Vitamin D — what it does, how to know if you’re low, and what to do
Vitamin D isn’t just for bones. It helps your immune system, muscle strength, and mood. Low levels show up as tiredness, weak muscles, slower healing, or frequent colds. If you feel off and don’t get sun or eat vitamin D foods, testing makes sense.
Doctors check 25-hydroxyvitamin D (25(OH)D) in the blood. Most clinicians aim for about 30–50 ng/mL as a comfortable range for general health. Below that, you may need supplements. If your level is under 20 ng/mL, that’s usually considered a deficiency and often needs a loading dose plus maintenance.
Sun, food, and supplements — what works best?
Sunlight on bare skin makes vitamin D fast. About 10–30 minutes of midday sun on arms and legs a few times a week can be enough for lighter skin. Darker skin needs more time. Cloudy weather, sunscreen, and being indoors cut production. You can’t rely on sun year-round in northern areas.
Food helps but rarely covers needs alone. Good sources: oily fish (salmon, mackerel), canned sardines, fortified milk and cereals, and egg yolks. A typical serving of salmon or fortified milk will not always get you into the optimal range if you’re already low.
Supplements are the practical fix. Vitamin D3 (cholecalciferol) raises blood levels more reliably than D2. For adults, common maintenance doses range from 1,000 to 4,000 IU daily depending on baseline levels. Many providers recommend 50,000 IU once weekly for 6–8 weeks for clear deficiency, then switching to a daily dose. Infants: 400 IU/day is standard; older kids often need 600–1,000 IU. Pregnant people usually take at least 600 IU, but some clinicians suggest higher if tests show low levels.
Safety, testing, and who should be careful
Vitamin D toxicity is rare but real. Taking more than 4,000 IU/day for long periods can raise calcium and cause nausea, weakness, confusion, or kidney problems. If you’re on high doses, your doctor will monitor blood calcium and 25(OH)D. Don’t mix very high vitamin D with calcium supplements without medical advice.
Get tested if you have risk factors: little sun exposure, dark skin, obesity, malabsorption (like after weight-loss surgery), chronic kidney disease, or certain meds (antiseizure drugs, steroids). Also test if you have unexplained muscle weakness or frequent infections.
Final practical tip: check your level before starting a high-dose plan, pick vitamin D3, and recheck after 8–12 weeks on supplements. That way you fix the deficit without overshooting. If you want, bring your lab results to your next appointment and ask for a tailored dose—simple and effective.
