Vitamin D Dosage: How Much Do You Actually Need?

The current RDA for vitamin D is 600 IU per day (800 IU for adults over 70). This was set in 2011 and is designed to prevent rickets, a bone disease. Preventing rickets is a low bar.

The Endocrine Society recommends 1,500-2,000 IU daily for most adults. Many researchers and functional medicine practitioners suggest 2,000-5,000 IU based on more recent evidence about optimal blood levels.

The disagreement comes down to what 'enough' means. The RDA targets a blood level of 20 ng/mL (just enough to prevent deficiency). Most current research suggests optimal levels are 40-60 ng/mL for immune function, mood, and chronic disease prevention.

To get from 20 to 40-60 ng/mL, most people need 2,000-5,000 IU daily, depending on their starting level, skin tone, latitude, and body weight. Heavier people need more because vitamin D gets stored in fat tissue.

Vitamin D3 scores 9/10 on IngredientMD. It's one of the few supplements where the evidence for widespread supplementation is genuinely strong.

Vitamin D3 (cholecalciferol) and D2 (ergocalciferol) are not the same thing. D3 is what your body makes from sunlight. D2 comes from fungi and fortified foods.

D3 is about 87% more effective at raising blood vitamin D levels than D2 at the same dose. It also has a longer half-life in your body (about 2-3 weeks vs 2-3 days for D2). So D3 maintains more stable blood levels.

Most prescription vitamin D is D2 (ergocalciferol). Most over-the-counter supplements are D3 (cholecalciferol). The OTC option is actually better in this case.

If your supplement label says 'Vitamin D' without specifying D3 or D2, check the fine print. You want cholecalciferol (D3). If it says ergocalciferol (D2), you'd need almost double the dose for the same effect.

Vegans: most D3 comes from lanolin (sheep wool). But there are now D3 supplements made from lichen that are fully vegan. They work the same way. Look for 'vegan D3' or 'lichen-derived D3' on the label.

Not everyone needs the same dose.

Higher risk of deficiency (may need 4,000-5,000 IU):
- People with darker skin (melanin reduces D synthesis by up to 95%)
- People over 65 (skin becomes less efficient at making D)
- People who live above 35 latitude (most of the US north of Atlanta)
- People who work indoors or cover most skin
- People who are overweight or obese (D gets trapped in fat tissue)

Standard supplementation (2,000-3,000 IU):
- Most adults who get some sun exposure
- People who eat fatty fish regularly

May need less or should be cautious:
- People with hypercalcemia or kidney stones
- People taking certain medications (thiazide diuretics, some heart meds)
- People with granulomatous diseases (sarcoidosis)

The safest approach: get a 25-hydroxyvitamin D blood test. It costs about $30-50 and tells you exactly where you stand. Target 40-60 ng/mL. Below 30 is deficiency. Below 20 is severe deficiency.

Take vitamin D with a meal containing fat. It's fat-soluble, meaning it needs dietary fat for absorption. Taking it on an empty stomach reduces absorption significantly.

Vitamin D increases calcium absorption. That's good for bones. But calcium needs to go to the right place (bones and teeth) not the wrong place (arteries and soft tissue).

Vitamin K2 directs calcium to bones and away from arteries. This is why many practitioners recommend taking D3 with K2.

The most studied form is MK-7 (menaquinone-7) at 100-200 mcg daily. It has a longer half-life than MK-4 and works well alongside D3.

Is this strictly necessary? The research isn't conclusive enough to say you MUST take K2 with D3. But the logic is sound, the risk is near zero, and many quality D3 supplements now include K2. If you're taking D3 at 2,000+ IU daily long-term, adding K2 is a reasonable precaution.

Note: if you're on blood thinners (warfarin), K2 affects clotting. Talk to your doctor before adding it. K2 is fine with most other medications.