The Influence of Prenatal Vitamin D Supplementation on Dental Caries in Infants

Early childhood caries (ECC) is a multifactorial disease, influenced by environmental factors, such as dietary intake, oral microbiome and social determinants of health.^1,2 Many children with ECC require rehabilitative surgery in hospital under general anesthesia.³ ECC is known to impact childhood health and well-being.⁴

The role of diet in the development and prevention of caries was the focus of much research during the 1920s and 1930s.^5-7 Lady May Mellanby’s pioneering studies⁵ explored the impact of vitamin D rich diets on caries and tooth resistance. Her 1928 paper concluded that diets rich in vitamin D helped prevent caries initiation and limited or arrested the spread of caries. Conversely, diets low in vitamin D showed no such suppression.⁵

The active form of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)₂D] regulates blood calcium by affecting the absorption of calcium from the intestines.⁸ Its role in calcium and phosphorus homeostasis is key in the proper formation and maintenance of hard tissues,⁸ including mineralization of teeth.^9,10 Vitamin D is also required in several cellular pathways including the immune response, cellular differentiation, proliferation and apoptosis.¹¹ Therefore, vitamin D may offer some protection against cariogenic microorganisms.^12-14

Vitamin D is obtained exogenously through diet and supplements or endogenously via solar radiation. Populations residing in northern latitudes are disadvantaged regarding endogenous production, especially during the winter months (i.e., November to March) when sun-induced vitamin D synthesis in the skin is severely limited by less exposure to sunlight as well as latitude, altitude and other environmental factors.¹⁵

In Canada, milk, margarine and milk alternatives are fortified with vitamin D and are the major sources of dietary vitamin D.¹⁶ Health Canada lists the dietary reference intake (DRI) of vitamin D as 600 international units (IU) for all age groups from 1 to 70 years and for pregnant and lactating women.¹⁷ Most people can achieve this DRI through daily supplements, including prenatal vitamins, which supply 400 IU vitamin D. The Canadian Paediatric Society recommends that infants receive 400 IU daily in the summer and up to 800 IU during the winter months.¹⁸

Clinically, measurement of vitamin D status is based on the dominant form of plasma vitamin D, 25(OH)D, which accounts for both cutaneous and dietary sources.¹⁹ Achieving optimal levels of 25(OH)D is especially important for pregnant women as fetal concentrations rely mainly on maternal concentrations. Optimal concentrations are ≥ 75 nmol/L.²⁰ However, the Institute of Medicine (IOM) lists adequate concentration as ≥ 50 nmol/L.²¹ Vitamin D inadequacy has been found to be associated with many disease outcomes.^11,22 Prenatal vitamin D deficiency has also been identified as a possible risk factor for ECC.¹²

Cockburn et al.²³ reported that 400 IU of vitamin D daily during pregnancy was significantly associated with a lower prevalence of enamel defects in offspring. Furthermore, a recent study by Schroth et al.¹² reported, for the first time, that maternal prenatal vitamin D levels may influence the development of ECC: mothers of infants with ECC demonstrated lower prenatal 25(OH)D levels than mothers of caries-free infants. It is during the second trimester, when primary tooth calcification begins in utero, that maternal vitamin D status affects the teeth.

The purpose of this study was to investigate whether prenatal vitamin D supplementation of pregnant women during pregnancy increases 25(OH)D levels in the umbilical cord and whether that affects caries development in their infants.

Methods

This study was undertaken because of a government priority in response to recommendations made to Manitoba’s Minister of Health by the Maternal and Child Healthcare Services Taskforce to improve prenatal 25(OH)D status and potentially improve infant oral health.²⁴ The taskforce recommended prenatal supplementation with 100 000 IU of vitamin D.²⁴

Participants were recruited from the Women’s Hospital Outpatient Department of the Health Sciences Centre, Winnipeg, Canada (latitude 49°53′ N) during 1 of their prenatal appointments. This clinic primarily serves an inner-city clientele, including Indigenous women, those with limited socioeconomic status (SES) and newcomers to Canada. Participants self-selected to 1 of 2 groups. Those in the intervention (i.e., supplementation) group were recruited during their first or second trimester and consented to take 2 oral doses of 50 000 IU of vitamin D in their second and third trimesters. Women not willing to take the vitamin D supplements and those recruited past the window of opportunity to be in the intervention group served as controls.

All participants received standard prenatal care, including prenatal vitamins. Those with known hypercalcemia, kidney disease, inborn errors of metabolism, chronic illness (excluding diabetes) and current involvement in a related clinical study were excluded.

All participants completed a questionnaire administered via interview; it collected information on demographics, nutrition, intake of foods containing vitamin D and sunlight exposure. Postal codes were used to examine socioeconomic status (SES) by calculating socioeconomic factor index (SEFI), an area-based measure. SEFI is derived from Canadian census data for unemployment rate at age ≥ 15, average household income at age ≥ 15, proportion of single-parent households and proportion of the population age ≥ 15 years not graduating from high school. Those in the intervention group received 2 oral doses of 50 000 IU vitamin D, administered by a nurse in the outpatient clinic during scheduled prenatal visits. The first dose was given during the second trimester, the second during the third trimester. This supplementation was in addition to regular prenatal vitamins.

At delivery, cord blood was collected and assayed for 25(OH)D. Samples were analyzed by Hospitals in Common Laboratory (HICL), Mount Sinai Hospital, in Toronto, Canada, using chemiluminescence immunoassay. In this study, thresholds used to quantify 25(OH)D levels were ≥ 75 nmol/L (optimal based on HICL and Winnipeg’s Health Sciences Centre), ≥ 50 nmol/L (adequate based on IOM) and < 35 nmol/L (common threshold used to denote deficiency).^14,21,25

Participants and their infants were then invited to return for a follow-up examination around the child’s first birthday. A questionnaire was administered to collect information on demographics, birthweight, prematurity and current or past health problems. Information regarding diet, oral hygiene, timing of the eruption of the first tooth and dental home status was also obtained. Primary dentition was assessed by the principal investigator (RJS) who was blinded to groups and cord 25(OH)D levels. ECC and severe ECC (S-ECC) were defined according to current standards.1 Caries scores using the dmft index (i.e., combined total for decayed, missing due to caries and filled primary teeth) and dmfs index (i.e., combined total for decayed, missing due to caries and filled primary tooth surfaces) were also recorded. Developmental defects of enamel, such as enamel hypoplasia, were assessed.²⁶

Data were entered into a database (Excel, Microsoft, Redmond, Wash.) and analyzed using statistical software (v. 9, NCSS, Kaysville, Utah) and R. Analysis involved descriptive statistics (frequencies, means ± standard deviation [SD]) and bivariate tests, Χ² tests, t tests and analysis of variance (ANOVA). Linear regression, logistic regression and negative binomial analyses were performed. A p value ≤ 0.05 was considered significant.

This prospective cohort study was approved by the University of Manitoba’s Biomedical Research Ethics Board. Participants provided written informed consent.

Results

Overall, 283 women were enrolled in the study (mean age 23.4 ± 5.6 years): 141 in the intervention group and 142 in the control group. No significant difference in age was found between groups (22.9 ± 5.3 years intervention v. 24.0 ± 5.9 control, p = 0.11). There was also no significant difference between participants in the intervention and control groups in terms of number of children (2.0 ± 1.6 v. 2.2 ± 1.8, p = 0.38) or socioeconomic characteristics, such as household income (p = 0.99), receiving social assistance (p = 0.26), education level (p = 0.85) and employment level of the mother (p = 0.72) or mother’s partner (p = 0.46). The groups were relatively well matched for prenatal vitamin use (p = 0.21), skin colour as rated by the participant (p = 0.34) and milk consumption (p = 0.064). Other characteristics of participants appear in Table 1.

Cord 25(OH)D concentrations were available for 216 participants (76.3%); the mean 25(OH)D level was 49.6 ± 24.3 nmol/L (Table 1). There were no significant differences between the intervention and control groups in terms of mean 25(OH)D cord level or the proportion attaining concentrations ≥ 50 nmol/L and ≥ 75 nmol/L (Table 1). Multiple regression analysis revealed that season of delivery and skin colour were significantly and independently associated with cord 25(OH)D levels (Table 2). Those who delivered in winter and those with darker skin colour had significantly lower 25(OH)D levels. Meanwhile, supplementation was not associated with higher mean 25(OH)D levels.

For follow up, 175 participants (61.8%) returned with their infants. Reasons for loss to follow up included moving (n = 4; 1 intervention and 3 control), fetal demise (n = 9; 6 intervention and 3 control) and infant placed in foster care (n = 11, 7 intervention and 4 control).

The proportion of study participants returning for follow up was consistent between groups (63.8% intervention v. 59.9% controls, p = 0.49). However, returning participants had significantly higher cord 25(OH)D levels at delivery than those lost to follow up (52.6 ± 23.1 nmol/L v. 44.0 ± 25.7 nmol/L, p = 0.013) and were significantly older (24.1 ± 5.6 years v. 22.3 ± 5.5 years, p = 0.01). Likewise, women who attended the follow-up study appointment were more likely to have completed high school or beyond than those lost to follow up (50.9% v. 37.0%, p = 0.024). They were also more likely to have taken prenatal vitamins than those lost to follow up (86.3% v. 75.9%, p = 0.028). Of interest, the proportion of women receiving government assistance was similar among those returning and those lost to follow up (42.8% v. 50.0%, p = 0.24) and among those who were regular milk drinkers (88.0% v. 86.1%, p = 0.45). However, women returning for follow up were less likely to be of in a lower income level than those lost (64.0% v. 80.0%, p = 0.042). There was also no difference in the prevalence of participants who identified as Indigenous between those returning and those lost to follow up (p = 0.086).

The mean age of returning infants was 19.7 ± 8.1 months, and this did not differ between groups (19.4 ± 7.8 months v. 20.0 ± 8.5 months, p = 0.60). Overall, 52% were male.

Table 1 shows results from the follow-up visit. There were no differences between groups in how much milk mothers consumed during pregnancy (p = 0.26), prenatal vitamins taken during pregnancy (p = 0.71) or the child’s current health (p = 0.67).

Overall, 26.3% of the infants had both ECC and met the criteria for S-ECC; mean decayed tooth (dt) score was 0.94 ± 2.16 teeth (range 0–16). Other dental findings appear in Table 3. There was no apparent difference in the proportion of infants with S-ECC between the two groups (22.2% intervention v. 30.6% control, p = 0.21). Caries tooth and tooth surface scores did not appear to differ statistically between infants born to mothers in the intervention and control groups (Table 3). Poisson regression revealed a statistically significant inverse relation between cord 25(OH)D levels and dt scores (p = 0.001).

Two negative binomial model analyses were undertaken for dt scores (Table 4). Model 1 included which group they were in, while model 2 included 25(OH)D levels. Overall, SEFI, child age and enamel hypoplasia were significantly and independently associated with higher dt scores. In mode…