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In France, over 70% of adults are believed to have vitamin D levels below 30 ng/mL, according to the French National Academy of Medicine. This silent deficiency can impact bone and muscle health, as well as immunity. How do you know if you are affected? Which foods or supplements should you prioritize? And most importantly, how can you effectively correct a deficiency?
Why is vitamin D so essential?
Vitamin D is a fat-soluble vitamin essential for the normal functioning of the immune system, calcium absorption, and the maintenance of good bone health. It exists in two forms: vitamin D2 (ergocalciferol), of plant origin, and D3 (cholecalciferol), which is better absorbed by the body. It is synthesized by the skin when exposed to UVB rays, but is also present in some rich foods such as fatty fish (salmon, mackerel, sardines), fortified dairy products, or cod liver oil.
What are the symptoms of vitamin D deficiency?
A serum vitamin D level below 30 ng/mL is considered insufficient. Below 20 ng/mL, it is considered a true deficiency. Warning signs include:
- unexplained bone and muscle pain,
- muscle weakness, especially in the legs,
- persistent fatigue,
- increased susceptibility to infections,
- in children, a risk of rickets,
- in adults, an increased risk of fractures and osteomalacia.
Vitamin D deficiency can also impair athletic performance, slow down recovery, and disrupt hormonal balance, particularly through insufficient cortisol regulation.
What causes vitamin D deficiency?
Several factors can limit vitamin D production or intake:
- lack of sun exposure, especially in winter or with frequent use of sunscreen,
- a diet poor in vitamin D-rich foods (fatty fish, egg yolks, fortified dairy products),
- aging, which reduces the skin's ability to synthesize vitamin D,
- certain diets (vegan, low-fat),
- impaired intestinal absorption (inflammatory diseases),
- taking certain medications.
Pregnant women, athletes with high training volumes, and the elderly are particularly at risk.
How to confirm a vitamin D deficiency?
A blood test measures the level of 25-hydroxyvitamin D in the blood, the circulating form used to assess vitamin status. If in doubt or if you experience symptoms, it is recommended to consult your doctor for an analysis and possible supplementation.
What strategy should be adopted to correct a deficiency?
Diet alone is rarely enough to meet daily needs (between 600 and 800 IU per day for adults, 1000 to 2000 IU in case of confirmed deficiency). Vitamin D3 supplementation is therefore often necessary, especially in winter. It should preferably be taken with a meal containing fats for better absorption. The frequency depends on the chosen product (daily, weekly, or monthly). It is essential to respect the recommended doses to avoid any risk of overdose (hypercalcemia, abdominal pain, fatigue, etc.).
Diet, sun, and supplements: a combined approach
To maintain good vitamin D levels all year round:
- Expose yourself to the sun for 15 to 20 minutes a day (outside of peak risk hours),
- Regularly consume foods rich in vitamin D: cod liver, fatty fish, eggs, fortified dairy products, dark chocolate,
- Supplement if necessary, taking into account your status, dietary intake, season, and specific needs.
Scientific references
Académie Nationale de Médecine. Vitamine D : une carence fréquente en France. https://www.academie-medecine.fr
Holick MF. Vitamin D deficiency. N Engl J Med. 2007 Jul 19;357(3):266–81. https://pubmed.ncbi.nlm.nih.gov/17634462
