Vitamin D: What It Does and Why You Should Care

Most people think vitamin D is only about bones. True, calcium needs vitamin D, but D also helps your immune system, mood, and muscle strength. Low levels show up as fatigue, frequent colds, bone or muscle pain, and mood dips. Want clear steps to check and fix your D? Keep reading.

Common signs of low vitamin D and who’s at risk

If you feel tired a lot, catch colds often, or have unexplained aches, low vitamin D might be part of the problem. People who spend little time outdoors, wear covering clothing, have darker skin, are older, or live far from the equator are more likely to be low. Certain medical conditions and some medicines — like steroids and some seizure drugs — can also lower D levels.

Lab tests measure 25-hydroxyvitamin D. Rough ranges most doctors use: under 20 ng/mL is deficient, 20–30 ng/mL is low, and above 30 ng/mL is usually considered adequate for most people. Talk to your provider about what target level is best for you.

Real ways to raise and keep vitamin D in a healthy range

Sunlight is the fastest way. Around 10–30 minutes of midday sun on face and arms a few times a week often helps — less time if you’re fair-skinned, more if you’re darker. Seasonal changes and sunscreen reduce production, so don’t rely on sun year-round.

Eat vitamin D-rich foods: fatty fish (salmon, mackerel, sardines), fortified milk or plant milks, fortified cereals, egg yolks, and some mushrooms. Food alone usually isn’t enough for many people, which is why supplements are common.

When choosing a supplement, vitamin D3 (cholecalciferol) is the preferred form for most adults; it raises blood levels more reliably than D2. Typical maintenance doses range from 600–2,000 IU daily for many adults. People with confirmed deficiency often need higher short-term doses — sometimes 5,000–10,000 IU daily or a weekly high dose under medical supervision. Long-term daily doses above 4,000 IU should only be taken under a doctor’s advice.

Watch for interactions and risks. High vitamin D increases calcium absorption, so combining high-dose D with calcium supplements can raise the risk of hypercalcemia. Certain drugs can change how your body handles vitamin D. If you’re pregnant, nursing, on medication, or have health issues, ask a clinician before starting big doses.

Quick checklist: get a 25(OH)D test if you have risk factors or symptoms, aim for sensible sun exposure, eat D-rich foods, and use D3 supplements when needed. Simple steps often give clear results within weeks to months. Want tailored advice? Contact your healthcare provider for a test and a plan that fits your life and health goals.