Asking for a blood test to check your vitamin D level has become something of a trend in recent years. In reality, routine testing is unnecessary for most healthy people — a preventive daily dose from autumn to spring keeps the level safely within range.
A preventive dose is enough for a healthy person
At Estonian latitudes it is entirely sufficient for a healthy adult to take a supplement from autumn to spring — the months with an R in their name, September to April — at a preventive dose of 1000–2000 IU (25–50 µg) per day, without any blood test. May, June, July and August are the months when the required amount comes from summer sunlight.
How to improve vitamin D absorption
Vitamin D is fat-soluble, so how well it is absorbed depends directly on how and when you take it.
- Take it with a meal containing fat. Vitamin D needs fat to be absorbed. A breakfast or lunch containing healthy fats (nuts, seeds, avocado, eggs, butter, oily fish or olive oil) can increase absorption by up to 30–50%.
- Prefer oil-based capsules or drops. Softgel capsules or oil drops (coconut, hemp or olive oil based) help the active ingredient absorb better.
- Take it in the first half of the day. Taken in the evening, vitamin D may in some people interfere with the production of melatonin, the sleep hormone.
- Keep an eye on magnesium and vitamin K2. Magnesium is needed to convert vitamin D into its active form. Vitamin K2 helps direct the absorbed calcium into bones and teeth.
When is a blood test medically justified?
If you have health concerns, discuss the need for a blood test with your doctor. Testing is indicated when there are specific health conditions, absorption disorders or particular risk factors.
1. Disorders of bone and mineral metabolism
- Osteoporosis and osteopenia. When bone density is reduced, knowing the exact vitamin D level is needed to set the right treatment dose.
- Frequent fractures. Especially when they follow minor injuries or occur in older people.
- Unexplained joint, muscle or bone pain. Severe vitamin D deficiency can cause softening of the bones (osteomalacia) or chronic muscle weakness.
2. Absorption disorders and digestive diseases
- Coeliac disease and inflammatory bowel disease (Crohn’s disease, ulcerative colitis).
- Condition following bariatric surgery.
- Chronic liver disease or pancreatic insufficiency.
3. Long-term use of certain medicines
- Glucocorticosteroids, for example long-term prednisolone treatment.
- Anticonvulsant medicines.
- Certain antifungal and weight-loss medicines.
4. Kidney and liver failure
Vitamin D is converted into an active hormone only in the liver and the kidneys. In patients with severe kidney or liver failure the level needs to be monitored, and active forms of vitamin D are often required.
5. Significant obesity
Visceral and subcutaneous fat tissue binds vitamin D, so less of it reaches the bloodstream. With a body mass index above 30, people often need higher than usual doses and the level is worth checking.
6. Checking the effect and safety of treatment
- If a test has previously shown severe deficiency and a doctor has prescribed a treatment dose, a repeat test is done after 3–6 months to confirm that the level has recovered.
- If very high doses are taken over a long period, to rule out overdose and hypercalcaemia — an excessively high blood calcium level.
In summary
If none of the conditions above apply to you, it is entirely sufficient to take a preventive dose of 1000–2000 IU (25–50 µg) per day from autumn to spring, together with a meal containing fat — without a blood test.
If something on the list does apply to you, the test is worth doing on your doctor’s advice. At Valvekliinik blood tests can be taken without a referral and the results discussed with a doctor.
Frequently asked questions
Do I need to have my vitamin D level measured?
Most healthy people do not. A preventive dose of 1000–2000 IU (25–50 µg) per day from September to April keeps the level safely within range without testing. A blood test is needed when there are specific conditions, absorption disorders or risk factors.
How much vitamin D should I take per day?
For a healthy adult, 1000–2000 IU (25–50 µg) per day from autumn to spring. EFSA considers up to 4000 IU (100 µg) per day safe for a healthy adult. That figure does not apply to everyone: in some conditions — sarcoidosis, an overactive parathyroid gland or severe kidney disease, for example — even a smaller dose can be too much. To treat a deficiency a doctor sometimes prescribes higher doses, but those are always taken under medical supervision.
Is it better to take vitamin D in the morning or the evening?
In the first half of the day, with a breakfast or lunch containing fat. Taken in the evening it may interfere with melatonin production in some people.
Do I need to take vitamin D in summer?
From May to August a healthy person gets the required amount from sunlight. Supplementation is usually resumed in September.
This article is general health information and does not replace a doctor’s assessment. Always consult your own doctor about treatment and dosage.
References
- Tartu University Hospital and the Estonian Society of Internal Medicine. Estonian expert-approved guidance on vitamin D use.
- EFSA (European Food Safety Authority). Scientific Opinion on Dietary Reference Values for Vitamin D.
- Endocrine Society Clinical Practice Guideline. Evaluation, Treatment, and Prevention of Vitamin D Deficiency.
- Synlab Estonia / Estonian Society for Laboratory Medicine. 25-hydroxyvitamin D (S,P-25-OH-VitD) laboratory handbook guidance.
- Journal of Bone and Mineral Research. Dietary Fat Increases Vitamin D Absorption.
