Vitamin D levels — how to check them and what to do next
Low vitamin D is more common than most people think. Feeling tired, getting frequent colds, or noticing muscle aches? Those can be signs, but the only clear answer comes from a blood test: the 25‑hydroxyvitamin D (25(OH)D) level. Here's a plain guide to understanding your numbers and improving them without guesswork.
What the numbers mean
The lab report gives a number in ng/mL or nmol/L (multiply ng/mL by 2.5 to get nmol/L). Use these easy targets: under 20 ng/mL = deficiency; 20–30 ng/mL = low/insufficient; 30–50 ng/mL = good for most people. Very high levels (above ~150 ng/mL) can cause problems. Doctors often aim for 30–50 ng/mL for bone and immune health.
If your level is low, don’t panic. Many things affect vitamin D: living far from the equator, spending most time indoors, darker skin, obesity, certain medicines, and aging can all lower levels. Tests are quick and the fixes are straightforward.
How to raise your vitamin D safely
1) Sun: Short, regular sun exposure helps. Aim for about 10–30 minutes of midday sun on arms and legs, 2–3 times a week. Darker skin needs more time. Wear sunscreen after you’ve gotten a brief dose. Avoid sunburn.
2) Food: Add fatty fish (salmon, mackerel, sardines), fortified milk or plant milk, egg yolks, and fortified cereals. Food helps but often isn’t enough alone if you’re deficient.
3) Supplements: For mild low levels, 1,000–2,000 IU (25–50 mcg) daily often works. Many clinicians use up to 4,000 IU daily as a safe upper limit for most adults. For clear deficiency (under 20 ng/mL), short courses of higher doses are common—examples include 50,000 IU once a week for 6–8 weeks—but that should be guided by a clinician. After starting supplements, recheck your 25(OH)D in about 8–12 weeks.
4) Special cases: If you have malabsorption, take certain meds, or are obese, you may need higher doses or different strategies. Pregnant people, older adults, and those with chronic illness should work with a provider to set a plan.
Testing frequency: If you’re changing doses or treating deficiency, test after 8–12 weeks. If levels are stable and in range, annual checks are usually enough.
Watch for symptoms of too much vitamin D: nausea, weakness, frequent urination, or high blood calcium. Very high doses over time can be harmful.
If you’re unsure what dose is right, ask your doctor or pharmacist. A short test and a simple plan often fix low vitamin D, and you’ll likely notice better energy and fewer aches once levels come up.
