The importance of vitamin D during pregnancy

By Jessamy Kaval, Registered Midwife and Nutrition Consultant

Vitamin D is an essential nutrient during pregnancy, supporting the health of both mother and baby. While it is best known for its role in maintaining healthy bones, vitamin D also contributes to immune function, muscle health, cell growth, and fetal development. Despite Australia's sunny climate, vitamin D deficiency remains relatively common, making it an important nutrient to consider throughout pregnancy.

Even in sunny climates, deficiency can occur, particularly during winter or in people with limited sun exposure.

Why is vitamin D important during pregnancy?

Vitamin D helps the body absorb calcium and phosphorus, two minerals that are essential for building your baby's bones and teeth. Throughout pregnancy, your baby's skeleton develops rapidly, particularly during the second and third trimesters, making adequate vitamin D status increasingly important.

For mothers, maintaining sufficient vitamin D supports bone health, muscle function, and normal immune regulation. Low maternal vitamin D status has also been associated with several pregnancy complications, although research is ongoing to better understand these relationships.^[7]

Current evidence suggests that low maternal vitamin D status is associated with an increased risk of:

• Reduced fetal and neonatal bone mineralisation
• Lower vitamin D status in newborns
• Gestational diabetes
• Hypertensive disorders of pregnancy, including pre-eclampsia
• Preterm birth
• Low birth weight

How much vitamin D do you need?

Vitamin D requirements vary considerably depending on sunlight exposure, skin pigmentation, geographic location, and existing vitamin D status. In Australia, the Nutrient Reference Values recommend an adequate intake of 10 micrograms (400 IU) per day during pregnancy, assuming adequate sun exposure.^[1][2] However, this recommendation is likely to be well below the requirement for most women and is not intended to treat or prevent deficiency.

Many prenatal vitamins contain approximately 400 to 1,000 IU of vitamin D daily. Women with low vitamin D levels or those at increased risk of deficiency may require additional vitamin D3 supplementation, often between 1,000 and 4,000 IU per day, under the guidance of their healthcare provider following blood testing.^[4][6]

Food sources of vitamin D

Unlike many other nutrients, vitamin D is naturally found in only a small number of foods. Diet contributes to overall vitamin D intake but usually provides only a small proportion of total vitamin D requirements.

Good food sources include:

• Oily fish such as salmon, sardines, trout and mackerel
• Eggs (particularly the yolk)
• Fortified milk, plant-based milks, breakfast cereals and some margarines
• UV-exposed mushrooms
• Cod liver oil (being aware of vitamin A content)

Including vitamin D-rich foods regularly can help support overall intake alongside appropriate sun exposure where possible.

Sunlight: our primary source of vitamin D

The majority of vitamin D is produced in the skin following exposure to ultraviolet B (UVB) sunlight.

However, many factors influence how much vitamin D your body produces, including:

• Season of the year
• Time of day
• Latitude and where you live
• Cloud cover and air pollution
• Skin pigmentation
• Age
• Sunscreen use
• Clothing that covers most of the skin
• Time spent indoors

In Australia, recommendations around sun exposure vary depending on the season and location to balance vitamin D production with skin cancer prevention. Even in sunny climates, deficiency can occur, particularly during winter or in people with limited sun exposure.

Who may be at higher risk of vitamin D deficiency?

Some women are more likely to have low vitamin D levels during pregnancy, including those who:

• Have darker skin pigmentation
• Wear clothing that covers most of their skin
• Spend limited time outdoors
• Live in southern regions during winter
• Have obesity
• Have gastrointestinal conditions that affect nutrient absorption, such as coeliac disease or inflammatory bowel disease
• Have previously been found to have low vitamin D levels

If you have one or more of these risk factors, your healthcare provider may recommend a blood test to assess your vitamin D status.

When should supplementation be considered?

Vitamin D supplementation is generally recommended for women with confirmed deficiency or those considered at increased risk based on their individual circumstances.^[3][5]

The appropriate dose depends on your blood vitamin D level, risk factors and medical history. While most prenatal multivitamins contain vitamin D3, the amount is often insufficient to correct an existing deficiency.

If additional supplementation is required, your healthcare provider may recommend a separate vitamin D3 supplement. Because vitamin D3 is a fat-soluble vitamin, absorption is enhanced when taken with a meal containing healthy fats.

If you're unsure whether supplementation is appropriate for you, speak with your healthcare provider. They may recommend a blood test if indicated.

Practical tips to support healthy vitamin D levels

• Include vitamin D-rich foods regularly.
• Follow local sun safety recommendations while aiming for appropriate sunlight exposure.
• Discuss vitamin D testing if you have risk factors for deficiency.
• Place mushrooms in direct sunlight for 30 to 60 minutes before cooking to naturally increase their vitamin D2 content.
• Include eggs regularly as part of a balanced diet, as they provide small amounts of vitamin D.

Vitamin D plays an important role in supporting both maternal health and your baby's growth and development throughout pregnancy, and in building your baby's stores for after birth. While food sources contribute to overall intake, sunlight remains the primary source of vitamin D for most people. Because deficiency is relatively common and risk varies between individuals, it's worthwhile discussing your vitamin D status with your healthcare provider, particularly if you have known risk factors. Identifying and treating deficiency when present is an important part of supporting a healthy pregnancy.

Read this article on Her Journey · Health education, not medical advice.