High-Dose Vitamin D in Pregnancy Fails to Strengthen Children’s Bones by Age 13, Landmark Trial Finds

One of the most persistent hopes in preventive medicine has been that a simple nutrient taken during pregnancy could lay the foundations of a child’s skeleton for life. Vitamin D, the so-called sunshine vitamin, regulates how the body absorbs calcium and phosphate, the raw materials of the hydroxyapatite crystals that give bone its rigidity. Because low maternal levels of 25-hydroxyvitamin D have repeatedly been linked to reduced bone mineral content in newborns and toddlers, researchers have long speculated that boosting those levels in pregnancy might raise a child’s peak bone mass in early adulthood and, in turn, push back the onset of osteoporosis by years or even decades. A new thirteen-year follow-up of a rigorously controlled Danish trial now delivers a sobering answer: the early benefits of prenatal high-dose vitamin D supplementation appear to fade, leaving no measurable trace on adolescent bone strength or fracture risk.

The study, published in The Lancet Regional Health – Europe, is a secondary analysis of the Copenhagen Prospective Studies on Asthma in Childhood 2010 (COPSAC2010) randomized clinical trial. Between March 2009 and November 2010, the team enrolled 623 pregnant women from the Greater Copenhagen area at week 24 of gestation and randomized them in a 1:1 ratio to receive either high-dose vitamin D3 or placebo. Crucially, both groups were advised to follow the Danish Health Authority’s standard recommendation of 400 IU per day, so the trial effectively compared 2800 IU per day against 400 IU per day from pregnancy week 24 until one week after birth. Adherence and biological effect were confirmed by measuring maternal serum 25-hydroxyvitamin D at the end of the supplementation period using isotope dilution liquid chromatography-tandem mass spectrometry, a gold-standard analytical method.

The original trial had already produced encouraging results. In earlier analyses, the children whose mothers received the high-dose supplement showed significantly higher whole-body bone mineral density and bone mineral content at ages three and six years, measured by dual-energy X-ray absorptiometry, or DXA. The effects were largest among children born during the dark Danish winter months, when maternal vitamin D status is naturally at its lowest, and an exploratory analysis even suggested a reduced risk of radiologically verified fractures when supplementation was combined with sufficient vitamin D levels in the child’s first year of life. Those findings fed directly into the influential hypothesis that prenatal vitamin D could be a cheap, safe lever for lifelong skeletal health, because bone mineral content tracks from childhood into adulthood and peak bone mass is considered the single most important determinant of osteoporosis risk.

The new analysis tested whether those early gains endure. At age thirteen, 416 children, roughly seventy-one percent of those randomized, returned for whole-body DXA scans performed on Lunar iDXA and Hologic densitometers, with each scan validated by two independent specialists blinded to treatment allocation. The results were unambiguous. There were no differences between the high-dose and standard-dose groups in total body bone mineral content, total body bone mineral density, or the equivalent total-body-less-head measures. The adjusted mean differences were vanishingly small: for total body bone mineral content, just 6.7 grams in favor of the supplemented group, with a confidence interval spanning zero and a p-value of 0.71. Sex-stratified analyses, adjustments for pubertal Tanner stage, stratification by maternal baseline vitamin D status, birth season, and a concurrent fish-oil trial all failed to uncover any hidden subgroup benefit.

The longitudinal picture tells the same story. Pooling DXA measurements from ages three, six, and thirteen in a random-intercept mixed-effects model, the researchers found no overall effect of the prenatal intervention across the entire follow-up period, and no statistical interaction between the intervention and the child’s age at scanning. In other words, the early advantage seen at ages three and six did not simply persist quietly below the threshold of a single timepoint; it dissipated as the children grew. This pattern is consistent with a transient effect of the intrauterine vitamin D environment on early bone mineralization that is progressively overtaken by the powerful hormonal and nutritional drivers of growth during childhood and puberty.

Fracture outcomes proved equally unpersuasive. Among 550 children with complete clinical follow-up to age thirteen, a remarkable 94 percent retention rate, 114 radiologically verified fractures were recorded in 99 children, spanning the clavicle, radius, ulna, tibia, fibula, femur, and humerus. Comparing the intervention groups, the hazard ratio for time to first fracture was 0.85 with a p-value of 0.40, and the incidence rate ratio was 0.84 with a p-value of 0.39, neither approaching statistical significance. Even the exploratory combined analysis, which contrasted children whose mothers received high-dose vitamin D and who themselves had sufficient 25-hydroxyvitamin D levels at six months against children with neither advantage, showed no significant reduction in fracture risk, in contrast to the team’s own earlier findings at younger ages.

One intriguing signal did survive, however. Within the supplemented group, children who had sufficient vitamin D levels at six months tended to show higher bone mineral outcomes at thirteen than those who were insufficient, and the interaction between the prenatal intervention and early-life vitamin D status reached significance for total body bone mineral content, with a p-value of 0.002. The authors interpret this cautiously as evidence that the vitamin D status of the child in the first months of life, not merely the prenatal dose, may modulate any potential skeletal benefit. Yet this exploratory observation stops short of a clinically actionable conclusion, and the corresponding fracture analyses in the same subgroup yielded only non-significant trends.

The study’s strengths are considerable and worth emphasizing in an era of nutrition headlines built on observational associations. Randomization eliminates the confounding that plagues cohort studies, where mothers who take supplements also tend to differ in diet, activity, and socioeconomic status. The double-blinded, placebo-controlled design, predefined bone endpoints, ninety-four percent longitudinal follow-up, radiologically verified fracture diagnoses, and sensitivity analyses across scanners, seasons, sex, and puberty stage collectively make this the most definitive test to date of prenatal vitamin D effects on offspring bone health. The authors acknowledge limitations, including that the trial was originally powered for persistent wheeze and asthma rather than bone outcomes, that twenty-nine percent of children lacked a thirteen-year DXA scan, and that interpreting areal bone density during the adolescent growth spurt is inherently challenging.

The findings also sharpen the contrast with the only comparable trial. The UK-based MAVIDOS study, which tested a lower dose of 1000 IU per day, reported higher offspring bone mineral density at ages six to seven, and its longer-term results have not yet been published. Whether MAVIDOS will show the same attenuation seen in COPSAC2010 is now one of the most consequential open questions in pediatric bone research. For now, the Danish data challenge the seductive idea that a single prenatal intervention can durably sculpt peak bone mass and defer osteoporosis by more than a decade. Mathematical models have predicted that a ten percent increase in peak bone mass around age twenty could delay osteoporosis onset by thirteen years, which is precisely why the field invested so much in the pregnancy hypothesis. The new results suggest that if such a shift is achievable, it will not come from prenatal supplementation alone, and that protecting children’s vitamin D status through infancy and beyond may matter at least as much as what happens in the womb.

Subject of Research: Prenatal high-dose vitamin D supplementation and offspring bone mineral content and density at age 13 years: a secondary analysis of a randomised clinical trial

Article Title: Prenatal high-dose vitamin D supplementation and offspring bone mineral content and density at age 13 years: a secondary analysis of a randomised clinical trial

Article References: Brustad, N., Sultan, T., Vahman, N., Jensen, S. K., Vinding, R., Aagaard, K., Gørtz, P. M., Haarmark, C., Bønnelykke, K., & Chawes, B. (2026). Prenatal high-dose vitamin D supplementation and offspring bone mineral content and density at age 13 years: a secondary analysis of a randomised clinical trial. The Lancet Regional Health – Europe, 71, Article 101870. https://doi.org/10.1016/j.lanepe.2026.101870

Image Credits: AI Generated

DOI: 10.1016/j.lanepe.2026.101870

Keywords: Prenatal, high-dose, vitamin, supplementation, offspring, bone, mineral, content, density, years, secondary, analysis