Maternal vitamin D status in pregnancy and offspring bone development: the unmet needs of vitamin D era

The Influence of Maternal Levels of Vitamin D and Adiponectin on Anthropometrical Measures and Bone Health in Offspring

BACKGROUND

From the conception onward, certain parameters associated with maternal health may affect foetal body composition, growth and bone mineral content. The objective of the study was to determine the association between maternal vitamin D and adiponectin status with the anthropometrical measures of newborns, and bone health status measured by Quantitative Ultrasound (QUS) at birth.

METHODS

Circulating 25OHD and adiponectin concentration were measured in 73 pregnant women. Correlations with the anthropometrical measures and bone health status in their infants were studied. Bone health was evaluated using QUS with the measurements of speed of sound (SOS, in m/s) and Z score on the right tibia.

RESULTS

There was no significant association between maternal 25OHD and newborn's anthropometrical measures at birth (weight p=0.35, length p=0.59 and head circumference p=0.47). There was a significant negative correlation between a maternal serum adiponectin and a) weight of infants at birth (R= -0.37, p=0.002); b) birth length (R= -0.31, p=0.008) and c) head circumference (R= -0.29, p=0.014). There was no significant correlation between maternal 25OHD blood levels during pregnancy and SOS in newborns (p=0.48). Additionally, a correlation between maternal adiponectin concentration during pregnancy and SOS in newborns was not significant (p=0.82).

CONCLUSION

Although a high prevalence of low 25OHD level among pregnant women was found, maternal vitamin D status did not influence growth and bone health of their offspring at birth. Maternal adiponectin levels in plasma showed an inverse relationship with anthropometrical measures of infants at birth, while no correlation with the newborn's bone health was found.

Maternal vitamin D in pregnancy and offspring bone measures in childhood: The Vitamin D in Pregnancy study

Previously we have demonstrated an association between maternal serum 25-hydroxyvitamin D (25(OH)D) during pregnancy and knee-heel length in offspring at birth. However, it is unknown whether maternal serum 25(OH)D is associated with bone measures in childhood. Thus, we aimed to examine associations between 25(OH)D at two stages of pregnancy and offspring bone measures at 11 years. Women were recruited from a single antenatal clinic in Victoria, Australia before 16 weeks gestation and provided two serum samples to determine 25(OH)D status at recruitment and 28-32 weeks gestation. Children and their mothers were followed up at 11 years of age. Children undertook dual energy X-ray absorptiometry scans at the lumbar spine and total body. Maternal 25(OH)D at recruitment (before 16 weeks gestation) was positively associated with the children's bone mineral content and density in boys, but not girls. In boys, a 10 nmol/L (4 ng/mL) increase in maternal 25(OH)D was associated with a median 0.5 g (95% CI 0.1,0.8) and 0.009 g/cm² (95% CI 0.001,0.017) increase in bone mineral content and density at the spine, respectively, and a median 0.006 g/cm² (95% CI 0.001,0.011) increase in at the total body. There was no sustained associations with 25(OH)D at the later timepoint (28-32 weeks) with any outcome. At age 11 years, maternal 25(OH)D levels during early pregnancy, but not late were positively associated with bone measures in boys, but not girls.

Vitamin D Deficiency, Prevalence and Treatment in Neonatal Period

OBJECTIVE

Maternal vitamin D deficiency is an important risk factor that causes infantile rickets in the neonatal and infantile period. The aim of this study was to review the prevalence, clinical characteristics, and treatment of vitamin D deficiency and the follow-ups with infants and their mothers by the neonatal intensive care unit of Afiyet Hospital in Turkey.

METHODS

Calcium (Ca), phosphorus (P) and 25 (OH) vitamin D were studied and prospectively recorded in infants and their mothers detected to have hypocalcemia during routine biochemistry tests performed on the third postnatal day of the patients follow up and treated with different diagnoses.

RESULTS

A total of 2,460 infants were admitted into the neonatal intensive care unit between August 2014 and January 2018. Of the infants included in the study, 324 (66.1%) were male and 166 (33.8%) were female, and 366 (74.6%) of them had been delivered by cesarean section (C/S), 124 (25.3%) of them had been delivered by Normal Spontaneous Delivery (NSD). Hypocalcemia was detected in 490 (19.9%) of the infants. In a total of 190 (38.7%) infants and 86 mothers (17.5%), the levels of 25 (OH) vitamin D were found to be below the laboratory detection limit of <3 ng/ml. When vitamin D deficiency + insufficiency is assessed by season, 151 of them were found to be in summer (30.99%), 118 in spring (24.18%), 117 in the winter season(23.87%), and 93 in autumn(18.97%), respectively. There was a statistically significant positive correlation of 78.7% between the vitamins D values of the mothers and the infants (p: 0.000, p<0.05).

CONCLUSION

This study conducted that a positive correlation of between the vitamin D values of the mothers and the infants. In order to prevent maternal vitamin D deficiency, the appropriate dose of prophylaxis providing optimal levels of vitamin D and should be given by according to the levels of 25 (OH) D vitamin during pregnancy.

Understanding vitamin D metabolism in pregnancy: From physiology to pathophysiology and clinical outcomes

This critical time frame of intrauterine life development is considered of major importance on the metabolic imprinting of overall health of the offspring, in later life. This requires a delicate immune balance that nurtures the allogeneic fetus, while maintaining reactivity against pathogens. Dysregulation of these tightly controlled biophenomena at a systemic and placental level, have been considered as a potential mechanism mediating pathogenesis of preeclampsia and spontaneous birth. In this context, vitamin D has been considered as a significant regulator of both innate and adaptive immunity by regulating cell proliferation, differentiation and apoptosis. Vitamin D metabolism during pregnancy manifests striking differences as compared to the non-pregnant state. Calcitriol is increasing >2-3 fold in the first weeks of pregnancy whereas maternal 25-hydroxyvitamin D crosses the placental barrier and represents the main pool of vitamin D in the fetus. Moreover, during pregnancy, vitamin D receptor and regulatory metabolic enzymes are expressed in the placenta and decidua, indicating a potential critical point in the immunomodulation at the maternal-fetal interface. Considering these effects, maternal hypovitaminosis D during pregnancy has been associated with pregnancy related disorders. This review focuses on the mechanistic basis of these adaptive changes, as a background for the development of pregnancy related disorders, with a discourse on the pathophysiology relating hypovitaminosis D and clinical outcomes.

The roles of vitamin D and dietary calcium in nutritional rickets

The etiology and pathogenesis of nutritional rickets are becoming progressively clearer. Vitamin D deficiency has generally been considered the major or only player in the pathogenesis of nutritional rickets. However, recent research into calcium deficiency has now provided clinicians with reasons to investigate and manage patients with nutritional rickets more appropriately.

The important question when assessing cases of nutritional rickets is: “Is it calcium or vitamin D deficiency or both that play a major role in the pathogenesis of the disease?”

The case presentation in this review highlights the risk factors, clinical presentation and pathophysiology of nutritional rickets in a young South African black child from a semi-urban area in Johannesburg, a city with abundant sunshine throughout the year.

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Vitamin D and calcium deficiencies play synergistic roles in nutritional rickets.

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Dietary calcium intake of <300 mg/day increases the risk of nutritional rickets.

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Vitamin D status is worsened by dietary calcium deficiency itself.

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Marked elevation of 1,25-dihydroxyvitamin D is characteristic of calcium deficiency.

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Preventative strategies needed to decrease the prevalence of nutritional rickets.

Deconvoluting the Biological Roles of Vitamin D-Binding Protein During Pregnancy: A Both Clinical and Theoretical Challenge

The teleological purpose of an ongoing pregnancy is to fulfill its fundamental role of a successful, uncomplicated delivery, in conjunction with an optimal intrauterine environment for the developing fetus. Vitamin D metabolism is adapted to meet both these demands during pregnancy; first by stimulation of calcium absorption for adequate intrauterine bone mineral accrual of the fetus, and second, by enhancing systemic and local maternal tolerance to paternal and fetal alloantigens. Vitamin D-binding protein (VDBP) is one of the key biomolecules that optimize vitamin D homeostasis and also contributes as an immune regulator for a healthy, ongoing pregnancy. In this regard, recent results indicate that dysregulation of VDBP equilibrium could be a risk factor for adverse fetal, maternal, and neonatal outcomes, including preeclampsia, preterm birth, and gestational diabetes. Moreover, it has been hypothesized to be also implicated in the interpretation of vitamin D status in the pregnant state. The aim of this review is to assess available literature regarding the association of VDBP with clinical outcomes during pregnancy, as a potential biomarker for future clinical practice, with a discourse on current knowledge gaps and future research agenda.

Maternal vitamin D and offspring trabecular bone score

No studies have explored the relationship with maternal vitamin D (25(OH)D) in pregnancy and offspring trabecular bone score (TBS). Our data suggest that maternal 25(OH)D in early pregnancy, but not late, may be associated with offspring TBS in boys. These data act as hypothesis-generating findings for confirmation in larger, longer-term studies.

INTRODUCTION

Trabecular bone score (TBS), a novel tool derived from dual-energy X-ray absorptiometry (DXA), reflects the microarchitecture of the vertebrae. It has been shown to predict fracture independent of standard DXA parameters in adult populations. Previously, we demonstrated that maternal serum 25-hydroxyvitamin D (25(OH)D) during pregnancy is associated with offspring bone mineral content at age 11 years. However, associations with TBS have not been explored, thus we aimed to determine associations between maternal 25(OH)D and offspring TBS.

METHODS

Data were collected from the Vitamin D in Pregnancy (VIP) study. Venous blood samples were taken at recruitment and at 28-32 weeks' gestation. Maternal 25(OH)D was measured by radioimmunoassay. Offspring (n = 195, n = 181 with complete measures) underwent spine DXA (GE Lunar), at age 11 years (median = 10.9 (IQR 10.9-11.4)). TBS was calculated using TBS iNsight software.

RESULTS

Offspring of mothers with sufficient 25(OH)D levels (≥50 nmol/L) at recruitment had a higher TBS (1.363 vs. 1.340, p = 0.04). In multivariable linear regression models, after adjustment for child relative lean mass, sex and pubertal stage, a 10 nmol/L increase in maternal 25(OH)D was associated with a 0.005 (95% CI 0.000, 0.010, p = 0.04) increase in TBS. However when stratified by sex (p for interaction = 0.16), the association was significant in boys, but not girls. There were no associations with TBS and maternal 25(OH)D at 28-32 weeks.

CONCLUSIONS

We speculate that maternal 25(OH)D in early pregnancy may be associated with TBS in offspring at age 11 in boys. These hypothesis-generating findings warrant confirmation with larger interventional and long-term follow-up studies.

Status of Serum Vitamin D and Calcium Levels in Women of Reproductive Age in National Capital Territory of India

CONTEXT

In India, Vitamin D deficiency is a major public health problem, associated with lack of sunlight exposure in spite of abundant sunshine usually accompanied by reduced dietary intake. In women of reproductive age, Vitamin D deficiency in pregnancy has been associated with an increased risk of gestational diabetes mellitus, preeclampsia, maternal and perinatal morbidity and mortality.

AIMS

The aim of the present cross-sectional study was to evaluate the levels of serum Vitamin D 25(OH) D and calcium in women of reproductive age from India.

SETTINGS AND DESIGN

A cross-sectional study was carried on a total of 224 healthy nonpregnant and nonlactating women in the reproductive age group of 20-49 years.

MATERIALS AND METHODS

Demographic, socioeconomic class, and biochemical parameters for the estimation of serum 25(OH)D and calcium levels in women of reproductive age were studied.

STATISTICAL ANALYSIS

Statistical Package for Social Sciences version 20.0 was utilized for conducting the statistical analysis of the data.

RESULTS

Vitamin D deficiency (<20 ng/ml) was present in 88% of women. Women from middle socioeconomic class had the lowest mean serum 25(OH) D levels (9.6 ± 6 ng/ml) as compared to women from upper middle (11.4 ± 8 ng/ml), lower (11.2 ± 8 ng/ml), and upper (10 ± 8.6 ng/ml) socioeconomic class. Serum calcium levels were found in the normal range of 8.5-10.5 mg/dl for all the study subjects.

CONCLUSIONS

There is a high prevalence of hypovitaminosis D among women of reproductive age. These women may possibly have a higher risk of development of osteoporosis and pregnancy-related complications in future life.

Vitamin D administration during pregnancy as prevention for pregnancy, neonatal and postnatal complications

Pregnancy represents a time of rapid bodily change, which includes physical proportions, physiology and responsibility. At this context, maternal vitamin D stores have been the objective of extensive scientific research during the last decades, focusing on their potential effects on maternal an neonatal health. A growing body of observational studies indicated that maternal hypovitaminosis D (as defined by maternal 25-hydroxyvitamin D [25(OH)D] levels <20 ng/ml or <50 nmol/l) is a significant risk factor for adverse neonatal outcomes including asthma, multiple sclerosis and other neurological disorders. On that basis, this review aims to provide to the reader new insights into the vitamin D requirements and function during pregnancy supported by recent data and will not discuss the classical roles of vitamin D and skeletal function during pregnancy. In addition, we will focus on recent results that demonstrate that maternal vitamin D supplementation could reduce neonatal respiratory and neurological complications, suggesting that available guidelines should be updated, since it remains unclear why these recommendations are not updated according to recent results. Also, with regard to randomized controlled trials (RCT's) for vitamin D, we consider that they are largely doomed to fail. The reasons for this are many and specific cases of this failure will be presented in this text.

Vitamin D replacement in children, adolescents and pregnant women in the Middle East and North Africa: A systematic review and meta-analysis of randomized controlled trials

INTRODUCTION

Hypovitaminosis D affects one-third to two-thirds of children and pregnant women from the Middle East and North Africa (MENA) region.

OBJECTIVE

To evaluate in infants, children, adolescents and pregnant women, from the MENA region, the effect of supplementation with different vitamin D doses on the change in 25-hydroxyvitamin D [25(OH)D] level reached, and other skeletal and non-skeletal outcomes.

METHODS

This is a systematic review of randomized controlled trials of vitamin D supplementation conducted in the MENA region. We conducted a comprehensive literature search in 7 databases, without language or time restriction, until November 2016. Two reviewers abstracted data from the included studies, independently and in duplicate. We calculated the mean difference (MD) and 95% CI of 25(OH)D level reached when at least 2 studies were eligible in each comparison (low (<800IU), intermediate (800-2000IU) or high (>2000IU) daily dose of vitamin D, or placebo). We pooled data using RevMan version 5.3.

RESULTS

We identified a total of 15 eligible trials: one in infants, 4 in children and adolescents and 10 in pregnant women. In children and adolescents, an intermediate vitamin D dose (1901IU/d), resulted in a mean difference in 25(OH)D level of 13.5 (95% confidence interval (CI) 8.1-18.8) ng/ml, compared to placebo, favoring the intermediate dose (p<0.001). The proportion of children and adolescents reaching a 25(OH)D level≥ 20ng/ml was 74% in the intermediate dose group. In pregnant women, four trials started supplementation at 12-16weeks of gestation and continued until delivery, and six trials started supplementation at 20-28weeks' gestation and stopped it at delivery. The MD in 25(OH)D level reached was 8.6 (95% CI 5.3-11.9) ng/ml (p<0.001) comparing the high dose (3662IU/d) to the intermediate dose (1836IU/d), and 12.3 (95% CI 6.4-18.2) ng/ml (p<0.001), comparing the high dose (3399IU/d) to the low dose (375IU/d). Comparing the intermediate (1832IU/d) to the low dose (301IU/d), the MD in 25(OH)D level achieved was 7.8 (95% CI 4.5-10.8) ng/ml (p<0.001). The proportion of pregnant women reaching a 25(OH)D level≥20ng/ml was 80%-90%, 73% and 27%-43% in the high, intermediate, and low dose groups, respectively. The risk of bias in the included studies, for children, adolescents and pregnant women, ranged from low to high across all doamins.

CONCLUSION

In children, adolescents and pregnant women from the MENA, an intermediate vitamin D dose of 1000-2000IU daily may be necessary to allow for the majority of the population to reach a desirable 25(OH)D level of 20ng/ml. Further high quality RCTs are required to confirm/refute the beneficial impact of vitamin D supplementation on various clinically important outcomes.

Dysregulation of maternal and placental vitamin D metabolism in preeclampsia

INTRODUCTION

Epidemiology has linked preeclampsia (PET) to decreased maternal serum 25-hydroxyvitamin D3 (25(OH)D3). However, alterations in systemic and placental/decidual transport and metabolism of 25(OH)D3 during pregnancy suggest that other forms of vitamin D may also contribute to the pathophysiology of PET.

METHODS

In a cross sectional analysis of normal pregnant women at 1st (n = 25) and 3rd trimester (n = 21), pregnant women with PET (n = 22), and non-pregnant female controls (n = 20) vitamin D metabolites were quantified in paired maternal serum, placental, and decidual tissue.

RESULTS

Serum 25(OH)D3 was not significantly different in sera across all four groups. In normal 3rd trimester pregnant women serum active 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was significantly higher than non-pregnant, normal 1st trimester pregnant, and PET women. Conversely, PET sera showed highest levels of the catabolites 3-epi-25(OH)D3 and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3). Serum albumin was significantly lower in normal 3rd trimester pregnant women and PET relative to normal 1st trimester pregnant women, but there was no change in free/bioavailable 25(OH)D3. In PET placental tissue, 25(OH)D3 and 3-epi-25(OH)D3 were lower than normal 3rd trimester tissue, whilst placental 24,25(OH)2D3 was highest in PET. Tissue 1,25(OH)2D3 was detectable in 1st trimester decidua, which also showed 10-fold higher 25(OH)D3 relative to paired placentae. 3-epi-25(OH)D3 and 24,25(OH)2D3 were not different for decidua and placenta. In normal 3rd trimester pregnant women, total, free and bioavailable maternal 25(OH)D3 correlated with placental 25(OH)D3, but this was not conserved for PET.

DISCUSSION

These data indicate that PET is associated with decreased activation, increased catabolism, and impaired placental uptake of 25(OH)D3.

The Road Not So Travelled: Should Measurement of Vitamin D Epimers during Pregnancy Affect Our Clinical Decisions?

Observational studies suggest an adverse effect of maternal hypovitaminosis D during pregnancy. However, intervention studies failed to show convincing benefit from vitamin D supplementation during pregnancy. With analytical advances, vitamin D can now be measured in ten forms—including as epimers—which were thought to be biologically inactive, but can critically impair immunoassays. The aim of this commentary is to highlight the potential clinical and analytical significance of vitamin D epimers in the interpretation of vitamin D roles in pregnancy. Epimers may contribute a considerable proportion of total vitamin D—especially in the neonate—which renders the majority of common assays questionable. Furthermore, epimers have been suggested to have activity in laboratory studies, and evidence suggests that the fetus contributes significantly to epimer production. Maternal epimer levels contribute significantly to predict neonate circulating 25-hydroxyvitamin D concentrations. In conclusion, the existence of various vitamin D forms (such as epimers) has been established, and their clinical significance remains obscure. These results underscore the need for accurate measurements to appraise vitamin D status, in order to understand the current gap between observational and supplementation studies on the field.

Maternal vitamin D levels during pregnancy and neonatal health: evidence to date and clinical implications

Low maternal vitamin D levels during pregnancy have been associated with a plethora of adverse neonatal outcomes, including small for gestational age and preterm births, detrimental effect on offspring bone and teeth development, and risk of infectious diseases. Although most observational studies indicate a significant linear relationship between maternal 25-hydroxyvitamin D and the above outcomes, some randomized controlled trials to date are inconclusive, mostly due to differences in study design and supplementation regimen. The currently available results indicate that vitamin D supplementation during pregnancy reduces the risk of preterm birth, low birth weight, dental caries of infancy, and neonatal infectious diseases such as respiratory infections and sepsis. This narrative review aims to summarize available trial results regarding the effect of low maternal vitamin D levels during pregnancy, in conjunction with neonatal outcomes on the field, with a discourse on the appropriate clinical approach of this important issue.

Exposure to lithium through drinking water and calcium homeostasis during pregnancy: A longitudinal study

There is increasing evidence of adverse health effects due to elevated lithium exposure through drinking water but the impact on calcium homeostasis is unknown. This study aimed at elucidating if lithium exposure through drinking water during pregnancy may impair the maternal calcium homeostasis. In a population-based mother-child cohort in the Argentinean Andes (n=178), with elevated lithium concentrations in the drinking water (5-1660μg/L), blood lithium concentrations (correlating significantly with lithium in water, urine and plasma) were measured repeatedly during pregnancy by inductively coupled plasma mass spectrometry and used as exposure biomarker. Markers of calcium homeostasis included: plasma 25-hydroxyvitamin D3, serum parathyroid hormone (PTH), and calcium, phosphorus and magnesium concentrations in serum and urine. The median maternal blood lithium concentration was 25μg/L (range 1.9-145). In multivariable-adjusted mixed-effects linear regression models, blood lithium was inversely associated with 25-hydroxyvitamin D3 (-6.1nmol/L [95%CI -9.5; -2.6] for a 25μg/L increment in blood lithium). The estimate increased markedly with increasing percentiles of 25-hydroxyvitamin D3. In multivariable-adjusted mixed-effects logistic regression models, the odds ratio of having 25-hydroxyvitamin D3<30nmol/L (19% of the women) was 4.6 (95%CI 1.1; 19.3) for a 25μg/L increment in blood lithium. Blood lithium was also positively associated with serum magnesium, but not with serum calcium and PTH, and inversely associated with urinary calcium and magnesium. In conclusion, our study suggests that lithium exposure through drinking water during pregnancy may impair the calcium homeostasis, particularly vitamin D. The results reinforce the need for better control of lithium in drinking water, including bottled water.

Hypovitaminosis D in pregnancy in the Mediterranean region: a systematic review

Despite high levels of sunshine, maternal hypovitaminosis D during pregnancy is prevalent in the Mediterranean region. The aim of this study is to systematically review trials that investigated vitamin D concentrations during pregnancy in this region, in order to determine predictors of hypovitaminosis D and explain this phenomenon. After applying inclusion/exclusion criteria, 15 studies were entered into the systematic review involving 2649 pregnant women and 820 neonates. The main outcome was maternal vitamin D status, assessed by serum 25-hydroxy-vitamin D (25(OH)D) concentrations. Possible predictors of the outcome included maternal age, body mass index (BMI), race, socioeconomic status, skin type, gestational age, sun exposure, calcium and vitamin D intake and supplementation, smoking status, parity and season of delivery. Studies differed widely in vitamin D deficiency criteria, method of measurement and outcomes. The prevalence of vitamin D insufficiency ranges from 9.3 to 41.4%, whereas that of vitamin D deficiency from 22.7 to 90.3%. A positive association with 25(OH)D concentrations exists for light skin color, white race, uncovered dressing pattern, maternal vitamin D supplementation and season of gestation (spring/summer). An inverse association exists for BMI and gestational age, whereas data for smoking and socioeconomic status are controversial. We concluded that vitamin D deficiency in pregnancy seems to be quite common, even in the Mediterranean region. Racial, social and cultural habits, as well as the absence of preventive supplementation/dietary strategies, seem to negate the benefits of sun exposure.

Vitamin D heritability and effect of pregnancy status in Vervet monkeys (Chlorocebus aethiops sabaeus) under conditions of modest and high dietary supplementation

OBJECTIVES

The two objectives of the current study were to: 1) investigate the genetic contributions to variations in serum vitamin D concentrations under two dietary conditions (a standard monkey biscuit diet vs. a diet designed to model typical American consumption); and 2) explore the interaction of vitamin D with pregnancy status using a cohort of pedigreed female vervet/African green monkeys.

METHODS

This study includes 185 female (≥3.5 years) vervet/African green monkeys (Chlorocebus aethiops sabaeus) from a multi-generational, pedigreed breeding colony. The 25(OH)D3 concentrations were first measured seven to eight weeks after consuming a "typical American" diet (TAD), deriving 37, 18, and 45% of calories from fat, protein sources, and carbohydrates, and supplemented with vitamin D to a human equivalent of 1,000 IU/day. Vitamin D concentrations were assessed again when animals were switched to a low-fat, standard biscuit diet (LabDiet 5038) for 8 months, which provided a human equivalent of approximately 4,000 IU/day of vitamin D. All statistical analyses were implemented in SOLAR.

RESULTS

Pregnancy was associated with reduced 25(OH)D3 concentrations. Heritability analyses indicated a significant genetic contribution to 25(OH)D3 concentrations in the same monkeys consuming the biscuit diet (h(2) =0.66, P=0.0004) and TAD (h(2) =0.67, P=0.0078) diets, with higher 25(OH)D3 concentrations in animals consuming the biscuit diet. Additionally, there was a significant genotype-by-pregnancy status interaction on 25(OH)D3 concentrations (P<0.05) only among animals consuming the TAD diet.

DISCUSSION

These results support the existence of a genetic contribution to differences in serum 25(OH)D3 concentrations by pregnancy status and emphasize the role of diet (including vitamin D supplementation) in modifying genetic signals as well as vitamin D concentrations.

Vitamin D during pregnancy: why observational studies suggest deficiency and interventional studies show no improvement in clinical outcomes? A narrative review

A considerable number of studies have examined vitamin D status during pregnancy. Although data from observational studies denote vitamin D hypovitaminosis (deficiency or insufficiency) during pregnancy is associated with a plethora of adverse maternal and neonatal outcomes, data from interventional (supplementation) trials fail to reveal a significant impact on maternal and offspring health. The aim of this narrative review was to critically appraise the methodology of the most representative published randomized controlled trials in an attempt to explain the difference between observational and supplementation results. We found that this difference could be attributed to a variety of factors, namely: (i) study design (lack of a specific outcome in conjunction with timing of supplementation, enrolment of participants with heterogeneous vitamin D status); (ii) pitfalls in the interpretation of vitamin D equilibrium (lack of determination of plasma half-life); (iii) supplementation regimen (administration of a wide range of regimens, in terms of dose, bolus and form); (iv) geographical characteristics (vitamin D needs could vary significantly within a country, particularly in areas with a wide range of latitude gradient); (v) adaptations of vitamin D metabolism during pregnancy (vitamin D and calcium equilibrium are changed during pregnancy compared with the non-pregnant state) and (vi) supplementation of populations with low baseline 25(OH)D values would likely manifest beneficial effects. All these parameters should be taken into consideration in the design of future vitamin D supplementation trials.

Vitamin D Status and Its Determinants in Healthy Slovenian Pregnant Women

BACKGROUND/AIMS

Vitamin D deficiency is a common underdiagnosed condition. The aim of this was to analyze the status of vitamin D and its determinants in healthy Slovenian pregnant women.

METHODS

A total of 132 volunteer pregnant women completed a questionnaire including baseline demographics, food frequency, physical activities; anthropometrical measurements, body mass index and levels of 25-(OH)D in serum were performed during the third trimester, and dietary intakes were assessed during the 27-28th week of gestation.

RESULTS

Vitamin D deficiency was present in 14% while insufficiency was present in 41% of women. The risk for inadequacy was higher in women older than 30 years (p = 0.01), in those with less frequent outdoor physical activity (p = 0.01) and in pregnancies during the low sun exposure season (p = 0.04). Insufficiency was not significantly more frequent in less educated women, unemployed and in those living in urban area. The median value of vitamin D from habitual dietary intake was 1.5 µg/day (range 0.1-13.4) and did not influence 25-hydroxyvitamin D level (p = 0.91).

CONCLUSIONS

The prevalence of vitamin D inadequacy was 55% and was dependent on age, season and outdoor physical activities. The results suggest a discrepancy between vitamin D intake through habitual diet and the reference needs.

Serum 25-Hydroxyvitamin D Levels: Variability, Knowledge Gaps, and the Concept of a Desirable Range

Hypovitaminosis D is prevalent worldwide but proportions vary widely between regions, depending on genetic and lifestyle factors, the threshold to define deficiency, and accuracy of 25-hydroxyvitamin D (25OHD) assays used. Latitude, pollution, concealing clothing, sun exposure, gender, dietary habits, and lack of government regulation account for up to 50% in variations in serum 25OHD levels, whereas genetic polymorphisms in the vitamin D pathway account for less than 5%. Organizations/societies have developed guidelines for recommended desirable 25OHD levels and vitamin D doses to reach them, but their applicability across age groups and populations are still debated. This article and the accompanying online Supporting Information highlight sources of variations in circulating 25OHD levels, uncertainties and knowledge gaps, and analytical problems facing 25OHD assays, while keeping efficacy and safety data as the dominant factors when defining a desirable range for 25OHD levels. We propose a desirable range of 20 to 40 ng/mL (50 to 100 nmol/L), provided precise and accurate assays are used. Although slightly lower levels, 15 to 20 ng/mL, may be sufficient for some infants and adults, higher levels, 40 to 60 ng/mL, may still be safe. This desirable range allows physicians to tailor treatment while taking season, lifestyle, vitamin D intake, and other sources of variation into account. We reserve 25OHD measurements for at-risk patients, defined by disease or lifestyle, and the use of 25OHD assays calibrated against the recommended international standards. Most target groups reach desirable target levels by a daily intake of 400 to 600 IU for children and 800 IU for adults. A total daily allowance of vitamin D of up to 1000 IU in the pediatric age groups, and up to 2000 IU in adults, tailored to an individual patient risk profile, is probably safe over long durations. Additional data are needed to validate the proposed range and vitamin D doses, especially in children, pregnant women, and non-white populations.

Vitamin D in fetal development: findings from a birth cohort study

Birth cohort studies provide an invaluable resource for studies of the influence of the fetal environment on health in later life. It is uncertain to what extent maternal vitamin D status influences fetal development. Using an unselected community-based cohort of 901 mother-offspring pairs (the Western Australian Pregnancy Cohort [Raine] Study), we examined the relationship between maternal vitamin D deficiency at 18 weeks' pregnancy and long-term health outcomes of offspring who were born in Perth, Western Australia (32° South), in 1989-1991. Vitamin D deficiency (serum 25-hydroxyvitamin D [25(OH)D] <50 nmol/L) was present in 36% (323 of 901) of the pregnant women. After adjusting for relevant covariates, maternal vitamin D deficiency during pregnancy was associated with impaired lung development in 6-year-old offspring, neurocognitive difficulties at age 10, increased risk of eating disorders in adolescence, and lower peak bone mass at 20 years. In summary, vitamin D may have an important, multifaceted role in the development of fetal lungs, brain, and bone. Experimental animal studies support an active contribution of vitamin D to organ development. Randomized controlled trials of vitamin D supplementation in pregnant women with long-term follow-up of offspring are urgently required to examine whether the correction of vitamin D deficiency in pregnant women is beneficial for their offspring and to determine the optimal level of maternal serum 25(OH)D for fetal development.

Maternal vitamin D status during pregnancy: the Mediterranean reality

Vitamin D status during pregnancy is linked to bone mineralization of developing fetus, which justifies targeting sufficient levels of vitamin D in pregnant women. Despite high level of sunshine in the Mediterranean regions, maternal hypovitaminosis D remain common in these countries. The aim of this narrative review was to provide potential explanations for this phenomenon in an effort to guide future public health policies and vitamin D intakes during pregnancy. We searched Medline for publications regarding hypovitaminosis D during pregnancy in the Mediterranean region. Available studies confirmed the high prevalence of hypovitaminosis D among pregnant women in the Mediterranean regions (50-65% in most studies), resulting in severe skeletal and nonskeletal health events among the offspring. Reasons for this may rely on maternal darker skin pigmentation, poor dietary vitamin D intake, veiled clothing and reduced sunshine exposure, health policies and increased prevalence of obesity. Public health organizations should be aware of this phenomenon and develop specific policies to prevent hypovitaminosis D and its adverse outcomes in maternal and neonatal health.