Vitamin D: why 80% of the French population is deficient (and how to fix it)
80% of French people have insufficient vitamin D levels according to the latest national data. Behind this worrying figure lie millions of people exposed to increased fatigue, weakened immunity, and an underestimated bone risk. But the good news is that there are simple and effective solutions.
📑 Table of Contents
- Prevalence of vitamin D deficiency in France: current status
- Why are the French so deficient in vitamin D?
- Symptoms of a vitamin D deficiency
- How to diagnose a deficiency: the 25-OH-D test
- Solutions: supplementation and sensible sun exposure
📊 Prevalence of vitamin D deficiency in France: current status
Vitamin D is often cited as a nutrient with widespread deficiencies, but precise figures to measure the true extent are rare. In France, the Esteban study (2014-2016) conducted by Santé publique France constitutes the most recent and representative reference on this subject.
🔴 Figures that speak for themselves
The Esteban study measured serum 25-hydroxyvitamin D (25-OH-D) levels in a representative sample of the adult French population (18-74 years old). The results are telling:
- About 80% of French adults have a 25-OH-D level below 75 nmol/L (30 ng/mL), a threshold considered optimal by many learned societies and international experts.
- More than 40% of adults have a level below 50 nmol/L (20 ng/mL), which the French National Academy of Medicine classifies as a deficiency.
- Certain populations are even more affected: institutionalized elderly people, obese individuals, people with dark skin, and women who wear veils.
These data place France among the European countries most affected by vitamin D hypovitaminosis, despite theoretical sunshine levels more favorable than in Northern Europe.
📅 A marked seasonal variation
Vitamin D levels vary naturally according to the seasons, with a peak at the end of summer (after months of summer sunshine) and a trough at the end of winter (after several months of low UVB radiation). This seasonal variation is measured at approximately 20 to 30 nmol/L between the seasonal extremes in the French population. It explains why supplementation is particularly recommended during the autumn and winter periods (October to April).
🤔 Why are the French so deficient in vitamin D?
Several structural factors explain the high prevalence of vitamin D deficiency in the French population, despite theoretically favorable sunshine conditions.
🌍 Latitude and the seasonality of UVB radiation
Cutaneous synthesis of vitamin D (cholecalciferol, or D3) requires UVB rays with a wavelength of 290-315 nm. At France’s latitude (42° to 51° North), these rays do not reach the Earth's surface adequately between October and March (sometimes until April in the north of the country). During these 5 to 6 months, sun exposure, even in good weather, is ineffective at producing vitamin D in the skin.
In summer, the effective exposure window exists, but it is narrow: the UV index must be greater than 3, which in metropolitan France corresponds roughly to the 10 a.m. to 4 p.m. period from May to September. Outside these slots, the solar angle is too low.
🏢 The contemporary indoor lifestyle
Eurobarometer data and public health surveys estimate that French adults spend on average more than 90% of their time indoors (home, office, transport). However, vitamin D is only synthesized when the skin is directly exposed to the sun’s UVB rays—light filtered through a window is ineffective because glass blocks UVB.
Even for people who go out regularly, the widespread use of sunscreen (recommended for protection against skin cancer) considerably reduces vitamin D synthesis: an SPF 30 sunscreen reduces vitamin D synthesis by approximately 95% (Matsuoka et al., 1987).
🥗 Structurally insufficient dietary intake
Vitamin D is present in a limited number of foods:
- Fatty fish: salmon, mackerel, herring, sardines, anchovies (the most concentrated sources, with 400 to 1,000 IU per 100g depending on the species)
- Cod liver oil (highly concentrated: about 10,000 IU per 100 mL, but difficult to consume in large quantities)
- Egg yolk (about 40-50 IU per yolk)
- UV-exposed mushrooms (only in the D2 form, which is less active)
- Fortified foods: some fortified milks, yogurts, margarines, and orange juices (but levels vary)
The typical French diet provides 3 to 5 µg (120-200 IU) of vitamin D per day — far from the 15 µg/day (600 IU) recommended by EFSA, and even further from the 25 µg/day (1,000 IU) deemed necessary by many experts to maintain an optimal serum level.
⚠️ Aggravating risk factors
- Obesity: Vitamin D is fat-soluble and is stored in adipose tissue, which reduces its circulating bioavailability in overweight or obese individuals. These individuals need higher supplement doses to reach the same serum levels.
- Dark skin: Melanin absorbs UVB rays, reducing the efficiency of cutaneous synthesis. People with darker skin tones may need 5 to 10 times more sun exposure to produce the same amount of vitamin D as a person with light skin.
- Advanced age: The skin’s ability to synthesize vitamin D decreases with age (about 75% less at 70 compared to 20 years old). Furthermore, intestinal absorption and hepatic/renal conversion into the active form are reduced in the elderly.
- Digestive pathologies: Inflammatory bowel diseases (Crohn’s, ulcerative colitis), celiac disease, and bariatric surgeries reduce the absorption of fat-soluble vitamins, including D.
😔 Symptoms of a vitamin D deficiency
Vitamin D deficiency is often described as silent, as its symptoms are non-specific and can be attributed to other causes. Yet, certain signals should be taken seriously.
⚡ Persistent fatigue and lack of energy
Fatigue is one of the most commonly reported symptoms by people deficient in vitamin D. Vitamin D receptors are present in the mitochondria, the cells' power plants. A deficiency can disrupt cellular energy metabolism. Clinical studies have shown subjective improvement in fatigue after correcting a vitamin D deficiency.
🛡️ Frequent infections
Vitamin D contributes to the normal functioning of the immune system. People with low vitamin D levels tend to have more frequent or more severe infections, especially respiratory infections (colds, flu, bronchitis). This observation is consistent with the seasonal peak of respiratory infections in winter, a period when vitamin D levels are at their lowest.
🦴 Bone and muscle pain
Vitamin D contributes to the maintenance of normal bones and normal muscle function. A deficiency can lead to diffuse bone and muscle pain, sometimes confused with fibromyalgia or chronic fatigue syndrome. The pain often predominates in the lower back, hips, and lower limbs. In the elderly, severe vitamin D deficiency is associated with a loss of muscle strength (sarcopenia) and an increased risk of falls and fractures.
🧠 Low mood and mood disorders
Associations between low vitamin D levels and depression or depressive symptoms have been reported in many observational studies. The causal relationship is still debated, but the biological mechanisms are plausible: vitamin D influences serotonin synthesis and cortisol regulation. The famous "winter blues" (or seasonal affective disorder) coincides with the period of maximum decline in vitamin D levels.
🩺 How to diagnose a deficiency: the 25-OH-D test
🔬 Serum 25-OH-D testing
The gold standard biomarker for vitamin D status is serum 25-hydroxyvitamin D (25-OH-D), also called calcidiol. It is the main circulating form of vitamin D and the one that best reflects long-term body stores (it has a half-life of about 2 to 3 weeks).
The interpretation of results is a subject of debate between learned societies, but the thresholds generally accepted in France are:
- Below 25 nmol/L (10 ng/mL): severe deficiency (risk of rickets in children, osteomalacia in adults)
- 25 to 50 nmol/L (10-20 ng/mL): vitamin D deficiency
- 50 to 75 nmol/L (20-30 ng/mL): relative insufficiency according to many experts
- Above 75 nmol/L (30 ng/mL): level considered optimal
- Above 250 nmol/L (100 ng/mL): potential risk of toxicity
📋 Who should get tested?
The 25-OH-D test is not systematically reimbursed in France: the French National Authority for Health (HAS) recommends prescribing it in high-risk situations (the elderly, obese, dark-skinned individuals, those with digestive pathologies, osteoporosis, high-risk pregnancies, etc.). If you suspect a deficiency without identified risk factors, the test is available at the patient's own expense or through certain health insurance providers.
💡 Solutions: supplementation and sensible sun exposure
☀️ Optimize sun exposure
Sun exposure remains the most natural and effective source of vitamin D. For optimal cutaneous synthesis:
- Expose the arms, legs, and face (without sunscreen) for 15 to 30 minutes, ideally between 10 a.m. and 3 p.m., from May to September in France.
- The optimal duration varies according to skin type, latitude, time of day, and season.
- Sun exposure for vitamin D synthesis does not replace the need for sun protection during longer durations to avoid the risk of skin cancer.
💊 Vitamin D3 supplementation: effectiveness and doses
Vitamin D3 (cholecalciferol) supplementation is the most reliable method for correcting and maintaining an optimal 25-OH-D level, particularly from October to April. Key points:
- Form D3 (cholecalciferol) is preferable to D2: cholecalciferol is more effective at raising and maintaining 25-OH-D levels in the blood.
- Daily dose: 1,000 to 2,000 IU/day (25 to 50 µg) is generally recommended to maintain an optimal level in healthy adults. Higher doses may be necessary in case of a confirmed deficiency, under medical prescription.
- Take with fats: as a fat-soluble vitamin, D3 is better absorbed when taken with a meal containing fats.
- Combination with K2: as explained in our dedicated article, the D3+K2 combination is recommended to optimize calcium utilization and protect the arteries.
📅 When to supplement?
Ideally:
- From October to April: systematic supplementation for the entire population, due to the lack of effective cutaneous synthesis.
- From May to September: supplementation can be reduced or stopped for people who get regular sun exposure.
- Year-round for at-risk populations: elderly, obese, dark-skinned individuals, those living indoors, or those with pathologies reducing absorption or synthesis.
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✅ In summary
1️⃣ About 80% of French people have a vitamin D level below the optimal threshold according to the Esteban study by Santé publique France.
2️⃣ The main causes are geographic latitude, an indoor lifestyle, insufficient dietary intake, and the use of sunscreen.
3️⃣ Symptoms include fatigue, frequent infections, bone and muscle pain, and low mood — often non-specific and poorly understood.
4️⃣ Vitamin D3 supplementation (1,000 to 2,000 IU/day) is recommended from October to April for the entire French population, preferably in combination with vitamin K2.
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Scientific sources:
- Santé publique France (2019). Étude Esteban 2014-2016 — Volet nutrition : statut en vitamine D de la population adulte française. Bull Epidemiol Hebd. 2019;(3-4):43-55.
- Matsuoka LY, et al. (1987). Sunscreens suppress cutaneous vitamin D3 synthesis. Journal of Clinical Endocrinology & Metabolism, 64(6):1165-8.
- Holick MF. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3):266-81.
- EFSA Panel on Dietetic Products, Nutrition, and Allergies (2017). Dietary reference values for vitamin D. EFSA Journal, 14(10):4547.
- Martineau AR, et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ, 356:i6583.
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