Vitamin D deficiency: symptoms, causes, and how to address it in France

In France, 80% of the population has insufficient vitamin D levels according to ANSES - and this figure rises to over 90% in winter. Yet vitamin D contributes to the proper functioning of the immune system, bone strength, hormonal balance, and mental health. Here is how to recognize a deficiency, why it is so common at our latitudes, and how to supplement effectively.

Why vitamin D deficiency is almost universal in France

Vitamin D is synthesized by the skin when exposed to solar UVB radiation. In mainland France, the sun is high enough only from May to September to allow this synthesis. During the other 7 months, even prolonged exposure does not produce significant amounts of vitamin D. Office work, wearing covering clothing, using high-SPF sunscreen, and a diet that can cover only a small portion of the body's needs also contribute.

Signs of vitamin D deficiency

Fatigue and lack of energy

Vitamin D plays a role in cellular energy production and serotonin regulation. A deficiency can result in unexplained fatigue, reduced motivation, and low mood - particularly pronounced in autumn and winter.

Recurrent infections

Vitamin D contributes to the normal functioning of the immune system. Studies show a correlation between low levels and increased susceptibility to respiratory infections (colds, bronchitis, and flu).

Diffuse bone and muscle pain

Vitamin D is essential for the intestinal absorption of calcium and phosphorus. A prolonged deficiency can cause diffuse pain, particularly in the lower back, hips, or shins.

Seasonal depression and anxiety

The link between low vitamin D levels and mood disorders is one of the best scientifically documented. Vitamin D receptors are present in brain regions involved in emotional regulation.

Slow wound healing

Vitamin D plays a role in several stages of skin repair. Slower-than-usual healing may be an indirect sign of an established deficiency.

How to confirm a deficiency

A blood test measuring the level of 25-hydroxyvitamin D (25-OH-D) is the only reliable method. Reference values: insufficiency below 30 ng/mL, severe deficiency below 10 ng/mL, and an optimal level between 40 and 60 ng/mL.

Vitamin D2 or D3: which should you choose?

Vitamin D3 (cholecalciferol) is the form naturally produced by the skin and the most effective for sustainably increasing blood levels. For vegans, plant-based vitamin D3 extracted from lichen is available - it is just as effective as animal-derived D3. Vitamin D2 (ergocalciferol) is less effective at sustainably raising blood levels.

What dosage should you take, and when?

The recommended daily intake is 800 IU for an adult. At French latitudes, 1,000 to 2,000 IU per day is more suitable for maintaining optimal levels outside the summer period. Vitamin D is fat-soluble: take it with a meal containing fat. Morning or midday is preferable to evening.

Key takeaways

In France, not supplementing with vitamin D from September to April means accepting that you will spend a large part of the year deficient. The effects of regular supplementation can be felt in immunity, energy, mood, and bone health. Choose vitamin D3, take it with a fatty meal, and ideally combine it with vitamin K2.

Food supplements. A blood test by your doctor is recommended before taking high doses of supplements.