Vitamin D3: bones, immunity and winter support for your maternity

It is the only vitamin produced primarily through sun exposure, which sets it apart from all others. Once available, it is converted by the liver into 25(OH)D, its storage form, then activated by the kidneys into 1,25(OH)2D, the hormonal form that acts throughout the body. This dual hepatic and renal conversion makes it a vitamin that requires careful attention across the seasons. During pregnancy, it supports the development of the baby's skeleton and contributes to the maintenance of normal bone structure in the mother, which justifies particular attention to its form and the quality of the raw material used.

In its natural form, diet provides a fairly modest share of the vitamin D3 you need, as few foods are naturally rich in it. The main sources are oily fish such as salmon, herring, mackerel or sardines, as well as egg yolk, cod liver and certain fish liver oils. Vitamin D3 has the distinction of being the only vitamin produced primarily through sun exposure: your skin can produce it under the effect of UVB rays, which makes it unique among micronutrients. The limitation in mainland France comes from latitude: between October and March, UVB radiation becomes insufficient to allow effective skin synthesis, and diet alone then struggles to meet requirements, especially during pregnancy, breastfeeding, and for women with limited sun exposure for the rest of the year.

As a food supplement, two main forms coexist: vitamin D3, or cholecalciferol, and vitamin D2, or ergocalciferol. D3 cholecalciferol is better absorbed and stored more effectively in the body than D2, which is why it is now favoured in most quality formulations. Traditionally, D3 is extracted from sheep lanolin, but it can also be obtained from a lichen, which opens up an entirely plant-based option, particularly appreciated by vegan or vegetarian women. At Jolly Mama, we use only the vitamin D3 form. You can find our vitamin D supplements and our complete pregnancy supplements, in which D3 is often combined with vitamin K2 menaquinone (MK7) to direct calcium towards the bones. In terms of quality, the key things to look at are the exact form (cholecalciferol), the dosage per daily serving, the traceability of the raw material, and the synergy with K2.

Adequate vitamin D3 intakes by life stage

Recommended vitamin D intakes (µg/day)

• Adult women (18+): 15 µg/day — 600 IU (EFSA 2016)
• Pregnancy: 15 µg/day — 600 IU (EFSA 2016)
• Breastfeeding: 15 µg/day — 600 IU (EFSA 2016)
• Upper safety limit: 100 µg/day — 4,000 IU (EFSA)

D3 cholecalciferol

• Efficacy in raising serum 25(OH)D: superior (Tripkovic 2012)
• Tissue storage: superior
• Molecular stability: more stable
• Origin: animal (lanolin) or plant-based (lichen)

D2 ergocalciferol

• Efficacy in raising serum 25(OH)D: lower
• Tissue storage: lower
• Molecular stability: less stable
• Origin: plant-based (yeast)

Did you know: In mainland France, the UVB radiation needed for the skin to synthesise vitamin D3 becomes insufficient between October and March. During these six months, your skin can barely produce any vitamin D, regardless of your sun exposure. Your only possible sources then become food — rich in D3 mainly through oily fish and egg yolk — and supplementation, which is why D3 has become a winter habit for many women.