Vitamin D in winter: why 80% of Europeans miss the sun

At European latitudes, winter sun no longer suffices to synthesise vitamin D. Detail of the consequences and the correct dosage.

It's a geophysical fact: above the 40th parallel north (i.e. all of central and northern Europe), the angle of solar incidence from October to March is too low to allow cutaneous vitamin D synthesis. The result: 80% of European adults have low status at the end of winter.

From October to March above the 40th parallel, the sun no longer suffices to synthesise vitamin D, which explains the deficiency in 80% of Europeans. Prolonged deficiency weakens immunity and bone capital. The recommended winter floor dose is 10 to 25 µg (400, 1000 IU), without exceeding the UL of 100 µg.

The consequences of a winter deficiency

Immune system: vitamin D modulates the innate and adaptive immune response. A deficiency correlates with greater susceptibility to respiratory infections (Martineau et al. meta-analysis, BMJ 2017).

Bones: vitamin D promotes intestinal calcium absorption (authorised EFSA claim). Prolonged deficiency = compromised bone capital.

Mood: the association between low vitamin D status and depressive symptoms remains debated but documented in several cohorts (Holick, Nutrients 2017).

What dosage?

EFSA sets the NRV at 5 µg (200 IU), but this historical value is largely insufficient to maintain a status >75 nmol/L. Most learned societies now recommend 10 to 25 µg (400, 1000 IU) in winter for a healthy adult, without exceeding the UL of 100 µg (4000 IU).

Our Complete Multivitamin provides 10 µg of vitamin D3 (200% NRV), the floor dose recommended in winter. If blood status is very low (<30 nmol/L), a separate, higher-dose supplementation is justified, on medical advice.

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