What does vitamin D deficiency mean for a pregnancy and for the child’s health?

Around one billion people worldwide are believed to lack vitamin D. This gives cause for concern when it comes to public health, also with regard to pregnant women and their children. Several studies link vitamin D deficiency to a number of different pregnancy-related complications such as preeclampsia, increased risk of preterm delivery, and the need for a Caesarean section. There is also a risk of low birth weight, weak bones, and later development of bronchitis, asthma, type 1 diabetes, sclerosis, and autism, according to a review article published in Nutrients. The authors believe it is necessary to give supplements to help correct vitamin D deficiencies in the expecting mothers and even in the children after birth to prevent many of the diseases and complications linked to low vitamin D status.

Lack of vitamin D is a global concern. Our diet only provides limited quantities of the vitamin. UV rays from sunlight are our main source of vitamin D. At our latitudes, however, we can only synthesize vitamin D during the summer period where the sun is sufficiently strong. And there are factors besides the dark winter period that contribute to the vitamin D deficiency problem, for example spending too much time indoors, being dark-skinned, covering up in clothes, and using too much sunscreen.
The kind of vitamin D that we get from our diet or synthesize in response to sun exposure is inactive. It is converted in the liver to begin with, and then it is converted by the kidneys and various other tissues into its active steroid form (1,25 dihydroxy-vitamin D). It turns out that overweight people and diabetics have difficulty with converting vitamin D precursors into the active form of the nutrient.
Vitamin D is important for the body’s calcium balance and bone health, and it helps regulate different genes by way of multiple on-off switches that affect most of the body’s cells, tissues, and organs.
Judging from science, it looks like the official recommendations for vitamin D are based on bone health only. The actual need for the nutrient may be a lot higher. It’s a bit controversial.

• Vitamin D levels in the blood are measured as 25-hydroxyvitamin D
• The lower vitamin D threshold is 50 nmol/L
• The level for vitamin D sufficiency is above 75 nmol/L
• Many scientists believe that the optimal level is above 100 nmol/L
• The safe upper limit is 160 nmol/L

Vitamin D’s importance in pregnancy

Most of the body’s cells have vitamin D receptors (VDR). The nutrient is of vital importance for fertility, bone maturation in the fetus, teeth, immune defense, brain, nervous system, pancreas, and a number of other functions.
The unborn child is totally dependent on the mother’s vitamin D status, and the nutrient is transferred to the fetus through the placenta. Studies show that vitamin D is activated in the placenta and this process is vital for proper fetal development. If there is too little vitamin D in the placenta, a number of symptoms may occur that can affect the fetus and its development. The whole purpose of the new study was to look closer at vitamin D’s role in fertility, pregnancy, and child health in general.

Conclusion: Pregnant women need supplements that can optimize blood levels of vitamin D

The authors behind the new review article have analyzed a number of different studies and conclude that lack of vitamin D before, during, and after pregnancy is a global problem. Lack of sunlight during the winter period and having a high BMI are particularly concerning risk factors.
A vitamin D deficiency makes it more difficult to become pregnant, and the actual pregnancy may be complicated by different things like preeclampsia, gestational diabetes, and an increased risk of preterm delivery and Caesarean section. There is also a risk of low birth weight, rickets, and later development of weak teeth, bronchitis, asthma, type 1 diabetes, sclerosis, and autism. There is even evidence pointing to an increased risk of developing ADHD.
On the other hand, vitamin D supplementation is linked to positive changes in infant bone development and promising results in the prevention of respiratory diseases like bronchitis and asthma, and in conditions like type 1 diabetes, sclerosis, and autism.
The authors mention that several other researchers have advised women to aim for vitamin D levels above 75 nmol/L prior to conception and to keep them there throughout the entire pregnancy.
The authors conclude that vitamin D levels above 100 nmol/L offer better protection against non-classical deficiency symptoms such as respiratory diseases and autoimmune diseases. The new review article is published in Nutrients.

Supplements of vitamin D for pregnant women

The Danish Veterinary and Food Administration advises pregnant women to supplement with 10 micrograms of vitamin D daily all year round. Unfortunately, many women don’t comply or fail o take the vitamin supplement every day. It even looks as if the official recommendations are too low. Some individuals may need more vitamin D in order to reach optimal levels of the nutrient in the blood. This is the case with overweight people and diabetics, for example. The best way to know for sure is to measure levels with a blood sample – especially during the winter and spring where people are the most likely to be deficient.
It is also important not to get too much vitamin D, which is why there is a safe upper intake level of 100 micrograms daily for adults (including pregnant and breastfeeding women). This is an amount which most people with fair skin and dressed in light clothing can easily synthesize in their skin on a sunny day during the summer.

References:

Jose Luis Mansur et al. Vitamin D: Before, during and after Pregnancy: Effect on Neonates and Children. Nutrients. 2022

Claire Simner et al. Placental uptake and metabolism of 25(OH) vitamin D determine its activity within the fetoplacental unit. eLife 2022

Minna Sucksdorff et al. Maternal Vitamin D Levels and the Risk of Offspring Attention-Deficit/Hyperactivity Disorder. Journal of the American Academy of Child & Adolescent Psychiatry. 2019