From October to March the sun in Lithuania, Latvia and Estonia sits too low for the skin to make meaningful amounts of vitamin D. Stores built up over summer slowly run down, and by late winter many people are low without knowing it.
Why winter is the problem
The skin makes vitamin D when UVB rays reach it. The Baltic states lie between 54° and 59° north. In the darker months the sun is so low that very little UVB reaches the ground, so for roughly half the year food and supplements are the main sources.
Who is at higher risk
- People over 65
- People who spend little time outdoors or cover most of their skin
- People with darker skin
- People with overweight
- Pregnant and breastfeeding women
- People with bowel conditions that affect absorption, such as coeliac or Crohn’s disease
Signs that can point to low vitamin D
Tiredness, muscle weakness or aches, bone pain and low mood. These signs are common and non-specific, so they alone can’t tell you your level. A blood test can.
How to check your level at home
The Testera Vitamin D Test measures 25(OH)D, the form doctors use to assess vitamin D status, from a drop of fingertip blood. In 10 minutes it places your result in one of four ranges:
| Result | ng/ml | nmol/l |
|---|---|---|
| Deficiency | 0–10 | 0–25 |
| Insufficient | 10–30 | 25–75 |
| Sufficient | 30–100 | 75–250 |
| Excess | >100 | >250 |
What to do with the result
If the test shows deficiency or an insufficient level, ask your doctor or pharmacist which dose suits you. Don’t take high doses without advice. Excess is usually caused by taking too many supplements, so talk to a doctor before taking more. Testing again after about 3 months shows whether the dose is working.
Food sources
Oily fish (salmon, herring, mackerel), egg yolks and foods fortified with vitamin D. In winter it is hard to cover your needs with food alone. For reference, EFSA sets an adequate intake of 15 µg (600 IU) a day for adults.
Rapid tests are intended for preliminary screening and do not replace a doctor’s consultation.