Epidemiologic studies from South Asian countries have reported vitamin D deficiency among all age groups. However, there is very little information on vitamin D levels, especially in the vulnerable populations (pregnant/breast feeding mother and infants) in Sri Lanka. More data on vitamin D status of such populations will be important for policy decisions to be made at a national level. Similarly, it will be valuable for healthcare programs in other countries (e.g., United States, Australia, Europe, and Canada) as Sri Lankans are a fast-growing migrant population to those countries. The purpose of this study was to investigate maternal vitamin D status and its effects on infants in a state sector tertiary care centre in Sri Lanka. This prospective cohort study was conducted on 140 healthy pregnant mothers in the third trimester (mean gestational age 39±1 weeks). Blood was collected for 25(OH)D and parathyroid hormone (PTH). Sun exposure and feeding patterns of the infants were recorded based on maternal reporting. Mean age of the infants at follow-up visit was 36±7 days. Vitamin D (25 (OH)D) deficiency (<25 nmol/L) was observed in 12% pregnant mothers, 5% lactating mothers, and 63% infants. Insufficiency (<50 nmol/L) was found in an additional 51% and 43% in pregnant and lactating mothers and 25% of infants. Mean 25(OH)D was higher in pregnant (46.4±17.5 nmol/L) and lactating (51.9±17.0 nmol/L) mothers than infants (28.1±13.7 nmol/L). Maternal vitamin D level during pregnancy was a significant risk factor (OR: 6.00, 95%CI: 1.522-23.655) for infant deficiency and insufficiency. Sun exposure of infants showed a significant positive correlation with vitamin D level (OR: 3.23, 95%CI: 1.19-8.68). In conclusion, the presence of Vitamin D deficiency/insufficiency is higher in infants compared to pregnant/lactating mothers. Low maternal 25(OH)D during pregnancy was a risk factor for deficiency in infants. Although majority of lactating mothers had sufficient vitamin D, most of their exclusively breastfed offspring were deficient.
Countries near the equator receive more sunlight throughout the year. However, sun-seeking behavior is uncommon in these countries due to the hot climate. Epidemiological studies from our neighboring country, India, have shown high prevalence of low vitamin D (25 OHD (< 50 nmol/L) in all age groups: neonates, preschool and school children, pregnant women, and adult males [
Growing infants are more vulnerable to develop vitamin deficiencies. Cultural influences maintain a high breastfeeding rate in our country. Thus, the nutrition of infants solely depends on the maternal levels during their first 6 months of exclusive breastfeeding period. Vitamin D deficiency among infants and their breastfeeding mothers is not reported in Sri Lanka to date. Vitamin D deficiency leading to rickets and hypocalcaemic seizures has been shown among breastfed infants in Southern India [
There are no guidelines on vitamin D supplementation during pregnancy, infancy, or other age groups in Sri Lanka [
Thus, this present study was undertaken to determine the vitamin D status in pregnant mothers, lactating mothers, and their infants and to investigate the effect of maternal vitamin status on infant vitamin D levels, in a tertiary care centre in Sri Lanka.
Healthy women aged 18 years or more with singleton pregnancies in their 3rd trimester were recruited for this prospective cohort study at the antenatal clinic in a teaching hospital in Colombo district. Based on a previous study, sample size was calculated [
Following informed written consent, a pre-tested interviewer administered questionnaire was used to collect information on socio-demography, nutrition, past and present health and well-being. A physical examination, including anthropometry, was performed on all mothers at enrollment. Blood samples (4 ml) were collected from the eligible pregnant mothers and serum was stored at -20°C for laboratory analysis.
Infant-mother pairs were reviewed at 4-6 weeks of postpartum. Reminders via telephone calls (maximum of 3) and a stipend for transport were provided for these parents. Prematurity, congenital anomalies, or any neonatal problems in babies requiring high dependency were considered as exclusion criteria. Detailed physical examination of the infant, including weight, length, head circumference (OFC), and size of the anterior and posterior fontanel was recorded. Sun exposure and feeding (exclusive breastfeeding, formula feeding, and mixed feeding) of the infant were recorded based on maternal reporting. The approximate duration (in minutes) of sun exposure per day, frequency (days) per week, and infant clothing were taken to quantify the amount of sun exposure. Blood samples were drawn from both lactating mothers and their infants for laboratory analysis.
Biochemical analysis was performed at the University of Sri Jayewardenepura, Colombo, using the following methods: Vitamin D3 (25OHD) was measured by VIDAS® 25 OH Vitamin D Total using the Enzyme Linked Fluorescent Assay (ELFA). It has good correlation with the Liquid Chromatography-Mass Spectrometry reference method with good cross reactivity with vitamin D2 (91%) and D3 (100%). Intact PTH was measured by DRG (EIA-3645) ELISA method. Intra-assay variability is 6.08% for low concentration (32.4 pg/mL) and 3.68% for higher concentration (178.2 pg/mL). Interassay variability is 3.6% for low concentration (30.3 pg/mL) and 2.85 for higher concentration (159.1 pg/mL). Analysis of calcium, inorganic phosphorous (IP), and alkaline phosphatase (ALP) was performed by colorimetric method using the Thermo Scientific Konelab 20XT Analyzer.
Data were analyzed using the Statistical Package for the Social Sciences (SPSS) version 15.0. Vitamin D deficiency (VDD), vitamin D insufficiency (VDI), and sufficiency are defined as < 25 nmol/L, 25-50 nmol/L, and ≥50 nmol/L of 25OHD levels, respectively [
The STROBE cohort reporting guidelines were used during the manuscript preparation.
We recruited a total of 140 pregnant mothers. Twenty-five (18%) mothers/infants were excluded due to following reasons: not attending the follow-up visit (n=19), prematurity (n=3), congenital anomalies (n=1), and receiving neonatal intensive care (n=2). A final sample included 115 mothers and 112 infants (consent was not given for blood sampling for 3 infants).
Mean (SD) age of the infants at follow-up visit was 36±7 days. Almost equal gender distribution (M:F of 54:58) was observed among them. Mean (SD) age of the pregnant mothers was 29 (±6) years. Most (81%) mothers were housewives. Majority of mothers were Sinhalese (77.4%) and had either primary or secondary education (93.9%). Almost all of the study population is from low and middle income families (89%).
Mean values of 25OHD, PTH, and biochemical parameters are given in Table
Biochemical parameters of the study population.
25(OH)D | PTH | IP | ALP | Calcium | |
---|---|---|---|---|---|
Pregnant mothers (n=115) | 46.4 ± 17.5 | 23.7 ± 22.0 | 1.3 ± 0.2 | 193.6 ± 172.0 | 2.3 ± 0.2 |
Lactating mothers (n=115) | 51.9± 17.0 | 41.2 ± 38.1 | 1.3 ± 0.2 | 121.1 ± 25.4 | 2.2 ± 0.1 |
Infants (n=112) | 28.1 ± 13.7 | 28.6 ± 22.9 | 2.1 ± 0.2 | 415.7 ± 107.6 | 2.5 ± 0.1 |
Mean±SD unless otherwise indicated.
25(OH)D: vitamin D; PTH: Parathyroid Hormone; IP: Inorganic Phosphorous; ALP: Alkaline Phosphatase.
Low 25 (OH)D levels in pregnant/lactating mother and infants.
Groups | VDD | VDI |
---|---|---|
Pregnant mothers (n=115) | 14 (12) | 58 (50.9) |
Lactating mothers (n=115) | 06 (5) | 49 (42.6) |
Infants (n=112) | 71 (63) | 28 (25.0) |
Number (%) unless otherwise indicated.
VDD: Vitamin D Deficiency; VDI: Vitamin D Insufficiency.
Correlation between serum 25(OH)D and other biochemical parameters.
Group | Correlation r (p value) | |||
---|---|---|---|---|
PTH | ALP | Calcium | IP | |
Pregnant mothers (n=115) | - 0.295 (0.002) | - 0.084 (0.392) | - 0.019 (0.845) | 0.163 (0.096) |
Lactating mothers (n=115) | - 0.249 (0.011) | - 0.165 (0.092) | - 0.068 (0.492) | - 0.068 (0.490) |
Infants (n=112) | - 0.283 (0.004) | - 0.067 (0.502) | 0.122 (0.221) | 0.244 (0.013) |
25(OH)D: vitamin D; PTH: Parathyroid Hormone; IP: Inorganic Phosphorous; ALP: Alkaline Phosphatase.
Mean weight at birth and at follow up visit were 3000 ± 440 g and 4063 ± 713 g respectively. In Sri Lanka less than 2500 g is considered as low birth weight. Low birth weight was observed in 12.2%. The mean weight gain of the population was 1060 ± 544 g. However, two babies from this study population showed poor weight gain at follow-up visit.
Correlations between 25 OHD and weight (r = -0.172, p=0.069) and OFC (r =-1.61, p=0.089) at follow-up visit were not significant. Although correlation between length and vitamin D level was positively correlated, this finding was not statistically significant (r= 0.198, p=0.557). All these correlations were analyzed after eliminating confounding factors (gestational age, gender of the baby, and the height of the mother). None of the infants had evidence of rickets (craniotabes, wide skull sutures, rachitic rosary, and enlargement of the wrists and ankles) or hypocalcaemic convulsions.
Most of the infants (85.2%) were exposed to the sun either with (only a diaper) or without clothes. None of the babies have used sunscreen in this population. Maximum duration of exposure was 60 minutes/day. Duration of sun exposure had a significant effect on infant vitamin D levels (odds ratio: 3.23, 95% CI: 1.19-8.68). Majority (98.3%) of the infants was exclusively breastfed and two babies were on mixed feeding (formula feeding and breastfeeding).
VDD was observed more during pregnancy than lactation (Table
The odds ratio was calculated to compare maternal and infant vitamin D levels. Maternal deficiency or insufficiency during pregnancy was a significant risk factor for infant vitamin D deficiency/insufficiency (OR: 6.000; 95%CI: 1.522-23.655; p value: 0.009). Lactating mother’s vitamin D level was not seen as a risk factor for infant vitamin D deficiency/insufficiency (OR: 3.122; 95%CI: 0.789-12.217; p value: 0.127).
This study reports high rates (88%) of vitamin D deficiency/insufficiency (<50 nmol/L) among infants in a single centre in Western Sri Lanka. Jain et al. have reported high rate of vitamin D deficient mothers (81%) and their infants aged 2.5-3.5 months (66.7%) in New Delhi, India [
There are limited data on vitamin D levels in children and adults in Sri Lanka. Marasinghe et al. have reported <50 nmol/L among 35% in preschool children (2-5 years) in a study conducted in the Western Province [
25(OH)D passes from the placenta into the bloodstream of the fetus. Many studies have shown that maternal 25(OH)D during pregnancy has a good correlation with cord blood levels at birth [
After birth, vitamin D status of an exclusively breast fed infant depends on vitamin D of milk and sun exposure. Human breast milk and unfortified cow’s milk have very little vitamin D [
However, the supply of 25(OH)D through breast milk increases when vitamin D supplements are provided [
Clinical Practice Guidelines in Australia do not provide vitamin D supplementation to all exclusively breastfed newborns unless there are additional risk factors [
Kovacs has reported that vitamin D deficiency during pregnancy and lactation can lead to hypocalcaemia and rickets in infants [
Expected rise of PTH was not seen in the majority of the study population. We considered the threshold for secondary hyperparathyroidism to be 66.5pg/mL. Souberbielle et al. have shown that PTH starts to rise >46 pg/mL when 25OHD is falling below 30 nmol/L [
The American Academy of Pediatrics has recommended that infants below six months should be kept out of direct sunlight because of growing concerns about over exposure to sun and skin cancer [
Vitamin D deficiency/insufficiency is a likely risk factor for obesity in children [
There were a few limitations in this study. Present sample did not represent all ethnic, sociodemographic, and geological variations in Sri Lanka. Study sample was restricted to mother-infant pairs from lower and middle socioeconomic backgrounds in an urban setting who seek care from state sector hospitals. Further, due to nonavailability of equipment and funds the bone mineral content, density, and nonskeletal effects such as immune dysfunction were not assessed in this cohort of pregnant mothers and their infants.
The present study shows that vitamin D deficiency/insufficiency is seen among pregnant and lactating mothers and their offspring from a tertiary care centre in Sri Lanka. However, in contrast to mothers, infant vitamin D deficiency was higher. Maternal vitamin D deficiency during pregnancy was a risk factor for vitamin D deficiency in infants. We suggest further studies on vitamin D levels in a nationally representative sample of mothers and infant pairs to confirm the present findings to take a step forward towards formulation of guidelines for supplementation. Moreover, investigations into the suitability of the current cut-off values for our population, long-term impact of vitamin D deficiency in infants, and biological significance of PTH as a marker of vitamin D deficiency are other important areas for future research.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
Financial assistance by a University Research Grant (Grant No: ASP/01/RE/MED/2015/40).
The authors express their sincere gratitude to the University of Sri Jayewardenepura, Sri Lanka, for funding the study. We would also like to acknowledge the staff of Professorial Units of Pediatrics, Obstetrics, & Gynecology for their support and Dr. B.J.C Perera, Senior Consultant Pediatrician, for his contribution in language editing.