Intergenerational vitamin D deficiency: Correlation between maternal and neonatal levels and the role of supplementation

INTRODUCTION

Vitamin D plays a vital role in bone metabolism and maintaining overall bone health. The primary ways humans obtain vitamin D are through sun exposure and dietary intake.^[1] This fat-soluble vitamin, known as 25-hydroxyvitamin D (25-OH vitamin D), is essential for regulating calcium metabolism in both children and adults. During pregnancy, the body’s demand for calcium rises significantly, making vitamin D crucial for maternal well-being, foetal bone development and ensuring favourable maternal and neonatal outcomes.^[2]

Vitamin D deficiency is highly prevalent among pregnant women and breastfed infants in regions such as the Middle East and Asia, with rates ranging from 46-90.3% in pregnant women and 81-90.3% in infants.^[3-5] Research indicates that plasma levels of the active form of vitamin D increase approximately twofold during early pregnancy compared to pre-pregnancy levels, reaching their peak in the third trimester before returning to baseline or lower levels during lactation.^[6-8] Since monohydroxy vitamin D crosses the placenta, maternal and cord blood levels of this vitamin are strongly correlated.^[8-10]

Physiological changes during pregnancy help meet the foetal growth requirements, directly impacting vitamin D homeostasis. As the foetal vitamin D status depends on maternal levels, a deficiency during pregnancy results in low vitamin D levels in the foetus as well. This deficiency is widespread globally due to lifestyle factors such as reduced sun exposure, sunscreen application and insufficient dietary intake of vitamin D.^[11]

The prevalence and severity of vitamin D deficiency depend on the criteria used in different studies. According to the Endocrine Society, serum 25-OH vitamin D levels below 20 ng/mL indicate deficiency, a condition associated with persistently elevated parathyroid hormone levels and reduced intestinal calcium absorption.^[12] The optimal protective range for blood 25-OH vitamin D is between 30 and 100 ng/mL, as calcium absorption is maximised at 30 ng/mL, and parathyroid hormone levels continue to decline.^[13] The Institute of Medicine classifies 25(OH)D levels below 12 ng/mL as deficient, whereas the Endocrine Society sets the deficiency threshold at 20 ng/mL.^[12,14]

Despite its tropical location, the Indian subcontinent has a high prevalence of vitamin D insufficiency from 50-94% in various studies.^[15] Although breastfeeding is widely recognised as beneficial, it does not provide sufficient vitamin D to meet an infant’s daily requirement of 400 IU, as breast milk contains only 20–70 IU/L of vitamin D, particularly if the mother is deficient and the infant has limited sun exposure.^[16] The Indian Academy of Pediatrics recommends supplementing infants with 400 IU of vitamin D per day.^[17] A recent study by Rabbani et al. (2021) highlighted a significant deficiency of vitamin D among pregnant women and their newborns, reinforcing the strong association between maternal and neonatal 25-OH vitamin D levels.^[18]

Considering the above factors, this study was done to estimate serum 25-hydroxy cholecalciferol levels along with serum calcium and serum phosphorus levels, being intricately related in mother-bay dyads and to find a correlation between them and improvement in their levels with supplementation as per standard protocols during the first half of infancy.

MATERIAL AND METHODS

This prospective cohort study was conducted in the neonatal unit of the department of Pediatrics of a government medical college in northern India over a period of 1 year after approval from the ethical committee. All the prospective mothers admitted to the labour room were approached for the study after proper consent if birth took place in office hours. All the neonates born to apparently healthy mothers who were spontaneously breathing at birth and without any apparent congenital malformation were included in this study. The neonates were classified as term appropriate for gestational age (AGA), preterm AGA, term small for gestational age (SGA) and preterm SGA as per Fenton’s chart.

With a prevalence of vitamin D deficiency of around 80%, confidence interval of 95% and margin of error of 7.5%, the sample size was 62 after putting values in the formula n = Z²⋅p ⋅(1−p) E²

Where as

• Z is the Z-value (1.96 for a 95% confidence level)

• p is the prevalence (0.80)

• E is the margin of error (0.75).

Maternal venous samples were taken at the time of delivery and 25-OH vitamin D, calcium and phosphorus levels were measured after freezing the sample at −20 °C and then centrifuging it. The samples of the newborn were taken at birth by cord blood and were sent for 25-OH vitamin D, calcium and phosphorus levels after freezing at −20 °C and centrifugation. 25-OH vitamin D was measured by chemiluminescence microparticle immunoassay by Abbott Architect. The measuring range for the original assay is 32.5–240 nmol/L. Vitamin D <20 ng/mL was considered a deficiency.^[12]

Calcium was determined using the calcium assay (CA) method on the Dimension^® clinical chemistry system using the CA Flex^® cartridge. The CA Flex^® cartridge (Catalogue No. DF23A) is a prepackaged reagent cartridge specifically designed for use with the Dimension^® clinical chemistry system. It contains all the necessary reagents for performing the CA method. The system is calibrated using the Chemistry (CHEM) I Calibrator (Catalog No. DC18B or DC18C) with known concentrations of calcium. The assay range for calcium determination is 5.0–15.0 mg/dL (1.25–3.75 mmol/L. Total serum and ionic serum calcium <8 mg/dL and <4.8 mg/dL in term and <7 mg/dL and 4 mg/dL in preterm were defined as neonatal hypocalcaemia.^[19] Phosphorus was determined by phosphate (PHOS) method, which is a modification of the classical phosphomolybdate method. The PHOS Flex reagent cart (Catalog No. DF61A) is a set of reagents designed for use with the Dimension^® clinical chemistry system. The CHEM 2 calibrator (Catalog No. DC20) is used to calibrate the Dimension^® clinical chemistry system. A correlation coefficient of 0.9 indicates a very high degree of correlation between the measured values and the true values, suggesting that the method is highly reliable and accurate. Phosphorus <2.5 mg/dL was defined as a deficiency. All the findings were recorded in the well-designed pro forma. Calcium, phosphorus, and vitamin D supplementations were done as per the standard protocols. The neonates were then followed up, and their levels were repeated at 6 weeks and 6 months of age. The recorded data were compiled and entered in a spreadsheet (Microsoft Excel) and then exported to the data editor of the Statistical Package for the Social Sciences (SPSS) Version 20.0 (SPSS Inc., Chicago, Illinois, USA). Continuous variables were expressed as mean ± standard deviation (S.D.) and categorical variables were summarised as frequencies and percentages.

RESULTS

Among the 83 mother-baby dyads enrolled in the study, 57.8% neonates were male (48) and 42.2% were female (35). 78.3% (65) were term and a significant majority, 83.1% (69) were appropriate for age, as shown in Table 1.

52 out of 83 (62.7%) of mothers and 72 (86.7%) neonates had vitamin D deficiency. 17 out of 18 (94.4%) preterm neonates and 55 out of 65 (84.6%) term neonates had vitamin D deficiency, which was not statistically significant with P = 0.276.

Out of the 14 SGA neonates, 13 were found to have a vitamin D deficiency, which corresponds to a prevalence of 92.9%. Among the 69 neonates AGA, 59 had a vitamin D deficiency, amounting to a prevalence of 85.5%. Although SGA neonates were more affected than AGA neonates, this was not statistically significant with P = 0.681.

The prevalence of calcium deficiency was 9.6% in neonates (22.2% in preterm and 6.2% in term) and 1.2% in mothers. In our study group, no neonate or mother was found to have phosphorus deficiency.

Overall, the study results show significant changes in vitamin D, calcium and phosphorus levels from birth to 6 months of age. Vitamin D and calcium levels showed a significant increase over time, while phosphorus levels experienced a decrease at 6 weeks, followed by a slight increase at 6 months. All these changes were statistically significant, with P < 0.001 as shown in Table 2.

The intergroup comparisons show statistically significant changes in vitamin D and calcium levels at all 3 time points, with levels consistently increasing over time. Phosphorus levels showed significant changes between birth and 6 weeks and 6 weeks and 6 months, but there was no significant difference between birth and 6 months, indicating that phosphorus levels fluctuated but ultimately returned to their initial values, as shown in Table 3.

The Pearson correlation coefficient (r) for vitamin D levels between neonates and their mothers is 0.8, indicating a strong positive correlation with P < 0.001, which means this correlation is statistically significant. The Pearson correlation coefficient (r) for calcium levels is 0.4, indicating a moderate positive correlation with P < 0.001, indicating that this correlation is statistically significant. The Pearson correlation coefficient (r) for phosphorus levels is 0.3, indicating a moderate positive correlation with P = 0.003, indicating that this correlation is statistically significant. The results show that there are positive correlations between the levels of vitamin D, calcium and phosphorus in mothers and their infants. The correlation is strongest for vitamin D, followed by calcium and phosphorus, as shown in Table 4.

DISCUSSION

In our study, we started with 104 pairs of mothers and neonates. The mothers were sampled in the third trimester at the time of delivery, but the pairs were reduced to 83 for data analysis due to the loss of 21 neonates during the follow-ups.

The prevalence of vitamin D deficiency in mothers at the time of delivery and in neonates at birth was 62.7% and 86.7%, respectively. This was comparable to most studies done previously in different parts of the world, like Jaiswal et al.^[20] (65.7% and 78.4%), Rabbani et al.^[18] (61.5% and 99.5%) and Arora et al.^[21] (86% and 85%). The mean levels of vitamin D in mothers and neonates at birth were 21.1 ± 15 and 13.7 ± 6.8 ng/mL which were similar to values found by Jaiswal et al.^[20] (16.2 and 15.2 ng/mL) and Arora et al.^[21] (12.5 ng/mL and 12.3 ng/mL). Preterm and SGA neonates were more affected by vitamin D deficiency than term and appropriate for gestational age neonates, similar to the study of Burris et al.^[22] although it was not statistically significant.

Our study found a very strong correlation between maternal vitamin D levels at the time of delivery and vitamin D levels in neonates at birth, with Pearson’s correlation coefficient 0.8 and P < 0.001, similar to studies done by Jaiswal et al.^[20] (Pearson R-value of 0.7 and P < 0.001), Rabbani et al.^[18] (Pearson’s R value of 0.7 and P < 0.001) and Arora et al.^[21] (Pearson R value of 0.8 and P = 0.001). In our study, mean serum calcium and phosphorus levels were (8.9 ± 0.8 and 4.5 ± 0.9) and (8.5 ± 1.2 and 5.0 ± 1.0) in neonates at birth. The calcium deficiency was seen in 1.2% of mothers and 9.6% of neonates. None of the participants had phosphorus deficiency. Very few studies have been done on serum calcium and phosphorus in mother-baby dyads, like study done by Shabanian et al.^[23] from Iran, who found mean serum calcium and phosphorus in mothers (8.6 ± 0.4 and 2.8 ± 1.5) and in neonates at birth (9.9 ± 0.64 and 2.9 ± 2.2), with very high deficiency rates although comparable for both calcium and phosphorus in mothers (25% and 1%) and in neonates at birth (9.2% and 15.8%). The levels of calcium and phosphorus were significantly correlated in mother-baby dyads with P < 0.05 in our study. High-deficiency rates may be due to dietary differences or geographical location or in the case of neonates due to more preterm babies than in our study.

In the study, the follow-up of the neonates was done and neonates with vitamin D deficiency were treated with therapeutic doses of vitamin D and those without deficiency were supplemented as per current recommendations. The mean levels of vitamin D and serum calcium at birth, 6 weeks and 6 months were 13 ng/mL, 22 ng/mL, 48 ng/mL and 8.5 mg/dL, 8.9 mg/dL, 9.5 mg/mL, respectively. A significant improvement in the levels of vitamin D and calcium was seen at 6 weeks and 6 months with P < 0.001. This was like studies done by Tan et al.^[24] and Lin et el.^[25] At birth, 86.7% neonates were vitamin D deficient which decreased to 42.2% at 6 weeks and 6.0% at 6 months of life.

CONCLUSION

This study highlights the widespread prevalence of vitamin D deficiency in both mothers during the third trimester and their neonates at birth in North India. A significant positive correlation was found between maternal and neonatal vitamin D levels at birth. Our findings indicate that preterm and SGA neonates are more affected by vitamin D deficiency than term and AGA neonates, although this was not statistically significant.

Routine supplementation with vitamin D showed a statistically significant improvement in serum vitamin D and calcium levels in infants at 6 weeks and 6 months. These results underscore the importance of monitoring and addressing vitamin D levels in expectant mothers and neonates to improve neonatal health outcomes. The findings are consistent with previous studies conducted globally, affirming the need for public health interventions to combat vitamin D deficiency in this vulnerable population.

Further research is needed to explore the long-term health impacts of early vitamin D supplementation and to develop targeted strategies for preventing and treating vitamin D deficiency in both mothers and their infants.