Usual Nutrient Intake Distribution and Prevalence of Nutrient Intake Inadequacy among Japanese Children and Adults: A Nationwide Study Based on 8-Day Dietary Records

This cross-sectional study used data from the MINNADE (MINistry of Health, Labour and Welfare-sponsored NAtionwide study on Dietary intake Evaluation) survey. Details of the survey are available elsewhere [31]. Briefly, the survey consisted of three rounds of one-year data collection (first round: November 2016 to September 2017; second round: October 2017 to September 2018; third round: November 2019 to August 2020). The study included healthy Japanese individuals aged 1–79 years residing in the community. First, we selected 32 geographically diverse prefectures (out of 47) that accounted for more than 85% of Japan’s total population, taking into consideration the feasibility of the survey and the proportion of the population in each region [31,32]. The research dietitians at each prefecture (N = 453) were responsible for recruitment and data collection. For the first round of data collection, we included 256 individuals (128 males and 128 females) from each of the nine age bands (1–6, 7–13, 14–19, 20–29, 30–39, 40–49, 50–59, 60–69 and 70–79 years). This totalled 2304 participants. After accounting for the dropout rate from the first round, we recruited 110–119 participants for each sex-age category for the second round, totalling 2051 participants. In the third round, data were further collected from 438 children aged 1–6 years.

The primary inclusion criterion was free-living individuals who could conduct a DR independently or with the help of a guardian for children. The exclusion criteria comprised individuals who were dietitians themselves or lived with dietitians, individuals working with a research dietitian, individuals who had received dietary counselling from a doctor or dietitian, those undergoing insulin or dialysis treatment, pregnant or lactating women, and infants who exclusively consumed human milk. The survey participants were not randomly selected, and only one individual per household was eligible to participate in the survey.

Excluding dropouts, 4736 individuals participated in the MINNADE survey (first round: N = 2263; second round: N = 2036; third round: N = 437). All participants were asked to complete two non-consecutive days of the DR during each of the four seasons (8 days in total). Figure 1 illustrates the flowchart of the selection process for participants. We excluded 11 participants aged <1 year or >79 years, 136 who conducted the DR for less than 8 days, 102 with consecutive DR data, 20 who did not complete the DR during the appropriate months (i.e., October, November, and December for fall; January, February, and March for winter; April, May, and June for spring; and July, August, and September for summer), and five who were found living in a different geographic area than the one where they were initially recruited from (identified after data collection). Consequently, the current analysis involved 4450 participants, aged 1’79 years.

Dietary intake information was collected using the DR for two non-consecutive days in each of the four seasons, totalling 8 days. The details of the DR are provided elsewhere [31]. Briefly, each set of two recording days in each season comprised two weekdays (Monday to Friday) for half of the participants and one weekday and one weekend day (Saturday, Sunday, or national holidays) for the other half. This approach was taken to obtain approximate overall dietary data, with a 3:1 ratio (actually 5:2) of weekdays to weekends, while ensuring the feasibility and simplicity of the survey. The research dietitians provided participants with both verbal and written instructions on how to maintain the DR. The participants were requested to weigh and record all foods and beverages they consumed using a digital scale provided. The scale can measure up to 2 kg in 1 g increments (KS-812WT, Tanita, Tokyo, Japan).

The main items recorded were as follows: (i) Dish names, (ii) food names (including ingredients in mixed dishes), and (iii) measured weights or approximate amounts of foods and beverages. The research dietitians collected recording sheets within a few days after each recording day, usually the following day. They then checked the completeness of the DR, adding information if necessary. Each food item was assigned a food code from the Standard Tables of Food Composition in Japan (STFCJ) [33] in a consistent manner. For packaged foods and home-prepared meals, the dietitians estimated the weight of each ingredient as accurately as possible using information on approximate portion sizes, restaurant and manufacturer websites, ingredient labels, nutritional information on food packages, and cookbooks. Other research dietitians later reconfirmed all food codes and weights at the central office of the study. Finally, the STFCJ [33] was used to calculate daily energy and nutrient intakes from foods and beverages, excluding dietary supplements, for each participant.

At the beginning of each survey round, participants were measured barefoot and in light indoor clothing by family or research dietitians using standardised procedures to obtain body height (to the nearest 0.1 cm) and weight (to the nearest 0.1 kg). For participants who could not be measured for weight or height (N = 92), self-reported information was used. BMI was calculated as body weight (kg) divided by the square of height (m²). A questionnaire was used to gather information about the basic characteristics of the participants. Age (years) at the beginning of the study was calculated from the date of birth. Residential area was grouped into 1 of 6 regions (Hokkaido and Tohoku, Kanto, Hokuriku and Tokai, Kinki and Chugoku, or Kyushu and Okinawa). Annual household income was classified into three categories based on distribution: <5, ≥5 to <8, and ≥8 million Japanese yen. Educational attainment was assessed among adults and classified as follows: Junior high or high school, junior college or technical school, university or higher, or other. The employment status of adult participants was categorised into four categories: Student, unemployed, part-time, or full-time. The smoking habits of adults were categorised into three types: current smoker, past smoker, or non-smoker.

Misreporting of energy intake (EI) was evaluated based on the ratio of EI to estimated energy requirement (EER) [34]. EER was calculated using equations published in the DRIs of the US/Canada, based on sex, age, body height and weight, and physical activity [35]. Owing to the absence of an empirical measure of physical activity, we adopted ‘low-active’ for physical activity level [35]. Under-reporters, plausible reporters, and over-reporters were identified based on the cut-off values of the EI:EER calculated from the number of recording days (8 days), within-subject variation in EI at 23%, day-to-day variation in total energy expenditure at 8.2%, and the coefficient of variation in intakes and other components of energy balance (i.e., error in the EER equations at 2.97–14.8% according to sex and age) [34,36]. However, misreporters were not excluded from the analysis, as exclusion would have introduced bias [37,38].

The usual intake distribution of energy and nutrients was estimated using the MSM [39]. Briefly, the MSM estimates the consumption probability of a nutrient using logistic regression and then applies linear regression to compute the usual consumption-day amount for each individual. Finally, the usual intake on all days is computed by multiplying consumption probability and consumption-day amount [39]. We entered 8-day measurements of energy and nutrient intakes for each participant, including the percentages of energy from protein, total fat, saturated fats, and carbohydrates into the MSM online interface (https://msm.dife.de/↗, accessed on 23 October 2023). In this study, the consumption probability was set to one, assuming that all participants were habitual consumers of all nutrients evaluated. Covariates in the usual intake models included age (years), sex (male or female), and day of the week (weekday or weekend day) [8]. We also estimated the usual intake without covariates; however, this did not affect the subsequent assessment of nutrient inadequacy.

From the results of the MSM program, we obtained the usual intake of energy and each nutrient for each participant. Additionally, we obtained the usual intake distribution at the group level by sex, including the mean, standard deviation (SD), minimum and maximum values, and percentile distribution, for each of the 12 age groups adopted in the Japanese DRIs (i.e., 1–2 years, 3–5 years, 6–7 years, 8–9 years, 10–11 years, 12–14 years, 15–17 years, 18–29 years, 30–49 years, 50–64 years, 65–74 years, and ≥75 years) [30].

The adequacy of nutrient intake was assessed by comparing usual nutrient intakes with age- and sex-specific reference intakes in the Japanese DRIs [30]. The Japanese DRIs consist of several nutrient indicators with different objectives. The Estimated Average Requirement (EAR) is “the amount that would meet the nutrient requirements of 50% of the population” [30]. The Adequate Intake (AI), defined as “the amount that is adequate to maintain a certain nutritional status”, is used when the EAR cannot be determined in order to evaluate the median intake of a group [30]. The dietary intake of no less than the AI minimises the risk of inadequacy [30]. The Tolerable Upper Intake Level (UL) is “the maximum amount that avoids adverse health effects due to excessive intake”. The tentative dietary goal for preventing lifestyle-related diseases (DG) is the amount of nutrients necessary to prevent lifestyle-related diseases. It specifies the recommended intake ranges for macronutrient balance (the percentages of energy from protein, total fat, saturated fats, and carbohydrates), dietary fibre, sodium, and potassium. These indicators for nutrients were determined assuming physical activity level II (normal).

Of the 33 nutrients presented in the Japanese DRI, we have excluded five nutrients (i.e., biotin, iodine, selenium, chromium, and molybdenum) from the present analysis as the data for these nutrients in the STFCJ were insufficient [33]. For the remaining 28 nutrients, the proportion of inadequate intake was assessed based on the percentage of participants who did not meet the DRIs using the cut-point method (except for iron, as described later) [40]. The reference values for energy and nutrients are shown in Supplementary Tables S1–S4. For the EAR, an intake level below the EAR was considered inadequate for the following nutrients: Protein, vitamin A (retinol equivalents), thiamine, riboflavin, niacin (niacin equivalent), vitamin B-6, vitamin B-12, folate, vitamin C, sodium, calcium, magnesium, zinc, and copper [30,41]. For iron, the cut-point method is not suitable for children and menstruating females because their iron requirements are not normally distributed [40,42]. Therefore, the iron intake deficiency of these populations was assessed using the full probability method based on the values published by the World Health Organization (WHO) [42]. First, assuming the bioavailability of iron from the diet is 15% [30], the amount of iron that would result in a 50% chance of iron deficiency was determined (i.e., less than 3.6, 4.9, and 9.3 mg/day for children aged 1–2 years, children aged 3–9 years, and females aged 12–64 years, respectively) [42]. Thus, inadequate iron intake was identified when the individual’s iron intake was below these levels.

For nutrients with the DG (percentage of energy from protein, total fat, saturated fat, carbohydrates, dietary fibre, sodium, and potassium), we calculated the percentage of participants consuming nutrient intake outside (below or above) the range of the DG [30]. We also computed the percentage of participants whose intake was above the UL for 11 nutrients (i.e., vitamins A, D, E, and B-6, niacin, calcium, phosphorus, iron, zinc, copper, and manganese). The UL for niacin is presented as the amount of nicotinamide or nicotinic acid in the DRIs. Therefore, the adequacy of niacin intake was assessed by comparing the usual niacin intake with the sum of nicotinamide and nicotinic acid. The AI is set for nine nutrients in the DRIs (n-6 and n-3 polyunsaturated fatty acids, vitamins D, E, and K, pantothenic acid, potassium, phosphorus, and manganese). Although a person’s usual intake could be below the AI, it cannot be concluded that the intake is inadequate since the person’s actual requirement could be considerably lower than the AI values [43]. Nevertheless, if a group mean or median intake is below the AI, it may be desirable for intakes to increase [40,44]. Accordingly, we identified if the group’s median intake was below AI or not for the nine nutrients [30]. Analyses were conducted using the statistical software package SAS version 9.4 (SAS Institute Inc., Cary, NC, USA).

This analysis included 1648 children and adolescents aged 1–17 years and 2802 adults aged 18–79 years (Table 1). The mean BMI was 17.2 kg/m² for children and adolescents and 23.0 kg/m² for adults. The 8-day mean EI was 1766 kcal/day (SD: 635) for children and adolescents and 2003 kcal/day (SD: 461) for adults. The mean EI:EER was close to the expected ratio of 1.00 in both children and adults, ranging from 0.90 to 1.14. Of the participants, 14% were under-reporters, 78% were plausible reporters, and 9% were over-reporters. Among the under-reporters, 53% were children aged 1–5 years, while among the over-reporters, 78% were adults aged 18–49 years.

Table 2 and Table 3 present the mean usual intakes and the proportion of children and adolescents who did not meet the DRIs for energy and nutrients in males and females, respectively. In both sexes, almost all children and adolescents had intakes above the EAR for protein, niacin, vitamin B-12, and copper. However, a high percentage of children and adolescents had intakes below the EAR for other nutrients. For example, the estimated prevalence of inadequacy was high for vitamin A (3–57%), thiamine (7–52%), riboflavin (3–62%), vitamin C (5–53%), and calcium (29–83%). In addition, more than 91% of females aged 12–17 years had an insufficient iron intake, as assessed by the probability method. The intake of vitamin B-6, folate, magnesium, and zinc was generally adequate for children under 12 years, but mostly inadequate for those aged 12–17 years.

The DG was not in many nutrients. For instance, a high proportion of children and adolescents had intakes below the lower limit of the DG for the percentages of energy from protein and carbohydrates, dietary fibre, and potassium. Moreover, more than 20% of children and adolescents in each sex and age category had intakes exceeding the upper limit of the DG for the percentages of energy from total and saturated fats. Furthermore, almost all children (≥95%) exceeded the upper limit of the DG for sodium.

The AI was met in all sex and age groups for n-6 polyunsaturated fatty acids, vitamins E and K, and potassium (i.e., the group median usual intake was equal to or above the AI). However, the median usual intake of vitamin D and manganese was below the AI for both sexes in the 10–17 age group. None of the participants exceeded the UL for all nutrients, except for vitamin A. The percentage of participants exceeding the UL for vitamin A ranged from 0.5% to 4.9% for children aged 1–5 years. The distributions, including the 5th to 95th percentiles of energy and nutrient intakes among children and adolescents, are shown in Supplementary Tables S5–S11.

Table 4 and Table 5 show the nutrient intakes of male and female adults, respectively. In both sexes, the proportion of adults with intakes below the EAR was zero or very low for protein, niacin, vitamin B-12, sodium, and copper. However, a high percentage of adults had intakes below the EAR for other nutrients. In particular, more than 5% of male and female adults of all age groups did not meet the EAR for vitamins A, B-6, and C, thiamine, riboflavin, calcium, magnesium, and zinc. Additionally, over 78% of females aged 18–64 years had inadequate iron intake. Inadequate nutrient intakes were more prominent in younger age groups than in older age groups.

Similar to the results for children and adolescents, the DG was not in many nutrients. For instance, a high proportion of adults had intakes below the lower limit of the DG for the percentages of energy from protein and carbohydrates, dietary fibre, and potassium. Moreover, the highest proportion of inadequate protein intake was observed in the 75–79 years age group for both sexes. In addition, over 20% of adults had intakes above the upper limit of the DG for total and saturated fats, and over 88% of adults had sodium intakes above the upper limit of the DG.

The median usual intake was equal to or above the AI for n-6 polyunsaturated fatty acids, vitamins E and K, and phosphorus in all sex and age groups. However, the median usual intake of n-3 polyunsaturated fatty acids, vitamin D, potassium, and manganese was below the AI for people aged 18–29 years, regardless of sex. Equally, both males and females aged 30–49 had a median usual intake below the AI for vitamin D and manganese, while those aged 50–64 had a median vitamin D intake below the AI. None of the participants exceeded the UL for all nutrients, except for manganese. The percentage of the participants exceeding the UL for manganese ranged from 0.2% to 1.0% for males aged 18–49 and 65–79 years and from 0.2% to 0.8% for females aged 18–64 years. The usual intake distributions of energy and nutrients among adults are shown in Supplementary Tables S12–S16.

To our knowledge, this is the first study to estimate usual nutrient intakes in a large sample of the Japanese population and evaluate the adequacy of these nutrient intakes. Our results showed that the estimated usual intakes in this population were inadequate for most nutrients. For instance, all sex and age groups had a high percentage of inadequate intakes for macronutrients (including dietary fibre, the percentages of energy from protein, carbohydrates, and total and saturated fats) and micronutrients (including vitamins A and C, thiamine, riboflavin, calcium, iron, sodium, and potassium). Of particular concern, 29–88% of the participants had an inadequate calcium intake, and over 88% had an excessive sodium intake. Moreover, more than 20% of the participants had intakes above the recommended upper levels for the percentages of energy from total and saturated fats. Inadequate nutrient intakes were particularly pronounced in adolescents and young adults. The AI and UL were met for most age groups in both sexes with a few exceptions, such as excessive vitamin A intake for children aged 1–5 years. The present findings should serve as a reference for conducting future research and shaping nutrition policy related to nutrient intake and adequacy in Japanese children and adults.

Macronutrient inadequacy has been documented in Japan [26,27,28] and in many other countries [7,15,18,19,21,24]. Our results similarly indicated that the percentage of energy intake from energy-providing nutrients (i.e., protein, carbohydrates, and total and saturated fats) was inadequate for most age groups in both sexes. In comparison to the Japanese DRI [30], the percentage of energy was generally higher for total and saturated fats and lower for protein and carbohydrates in this study. However, the DG of saturated fats in the Japanese DRI was established in accordance with the median intake of the Japanese population [30], and its recommended intakes for children aged 15–17 years and adults (≤8% and ≤7% of energy, respectively) are more stringent than those of the WHO guideline (i.e., ≤10% of energy intake) [45]. In this study population, the median values for the percentage of energy from saturated fats were not extremely high, ranging from 7% to 10% across sex and age categories. Considering that the effects of saturated fat on health are still inconclusive [46,47], it is debatable whether stricter limits on saturated fat intake should be recommended for the Japanese. By contrast, inadequate protein intake (as a percentage of energy) was observed in males and females of all age groups but was more pronounced in older adults aged 75–79 years. This is a matter of great concern, as insufficient protein intake is a major contributor to age-related muscle loss [48]. Thus, increasing energy intake from protein would be beneficial for the Japanese population, especially older adults.

Insufficient dietary fibre intake has been reported worldwide [1,12,15,19,26,27,49]. Our investigation found that adolescents and adults did not consume enough dietary fibre. Nevertheless, this study saw a lower proportion of inadequacy compared with previous studies in Japan [26,27,28]. For instance, in 2014, the proportion of children aged 8–14 years with dietary fibre intake below the DG was 47% for boys and 43% for girls [28], whereas in this study it was 0% for boys and 2% for girls. This could be ascribed to the revision of the STFCJ rather than an actual increase in dietary fibre intake. The previous studies used the earlier editions of the STFCJ [50,51], which estimated the dietary fibre content of foods using the modified Prosky method. In contrast, this study used the latest edition [33], which uses both the modified Prosky method and the Association of Official Analytical Chemists (AOAC) 2011.25 method. A previous study has suggested that using the latest STFCJ edition would increase total dietary fibre intake, predominantly due to the contribution of rice [52]. Therefore, future dietary surveys should carefully monitor the dietary fibre intake of the Japanese population.

We observed that a considerable proportion of all sexes and ages had inadequate usual intakes of micronutrients (i.e., vitamins A and C, thiamine, riboflavin, calcium, iron, sodium, and potassium). Inadequate intakes of several vitamins and minerals have also been reported for children and adults in many countries [6,7,10,11,13,14,15,17,18,20,23,24,26,27,28]. For example, calcium intake is far below the optimal levels worldwide [1], including in Japan [26,27,28], China [6,23], the US [10,11], Canada [14], the Netherlands [17], Greece [20], the Philippines [24], and South Korea [7]. Results from this study indicated that 29–88% of the participants, irrespective of their sex or age, had insufficient calcium intake. This may be due to the low consumption of calcium-rich dairy products, such as milk, among the Japanese [1]. Milk is the top contributor to calcium intake in both the US [53] and Japan [5], whereas the average milk consumption of Japanese adults [5] is less than half that of US adults [54]. Moreover, we also found that over 79% of females aged 12–64 years had inadequate iron intake, which was much higher than the rest of the population. Correspondingly, a previous study revealed that 60% of Japanese females aged 13–14 years had inadequate iron intake [28]. The inadequate iron intake may be due to a higher iron requirement in this population. In addition, although fortified cereal foods largely contribute to iron intake in other developed countries [55], it is less common in Japan. Iron deficiency among females of childbearing age is also a serious concern in other countries, including China [6] and the Philippines [24]. Addressing iron deficiency in females of reproductive age is imperative, as iron deficiency anaemia at this stage can have serious maternal and foetal consequences [56].

Another problem is the excessive intake of sodium in both sexes. In this study, 89–100% of participants in each age group had a usual intake above the DG for sodium (as salt equivalent). The DG for sodium was determined as a midpoint between the WHO recommendation (5 g/day) [57] and the median sodium intake of the Japanese population [30]. The high proportion of the excessive sodium intake is, therefore, an expected consequence and indicates that the sodium intake of the Japanese population is much higher than the target level. In fact, our results showed that the mean salt intake among adults ranged from 10.5 g/day to 11.8 g/day for males and from 8.5 g/day to 10.5 g/day for females, almost double the WHO recommendation [57]. A previous study has shown that seasonings, such as salt or soya sauce, and fish and shellfish were the main contributors to sodium intake among Japanese adults [58]. Excessive sodium (salt) intake is a major nutrient problem not only in Japan [26,27,28], but also in China [6], South Korea [7], Finland [18], Greece [20], and the US [12]. Furthermore, our results showed that a high percentage (7–88%) of males and females in all age groups aged 3 years or older had potassium intake below the lower limit of the DG. Given that high sodium intake is the leading dietary risk for death and disability-adjusted life years in Japan [1] and that a high sodium-potassium intake ratio is a risk factor for stroke [59] and all-cause mortality [60], urgent action is needed to reduce sodium intake and the sodium-potassium intake ratio in the Japanese population.

Consistent with previous studies [7,26], the UL was met in most age groups. However, a small percentage (<5%) of participants in some subgroups exceeded the UL for vitamin A in children and manganese in adults. The prevalence of excessive intake of vitamin A by infants and toddlers from food and beverages in this study was comparable to that in the Netherlands (<5%) [17], but lower than that in the US (≥16%) [12]. In Japan, the main dietary sources of retinol are fish and eggs, β-carotene is obtained from carrots and green leaves [61], and manganese is sourced from white rice and Japanese tea [62]. Acute and chronic excessive vitamin A intake leads to liver damage and fibrosis [63]. In addition, the accumulation of manganese in the brain may lead to neurotoxicity and subsequent neurodegenerative diseases [64]. Since dietary supplements were not included in this study, the actual proportion of excess intake may be higher. Therefore, excessive intake of these nutrients from the total diet, including supplements, should be carefully monitored.

Previous studies have shown that nutrient adequacy may be associated with participant characteristics [17,24]. For instance, in the Netherlands, adolescents were more likely to have intakes below the EAR, and older adults were more likely to have adequate intakes [17]. Conversely, older adults in the Philippines and South Korea faced a greater prevalence of inadequacy than younger adults [7,24]. In this study, as the purpose of this study was to provide descriptive information on usual nutrient distribution and nutrient adequacy, no statistical comparisons were made between subgroups, such as by age, sex, and income. However, the intakes of vitamin B-6, folate, magnesium, and zinc were mostly inadequate for boys and girls aged 12–17 years. Moreover, among adults, the proportion of inadequate intakes seemed to be relatively higher in younger age groups than in older age groups. Thus, nutrient inadequacy may be particularly prevalent among adolescents and young adults. Socioeconomic and behavioural correlates of nutrient inadequacy should be explored in future studies.

This study highlighted the low adherence to nutrient intake goals among Japanese individuals. Given the serious health implications of inadequate nutrient intake, such as chronic disease mortality and morbidity [1], there is an urgent need for nutritional strategies to assist the Japanese in meeting nutrient recommendations. For instance, future strategies may include education on healthy food choices, restrictions on food marketing, food supply improvement through reformulation and fortification (e.g., reducing fat and salt and increasing dietary fibre), and dietary supplementation of nutrients that are unlikely to be provided by food intake alone [1,15,22]. However, implementing these strategies requires cross-sectoral policies and interactions between public health organisations [15]. In addition, continuous monitoring of nutrient intakes and health-related indicators is needed to ensure the effectiveness of the strategies.

Nevertheless, given that many values in the Japanese DRIs were derived from dietary guidelines and studies conducted in Western populations [30], these reference values may not be entirely suitable for the Japanese population. Consequently, the estimated proportion of inadequate nutrient intake in this study may differ from the actual percentage. Further studies involving Japanese populations are needed to determine more appropriate reference values.

The strength of this study lies in the detailed dietary data collected from 8-day DRs for each of the four seasons from a large sample of Japanese children and adults from geographically diverse regions throughout Japan. This survey design enabled us to represent dietary intake by accounting for day-to-day and seasonal variations [29]. To our knowledge, a detailed DR survey on this population size has never been conducted in Japan. Therefore, this study provides an invaluable resource for understanding the dietary intake of the Japanese. However, this study has several limitations. First, our participants were volunteers and not a representative sample of the general Japanese population. Therefore, they may be more health conscious and have healthier diets than the general population. In comparison with the nationally representative sample, the adults in this study had a slightly higher education level [31]. However, the distributions of household income, height, and weight were similar for both children [5,65] and adults [31]. Thus, there is no strong evidence to suggest that the participants in this study significantly differed from the general Japanese population. Second, self-reported dietary assessment methods are subject to both random and systematic measurement errors [37]. In particular, DRs are generally prone to measurement error due to incorrect recording and changes in dietary behaviour [37]. To minimise the possibility of systematic error, research dietitians checked the dietary information recorded by the participants’ caregivers. Our results showed that approximately 80% of the participants were plausible reporters, and the mean EI:EER ratio was close to the expected value, suggesting that dietary reporting bias was minimised. Third, due to the unavailability of composition databases in Japan, we could not account for nutrient intakes from dietary supplements or fortified foods. A recent study reported that 23% of Japanese adults were users of fortified foods or dietary supplements [66]. Subsequently, the proportions of participants with intakes below the recommended levels have likely been overestimated, while those with excessive nutrient intakes may have been underestimated [10,17]. Future studies should consider total nutrient intake, including dietary supplements and fortified foods. Fourth, since this study did not take into account the loss of nutrients during cooking [67], the true proportion of the participants with vitamin intakes below the EAR may be higher than our results. Fifth, the number of participants in each sex and age group ranged from 63 to 443 (mean: 185), with particularly low numbers in children, adolescents, and older adults. Therefore, caution is needed when interpreting the distribution of nutrient intakes in this population. Nevertheless, we analysed the data stratified by sex and age categories of the Japanese DRI [30] in order to provide basic information for its future development. Sixth, we did not include certain populations, such as infants under 1 year of age, individuals over 79 years of age, and pregnant or lactating women. Therefore, future research should include these groups to assess nutrient adequacy and establish nutritional policies. Finally, a general limitation in the assessment of nutrient intakes is that the food composition tables may not necessarily reflect the true nutrient composition of foods, as they may vary according to season and variety [29].

The datasets generated and analyzed during the present study are not publicly available due to restrictions imposed by the Ministry of Health, Labour and Welfare.