Vitamin D3 Dose Calculator

Vitamin D3 supplementation and sun exposure

In its 2017 position paper, the Brazilian Society of Endocrinology and Metabolism (SBEM) puts maintenance doses of cholecalciferol (D3) at 800–2000 IU/day for healthy adults with lighter skin. People with darker skin, older adults, patients who are obese and anyone who gets little sun usually need more, 2000–4000 IU/day, because their skin produces the vitamin less efficiently.

Sunlight is still where most of it comes from. At tropical latitudes, 15–30 minutes of midday sun on the arms and legs without sunscreen usually covers lighter skin; darker phototypes (Fitzpatrick V–VI) can need 3–6× that. Deficiency means a serum 25(OH)D <20 ng/mL, and it shows up everywhere, sunny Brazil included, because so many of us stay indoors, wear sunscreen and live around pollution. ANVISA RDC 263/2005 regulates fortified foods and supplements in Brazil.

Applications

An adult can use it to get a rough idea of how much to supplement based on skin tone and how much sun they get. Clinicians and nutritionists use it when prescribing prophylaxis, and it helps when screening risk groups such as older adults, post-bariatric patients, people with chronic kidney disease and dark-skinned individuals living at higher latitudes. Confirm with a 25(OH)D blood test first, and talk to a physician before starting any high-dose regimen.

FAQ

D3 or D2? Cholecalciferol (D3) raises 25(OH)D and keeps it up better than ergocalciferol (D2), which is why most patients are put on D3.

Can I overdose? In healthy adults, toxicity (hypercalcemia) is uncommon below 10,000 IU/day. The danger is piling up high doses, >50,000 IU/week, with no monitoring; that can bring on hypercalcemia, nephrocalcinosis and arrhythmias.

Does sunscreen block all D3 synthesis? In the lab, SPF 30+ cuts synthesis by more than 95%. In practice people apply it unevenly, so some synthesis still happens. This tool is informational and does not replace medical or nutritional advice.