Abstract
Objectives
Dietary supplement administration has steadily increased in Korea, but evidence on administration of dietary supplements to infants remains limited. This study investigated the longitudinal trends and determinants of supplement administration in infants from birth to 24 months of age.
Methods
A longitudinal birth cohort study enrolled 137 infants born at ≥28 weeks of gestation, and followed them at 2, 6, 12, and 24 months. Structured questionnaires assessed supplement administration, feeding methods, family history of allergic diseases, and demographics. Feeding was categorized as breastfeeding, formula feeding, or mixed feeding. Atopic dermatitis and food allergy were diagnosed using standardized criteria.
Results
Overall, 82% of infants were given supplements during the study period. Probiotics and vitamin D were the most frequently administered at all ages, while multivitamin administration increased markedly after 12–24 months (38.6%). Supplement administration differed by feeding method: breastfed (29.4%) and mixed-fed (5.0%) infants had a higher percentage of iron supplementation at 12 months compared with formula-fed (0%). Multivitamin administration was more common among infants without a family history of allergies (low-risk group: 32.6%) compared with those with a family history of allergies (high-risk group: 23.4%). Infants born via cesarean section were significantly more likely to be given dietary supplements at 2–6 months (OR = 8.09, 95% CI: 1.79–36.49), 6–12 months (OR = 14.88, 95% CI: 1.91–116.10), and 12–24 months (OR = 5.16, 95% CI: 1.09–24.35).
Conclusions
This study found a high percentage of supplement administration among Korean infants, with frequent administration of probiotics and vitamin D from early infancy. Over time, supplement types became more diverse, with usage trends varying by feeding method and allergy risk. Cesarean-born infants were more likely to be given supplements. These findings provide descriptive data on how supplements are administered to Korean infants and suggest a basis for exploring the implications of early-life supplement administration.
Keywords: birth cohort, cesarean section, dietary supplements, feeding methods, infants, longitudinal study
1. Introduction
The first 1,000 days, from conception to 24 months of age, are a critical period that significantly influences an infant's growth, development, and overall health. Nutritional intake during this period lays the foundation for lifelong health. Inadequate or excessive intake of nutrients during this period has been associated with developmental issues, such as impaired brain function, as well as increased risks of chronic diseases including obesity, type 2 diabetes, and hypertension (1–3).
Specifically, infants are particularly vulnerable to nutritional imbalances because their micronutrient requirements are remarkably high relative to their body weight due to rapid physical growth and neurodevelopment (4). While breast milk is the gold standard for infant nutrition and provides essential bioactive compounds, additional nutritional sources become important with growth and development. At the age of complementary feeding, nutrient requirements gradually begin to exceed the amounts provided by breast milk alone. In this context, dietary supplements may help address specific nutrient requirements that are difficult to meet through diet alone, even in the setting of a balanced diet (5). While dietary supplements are generally not considered essential for healthy children who consume a diverse and balanced diet (6), specific exceptions apply in infancy, when nutritional intake is primarily based on breast milk or formula and may not fully meet vitamin D requirements. Vitamin D is an essential nutrient for bone health and calcium metabolism during early infancy (7). Breast milk contains relatively low concentrations of vitamin D, which may be insufficient to maintain adequate vitamin D status without supplementation (7, 8). Sun exposure is also generally limited during early infancy, further supporting the importance of adequate vitamin D intake (7, 8). In accordance with international recommendations for rickets prevention, universal vitamin D supplementation (400 IU/day) is recommended for all infants beginning shortly after birth (9–11). There is no unified national guideline in Korea addressing routine nutritional supplementation in infants; instead, recommendations are distributed across dietary reference standards and consensus-based pediatric literature. The 2020 Dietary Reference Intakes for Koreans (KDRI), issued by the Ministry of Health and Welfare and the Korean Nutrition Society, recommend an adequate intake of 5 μg/day (approximately 200 IU) of vitamin D for infants, reflecting a population-based dietary standard rather than a clinical supplementation guideline (12). In contrast, pediatric subspecialty literature and society-endorsed reviews in Korea consistently support routine vitamin D supplementation of approximately 400 IU/day during infancy, largely based on international evidence and the high prevalence of vitamin D insufficiency reported in Korean children (7, 13).
Iron is a key micronutrient involved in physical growth, neurodevelopment, cellular function, and hormone synthesis (12, 14). Iron stores accumulated during gestation typically begin to deplete by 4 to 6 months of age, making breastfed infants susceptible to iron deficiency if complementary foods are inadequate (14). Based on recommendations from the American Academy of Pediatrics (AAP), iron supplementation (1 mg/kg/day of elemental iron) is recommended from approximately 4 months of age for exclusively breastfed infants (15). However, iron supplementation recommendations are not standardized at the national level in Korea. Current Korean pediatric practice follows a risk-based approach, recommending iron supplementation for exclusively breastfed infants and high-risk groups such as preterm or low-birth-weight infants, alongside the introduction of iron-rich complementary foods from 4 to 6 months of age (16). In this context, according to the KDRI, the recommended dietary allowance for iron is set at 6 mg/day for infants aged 6–11 months, reflecting increased physiological requirements during late infancy (12).
While vitamin D supplementation recommendations are relatively consistent across countries, iron supplementation guidelines vary considerably depending on regional and clinical contexts. In this regard, nutritional supplementation practices in Korea reflect a hybrid framework in which vitamin D supplementation is broadly recommended based on consensus-level evidence, whereas iron supplementation remains individualized in the absence of a standardized national policy.
Despite these clinical guidelines, data from the Korea National Health and Nutrition Examination Survey (KNHANES) indicate that among all children and adolescents in Korea, dietary supplement administration is most prevalent among toddlers aged 1–3 years (17). The types of supplements consumed have also shown changing trends that follow market trends. In a 2007–2009 survey, vitamin and mineral supplements were the most consumed type of supplement by children aged 2–6, followed by red ginseng, colostrum, and omega–3 fatty acids (18). Subsequently, in 2010–2012 and 2015–2017 surveys, probiotics emerged as the most consumed supplement, followed by vitamins and minerals (17, 19). These nationwide surveillance data play an important role in identifying nutritional trends and informing public health strategies for Korean children (13). These findings also suggest that the actual landscape of supplement administration may deviate from established clinical recommendations and may be increasingly influenced by commercial marketing and parental concerns regarding immune health.
Most previous studies have been limited to cross-sectional analyses, which restrict the ability to identify changes in consumption patterns over time and their associated factors (3, 5, 17–20). Therefore, this study utilizes birth cohort data to conduct a longitudinal analysis of dietary supplement administration up to 24 months of age. We aim to examine how supplement usage varies according to general characteristics, such as feeding method and allergy risk status, and to identify which supplements are predominantly administered, and at which specific time points.
2. Materials and methods
2.1. Study population and design
This prospective birth cohort study was conducted at Samsung Medical Center, Seoul, Korea. Pregnant women at ≥28 weeks of gestation were recruited between February 2017 and 2020. At enrollment, parents completed questionnaires on demographic characteristics and family history of allergic diseases and underwent skin prick tests to eight inhalant allergens. Based on allergy history and skin prick test results, infants were classified into allergy high-risk or control groups. Participants were excluded if they did not meet these eligibility criteria (e.g., sensitization without clinical allergic disease) or declined participation after screening (Supplementary Figure 1). Baseline infant clinical characteristics and dietary supplement administration during the first 2 months of life were assessed at the 2-month follow-up visit, which served as the baseline timepoint for postnatal analyses. Infants were followed at 2, 6, 12, and 24 months of age, and 137 infants who completed the follow-up questionnaires were included. This study was approved by the Institutional Review Board of Samsung Medical Center (IRB No. SMC-2016-12-111), and written informed consent was obtained from all parents prior to participation. The study protocol was registered in the World Health Organization International Clinical Trials Registry Platform (KCT0007979).
2.2. Demographic data collection
Information on infant sex, gestational age, mode of delivery, maternal age, maternal smoking status, parental education level, and household income was collected via a self-administered questionnaire. Postnatal anthropometric measurements were performed by trained medical staff during hospital visits using standardized clinical equipment. Body weight and recumbent length were measured using a pediatric anthropometric measurement system (GL-310, G-Tech International, Seoul, Korea), and measurements were recorded to the nearest 0.1 kg and 0.1 cm, respectively. Infants were measured without shoes and wearing light clothing and diapers. Recumbent length was measured up to 12 months of age, and standing height was measured at 24 months using a standard stadiometer (DS-B03, Jenix, Korea). Preterm birth was defined as delivery before 37 weeks of gestation. Smoking status was classified based on the question: “Have you ever smoked more than 100 cigarettes (5 packs) in your lifetime?” Participants who answered “No” were categorized as non-smokers, and those who answered “Yes” were categorized as smokers.
2.3. Data collection
A family history of allergic diseases was considered positive if one of the following criteria was met: (1) at least one parent had both a positive skin prick test and a history of asthma or allergic rhinitis, or (2) at least one parent or sibling had physician-diagnosed atopic dermatitis (AD). Infants were evaluated for AD and food allergy (FA) at each visit. AD was diagnosed according to the Hanifin and Rajka criteria (21). FA was confirmed by either a positive oral food challenge or a convincing history of immediate reactions within 2 h of food ingestion, together with a positive serum-specific IgE (≥0.35 kU/L, ImmunoCAP; Thermo Fisher Scientific, Waltham, MA, USA).
2.4. Dietary supplement and feeding method assessment
Dietary supplement administration was assessed through structured questionnaires completed by parents at each follow-up visit. Dietary supplements were defined as any orally administered products given to infants with the intention of supplementing the diet, including vitamins, minerals, probiotics, and other commercially available health-related products. At the 2-month visit, parents were asked whether their infant had received vitamin D or probiotic supplements during the first 2 months of life (0–<2 months) (yes/no). For other dietary supplements, parents were asked to report any products given to their infants using open-ended responses. If supplement administration was reported, parents were asked to provide additional information including the product name (brand) and the period of administration (start and end dates). At the 6-, 12-, and 24-month visits, parents reported supplement administration during the interval since the previous visit. Reported products were reviewed by the research team and categorized into predefined supplement groups. The number of parents who completed the supplement-related questionnaires was 137 at 2 months, 132 at 6 months, 127 at 12 months, and 107 at 24 months. Feeding practices were assessed at each follow-up visit by asking parents, “What type of milk has your baby consumed (breast milk and/or formula)?” Based on the cumulative responses over the first 12 months, participants were classified into three groups: Breastfeeding (BF): infants who received only breast milk for the entire period; Formula-feeding (FF): infants who received only formula for the entire period; and Mixed-feeding (MF): infants who received both breast milk and formula at any point during the follow-up period.
2.5. Statistical analysis
Analyses were performed separately at each age interval (0–<2, 2–<6, 6–<12, and 12–<24 months) using available cases with non-missing data for the variables included in that specific analysis. No imputation was performed. Because the sample size was determined by the number of participants available during follow-up, no a priori power calculation was performed. The subgroup analyses should therefore be considered exploratory. As this was an exploratory study aiming to identify potential associations and avoid missing clinically relevant trends (Type II error), multiple testing corrections were not applied. Data were analyzed using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). The Mann–Whitney U test was used to compare continuous variables, which are presented as median and interquartile range (IQR). Categorical variables were compared using Fisher's exact test due to small sample sizes in certain subgroups. Descriptive statistics were used to present dietary supplement administration by age, feeding method, and family history of allergies. Logistic regression analysis was used to examine predictors of dietary supplement administration in infants. P-values less than 0.05 were considered statistically significant.
3. Results
3.1. General characteristics of infants according to dietary supplement administration
A total of 137 infants were included in the analysis. Their baseline characteristics are summarized in Table 1. Among them, 58.4% were male, 40.9% were delivered by cesarean section, and 68.6% had a family history of allergic diseases. Table 2 presents the general characteristics of infants according to dietary supplement administration. Overall, 69.3% of infants received supplements in early infancy, rising to 84.8% at 2 to <6 months, 86.6% at 6 to <12 months, and 86.9% at 12 to <24 months. From 2 to 24 months, supplement administration was consistently higher in infants born via cesarean section, than in those delivered vaginally (p = 0.002 at 2 to <6 months; p = 0.001 at 6 to <12 months; p = 0.039 at 12 to <24 months). At 12 to <24 months, supplement administration was more frequent among infants diagnosed with AD at 12 months (p = 0.039). There were no significant differences in birth weight, sex, gestational age, prematurity, timing of complementary food introduction, maternal smoking, or AD at 2 or 6 months, or FA at 12 months.
Table 1.
Baseline characteristics of the study population.
| Variable | Total (n = 137) |
|---|---|
| Birth weight (kg) | 3.22 ± 0.41 |
| Male sex | 80 (58.4) |
| Gestational age (weeks) | 39.10 ± 1.27 |
| Cesarean section (yes) | 56 (40.9) |
| Family history of allergic diseases (yes) | 94 (68.6) |
| Maternal age (years) | 33.42 ± 3.22 |
| Maternal smoking (yes) | 14 (10.2) |
| Maternal education | |
| High school | 1 (0.7) |
| University | 100 (73.0) |
| Graduate degree or higher | 36 (26.3) |
| Paternal education | |
| High school | 6 (4.4) |
| University | 106 (77.4) |
| Graduate degree or higher | 25 (18.2) |
| Household income | |
| <4,000,000 KRW | 39 (28.5) |
| 4,000,000–5,999,999 KRW | 37 (27.0) |
| ≥6,000,000 KRW | 61 (44.5) |
Values are presented as number (%) or mean ± standard deviation.
Table 2.
General characteristics of infants according to dietary supplement administration.
| Characteristics | 0-<2 mo | 2-<6 mo | 6-<12 mo | 12-<24 mo | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Supplement administered (n = 95) | Non administered (n = 42) | p valuea | Supplement administered (n = 112) | Non administered (n = 20) | p value | Supplement administered (n = 110) | Non administered (n = 17) | p value | Supplement administered (n = 93) | Non administered (n = 14) | p value | |
| Birth weight (kg) | 3.2 (3.0–3.5) | 3.3 (3.0–3.4) | 0.994 | 3.2 (3.0–3.5) | 3.3 (3.0–3.4) | 0.936 | 3.2 (3.0–3.5) | 3.3 (3.0–3.4) | 0.781 | 3.3 (3.0–3.5) | 3.2 (3.0–3.4) | 0.535 |
| Sex | 0.059 | 1.000 | 0.605 | 0.394 | ||||||||
| Male | 50 (52.6) | 30 (71.4) | 66 (58.9) | 12 (60.0) | 66 (60.0) | 9 (52.9) | 58 (62.4) | 7 (50.0) | ||||
| Female | 45 (47.4) | 12 (28.6) | 46 (41.1) | 8 (40.0) | 44 (40.0) | 8 (47.1) | 35 (37.6) | 7 (50.0) | ||||
| Gestational age at birth (weeks) | 39.2 (38.3–40.0) | 39.4 (38.4–40.2) | 0.442 | 39.2 (38.3–40.1) | 39.6 (38.4–40.1) | 0.570 | 39.2 (38.3–40.0) | 39.6 (38.3–40.2) | 0.990 | 39.3 (38.4–40.0) | 39.5 (38.0–40.0) | 0.996 |
| Premature infant (<37 weeks) | 1.000 | 0.594 | 0.183 | 0.434 | ||||||||
| Yes | 7 (7.4) | 0 (0.0) | 7 (6.3) | 0 (0.0) | 4 (3.6) | 2 (11.8) | 3 (3.2) | 1 (7.1) | ||||
| No | 88 (92.6) | 42 (100.0) | 105 (93.8) | 20 (100.0) | 106 (96.5) | 15 (88.2) | 90 (96.8) | 13 (92.9) | ||||
| Birth mode | 0.132 | 0.002 | 0.001 | 0.039 | ||||||||
| Vaginal delivery | 51 (54.3) | 29 (69.1) | 59 (52.7) | 18 (90.0) | 57 (51.8) | 16 (94.1) | 50 (53.8) | 12 (85.7) | ||||
| Cesarean section | 43 (45.7) | 13 (31.0) | 53 (47.3) | 2 (10.0) | 53 (48.2) | 1 (5.9) | 43 (46.2) | 2 (14.3) | ||||
| Introduction of complementary food | 0.156 | 0.193 | 0.472 | 0.747 | ||||||||
| ≥4 mon | 17 (18.3) | 14 (34.2) | 23 (20.5) | 8 (40.0) | 23 (21.1) | 6 (35.3) | 22 (24.2) | 3 (21.4) | ||||
| ≥5 mon | 55 (59.1) | 20 (48.8) | 65 (58.0) | 9 (45.0) | 61 (56.0) | 8 (47.1) | 47 (51.7) | 9 (64.3) | ||||
| ≥6 mon | 21 (22.6) | 7 (17.1) | 24 (21.4) | 3 (15.0) | 25 (22.9) | 3 (17.7) | 22 (24.2) | 2 (14.3) | ||||
| Maternal smoking | 0.226 | 0.694 | 1.000 | 0.593 | ||||||||
| Yes | 12 (12.6) | 2 (4.8) | 13 (11.6) | 1 (5.0) | 11 (10.0) | 1 (5.9) | 8 (8.6) | 0 (0.0) | ||||
| No | 83 (87.4) | 40 (95.2) | 99 (88.4) | 19 (95.0) | 99 (90.0) | 16 (94.1) | 85 (91.4) | 14 (100) | ||||
| Atopic dermatitis at 2mon | 0.701 | 1.000 | 1.000 | 1.000 | ||||||||
| Yes | 5 (5.3) | 3 (7.1) | 6 (5.4) | 1 (5.0) | 6 (5.5) | 0 (0.0) | 5 (5.4) | 0 (0.0) | ||||
| No | 90 (94.7) | 39 (92.9) | 106 (94.6) | 19 (95.0) | 104 (94.6) | 17 (100) | 88 (94.6) | 5 (100) | ||||
| Atopic dermatitis at 6mon | 0.613 | 0.745 | 0.307 | 0.119 | ||||||||
| Yes | 14 (14.9) | 8 (19.5) | 18 (16.1) | 4 (20.0) | 19 (17.3) | 1 (5.9) | 17 (18.5) | 0 (0.0) | ||||
| No | 80 (85.1) | 33 (80.5) | 94 (83.9) | 16 (80.0) | 91 (82.7) | 16 (94.1) | 75 (81.5) | 14 (100) | ||||
| Atopic dermatitis at 12mon | 0.235 | 0.364 | 0.521 | 0.039 | ||||||||
| Yes | 15 (17.1) | 11 (27.5) | 20 (18.9) | 6 (30.0) | 23 (21.1) | 2 (11.8) | 22 (23.9) | 0 (0.0) | ||||
| No | 73 (83.0) | 29 (72.5) | 86 (81.1) | 14 (70.0) | 86 (78.9) | 15 (88.2) | 70 (76.1) | 14 (100) | ||||
| Food allergy at 12mon | 0.742 | 0.686 | 0.643 | 0.353 | ||||||||
| Yes | 7 (8.0) | 4 (9.8) | 9 (8.5) | 2 (10.0) | 9 (8.26) | 2 (11.8) | 10 (10.8) | 0 (0.0) | ||||
| No | 81 (92.1) | 37 (90.2) | 97 (91.5) | 18 (90.0) | 100 (91.7) | 15 (88.2) | 83 (89.3) | 14 (100) | ||||
Values are presented as number (%) or median (interquartile range).
P-values were calculated using the Mann–Whitney U test for continuous variables. Categorical variables were compared using Fisher's exact test due to the small sample sizes in certain subgroups.
3.2. Dietary supplement administration among infants
Table 3 summarizes the percentage of dietary supplement administration among infants from birth to 24 months. Figure 1 presents the overall trends in supplement use during this period. In addition, Supplementary Figure 2 illustrates the trajectories of supplement use across infancy, highlighting changes and transitions in usage behaviors over time. Probiotic and vitamin D supplements were the most frequently given across all age groups. At 0 to <2 months, 62.1% of infants received probiotic supplements, and 81.1% received vitamin D supplements. The intake of probiotics increased with age, reaching 91.8% at 6 to <12 months, and 90.3% at 12 to <24 months. Vitamin D intake remained consistently high throughout infancy, ranging from 75.2% to 81.1%. From 6 months of age, the variety of supplements administered increased. Multivitamin supplementation was initiated in later infancy, with 3.6% of infants receiving it at 6 to <12 months, and 38.6% at 12 to <24 months. At 12 to <24 months, the most commonly administered supplements, in descending order: probiotics, vitamin D, multivitamins, iron, zinc, red ginseng, calcium, n–3 fatty acids, colostrum, magnesium, propolis, and vitamin C. Intake of iron and zinc supplements also increased with age, reaching 9.7% at 12 to <24 months for both. Colostrum supplement administration peaked at 6 to <12 months (6.4%). Other supplements, such as calcium, n–3 fatty acids, red ginseng, magnesium, propolis, and vitamin C were given to 0.9% to 7.5% of infants.
Table 3.
Dietary supplement administration in infants from birth to 24 months of age.
| 0-<2 mo | 2-<6 mo | 6-<12mo | 12-<24mo | |||||
|---|---|---|---|---|---|---|---|---|
| (n = 95) | (n = 112) | (n = 110) | (n = 93) | |||||
| n | % | n | % | n | % | n | % | |
| Probiotic | 59 | 62.1 | 92 | 82.1 | 101 | 91.8 | 84 | 90.3 |
| Vitamin D | 77 | 81.1 | 89 | 79.5 | 82 | 75.2 | 70 | 75.3 |
| Multivitamin | 0 | 0.0 | 0 | 0.0 | 4 | 3.6 | 36 | 38.6 |
| Iron | 0 | 0.0 | 1 | 0.9 | 10 | 9.1 | 9 | 9.7 |
| Zinc | 0 | 0.0 | 1 | 0.9 | 3 | 2.7 | 9 | 9.7 |
| Colostrum | 1 | 1.1 | 4 | 3.6 | 7 | 6.4 | 4 | 4.3 |
| Calcium | 0 | 0.0 | 0 | 0.0 | 1 | 0.9 | 5 | 5.4 |
| n-3 fatty acids | 0 | 0.0 | 0 | 0.0 | 1 | 0.9 | 5 | 5.4 |
| Red ginseng | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 7 | 7.5 |
| Magnesium | 0 | 0.0 | 0 | 0.0 | 1 | 0.9 | 3 | 3.2 |
| Propolis | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 2 | 2.2 |
| Vitamin C | 0 | 0.0 | 0 | 0.0 | 1 | 0.9 | 1 | 1.1 |
Figure 1.
Supplement administration trends in infants aged 0–24 months.
3.3. Dietary supplement administration in infants by feeding method
Table 4 presents the percentage of dietary supplement administration according to feeding method. At 0 to <2 months, the administration of probiotic supplements was highest in the FF group (54.6%), followed by the MF group (45.8%) and the BF group (25.9%). Vitamin D supplementation was comparable between the MF group (59.4%) and the BF group (59.3%), while notably lower in the FF group (18.2%). At 2 to <6 months, probiotic intake increased across all feeding groups, with the highest percentage observed in the MF group (73.3%), followed by the FF group (71.8%) and the BF group (62.1%). Vitamin D supplement administration was highest in the BF group (82.8%), followed by the MF group (70.0%) and the FF group (53.9%). The intake of colostrum supplements remained low overall, but was highest in the FF group (7.7%). At 6 to <12 months, probiotic intake remained high across all groups: 82.5% in the MF group, 75.0% in the FF group, and 64.7% in the BF group. Similarly, vitamin D supplementation was most prevalent in the MF group (67.7%), followed by the BF group (70.6%) and the FF group (33.3%). The intake of multivitamins, iron, zinc, colostrum, calcium, n–3 fatty acids, magnesium, and vitamin C were generally low, and primarily observed in the FF and MF groups.
Table 4.
Dietary supplement administration in infants by feeding method.
| BF | FF | MF | ||||
|---|---|---|---|---|---|---|
| n | % | n | % | n | % | |
| 0-<2 mo | ||||||
| n | 27 | 11 | 96 | |||
| Probiotic | 7 | 25.9 | 6 | 54.6 | 44 | 45.8 |
| Vitamin D | 16 | 59.3 | 2 | 18.2 | 57 | 59.4 |
| Colostrum | 0 | 0.0 | 0 | 0.0 | 1 | 1.0 |
| 2-<6 mo | ||||||
| n | 27 | 11 | 96 | |||
| Probiotic | 18 | 62.1 | 28 | 71.8 | 44 | 73.3 |
| Vitamin D | 24 | 82.8 | 21 | 53.9 | 42 | 70.0 |
| Colostrum | 0 | 0.0 | 3 | 7.7 | 1 | 1.6 |
| Iron | 0 | 0.0 | 0 | 0.0 | 1 | 1.6 |
| Zinc | 0 | 0.0 | 0 | 0.0 | 1 | 1.6 |
| 6-<12 mo | ||||||
| n | 25 | 76 | 29 | |||
| Probiotic | 11 | 64.7 | 9 | 75.0 | 80 | 82.5 |
| Vitamin D | 12 | 70.6 | 4 | 33.3 | 65 | 67.7 |
| Multivitamin | 1 | 5.9 | 1 | 8.3 | 2 | 2.0 |
| Iron | 5 | 29.4 | 0 | 0.0 | 5 | 5.0 |
| Zinc | 1 | 5.9 | 0 | 0.0 | 2 | 2.0 |
| Colostrum | 0 | 0.0 | 1 | 8.3 | 6 | 5.9 |
| Calcium | 0 | 0.0 | 1 | 8.3 | 0 | 0.0 |
| n-3 fatty acids | 0 | 0.0 | 1 | 8.3 | 0 | 0.0 |
| Magnesium | 0 | 0.0 | 1 | 8.3 | 0 | 0.0 |
| Vitamin C | 0 | 0.0 | 1 | 8.3 | 0 | 0.0 |
BF, breastfeeding; FF, formula feeding; MF, mixed feeding.
3.4. Dietary supplement administration in infants by family history of allergies
The percentage of dietary supplement administration according to family history of allergies is presented in Table 5. At 0 to <2 months, probiotic intake was higher in the high-risk group (47.9%) compared to the low-risk group (32.6%), while vitamin D intake was similar between groups (55.3% vs. 58.1%). At 2 to <6 months, probiotic and vitamin D intake increased, reaching comparable levels in both groups (approximately 69%–70%). Colostrum, iron, and zinc supplements were given at low rates, primarily in the high-risk group. At 6 to <12 months, probiotic intake remained high in both groups (79.1%, 80.5%), and vitamin D supplementation was more frequent in the high-risk group (68.2%). Intake of colostrum, iron, and zinc was slightly higher in the low-risk group. Multivitamins and other supplements were given to 1.1% to 4.3% of high-risk infants. At 12 to <24 months, probiotic and vitamin D intake remained high and similar between groups. Multivitamin intake was more common in the low-risk group (32.6%) than in the high-risk group (23.4%). Iron and zinc intake also showed a slightly higher proportion in the low-risk group. Other supplements were given to 1.1% to 7.0% of infants
Table 5.
Dietary supplement administration in infants by family history of allergies.
| High-risk group | Low-risk group | |||
|---|---|---|---|---|
| (n = 94) | (n = 43) | |||
| n | % | n | % | |
| 0-<2 mo | ||||
| Probiotic | 45 | 47.9 | 14 | 32.6 |
| Vitamin D | 52 | 55.3 | 25 | 58.1 |
| Colostrum | 0 | 0.0 | 1 | 2.3 |
| 2-<6 mo | ||||
| Probiotic | 62 | 69.7 | 30 | 69.8 |
| Vitamin D | 59 | 66.3 | 30 | 69.8 |
| Colostrum | 2 | 2.1 | 2 | 4.7 |
| Iron | 1 | 1.1 | 0 | 0.0 |
| Zinc | 1 | 1.1 | 0 | 0.0 |
| 6-<12 mo | ||||
| Probiotic | 68 | 79.1 | 33 | 80.5 |
| Vitamin D | 58 | 68.2 | 24 | 58.5 |
| Colostrum | 3 | 3.2 | 4 | 9.3 |
| Iron | 6 | 6.4 | 4 | 9.3 |
| Zinc | 2 | 2.1 | 1 | 2.3 |
| Multivitamin | 4 | 4.3 | 0 | 0.0 |
| Vitamin C | 1 | 1.1 | 0 | 0.0 |
| Magnesium | 1 | 1.1 | 0 | 0.0 |
| Calcium | 1 | 1.1 | 0 | 0.0 |
| n-3 fatty acids | 1 | 1.1 | 0 | 0.0 |
| 12-<24 mo | ||||
| Probiotic | 56 | 77.8 | 28 | 80.0 |
| Vitamin D | 47 | 65.3 | 23 | 65.7 |
| Colostrum | 3 | 3.2 | 1 | 2.3 |
| Iron | 5 | 5.3 | 4 | 9.3 |
| Zinc | 6 | 6.4 | 3 | 7.0 |
| Multivitamin | 22 | 23.4 | 14 | 32.6 |
| Vitamin C | 1 | 1.1 | 0 | 0.0 |
| Magnesium | 3 | 3.2 | 0 | 0.0 |
| Calcium | 3 | 3.2 | 2 | 4.7 |
| n-3 fatty acids | 3 | 3.2 | 2 | 4.7 |
| Red ginseng | 4 | 4.3 | 3 | 7.0 |
| Propolis | 2 | 2.1 | 0 | 0.0 |
3.5. Predictors of dietary supplement administration in infants
Univariable logistic regression analyses identified predictors of dietary supplement administration among infants from birth to 24 months of age (Table 6). Male infants were less likely than female infants to receive supplements at 0 to <2 months (OR = 0.44, 95% CI: 0.20–0.97). Delivery by cesarean section was significantly associated with an increased likelihood of receiving supplement compared to vaginal delivery at 2 to <6 months (OR = 8.09, 95% CI: 1.79–36.49), 6 to <12 months (OR = 14.88, 95% CI: 1.91–116.10), and 12 to <24 months (OR = 5.16, 95% CI: 1.09–24.35). AD at 24 months was inversely associated with supplement administration at 0 to <2 months (OR = 0.39, 95% CI: 0.15–0.99). Higher maternal age was positively associated with supplement administration at 6 to <12 months (OR = 1.21, 95% CI: 1.02–1.43). No statistically significant associations were observed with birth weight, birth order, gestational age, parental education, maternal smoking, or household income in any age group.
Table 6.
Predictors of dietary supplement administration in infants.
| Variable | 0-<2 mo | 2-<6 mo | 6-<12 mo | 12-<24 mo | ||||
|---|---|---|---|---|---|---|---|---|
| OR (95% CI) | p value | OR (95% CI) | p value | OR (95% CI) | p value | OR (95% CI) | p value | |
| Infant characteristics | ||||||||
| Birth weight (kg) | 1.10 (0.44–2.73) | 0.846 | 0.93 (0.29–3.02) | 0.905 | 0.97 (0.28–3.42) | 0.967 | 1.12 (0.27–4.66) | 0.878 |
| Birth order (≥2 vs first-born) | 1.92 (0.50–7.34) | 0.342 | 0.93 (0.18–4.66) | 0.926 | 0.73 (0.14–3.77) | 0.708 | 0.56 (0.10–3.04) | 0.500 |
| Male sex (vs female) | 0.44 (0.20–0.97) | 0.042 | 0.96 (0.36–2.53) | 0.929 | 1.33 (0.48–3.72) | 0.583 | 1.66 (0.54–5.12) | 0.380 |
| Gestational age at birth (weeks) | 0.88 (0.65–1.19) | 0.400 | 0.90 (0.61–1.33) | 0.605 | 1.00 (0.67–1.49) | 0.990 | 1.09 (0.70–1.70) | 0.700 |
| Cesarean section (vs vaginal delivery) | 1.88 (0.87–4.06) | 0.108 | 8.09 (1.79–36.49) | 0.007 | 14.88 (1.91–116.10) | 0.010 | 5.16 (1.09–24.35) | 0.038 |
| Introduction of complementary food (Reference category: ≥4 mon) | ||||||||
| ≥ 5 mon | 2.27 (0.95–5.42) | 0.343 | 2.51 (0.87–7.28) | 0.424 | 1.99 (0.62–6.36) | 0.576 | 0.71 (0.18–2.89) | 0.368 |
| ≥ 6 mon | 2.47 (0.81–7.50) | 0.312 | 2.78 (0.66–11.80) | 0.401 | 2.17 (0.49–9.72) | 0.524 | 1.50 (0.23–9.87) | 0.483 |
| Atopic dermatitis at 24 months | 0.39 (0.15–0.99) | 0.047 | 0.42 (0.14–1.27) | 0.125 | 0.96 (0.25–3.67) | 0.946 | 1.56 (0.32–7.58) | 0.580 |
| Food allergy at 24 months | 0.71 (0.25–2.00) | 0.516 | 1.67 (0.35–7.93) | 0.516 | 0.79 (0.20–3.07) | 0.730 | 2.74 (0.33–22.43) | 0.348 |
| Parental characteristics | ||||||||
| Maternal age | 0.97 (0.86–1.09) | 0.582 | 1.15 (0.99–1.34) | 0.077 | 1.21 (1.02–1.43) | 0.028 | 1.15 (0.97–1.37) | 0.116 |
| Maternal smoking (vs non-smoking) | 2.89 (0.62–13.54) | 0.178 | 2.50 (0.31–20.21) | 0.392 | 1.78 (0.22–14.72) | 0.594 | 2.88 (0.13–62.41) | 0.500 |
| Maternal education Graduate degree or higher (vs University graduation) | 0.72 (0.32–1.62) | 0.429 | 1.01 (0.34–3.04) | 0.983 | 1.69 (0.45–6.32) | 0.434 | 1.37 (0.35–5.31) | 0.651 |
| Paternal education Graduate degree or higher (vs University graduation) | 2.73 (0.88–8.54) | 0.084 | 2.10 (0.45–9.76) | 0.344 | 1.69 (0.36–7.97) | 0.510 | 1.26 (0.26–6.20) | 0.774 |
| Monthly household income (Reference category: <4,000,000 KRW) | ||||||||
| 4,000,000–5,999,999 KRW | 1.23 (0.47–3.25) | 0.817 | 0.81 (0.22–2.92) | 0.819 | 0.73 (0.18–2.96) | 0.813 | 1.29 (0.26–6.29) | 0.574 |
| ≥ 6,000,000 KRW | 1.24 (0.52–2.96) | 0.761 | 0.83 (0.26–2.72) | 0.878 | 0.70 (0.19–2.51) | 0.701 | 0.76 (0.20–2.84) | 0.482 |
OR, odds ratio; CI, confidence interval.
Odds ratios, 95% confidence intervals, and p-values were obtained from univariable logistic regression models.
Reference categories are indicated in parentheses.
4. Discussion
In this longitudinal birth cohort study, we observed a high percentage (82%) of dietary supplement administration in Korean infants from birth to 24 months of age, considerably higher than rates previously reported in community-based studies from Korea (39.2%), the United States (18.2%), and Australia (23.5%) (17, 22, 23). One plausible explanation is that although our cohort was designed as a general population study, many participants were recruited from families residing near the study hospital. This catchment area is characterized by relatively high socioeconomic status and strong parental concern for child health, which may have contributed to the elevated prevalence of supplement administration.
Current pediatric guidelines, including those from the AAP, recommend vitamin D supplementation of 400 IU/day for all infants beginning shortly after birth to prevent deficiency and support bone health (10, 11, 15, 16). Iron supplementation is also recommended from approximately 4 months of age for predominantly breastfed infants because breast milk alone may not provide sufficient iron to meet increasing requirements during later infancy (15, 16). In Korea, routine supplementation recommendations for healthy infants primarily focus on these nutrients, while the routine administration of other dietary supplements is not formally recommended. Consistent with these recommendations, vitamin D supplementation was commonly reported in our cohort. Notably, a recent systematic review reported that global adherence to vitamin D guidelines varies widely (20%–90%), with higher rates often observed during early infancy (24). Our findings of sustained high intake up to 24 months suggest that caregivers in this study area maintain an exceptionally high commitment to clinical guidelines, possibly due to elevated health literacy. Although dosage information was not available, the high prevalence suggests good adherence to current vitamin D supplementation recommendations.
From 6 to 12 months of age, the types of supplements administered became more diverse, with a marked increase in the intake of colostrum and iron supplements. Iron supplementation in particular was more common among infants who were breastfed or mixed-fed. This may be explained by the fact that while breast milk offers numerous immunological benefits, its iron content is low (approximately 0.35 mg/L), making it insufficient to meet the iron requirements of infants after six months of age (15). This pattern may reflect adherence to clinical recommendations encouraging iron supplementation among predominantly breastfed infants. These findings underscore the importance of reinforcing guideline-based iron supplementation practices, particularly among breastfed infants at risk of iron deficiency. Despite these recommendations, the relatively low rate of iron supplementation observed among breastfed infants in our cohort suggests a gap between clinical guidance and real-world practice. Further research is needed to better understand the factors influencing caregiver decision-making and adherence to iron supplementation recommendations.
Similarly, a 2025 nationwide study in Germany identified iron as a critical nutrient, noting that many infants do not meet the required intake levels through complementary foods alone (25). The essential nutrients considered critical for infants in Korea primarily include vitamin D, iron, calcium, DHA, and zinc (26, 27). These align with the types of nutrients currently being supplemented by the infants in this study. Previous research has reported that breastfed and mixed-fed infants had a significantly higher risk of iron-deficiency anemia, highlighting the necessity for iron supplementation in these groups (28). However, our data do not allow us to determine whether parents’ supplementation practices were influenced by clinical recommendations, or by their own awareness, so it remains unclear to what extent these practices reflect adherence to professional guidance. After 12 months of age, multivitamins use increased, with a higher percentage among infants in the low-risk allergy group, compared to those in the high-risk group. This suggests that caregivers of high-risk infants may be more cautious about the efficacy of multivitamins, or may be using them more selectively, based on recommendations from healthcare professionals.
Supplement intake was observed from the early stages of infancy, with vitamin D and probiotics being the first supplements introduced and consistently given up to 24 months of age, regardless of feeding method or family history of allergy. Notably, probiotic use showed an increasing trend from 62% at 0 to <2 months, to 82% at 2 to <6 months. This suggests an age-related increase in probiotic use during early infancy, consistent with previous reports describing early introduction of probiotics (17, 19, 29). We did not observe a clear association between antibiotic exposure and probiotic use in our cohort (data not shown). This pattern may instead reflect parental perceptions of benefits for infant gut and immune health, as well as increasing public interest and the widespread availability of probiotic products for infants (23). In contrast, probiotics were the most frequently administered supplement across all age groups despite the absence of guideline-based recommendations. This discrepancy may reflect parental perceptions of potential health benefits rather than evidence-based recommendations, highlighting the need for clearer guidance regarding appropriate supplement administration during infancy.
Feeding method may also explain some of the observed supplementation patterns. For example, iron supplementation was not observed among formula-fed infants in our cohort, which is clinically plausible because commercially available infant formulas are typically iron-fortified and provide sufficient iron intake (14, 30). Similarly, vitamin D supplementation was less frequently reported among formula-fed infants in early infancy, possibly because vitamin D-fortified formulas can provide adequate vitamin D intake when consumed in sufficient amounts (11).
Infants born via cesarean section were significantly more likely to be given dietary supplements, compared to those born vaginally. Vaginal delivery facilitates the transfer of beneficial bacteria and immune-related substances from the mother's birth canal to the infant, which positively influences the development of the early immune system. In contrast, cesarean delivery bypasses this exposure, leading to the establishment of microbial communities that resemble maternal skin flora (31–33). This may raise caregiver concerns regarding immune competence, potentially resulting in a greater reliance on dietary supplementation. Indeed, systematic reviews have demonstrated that supplementation with Lactobacillus and Bifidobacterium in cesarean-born infants can improve gut microbial composition and enhance immune function (34). Our findings illustrate how both biological considerations and caregiver perceptions converge to influence supplement administration in this subgroup.
This study has several limitations. First, the relatively small sample size limits the generalizability of the findings, and larger, population-based cohort studies are needed to confirm these results. Second, although designed as a general population cohort, the recruitment setting may have overrepresented families with higher socioeconomic status and strong health interest, which may limit generalizability. Third, multiple testing corrections were not performed in our analyses. While this approach was chosen to maintain the exploratory power of the study and avoid missing potentially important associations (Type II error), the results should be interpreted with caution regarding the risk of Type I error. Despite these limitations, this study holds significant value, as it provides a longitudinal follow-up across the critical first 24 months of life, standardized diagnostic criteria for allergic diseases confirmed by pediatric allergists, and high-quality data collection through face-to-face interviews by trained research personnel. To our knowledge, few studies in Korea have examined infant supplement administration using this level of temporal detail. The findings can serve as foundational data to develop evidence-based guidelines for supplement administration and nutrition policies targeting infants and young children.
In conclusion, dietary supplement administration was highly prevalent among Korean infants, with probiotics and vitamin D most frequently consumed from early infancy. The mode of delivery, sex, maternal age, and allergic disease risk were significantly associated with variations in supplement use over time. Infants born via cesarean section were more likely to be given supplements, possibly due to caregiver concerns about gut and immune health resulting from altered microbial colonization. These findings highlight the gap between clinical guideline recommendations and real-world practices, emphasizing the interplay of clinical needs, parental perceptions, and societal influences. A key strength of this study is its longitudinal tracking of temporal changes in supplement use throughout infancy, which provides foundational evidence to support the development of updated, evidence-based public health guidelines and caregiver education for safe supplement administration in early childhood.
Acknowledgments
We would like to thank Prof. Mi Jin Kim for her valuable input on the interpretation of infant nutritional supplement guidelines and for her critical review of the manuscript.
Funding Statement
The author(s) declared that financial support was received for this work and/or its publication. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2025-21532992) and the SMC-Otoki Research Fund (No. SMX125102).
Footnotes
Edited by: Paul Rufo, Boston Children's Hospital and Harvard Medical School, United States
Reviewed by: Atta Al- Sarray, Middle Technical University, Iraq
Leonie Burgard, Universitätsklinikum Erlangen, Germany
Data availability statement
The datasets presented in this article are not publicly available due to privacy and ethical restrictions but may be available from the corresponding author upon reasonable request and with appropriate institutional approval.
Ethics statement
This study was approved by the Institutional Review Board of Samsung Medical Center (IRB No. SMC-2016-12-111), and written informed consent was obtained from all parents prior to participation. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants’ legal guardians/next of kin.
Author contributions
JJ: Conceptualization, Formal analysis, Methodology, Writing – original draft, Writing – review & editing. SK: Methodology, Writing – review & editing. MJ: Methodology, Writing – review & editing. SC: Methodology, Writing – review & editing. SO: Methodology, Writing – review & editing. SJ: Writing – review & editing. YY: Conceptualization, Formal analysis, Methodology, Writing – original draft, Writing – review & editing. JK: Conceptualization, Formal analysis, Methodology, Writing – original draft, Writing – review & editing. KA: Methodology, Writing – review & editing.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
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Supplementary material
The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fped.2026.1807460/full#supplementary-material
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The datasets presented in this article are not publicly available due to privacy and ethical restrictions but may be available from the corresponding author upon reasonable request and with appropriate institutional approval.