Vitamin D is not simply a vitamin in the conventional sense; it functions as a secosteroid hormone with receptors present in nearly every tissue of the human body. Its best-understood role is in calcium and phosphate homeostasis, the biochemical machinery that mineralises the developing skeleton. During pregnancy, the demands escalate dramatically, because the fetus must accumulate roughly 25 to 30 grams of calcium by term, most of it in the third trimester, and virtually all of it drawn across the placenta from the maternal circulation. The placenta itself expresses the enzyme 1-alpha-hydroxylase, which activates vitamin D, and the hormone is thought to contribute to placental function, immune modulation and fetal bone development. When maternal stores run low, the fetus has no independent supply to fall back on.

The Nigerian study set out to quantify exactly how tightly maternal and neonatal vitamin D status are coupled at birth. The researchers enrolled women presenting in labour or at delivery at the hospital’s labour ward and collected paired samples: maternal serum and umbilical cord blood from their term neonates. Serum concentrations of 25-hydroxyvitamin D, abbreviated 25(OH)D, served as the standard biomarker. This metabolite is the preferred measure of vitamin D status because it reflects cumulative supply from both sun exposure and diet, has a half-life of several weeks, and is the form most tightly correlated with clinical deficiency. The samples were analysed using a commercial enzyme-linked immunosorbent assay, or ELISA, from Calbiotech, a technique in which antibodies capture the 25(OH)D molecule and an enzyme-driven colour reaction allows its concentration to be quantified against a calibration curve.

The numbers were stark. Mean maternal 25(OH)D stood at 18.3 nanograms per millilitre, with a standard deviation of 6.9, while cord blood averaged 20.5 nanograms per millilitre, with a standard deviation of 8.6. Counterintuitively, the babies’ levels were slightly higher than their mothers’, a difference that was statistically significant in a paired t-test (t = -3.601, p < 0.001). This maternal-neonatal gradient, in which cord blood exceeds maternal blood, has been reported in other populations and is thought to reflect active placental transport mechanisms that prioritise the fetus, including the upregulation of vitamin D-binding proteins and the placental conversion of 25(OH)D. But the gradient offers only partial comfort: a fetus prioritised at the expense of a deficient mother is still being supplied from a depleted reservoir.

Deficiency itself was rampant. Using conventional cutoffs, 76 of the 128 mothers, or 59.4 percent, were vitamin D deficient, and 64 of the neonates, exactly 50.0 percent, fell into the deficient category. When the analysis widened to include insufficiency as well as outright deficiency, the prevalence of hypovitaminosis D climbed to 86.7 percent among the mothers and 76.6 percent among the newborns. In other words, fewer than one in seven mothers and one in four babies had adequate vitamin D status at the moment of birth. For a population living at roughly 7 degrees north of the equator, where year-round sunlight should make deficiency nearly impossible, the figures are a vivid demonstration that latitude is not destiny.

The statistical heart of the study lies in the association between maternal and neonatal status. The chi-square test for the relationship between maternal and cord blood vitamin D categories yielded a value of 21.297 with a p-value of 0.001, confirming that the two are far from independent. More striking still is the odds ratio: neonates whose mothers were vitamin D deficient had 6.12 times higher odds of being deficient themselves compared with neonates of non-deficient mothers, with a 95 percent confidence interval of 2.78 to 13.48 and a p-value of 0.008. Translated into clinical terms, a mother’s deficiency status at delivery is one of the strongest predictors of her baby’s status, effectively doubling to sextupling the risk depending on where a given infant falls within that confidence interval. The mother, as the study’s authors note, is the main source of circulating vitamin D in the neonate, and the data bear that out with unusual force.

Why would deficiency be so common in a sun-drenched region? The answer lies in the gap between sunlight and the biologically active molecule. Cutaneous vitamin D synthesis requires ultraviolet B radiation to convert 7-dehydrocholesterol in the skin into pre-vitamin D3, but that process is easily derailed. Cultural and religious dress practices that cover most of the skin, urban air pollution that filters UVB, dark skin pigmentation that reduces synthesis efficiency by as much as sixfold compared with lighter skin, indoor lifestyles in rapidly urbanising cities, and low dietary intake of oily fish, fortified dairy and other vitamin D-rich foods all conspire against adequate production. Pregnancy compounds the problem, since the growing fetus consumes maternal 25(OH)D and the increased maternal blood volume dilutes it further. None of these mechanisms is unique to Nigeria, but their combination in a tropical setting makes the finding especially instructive for other low- and middle-income countries where supplementation programmes remain patchy or absent.

The clinical stakes are not trivial. Neonatal vitamin D deficiency has been linked in the broader literature to impaired bone mineralisation, hypocalcaemic seizures in early infancy, and an increased vulnerability to infections, given the hormone’s role in innate immune defences such as antimicrobial peptide production. Severe early deficiency can present as craniotabes, rachitic rosary or frank rickets in the first months of life, and subclinical deficiency may quietly compromise skeletal accrual during the fastest growth phase of the human lifespan. Because the study was cross-sectional, it establishes association rather than causation and cannot follow the infants forward to measure outcomes, but the strength of the maternal-neonatal odds ratio suggests that intervening in pregnancy could pay dividends at birth and beyond.

The authors, a team spanning the Department of Paediatrics at University College Hospital Ibadan, the College of Medicine at the University of Ibadan, the Department of Chemical Pathology, the Institute of Child Health and Federal Medical Centre Owo, are careful about the limits of their design. A single tertiary hospital cannot speak for the whole population; women delivering in such facilities may differ systematically from community births in nutrition, antenatal care and socioeconomic status. They therefore call for community-based studies to establish the true prevalence of maternal-neonatal vitamin D shortfall across the wider population. The study received no external funding, was approved by the University of Ibadan/University College Hospital Ethics Committee, and all participants gave written informed consent after a detailed explanation of the procedures, with data anonymised through serial numbers and password protection in line with the Declaration of Helsinki.

What the study ultimately delivers is a clear and actionable message wrapped in a paradox. Sunshine is abundant, yet the hormone it is supposed to generate is missing at the very first blood test a Nigerian baby effectively undergoes, and the reason is written in the mother’s blood beside it. The maternal-neonatal coupling, quantified here with an odds ratio above six, means that any serious public health response must target women before and during pregnancy rather than waiting to treat deficient infants after the fact. Antenatal vitamin D supplementation, food fortification programmes and education about sensible sun exposure are the obvious levers, and the authors’ call for community-based prevalence studies is the logical next step in calibrating them. Until then, the delivery rooms of southwest Nigeria hold a quiet warning for tropical countries everywhere: the sun overhead is no guarantee of the vitamin in the vein.

Subject of Research: The relationship between maternal and neonatal vitamin D status at birth in southwest Nigeria

Article Title: The relationship between the neonatal and maternal vitamin D level at birth in a tertiary hospital in southwest, Nigeria

Article References: The relationship between the neonatal and maternal vitamin D level at birth in a tertiary hospital in southwest, Nigeria. (n.d.). https://doi.org/10.1186/s12902-026-02675-3

Image Credits: AI Generated

DOI: 10.1186/s12902-026-02675-3

Keywords: vitamin D deficiency, 25-hydroxyvitamin D, cord blood, pregnancy, neonates, Nigeria, maternal health, ELISA, hypovitaminosis D, odds ratio, public health, tropical medicine