If you’re deficient in vitamin D, most treatment plans start with a high weekly dose of 50,000 to 60,000 IU for several weeks, then shift to a daily maintenance dose of 1,000 to 2,000 IU to keep your levels steady. The exact amount depends on how low your blood levels are, your body weight, and whether you’re an adult or a child.
What Counts as Deficient
Vitamin D status is measured with a blood test called 25-hydroxyvitamin D, reported in ng/mL. The NIH defines the ranges like this:
- Below 12 ng/mL: Deficient. This level raises the risk of bone-softening conditions in both adults and children.
- 12 to 19 ng/mL: Insufficient. Not low enough to cause obvious bone disease, but generally inadequate for overall health.
- 20 ng/mL or above: Sufficient for most people.
- Above 50 ng/mL: Potentially harmful, with risk increasing above 60 ng/mL.
Your starting number matters because it determines how aggressive your supplementation needs to be. Someone at 8 ng/mL needs a different approach than someone sitting at 16 ng/mL.
The Loading Phase: Raising Your Levels Fast
When blood levels are genuinely low, a short course of high-dose vitamin D is used to bring them up quickly. The most common approach is 50,000 IU taken once a week for 6 to 12 weeks. For severe deficiency (below 10 ng/mL), some protocols extend this to a full 12 weeks or use three doses per week for one month to deliver the same total amount faster.
A well-studied loading protocol uses a total of 300,000 IU spread over either 5 or 10 weeks. In clinical trials, giving 60,000 IU per week for 5 weeks reliably pushed all deficient participants above 30 ng/mL regardless of their body weight. The same total dose spread over 10 weeks (30,000 IU per week) also worked, just with a slower rise. Neither schedule caused calcium overload or other safety problems.
These high doses are prescription-level in many countries, so your doctor will typically hand you a specific regimen based on your blood work. Over-the-counter vitamin D supplements top out at around 5,000 to 10,000 IU per capsule, which some providers use as an alternative daily loading strategy.
The Maintenance Phase: Staying in Range
Once your levels reach a healthy range, the goal shifts to preventing another drop. A daily maintenance dose of 1,000 to 2,000 IU is the standard recommendation for most adults. Some guidelines also support 50,000 IU once a month as an equivalent alternative for people who prefer less frequent dosing.
Without ongoing supplementation, levels tend to slide back down, especially if you have limited sun exposure, darker skin, or spend most of your time indoors. A maintenance dose of 2,000 IU per day falls within established safety limits and is enough to hold most people at or above 20 ng/mL year-round.
Why Body Weight Changes the Dose
Vitamin D is fat-soluble, meaning it gets stored in body fat rather than circulating freely in the blood. People with a higher body mass index absorb and sequester more vitamin D in fat tissue, so less of it reaches the bloodstream. The Endocrine Society has noted that individuals with obesity may need roughly three times the dose that a lean person requires to reach the same blood level.
One clinical study found that a weight-based formula of 125 IU per kilogram of body weight per square meter of BMI was effective at normalizing levels in people with obesity. In practical terms, if a standard maintenance dose is 2,000 IU for someone at a healthy weight, a person with a BMI over 35 might need 4,000 to 6,000 IU daily to achieve the same result. Your doctor can adjust your dose based on follow-up blood work.
Vitamin D3 vs. D2
Supplements come in two forms: D3 (cholecalciferol) and D2 (ergocalciferol). D3 is the clear winner. A large meta-analysis found that D3 raised total blood levels about 15.7 nmol/L higher than D2 at the same dose, and the difference held across all age groups, dosing schedules, and supplement types. D3 also lasts longer in the body, with a slightly longer half-life (about 15 days compared to 14 for D2), and does a better job of sustaining elevated levels after you stop taking it.
Prescription loading doses are sometimes dispensed as D2 because that was the form historically available in 50,000 IU capsules. If you have a choice, D3 is more effective. If your pharmacy gives you D2, it still works, just somewhat less efficiently.
Doses for Infants and Children
Pediatric dosing follows a different scale. The American Academy of Pediatrics recommends treating confirmed deficiency with a 2- to 3-month course of high-dose vitamin D:
- Newborns: 1,000 IU daily
- Infants 1 to 12 months: 1,000 to 5,000 IU daily
- Children over 12 months: 5,000 IU daily
After levels normalize, all age groups step down to a maintenance dose of 400 IU daily. For children who struggle with daily compliance, a single large oral dose of 100,000 to 600,000 IU (known as “stoss therapy”) can be given under medical supervision, followed by the standard 400 IU daily maintenance.
Nutrients That Work Alongside Vitamin D
Vitamin D increases your body’s production of certain proteins that depend on vitamin K to function. These proteins help direct calcium into bones and keep it out of soft tissues like blood vessels. When vitamin D levels are high but vitamin K intake is low, those proteins can’t do their job properly. Research supports the idea that supplementing both vitamins together is more effective for bone and cardiovascular health than taking either one alone.
Vitamin K is found in leafy greens (K1) and fermented foods like natto (K2). If you’re taking significant doses of vitamin D, eating plenty of green vegetables or adding a K2 supplement is a reasonable strategy. Taking your vitamin D supplement with a meal that contains some fat also improves absorption, since it’s a fat-soluble vitamin.
When to Retest Your Levels
A measurable response to supplementation typically appears within 4 to 6 weeks, but the standard recommendation is to recheck your blood levels at 6 to 12 weeks after starting treatment or changing your dose. Testing too early can be misleading because your body is still adjusting. Once you’ve confirmed your levels are in range and you’re on a stable maintenance dose, annual testing is usually sufficient unless your weight, sun exposure, or health status changes significantly.
Upper Limits and Toxicity
The tolerable upper intake for adults is 4,000 IU per day for long-term unsupervised use, though short-term loading doses prescribed by a doctor safely exceed this. Toxicity is rare but real, and it typically occurs when blood levels climb above 150 ng/mL, well beyond what any standard treatment protocol would produce.
The danger comes from excess calcium in the blood. Early symptoms include fatigue, weakness, loss of appetite, and bone pain. As calcium levels rise further, you may experience nausea, vomiting, constipation, excessive thirst, and frequent urination. Severe cases can cause confusion, kidney stones, irregular heartbeat, and in extreme situations, kidney failure. These complications come from sustained mega-dosing over weeks or months, not from a single accidental double dose. Sticking to a prescribed loading schedule and retesting on time keeps you well within safe territory.