Why is vitamin D crucial right now? A winter "power-up" for your immunity.
In winter, sunlight becomes scarce. Days are short, sunlight is weak, and most of us spend our time in offices, schools, and homes. With the decline of sunlight, our levels of vitamin D—one of the most important health regulators—dramatically drop. Although often associated with strong bones, vitamin D affects almost every system in our body: immune, nervous, cardiovascular, and hormonal.
After summer – an apparent supply of sunshine
In the summer, it seems like we're "in the black" with vitamin D. Under the influence of UVB rays, the skin synthesizes it from cholesterol, and just 15–20 minutes of daily sun exposure is enough to increase vitamin D levels. The problem is, the body only stores it for a few weeks.
Why do we have a deficiency in winter?
There are several reasons – and almost every one of us meets at least one of them:
- Too little sun: in Poland, for half the year, the angle of incidence of UVB rays prevents them from working effectively.
- Sunscreens: SPF 30 reduces vitamin D synthesis by as much as 95%.
- Lifestyle: working and studying indoors, little outdoor exercise.
- A diet poor in vitamin D sources.
- Overweight and obesity: vitamin D dissolves in fat and “hides” in fatty tissue, making it less available to the body.
Effects of vitamin D deficiency
Vitamin D deficiency is a silent but very serious health problem. Here's how it affects our bodies:
- Skeletal system: reduced calcidiol levels lead to bone demineralization – increases the risk of osteoporosis, fractures, and in children causes rickets.
- Immune system: Vitamin D stimulates the production of antimicrobial peptides, strengthening natural immunity. Vitamin D deficiency is associated with an increased incidence of respiratory infections.
- Brain and mood: Vitamin D receptors are found in the central nervous system. Low concentrations contribute to seasonal depression and sleep disturbances.
- Circulatory system and metabolism: deficiency increases the risk of hypertension, insulin resistance and type 2 diabetes.
- Anti-cancer immunity: adequate levels of vitamin D may reduce the risk of certain cancers (e.g. colon, breast, prostate).
Vitamin D level test
The laboratory measures serum levels of 25-hydroxyvitamin D (25-OH D), the storage form of vitamin D. This is the most accurate way to assess its status in the body.
Interpretation of results (according to the guidelines of the Polish Endocrine Society):
| 25(OH)D level | Interpretation |
|---|---|
| < 20 ng/ml (50 nmol/l) | Deficiency |
| 20–30 ng/ml (50–75 nmol/l) | Insufficient level |
| 30–50 ng/ml (75–125 nmol/l) | Optimal level |
| 50–100 ng/ml (125–250 nmol/l) | High, safe level |
| > 100 ng/ml (250 nmol/l) | Risk of toxicity |
It is recommended to have your vitamin D level checked once a year, preferably in late autumn or winter when the risk of deficiency is highest.
Supplementation – sun in a capsule
In Poland, vitamin D supplementation is recommended from October to April, and in people with little sun exposure – year-round.
Recommended doses of vitamin D (for healthy people):
| Age group / condition | Recommended daily dose |
| Children 1–10 years old | 600–1000 IU (15–25 µg) |
| Youth and adults (11–65 years) | 800–2000 IU (20–50 µg) |
| Seniors >65 years old | 1000–2000 IU (25–50 µg) |
| People with obesity | 1600–4000 IU (40–100 µg) |
| Pregnant and breastfeeding women | 1500–2000 IU (37.5–50 µg) |
It is worth remembering to take vitamin D with a meal containing fat, which increases its absorption.
In winter, our body produces almost no vitamin D, so it is worth supplementing it after having your level checked and consulting with your doctor what dose will be most appropriate for you.
Maintaining healthy levels of this “sunshine vitamin” supports immunity, mood, and bone health year-round.
Bibliography
https://journals.viamedica.pl/endokrynologia_polska/article/view/EP.2013.0012
https://www.nejm.org/doi/full/10.1056/NEJMra070553https://pubmed.ncbi.nlm.nih.gov/26977036/
https://www.endokrynologia.net/poradnik-pacjenta/wpis/niedobor-witaminy-d
https://www.poradnikzdrowie.pl/aktualnosci/witamina-d-dla-polakow-sprawdz-te-normy-jesli-mieszkasz-w-polsce-aa-P1WZ-pwqF-oabs.html
The information contained in this article is for general informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. It is recommended that you consult a physician or other qualified healthcare professional for advice regarding specific symptoms, ailments, or health conditions.