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. Author manuscript; available in PMC: 2023 Jun 1.
Published in final edited form as: J Nutr Educ Behav. 2022 Mar 11;54(6):499–509. doi: 10.1016/j.jneb.2021.11.009

Vitamin D intake and meeting recommendations among infants participating in WIC nationally

Sina Gallo 1, Jaime Gahche 2, Panagiota Kitsantas 3, Priyal Makwana 4, Yu Wang 5, Xianyan Chen 6, Janani Rajbhandari-Thapa 7
PMCID: PMC9149040  NIHMSID: NIHMS1788517  PMID: 35288058

Abstract

Objective:

To report and examine associations with infant vitamin D intake and meeting recommendations among a national sample participating in WIC.

Design:

Secondary analysis from the 2013–2015 WIC Infant Toddler Feeding Practices Study-2.

Participants:

US Infants.

Variables Measured:

Total reported vitamin D intake from diet and supplementation at the time of data collection.

Analysis:

Descriptive statistics and generalized estimating equations.

Results:

The median total vitamin D intake ranged from 5.43 (95% CI: 5.40, 5.46) mcg/day at month 1 to 8.18 (95% CI: 8.11, 8.20) mcg /day at month 13, with 16–36% of infants meeting the infant vitamin D recommendation over that time. Overall 6 to 12% of all participants reported supplementation, across all time points. Although most (between 78–98%) of supplemented breastfed infants met the recommendation, very few were supplemented as a group. Hence, breastfed infants were less likely to meet the recommendation as compared to those who were formula fed across at time points except month 1 (P < 0.001 for all). Whereas infant age, feeding type, and/or their interaction were significant predictors of both receiving supplementation and meeting the recommendation, maternal nativity (P = 0.006) and parity (P = 0.01 and P < 0.001) predicted receiving supplementation, and child sex (P < 0.001) and maternal race/ethnicity (P < 0.001) predicted meeting the recommendation.

Conclusions and Implications:

Among a national sample of infants participating in WIC between 2013–2015, a high proportion were not meeting the current vitamin D recommendation. The WIC program is one resource for promoting strategies for increasing the number of American infants meeting D recommendations yet, a coordinated approach involving other health care providers is likely needed. Future research exploring the reason for lack of supplementation, from both the perspective of parents and providers, as well as the clinical impact of low vitamin D intake is warranted.

INTRODUCTION

Breastfeeding is the recommended form of infant feeding1–3 as it protects infants from a variety of health problems,2,4–6 provides long-term developmental behavior benefits6 and improves maternal outcomes.4 This provides benefits to society via reduced health care costs.7Although there are many benefits to breastfeeding, the vitamin D content of breastmilk is low.8,9 Further, sun exposure as a source for vitamin D is limited due to skin pigmentation, sunscreen and latitude.3 It is for this reason that public health recommendations in North America states that exclusively and partially breastfed infants be supplemented with 10 mcg (400 IU) of vitamin D from birth until a dietary source is available.10,11 In 2008, the American Academy of Pediatrics (AAP) revised their infant guideline to double their previous recommendation of 5 to 10 mcg of supplemental vitamin D daily. AAP further endorsed this recommendation after the Institute of Medicine (now National Academies of Sciences, Engineering and Medicine) released their updated Dietary Reference Intakes for vitamin D in 2011that re-emphasized an Adequate Intake (AI) level of 10 mcg for infants.10,11 Further, the 2020–2025 Dietary Guidelines for Americans was the first edition to provide nutrition guidance for infants, and included recommendations for vitamin D supplementation.3 Breastfed infants without supplementation represent a group at heightened risk of vitamin D deficiency; however, vitamin D deficiency has also been reported among formula-fed infants who were receiving less than 32 oz. of vitamin D fortified formula per day.12,13 Few dietary sources of vitamin D exist in the infant diet other than fortified sources such as infant formula hence, the reliance on supplemental sources.

The foremost functions of vitamin D include calcium homeostasis and skeletal development with severe vitamin D deficiency during childhood leading to rickets and osteomalacia. Rickets continues to be a problem worldwide,14,15 although it is not a disease that requires reporting to government agencies nor are there national surveillance systems that capture this information in the United States (US). Hence, the national prevalence of rickets in the US is unknown. Albeit rare, rickets cases in developed countries occur mostly among immigrant/refugee and dark-skinned children,16,17 and commonly due to a vitamin D deficiency.15,18,19 In Olmsted county, MN, there were 24 per 100,000 rickets cases identified from healthcare facilities data between 2000–2009, with Black children having the highest risk at ~220 per 100,000.20 The US prevalence of vitamin D deficiency (defined as 25(OH)D <30nmol/L) ranged between 10% and 66% based on cord samples21,22 with a 4.7-fold increased risk among Black as compared to White infants.23 Despite the long-standing infant recommendation in the US, vitamin D supplementation use is low24,25 and in stark contrast to much higher rates worldwide.26,27 Although dietary intakes below the current recommendation or AI are not conclusive of deficiency, lower than recommended intakes in this population are a concern.

The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) is a federal food assistance program. In 2018, WIC served 1.7 million infants representing ~45% of all US births.28 There is ethnic and racial diversity in the WIC population since 40% report as non-white.29 In the last decade, WIC has instituted many policies to further incentivize breastfeeding;30,31 yet vitamin D supplementation is not a WIC role and may not be consistently addressed as part of breastfeeding education.32 Costs of vitamin D supplementation may be a deterrent to use among those of low-income status,33 and WIC recipients have lower use of dietary supplements.34 Not meeting vitamin D recommendations is an important public health issue that demands more consideration.35,36 The aim of this study is to report vitamin D intake and the proportion meeting current recommendations among a national sample of infants participating in WIC. The secondary aim is to identify the factors associated with receiving vitamin D supplementation and meeting the recommendation during infancy. It was hypothesized that the ability to meet the recommendation would differ by age and feeding type.

METHODS

Design

This research is a secondary analysis of data collected from the WIC Infant Toddler Feeding Practices Study-2 (ITFPS-2). Harrison et al.37 described the design of WIC ITFPS-2. The ITFPS-2 is the most recent national longitudinal prospective cohort of mothers-children dyads participating in WIC, conducted between 2013 and 2020. However, since this study only included data from the prenatal and infant year, data was limited to 2013–2015. The Institutional Review Board of the University of Georgia determined this research to not be human subjects research because all data provided to the investigator from the WIC ITFPS-2 were de-identified.

Setting and Sample

Data were collected from mother-infant or caregiver-infant dyads participating in the WIC ITFPS-2 from over 80 WIC sites across 27 WIC states and national territories. Women were invited to participate if they were ≥16 years of age, spoke English or Spanish and were either pregnant or their infant was less than 2.5 months old.38 Mothers or caregivers are used interchangeably to describe adult WIC ITFPS-2 participants yet, WIC eligibility requires women to be pregnant, postpartum or breastfeeding. Data for the first interview were conducted with each participant in person at a WIC site. Follow-up interviews were conducted over the telephone at months 1, 3, 5, 7, 9, 11, 13, 15, 18, 24, 30, 36, 42, 48, 54, and 60 of the child’s birth. Only data collected through month 13 were included in the current analysis. Figure 1 shows the flow of participants through each time point. The current analysis included participants from both the core and the supplemental sample. The core sample was interviewed at each timepoint across the first 24 months; however, the supplemental sample was only interviewed at months 1, 7, and 13 and was designed to focus on subpopulations with specific characteristics. A description of sample selection for WIC ITFPS-2 is provided in chapter 1 of the first year report.39

FIGURE 1. Flow diagram of participants1–2.

FIGURE 1

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1The current analysis included participants from both the core and the supplemental sample. The core sample was interviewed at all interviews across the first 24 months; however, the supplemental sample was only interviewed at months 1, 7, and 13 and was designed to focus on subpopulations with specific characteristics. A description of sample selection for WIC ITFPS-2 is provided in chapter 1 of the first year report.39

2Added refers to participants who were not included since the previous visit because they were missing or the visit was not required because they were part of the supplemental sample.

Vitamin D Intake

As part of the interview, mothers or infant caregivers were asked to complete a 24-hour dietary recall and report all foods, beverages, and dietary supplements consumed by their child from 12:00 a.m. through 11:59 p.m. on the previous day. Participants received necessary guidelines on reporting child portions before the interview through a mailed package. This dietary recall was administered by phone interviewers using the United States Department of Agriculture (USDA) Automated Multiple-Pass Method.40 Conversion to measure food and nutrient intake was done using the USDA Food and Nutrient Database for Dietary Studies 5.0 (2012) based on the time of data collection.41 The dietary intake coding procedures are described in Appendix B4 of the WIC-ITFPS-2 report.38 Total vitamin D intake from day one was calculated based on both dietary and supplemental sources. The breastmilk vitamin D value in the nutrient database is 1 mcg of vitamin D per liter (L) or 32 oz.42 It is well established that human milk values in the nutrient database are limited,43,44 but unless the mother is being supplemented with high doses of vitamin D,45,46 the vitamin D content of human milk will be considerably less than 10 mcg per L.8,9 High dose maternal supplementation of vitamin D is not common practice and most prenatal supplements will contribute ~10 mcg per day of vitamin D.47 Brand names were included for infant formulas and hence, carry separate nutrient profiles in the nutrients component of the database. Infant formulas in the US are regulated by the Title 21 Code of Federal Regulations (Part 107.10 Nutrient Information for Infant Formula) and are mandated to be fortified with 1–2.5 mcg (40–100 IU) /100 kcal of vitamin D.48 Infants were categorized as whether they were able to achieve the recommended 10 mcg of vitamin D daily through all sources or not.

Other Measures

The independent variables used in this study included the following maternal and infant characteristics: maternal age, race/ethnicity, educational level, marital status, nativity, the language that interview was conducted, health insurance, parity and household poverty, as well as infant sex and birth weight, and infant feeding type. Maternal ethnicity was self-reported by the mother/caregiver as Hispanic/Latino or Non-Hispanic/Latino, and race from a list that included White, Black or African American, Asian, American Indian or Alaska Native or other. Race and ethnicity were combined as a single variable and described in the current analysis as follows: Hispanic, Non-Hispanic White, Non-Hispanic Black, or Non-Hispanic Other. Household poverty was described using the Department of Health and Human Services 2013 poverty guideline as a reference,49 that takes into account household size, and classified as either ≤75%, >75 to ≤130%, or >130% of the poverty guideline. Infant feeding was determined at each postnatal interview using the four answers to the following question “Are you or anyone currently feeding the child breastmilk either from the breast or from a bottle, formula, or both?”: 1) only breastmilk, 2) only formula, 3) both breastmilk and formula, and 4) neither breastmilk nor formula.

Statistical analysis

The dataset was weighted to be representative of the population of infants enrolling in eligible WIC sites during the initial recruitment period (July through November 2013). The weighting procedure was followed as outlined in Appendix B1 of the WIC-IFTPS-2 report.38 All categorical variables are presented as the weighted number and percentage of participants belonging in each category at the time of the visit. Vitamin D intake is presented as weighted median with the 25th and 75th percentiles as data were non-normally distributed. Differences in the proportion of infants meeting the recommendation by feeding type were assessed using the chi-square test of independence (P < 0.05). Generalized estimating equation (GEE) models with sampling weights for binary outcomes were constructed to assess predictors of receiving supplementation and meeting the vitamin D recommendation. Parameter estimates from GEE produce valid inferences when the data are missing at random.50 The odds ratio and 95% confidence intervals were computed (95% CI). Contrast statements were used to test for differences among interaction terms in the GEE models, specifically infant feeding at each time point. Although descriptive data were presented by time point, regression models took into account the repeated measures within each individual of the longitudinal follow up design and interaction models included the main effects. The feeding category could change over time and was treated as time varying part of GEE. Statistical significance level for all analyses was set at α = 0.05 and the P-values in the GEE models are adjusted using the Bonferroni method. All analyses were conducted in SAS software version 9.4 released in 2013 (SAS Institute Inc., Cary, NC).

RESULTS

Table 1 shows a total of 3,398 infants were included in the analysis at month 1, of which, 39% were Hispanic, 62% were living in a household ≤75% of the poverty level, 62% had a maternal education level of 12th grade or less, and 42% were 1st born. Of the 7 study visits, the mean number of visits completed by participants was 5.1 (± 2.0). The total median vitamin D intake from diet (includes breast milk and infant formula) and/or supplementation was <10 mg / day across all time points (Table 2). Overall, between 6 to 12% of participants reported vitamin D supplementation and 16% to 35% of infants met the infant vitamin D recommendation of 10 mcg per day (from both diet and/or supplementation) (Table 2). Among infants taking supplementation, between 69 to 87% met the recommendation (Table 2). There were significant differences noted in the ability to meet the recommendation between only formula-fed and only breastfed infants at months 3, 5, 7, 9, 11 and 13 (P < 0.001 for all) and differences between only formula-fed and those receiving both breastmilk and formula at month 3 (P < 0.001), 5 (P < 0.001), 7 (P < 0.001) and 9 (P = 0.01) (Supplemental Table 1). Among breastfed infants who received supplementation, a significantly higher proportion were able to meet the vitamin D recommendation of 10 mcg daily as compared to formula fed infants across all time points (P < 0.001) (Figure 2). Among infants breastfed without supplementation, the proportion meeting the recommendation ranged from 0–7%, across all time points.

TABLE 1.

Maternal Sociodemographic, Infant Birth and Feeding Type at Month 1 (n = 3398). Presented as n (%).

Maternal characteristics Infant characteristics
Age, years Birth weight 4
16–19 396 (11.7) Low 247 (7.3)
20–25 1414 (41.6) Normal 3107 (91.5)
≥26 1586 (46.7) High 42 (1.2)
Race/ethnicity Sex
Hispanic 1311 (38.6) Male 1744 (51.4)
Non-Hispanic White 1060 (31.2) Female 1652 (48.7)
Non-Hispanic Black 828 (24.2) Feeding type 5
Non-Hispanic Other 197 (5.8) Breastmilk 1031 (30.4)
Language 1 Formula 1366 (40.2)
English 2769 (81.5) Both 996 (29.3)
Spanish 620 (18.3) Neither 0 (0.0)
Nativity Child WIC participation status
US born 2526 (74.4) Current WIC child 3258 (95.9)
Not US born 870 (25.6) Child formerly on WIC 134 (4.0)
Parity
1st born 1409 (41.5)
2nd born 922 (27.2)
3rd or subsequent born 1065 (31.4)
Marital status
Married 1006 (29.6)
Not Married 2390 (70.4)
Education level, grade
≤9th 327 (9.7)
10–11th 481 (14.2)
12th 1289 (38.1)
>12th 1291 (38.1)
Household poverty level 2
≤75% 2118 (62.4)
>75% and ≤130% 937 (27.6)
>130% 341 (10.0)
Medicaid 3
Yes 1642 (74.0)
No 577 (26.0)
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WIC: Special Supplemental Nutrition Program for Women, Infants, and Children

1

Categories do not add up to 100% due to not including those categorized as analytic complete (answered 50% or more of core questions in the interview)

2

Defined on basis of poverty level guideline Department of Health and Human Services 2013, https://aspe.hhs.gov/2013-poverty-guidelines

3

A total of 1728 participants were missing Medicaid information.

4

Defined as infant birth weight category as either low (≤ 2523 grams), normal (>2523 and <4479 grams) or high (≥ 4479 grams)

5

Defined on basis of the following interview question at given time point: “Are you or anyone currently feeding the child breastmilk either from the breast or from a bottle, formula, or both

TABLE 2.

Median1,2 Infant Daily Vitamin D Intake (in mcg/day) and Proportion3 Receiving Vitamin D Supplementation and Meeting the Vitamin D Recommendation (10 mcg/day)4 among Infants Enrolled in WIC by Time and Feeding Type

Month 1 n = 3398 Month 3 n = 2881 Month 5 n = 2631 Month 7 n = 3121 Month 9 n = 2443 Month 11 n = 2316 Month 13 n = 2799
Vitamin D intake (mcg), median (25th percentile, 75th percentile)
Total 4 5.43 (0.81,8.22) 7.89 (4.59,10.52) 8.58 (5.84,10.87) 7.80 (5.14,10.52) 7.52 (5.10,10.13) 7.40 (5.07,10.13) 8.18 (5.55,11.53)
Diet only 4.24 (0.81,7.01) 7.17 (2.38,9.35) 8.16 (4.67,10.52) 7.43 (4.53,9.67) 7.23 (4.73,9.41) 7.16 (4.73,9.50) 7.88 (5.40,10.95)
Total vitamin D intake, by feeding type
Breastmilk 0.811 (0.81,0.81) 0.811 (0.81,1.39) 0.811 (0.811,1.11) 0.639 (0.62,0.99) 0.747 (0.62,1.80) 1.20 (0.74,2.53) 3.25 (1.30,6.55)
Formula 7.25 (5.84,9.02) 8.77 (7.25,10.83) 9.45 (7.87,11.69) 8.62 (6.77,10.81) 8.20 (6.35,10.52) 7.93 (6.05,10.50) 8.18 (6.08,11.48)
Both 4.44 (2.63,7.09) 5.50 (2.90,8.79) 5.13 (2.90,8.27) 4.20 (1.97,7.07) 4.47 (2.54,7.33) 4.81 (2.54,8.51) 5.24 (3.76,7.56)
Neither 8.93 (6.72,10.75) 8.99 (6.20,12.71) 9.04 (6.49,12.16)
Proportion receiving supplemental vitamin D, n (%)
All 410 (12.1) 321 (11.1) 218 (8.29) 198 (6.34) 153 (6.26) 142 (6.13) 165 (5.89)
By feeding type
Breastmilk 198 (19.3) 130 (23.0) 86 (21.2) 78 (27.6) 51 (15.8) 46 (15.8) 45 (12.3)
Formula 71 (5.22) 89 (5.18) 77 (4.24) 82 (3.62) 80 (4.29) 72 (4.10) 30 (5.60)
Both 140 (14.1) 102 (17.4) 55 (13.8) 37 (10.7) 20 (10.3) 15 (10.3) 6 (11.3)
Neither 1 (2.13) 2 (3.45) 9 (7.69) 84 (4.59)
Proportion meeting vitamin D recommendation (≥10 mcg/day) 5 , among all participants, n (%)
All 539 (15.9) 852 (29.6) 954 (36.3) 895 (28.7) 638 (26.1) 611 (26.4) 975 (34.8)
By feeding type
Breastmilk 181 (17.6) 123 (21.8) 84 (20.7) 74 (16.7) 48 (14.9) 43 (14.7) 57 (15.5)
Formula 217 (15.9) 601 (35.0) 786 (43.3) 758 (33.4) 544 (29.2) 488 (27.8) 182 (34)
Both 140 (14.1) 125 (21.3) 82 (20.5) 43 (12.4) 27 (13.9) 29 (19.9) 10 (18.9)
Neither 19 (40.4) 18 (31) 50 (42.7) 723 (39.5)
Proportion meeting infant vitamin D recommendation (≥10 mcg/day) 5–6 , among those receiving supplementation, n (%)
All 356 (86.8) 270 (84.1) 189 (86.7) 169 (85.4) 131 (85.6) 121 (85.2) 114 (69.1)
By feeding type
Breastmilk 181 (91.4) 123 (94.6) 84 (97.7) 74 (94.9) 46 (90.2) 43 (93.5) 33 (73.3)
Formula 59 (83.1) 62 (69.7) 56 (72.7) 64 (78) 66 (82.5) 58 (80.6) 21 (70)
Both 115 (82.1) 85 (83.3) 49 (89.1) 30 (81.1) 18 (90) 13 (86.7) 5 (83.3)
Neither 1 (100) 1 (50) 7 (77.8) 55 (65.5)
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WIC: Special Supplemental Nutrition Program for Women, Infants, and Children; mcg: microgram; IU: International unit

1

Data presented as median (25th, 75th percentiles) for continuous variables and n (%) for categorical variables. We are describing n and % of infants meeting recommendation from total n at time of visit. Then within categories for feeding type, we describe n and % from total of each corresponding feeding type.

2

Data for continuous variables was weighted to be representative of participants enrolling in eligible WIC clinics in 2013, as per Appendix B1 of [38].

3

Categorical used unweighted proportions, counts were based on the sample for each month hence will not add up to 100% within feeding type category due to additional categories “refusal” and “don’t know”.

4

To convert mcg to IU of vitamin D × mcg by 40

5

Proportion meeting infant vitamin D recommendation is based on total vitamin D intake from diet and supplementation

6

The median vitamin D intake was 10 (95% CI: 10, 10) mcg/day across all time points among the group receiving supplementation, sample size ranged from: 410 (month 1), 321 (month 3), 218 (month 5), 198 (month 7), 153 (month 9), 142 (month 11), 165 (month 13).

FIGURE 2. Comparison of the proportion of infants meeting the vitamin D recommendation among those breastfed with and without supplementation and formula fed at each time point1.

FIGURE 2

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1The proportion meeting the recommendation differed by feeding type across all time points as assessed using chi-square test of independence (P < 0.001).

Whereas time of visit, feeding type and/or their interaction were significant predictors of both receiving supplementation and meeting the recommendation (P ranged from 0.05 to < 0.001) (Table 3), maternal nativity (P = 0.006) and parity (P = 0.01 and P < 0.001) predicted receiving supplementation and child sex (P < 0.001) and maternal race/ethnicity (P < 0.001) predicted meeting the vitamin D recommendation (Table 3). Maternal nativity outside the USA (OR = 1.45, P = 0.006), as compared born in the USA, significantly increased the odds of receiving supplementation. Being 2nd born (OR = 0.72, P = 0.01) and 3rd or subsequent born (OR = 0.56, P < 0.001), as compared to 1st born, significantly decreased the odds of receiving supplementation. Being a female child (OR = 0.80, P < 0.001), as compared to male, significantly decreased the odds of meeting the recommendation. Being non-Hispanic Black (OR= 1.43, P < 0.001) or non-Hispanic Other (OR = 1.57, P < 0.001), as compared to non-Hispanic White mother, increased the odds of meeting the recommendation (Table 3).

Table 3.

Parameter Estimates from GEE Models for Receiving Vitamin D Supplementation and Meeting the Vitamin D Recommendation (10 mcg/day) Among Infants Enrolled in WIC. Presented as OR (95% CI) P-value.1–2

Independent variables Category Outcome
Receiving vitamin D supplementation Meeting vitamin D recommendation (10 mcg/day)
Time of visit 1 month Reference Reference
3 month 1.11 (0.86, 1.43) 0.42 1.21 (0.95, 1.55) 0.12
5 month 1.11 (0.83, 1.47) 0.49 1.24 (0.93, 1.65) 0.14
7 month 0.84 (0.62, 1.14) 0.26 0.97 (0.72, 1.30) 0.82
9 month 0.69 (0.48, 1.00) 0.05 0.79 (0.55, 1.13) 0.19
11 month 0.67 (0.44, 1.02) 0.06 0.83 (0.56, 1.24) 0.37
13 month 0.45 (0.29, 0.70)* < 0.001 0.78 (0.53, 1.15) 0.21
Feeding type Breastmilk Reference Reference
Formula 0.34 (0.25, 0.46)* < 0.001 0.92 (0.68, 1.23) 0.56
Both 0.70 (0.49, 1.00)* 0.05 0.75 (0.51, 1.09) 0.13
Neither 0.50 (0.31, 0.79)* 0.003 3.81 (2.67, 5.44)* < 0.001
Maternal age, years 16–19 Reference Reference
20 – 25 0.90 (0.58, 1.40) 0.64 0.88 (0.73, 1.06) 0.19
≥26 1.43 (0.87, 2.36) 0.16 1.02 (0.83, 1.27) 0.83
Education level, grade ≤9th Reference Reference
10th–11th 0.95 (0.62, 1.46) 0.82 0.92 (0.73, 1.15) 0.46
12th 1.20 (0.79, 1.82) 0.38 0.93 (0.75, 1.15) 0.49
>12th 1.41 (0.92, 2.17) 0.11 0.87 (0.70, 1.08) 0.21
Maternal nativity USA born Rference Reference
Not USA born 1.45 (1.11, 1.89)* 0.006 0.96 (0.82, 1.12) 0.59
Parity 1st born Reference Reference
2nd born 0.72 (0.56, 0.94)* 0.01 1.12 (0.97, 1.30) 0.13
3rd or subsequent born 0.56 (0.42, 0.74)* < 0.001 1.13 (0.96, 1.32) 0.13
Child sex Male Reference Reference
Female 0.98 (0.80, 1.20) 0.89 0.80 (0.71, 0.89)* < 0.001
Maternal race/ethnicity Non-Hispanic White Reference Reference
Hispanic 0.91 (0.70, 1.18) 0.48 1.02 (0.88, 1.18) 0.81
Non-Hispanic Black 1.29 (0.95, 1.75) 0.10 1.43 (1.23, 1.67)* < 0.001
Non-Hispanic Other 1.03 (0.67, 1.58) 0.91 1.57 (1.21, 2.02)* < 0.001
Household poverty level ≤75% Reference Reference
>75% and ≤130% 1.31 (0.97, 1.76) 0.08 0.96 (0.84, 1.10) 0.62
>130% 1.16 (0.90, 1.48) 0.25 1.05 (0.87, 1.28) 0.60
Time of Visit & feeding type interaction 3 1 month*breastmilk Reference Reference
1 month*formula 1 1
1 month*both 1 1
3 month*breastmilk 1 1
3 month*formula 0.77 (0.52, 1.14) 0.20 2.04 (1.46–2.84)* < 0.001
3 month*both 0.87 (0.56, 1.35) 0.52 1.11 (0.72, 1.71) 0.64
5 month*breastmilk 1 1
5 month*formula 0.68 (0.44, 1.04) 0.07 2.90 (1.99, 4.22)* < 0.001
5 month*both 0.62 (0.37, 1.05) 0.08 1.04 (0.63, 1.71) 0.87
7 month*breastmilk 1 1
7 month*formula 0.69 (0.45, 1.07) 0.10 2.27 (1.53, 3.38)* < 0.001
7 month*both 0.75 (0.44, 1.28) 0.30 1.01 (0.61, 1.70) 0.96
7 month*neither 0.42 (0.21, 0.83)* 0.01 0.77 (0.35, 1.68) 0.51
9 month*breastmilk 1 1
9 month*formula 0.89 (0.55, 1.44) 0.63 2.33 (1.50, 3.63)* < 0.001
9 month*both 0.80 (0.43, 1.50) 0.49 1.42 (0.77, 2.59) 0.26
9 month*neither 0.67 (0.23, 1.94) 0.46 0.47 (0.22, 1.00) 0.05
11 month*breastmilk 1 1
11 month*formula 0.94 (0.55, 1.59) 0.81 2.12 (1.33, 3.40)* 0.002
11 month*both 1.11 (0.54, 2.31) 0.78 1.37 (0.68, 2.74) 0.37
11 month*neither 1.13 (0.45, 2.88) 0.79 1.02 (0.58, 1.80) 0.94
13 month*breastmilk 1 1
13 month*formula 1.57 (0.78, 3.15) 0.21 2.75 (1.69, 4.48)* < 0.001
13 month*both 1.28 (0.51, 3.18) 0.60 1.81 (0.73, 4.54) 0.20
13 month*neither 1 1
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WIC: Special Supplemental Nutrition Program for Women, Infants, and Children; GEE: Generalized estimating equation; OR: Odds ratio, CI: Confidence Interval, mcg: microgram

1

Number of participants in the GEE model = 3,830

2*

P < 0.05 after Bonferroni adjustment applied

3

Interactions ORs refer to the ratios of ORs and were used to calculate the marginal ORs. For example, for 3-month-old infants, the odds for “formula fed” infants meeting the recommendation was 0.92 (formula fed vs. breastfed) × 2.04 (3 month*formula) = 1.88 times the odds for “breastfed” infants meeting the recommendation, controlling for all other variables.

DISCUSSION

Public health agencies recommend breastfeeding as the optimal food for infants with vitamin D supplementation until the child’s diet can provide sufficient amounts.1–3,10,11 In human evolution, endogenous sun exposure likely complemented vitamin D intake from breastmilk for populations. Although subgroups of the population, such as those living at higher latitudes and with darker skin pigmentation, may be at highest risk for insufficient intake.51 With more recent sun safe practices, including no direct sunlight exposure for infants less than 6 months and use of sunscreens,52 the risks of low vitamin D intake and associated deficiency increases for all infants. Hence meeting current infant vitamin D supplement recommendation is critically important. The results from this study indicate that at the time of data collection, breastfed infants with supplementation were more likely to meet the vitamin D recommendation. However, a minority (6–12%) of infants enrolled in WIC nationally were receiving supplemental vitamin D over the first year of life. Overall, the ability to meet the vitamin D recommendation ranged between 16–36% and a little over 1/3 of infants (35%) were meeting 10 mcg of vitamin D daily by 13 months. Further, formula feeding without vitamin D supplementation cannot be relied on to meet current vitamin D recommendations as 16–43% of infants who were formula fed were meeting the recommendation. These results are consistent with a growing body of litterature24,25,54 among both WIC and non-WIC infants that suggests a US-wide problem with lack of meeting infant vitamin D guidance.1–2 Guthrie et al. identified a lower proportion of infants were below the requirement for vitamin D if participating in WIC, as compared to non-WIC (76 vs. 92%), however, the WIC sample was limited (i.e. n=375, 6–11.9 months).54

Vitamin D supplementation rates in the US have historically been much lower than other countries — 74% of breastfed infants in Canada received supplementation,26 and good adherence (≥80% of infants) was reported by 59% of European countries surveyed.27 Consistent with the current study, Simon and Ahrens25 identified 27% of US infants (0–11 months) were meeting the recommendation based on data from the 2009–2012 NHANES, with no significant changes over time. This was similar among infants participating in the Nestlé Feeding Infants and Toddlers Study (FITS) with 17% and 24% meeting the AI for vitamin D among 0–5.9 and 6–11.9 months respectively.53 Parental education by health care professionals may explain these differences as physicians’ knowledge of the recommendations has been positively associated with the likelihood of their recommending vitamin D supplementation to the parents.34,55 Another US study found 36% of providers were recommending vitamin D.56 Reasons for this may be due to lack of recognition of rickets as a concern, area and location of training as well as misconceptions and risk associated with sun exposure.55,57 More recently quality improvement initiatives have focused on providing vitamin D supplementation education in the hospital setting during the immediate postpartum period.58 Limited time during a physician visit for nutrition counseling59,60 highlights the important role of other health care professionals in supporting parental education regarding vitamin D sources and recommendations.

While this study had many strengths, there are several limitations to the findings. Geographic data are not released as part of WIC ITFPS-2 public files hence, we were unable to assess regional differences in the ability to meet recommendations. Dietary data presented in this study reflect nutrient values at the time of data collection, hence between 2013–2015. However as vitamin D content of formula is federally mandated,48 values have likely remained fairly constant over the years. Although it is possible vitamin D content of formulas may change over time, no significant changes in vitamin D fortification policies or maternal supplementation guidance were implemented since the time of data collection.61 Further, vitamin D intake from formula and supplementation was based on label claims at the time of data collection, however, this may not reflect the 10–25% overage that may be present in some products.62 The significant differences noted between only breastfed and those receiving neither formula nor breastmilk should be interpreted with caution as these are limited to older infants and based on lower sample size in this latter group. Furthermore, this study assessed vitamin D intake that may or may not reflect infant’s vitamin D status hence, the prevalence of vitamin D deficiency cannot be inferred from this study.

Implications for Research and Practice

The current study was able to show that low vitamin D intakes vary extensively among a large national WIC sample and will likely require interventions that address all infants, regardless of feeding practices - breastfed or formula fed. There is a need to explore whether the insufficient vitamin D intake observed in the current, as well as other infant studies,25,53,54 has clinical consequences for infants as the impact of vitamin D status and other associated clinical markers have not been assessed in this population. Although the current recommendation of 10 mcg is an average requirement, it is not clear whether intakes of lower amounts would be of clinical concern. Therefore, research on the effectiveness of vitamin D supplementation for high-risk maternal infant pairs is warranted as these infants may be starting life with very low vitamin D status and are at high risk for hypocalcemia and rickets, and would benefit most from supplementation.63 Further more research on the reasons for lack of adherence with supplementation from the perspective of both parents and providers is warranted. This would be needed in both WIC and non-WIC settings to inform effective strategies for increasing vitamin D supplementation.

Under federal regulations WIC is prohibited from providing anything besides the supplemental food package (hence, cannot distribute supplements), and any change would be lengthy and require legislative debate. However improving access to vitamin D supplementation alone does not appear effective in increasing supplementation rates,64 without appropriate and tailored education.65 Infant vitamin D recommendations, different supplement preparations (alcohol vs. oil based), costs/insurance coverage, and supplement delivery methods as well as appropriate health and social service referrals can be included as part of vitamin D education. Vitamin D is an approved Medicaid supplement but requires both a health screening and prescription by a provider for coverage. Hence, future efforts exploring how the collaboration between WIC, pediatric leadership groups and those entities providing maternal and infant services might promote broad changes in vitamin D awareness, policies and actions.

Supplementary Material

1

Practice Points.

  1. A high proportion of infants participating in WIC were not meeting the current vitamin D recommendation.

  2. The WIC program is one resource for increasing the number of American infants meeting D recommendations yet, a coordinated health care approach is warranted.

Source of support:

No funding to declare

Abbreviations:

(AAP)

American Academy of Pediatrics

(GEE)

Generalized estimating equation

(ITFPS-2)

Infant Toddler Feeding Practices Study-2

(NHANES)

National Health and Nutrition Examination Survey

(WIC)

Special Supplemental Nutrition Program for Women, Infants, and Children

(US)

United States

(USDA)

United States Department of Agriculture

Footnotes

Conflict of Interest and Funding Disclosure: All authors have no conflicts of interest

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