Study: Maternal vitamin D influences pubertal timing in boys

The authors from Aarhus University Hospital, Denmark, observed half a month later pubertal timing in boys of mothers with no or low intake of vitamin D supplements in mid-pregnancy compared to boys of mothers having a higher intake of vitamin D supplements.

Maternal intake of vitamin D supplements was not associated with pubertal timing in girls in the study of 12,991 Danish boys and girls born between 2000 and 2003.

The authors conclude: “We observed slightly later pubertal timing in boys of mothers with no or low intake of vitamin D supplements in mid-pregnancy compared to boys of mothers having a higher intake of vitamin D supplements. 

“Whether this minor delay is clinically relevant from a public health perspective is unknown. Maternal intake of vitamin D supplements was not associated with pubertal timing in girls.”

Vitamin D intake​

Worldwide, there are no consistent recommendations​ regarding the intake of vitamin D supplements during pregnancy​.

The World Health Organisation recommends​ pregnant women engage in sensible sun exposure and a balanced diet, while the Institute of Medicine and the US Endocrine Society​ recommend a total intake of 15 µg/day and 25–50 µg/day respectively from dietary sources including vitamin D supplements. 

In the new study, the mean total intake of vitamin D from dietary sources was 10.7 (SD: 5.2), as the women were pregnant before the current recommendations were deployed. 

Even after the official recommendation of 10 µg vitamin D per day​ throughout pregnancy was implemented in 2009 in Denmark, many Danish pregnant women reportedly still suffer from low vitamin D levels​.

This trend of low vitamin D levels in pregnant women is observed worldwide, which is why the authors note that low vitamin D during pregnancy is a public health concern​, not only for the health of the offspring​.

Significance​ 

Vitamin D is a prohormone​ essential to humans. Once activated, it exhibits its effects through binding to the vitamin D receptor (VDR) and thereby regulates cell proliferation and differentiation​.

In addition to well-described effects in bone metabolism​, vitamin D is involved in the function of several other organ systems, including the reproductive system​.

Its supplementation during pregnancy can influence pregnancy outcomes, with vitamin D deficiency potentially leading to conditions​ like hypertensive disorders and gestational diabetes. 

Additionally, it may impact the developing foetus​ and affect the long-term health of children​ through potential epigenetic changes​. 

Low maternal vitamin D levels might interfere with the hypothalamic-pituitary-gonadal (HPG) axis​, a key regulator of reproductive maturation​.

The presence of vitamin D receptors and activating enzymes in the HPG axis​ suggests a local role of vitamin D during development.

One study​ previously found that men exposed to low maternal vitamin D levels in utero had lower testes volume compared to men exposed to >75 nmol/L 25(OH)D3 levels.

Changes in pubertal timing are of concern for long-term health​, as they are linked to cardiovascular, metabolic, and psychiatric diseases​ in adulthood.

The authors of the new study note that no previous epidemiological research has explored the connection between taking vitamin D supplements during pregnancy and the timing of puberty in offspring. 

Therefore, investigating modifiable factors like maternal vitamin D supplementation during pregnancy is essential, and the study aimed to explore the association between maternal vitamin D intake and pubertal timing in boys and girls within a large population-based puberty cohort.

The study ​

The authors obtained information on maternal intake of vitamin D supplements through self-reports by participants in mid-pregnancy.

Self-reported information on the status of various pubertal milestones was obtained every six months throughout puberty. 

An average reading of the results showed that boys had 0.5 months (95% CI 0.1; 0.9) later pubertal timing per 5 µg/day lower maternal vitamin D supplement intake.

However, maternal intake of vitamin D supplements was not associated with pubertal timing in girls. 

Strengths and weaknesses ​

The authors report: “The major strength of this study is the longitudinal design with detailed information on maternal intake of vitamin D supplements during pregnancy, various pubertal milestones throughout pubertal development, and many potentially important confounding and mediating factors. 

“The large sample size limited the risk of type II errors, and we were able to adjust for many important potential confounders measured at baseline; e.g., maternal pre-pregnancy BMI, which is an important factor in determining vitamin D bioavailability, since vitamin D is stored in adipose tissue​.”

They do however add that due to the observational design applied in this study, they cannot eliminate the risk of residual confounding.

Journal: Nutrients

https://www.mdpi.com/2072-6643/15/18/4039​

“Maternal Intake of Vitamin D Supplements during Pregnancy and Pubertal Timing in Children: A Population-Based Follow-Up Study.”

Authors: Anne Gaml-Sørensen, Nis Brix, Lea Lykke Harrits Lunddorf, Andreas Ernst, Birgit Bjerre Høyer, Gunnar Toft, Tine Brink Henriksen, and Cecilia Høst Ramlau-Hansen.