As winter approaches here in Australia, especially in the southern states like Victoria, I am starting to remind my patients about the importance of Vitamin D particularly for pregnant women.

I don’t know about you, but I am started to rug up. This means that in places like Ballarat, where sunlight is limited in the colder months, getting enough Vitamin D becomes a real challenge.

Vitamin D plays a crucial role in pregnancy. It helps your body absorb calcium, which is vital for building your baby’s bones and teeth. Low Vitamin D levels during pregnancy have been linked to complications such as increased risks of asthma and autoimmune conditions in children. Some studies have also shown that low vitamin D levels while pregnancy are associated with complications like preeclampsia and diabetes.

Where do we get Vitamin D from?

Our primary source of Vitamin D is sunlight.

When your skin is exposed to UVB rays from the sun, it synthesises Vitamin D. In summer generally fair-skinned people need just a few minutes of sun exposure on their hands, arms, and face to produce adequate Vitamin D. However, darker-skinned individuals require significantly more sunlight, sometimes three to six times as much, because melanin reduces the skin’s ability to produce Vitamin D.

How do we balance getting enough Vitamin D without increasing our skin cancer risk?

Sun safety is critical. We talk about avoiding direct sun exposure during peak UV hours (11:00 AM to 3:00 PM) to reduce skin cancer risk. A practical tip is to check the UV index on your phone. If it’s above three, a few minutes of sun exposure to your face and arms can help top up your Vitamin D levels without risking sunburn.

In winter, particularly in our hometown of Ballarat, the UV index rarely gets about 3. It’s often dark when you leave for work and dark when you come home, which means less opportunity for sunlight exposure. On top of that, many of us cover up and wear layers for warmth, which blocks Vitamin D synthesis.

With the lack of sun at this time of year, I am often surprised at how quickly a patient will have a drop in Vitamin D during winter.

Are there other sources of Vitamin D?

Vitamin D is a fat-soluble vitamin, meaning it requires dietary fat for absorption and can be stored in the body. Unfortunately, natural food sources of Vitamin D are limited and not easily absorbed. Fatty fish like salmon and sardines, eggs fortified with Vitamin D, and specially treated mushrooms are good options but may not be enough on their own.

Supplements can help fill the gap, but it’s important to get the dose right. Prenatal vitamins typically contain between 400 to 1,000 international units (IU) of Vitamin D daily, enough to maintain levels in most people but not enough to correct a deficiency. Pregnant women who are deficient may require higher doses, up to 4,000 IU. When this is the case, our dietitian Rachel Jeffery helps to monitor dosage to avoid excess.

Do I need my Vitamin D tested?

Vitamin D testing isn’t routine in pregnancy but probably should be, especially in winter or for women at higher risk of deficiency. Conditions like polycystic ovary syndrome (PCOS) also increase the risk of low Vitamin D. Testing helps ensure that supplementation is effective and safe. Like iron, Vitamin D levels and stores matter, simply taking the recommended daily intake won’t fix a deficiency quickly.

My take home message…

For pregnant women, Vitamin D is more than just a nutrient, it’s a key player in maternal and baby health. In the winter months, sunlight alone often isn’t enough. Talk to your healthcare provider about getting your Vitamin D levels checked and whether you might need supplementation. Remember to balance safe sun exposure with your skin cancer risk, and don’t rely solely on prenatal vitamins if you’re deficient.

Winter is coming, and so is the need to be vigilant about Vitamin D especially if you’re growing a whole new human.

Written by Obstetrician & Gynaecologist, Dr Patrick Moloney