2020. The frequency of energy drink consumption was categorized into three groups: "no intake," "less than one bottle per week," and "one or more bottles per week." Insomnia was assessed using the Japanese version of the Athens Insomnia Scale (AIS-J); a score of ≥6 indicated the presence or suspicion of insomnia. The prevalence of insomnia tendencies based on the frequency of energy drink consumption was analyzed using a multiple logistic regression analysis. A total of 730 participants (401 males and 329 females) were included in the analysis.

Results: The percentages of suspected insomnia by frequency of energy drink intake were 38.2% for "no intake," 37.8% for "less than one bottle per week," and 53.2% for "one or more bottles per week." After adjusting for potential confounders, an association between the group drinking at least one bottle per week and the suspicion of insomnia was found; the adjusted odds ratio (95% confidence interval, p-value) was 2.15 (1.22~3.96, p = 0.033).

Conclusions: The study findings suggest that high school students who consume one energy drink per week are at a higher risk of insomnia. Further studies require a longitudinal design to examine causal relationships.

Objective: This study investigated the weights of vegetables, the most frequently appearing vegetables and their cooking methods in commercial boxed lunches.

Methods: We investigated 94 boxed lunches sold by food-related businesses in Yokohama (general boxed lunches) and 94 boxed lunches sold as "Smart Meal" products certified under the "Healthy Meal and Food Environment" certification system. The weights of vegetables included in the general boxed lunches were divided into four groups based on the quartiles of vegetable weights. Prices and nutrient weights were compared between the four groups using the Kruskal-Wallis test. Descriptive statistics were compiled for the types of vegetables and cooking methods used for both types of boxed lunches.

Results: The median weight of vegetables in general boxed lunches was 29 g/serving, and no boxed lunches contained the standard amount of vegetables for Smart Meal products. Prices were higher in the group with the highest vegetable weight (p < 0.001). Root vegetables were the most frequently used vegetables in both types of boxed lunches. In terms of cooking methods, pickling was used most frequently for vegetables in the general boxed lunches.

Conclusions: None of the general boxed lunches contained the standard amount of vegetables for Smart Meal products, and boxed lunches with higher vegetable weights were priced higher. In boxed lunches, root vegetables were used most frequently, and pickling was the most frequently used cooking method.