Vitamin D3 (cholecalciferol) is the best form of vitamin D for most people. It raises blood levels more effectively than vitamin D2 (ergocalciferol) and maintains those levels longer. Both forms are available over the counter, but D3 is the one you’ll find in most high-quality supplements for good reason.
Why D3 Beats D2
Your body can use both D2 and D3, but it handles them differently. A systematic review and meta-analysis found that D3 raised blood levels of 25(OH)D, the standard marker for vitamin D status, by roughly 15.7 nmol/L more than D2 did at equivalent doses. That’s a meaningful gap. The difference comes down to chemistry: D2 has a slightly different molecular structure that makes it bind less tightly to the carrier protein in your blood, so it breaks down faster. D2’s half-life in the bloodstream is about 13.9 days compared to 15.1 days for D3.
D2 isn’t useless. It’s the form historically prescribed in high-dose capsules (50,000 IU), and it still works for correcting deficiency under medical supervision. But for everyday supplementation, D3 is the stronger choice.
Vegan and Plant-Based D3
Most D3 supplements come from lanolin, a waxy substance in sheep’s wool. For years, that meant vegans were stuck with D2 as their only option. That’s no longer the case. Several brands now sell D3 sourced from lichen, a plant-like organism that naturally produces cholecalciferol. Lichen-derived D3 is chemically identical to the lanolin version, so it works the same way in your body. If you follow a vegan diet, look for “lichen-sourced” or “vegan D3” on the label.
How Much You Need
The recommended daily allowance set by the National Academies of Sciences, Engineering, and Medicine is 600 IU (15 mcg) for most adults ages 1 through 70, and 800 IU (20 mcg) for adults over 70. Infants need 400 IU daily. These amounts apply equally during pregnancy and lactation.
Those numbers are designed to keep blood levels above 20 ng/mL (50 nmol/L), which the Institute of Medicine considers adequate for 97.5% of the population. Some experts argue the target should be higher. The Endocrine Society previously recommended levels above 30 ng/mL, and a 2018 multi-expert publication suggested 30 to 50 ng/mL for benefits beyond bone health. The reality is that many people, especially those with darker skin, limited sun exposure, or higher body weight, need more than 600 IU to reach even the lower target. A blood test is the only way to know where you stand.
Capsules, Sprays, and Liquids
Vitamin D3 comes in softgels, liquid drops, gummies, tablets, and oral sprays. The good news: the delivery method doesn’t matter much. A randomized crossover trial giving healthy adults 3,000 IU of D3 daily for four weeks found no significant difference in blood level increases between capsules and oral spray. Pick whichever format you’ll actually take consistently.
One thing that does matter is fat. Vitamin D is fat-soluble, meaning it absorbs best when taken alongside a meal containing some dietary fat. An oil-based softgel already contains a small amount of fat, which helps. If you take a dry tablet or gummy, pairing it with food improves absorption.
Nutrients That Work With Vitamin D
Vitamin D doesn’t work in isolation. It increases calcium absorption from your gut, but that calcium needs to end up in your bones rather than your arteries. That’s where vitamin K2 comes in. Vitamin D triggers the production of certain proteins that require vitamin K2 to become active. These proteins direct calcium into bone tissue and keep it out of blood vessel walls. When vitamin D intake is high but vitamin K is low, excess calcium can deposit in the wrong places.
Magnesium also plays a supporting role. Your body needs magnesium to convert vitamin D into its active form. Many people are already low in magnesium, which can blunt the effectiveness of supplementation. You don’t necessarily need a combo supplement, but making sure your diet includes magnesium-rich foods (nuts, seeds, leafy greens, whole grains) and vitamin K2 sources (fermented foods, egg yolks, certain cheeses) supports the full picture.
If You Have a Digestive Condition
People with celiac disease, Crohn’s disease, cystic fibrosis, or a history of gastric bypass surgery face a unique challenge: fat malabsorption. Since vitamin D requires fat to be absorbed, these conditions can make standard supplements far less effective. In some cases, particularly active celiac disease at the time of diagnosis, doses as high as 10,000 to 50,000 IU per day may be needed temporarily. Activated forms of vitamin D, which bypass some of the normal processing steps, are sometimes prescribed because they absorb better when fat absorption is impaired and have shorter half-lives that allow for closer dose control.
If you have any condition affecting your gut, your vitamin D needs and the form you take should be guided by bloodwork and a provider familiar with malabsorption.
Checking Your Levels
A simple blood test measuring 25(OH)D tells you exactly where your levels are. If you’re starting supplementation to correct a deficiency, retest after three months. That’s how long it takes for levels to stabilize and for the parathyroid hormone response to fully adjust. After that, annual testing at the end of winter, when levels are naturally lowest, is a reasonable schedule. If your risk factors change (new medication, weight change, less sun exposure), it’s worth checking again sooner.
Staying Under the Safe Limit
Vitamin D toxicity is rare from normal supplementation but real at very high doses sustained over time. The tolerable upper intake level for adults is 4,000 IU per day. Going above that doesn’t automatically cause harm, but prolonged intake well beyond that threshold can lead to dangerously high calcium levels in the blood, causing nausea, kidney problems, and calcification of soft tissues. Doses above 4,000 IU should only be taken when bloodwork confirms a deficiency and a provider is monitoring your levels.