Vitamin D3 is the type you should take. It raises blood levels of vitamin D more effectively than D2, and it’s the form your body naturally produces when sunlight hits your skin. A meta-analysis of randomized controlled trials found that D3 had a statistically significant advantage over D2 in raising serum vitamin D levels. Most supplements on store shelves are D3, but it’s worth checking the label to be sure.
Why D3 Outperforms D2
Vitamin D comes in two supplemental forms: D2 (ergocalciferol, derived from plants and fungi) and D3 (cholecalciferol, typically derived from sheep wool lanolin or, for vegan options, lichen). Both get converted in the liver and kidneys into the active hormone your body uses, but D3 does the job more efficiently.
The difference is especially pronounced with larger, less frequent doses. When researchers compared the two forms given as a single large dose, D3 raised blood levels significantly more than D2. Interestingly, the gap narrowed with daily supplementation, suggesting that if you do end up with D2 for some reason, taking it every day rather than weekly or monthly will get you closer to the same result. Still, D3 remains the stronger overall choice and is what most clinical guidelines now favor.
How Much to Take
The standard Recommended Dietary Allowance is 600 IU (15 micrograms) daily for adults under 70, and 800 IU (20 micrograms) daily for those over 70. These numbers assume minimal sun exposure and are designed to maintain adequate bone health in most people.
In practice, many people take 1,000 to 2,000 IU daily, particularly during winter months or if they spend most of their time indoors. Your body weight plays a significant role in how much you actually need. Research on dose-response relationships found that for every 1,000 IU taken daily, normal-weight people raised their blood levels by about 13 nmol/L, overweight people by about 11.5 nmol/L, and obese people by only 8.6 nmol/L. The study’s authors recommended that overweight individuals take roughly 1.5 times the standard dose and obese individuals take 2 to 3 times more to reach the same blood levels as someone at a normal weight.
What Your Blood Levels Mean
Vitamin D status is measured through a blood test that checks your 25-hydroxyvitamin D level, reported in ng/mL. According to the Endocrine Society, anything below 30 ng/mL qualifies as deficient. National survey data from 2011 to 2014 found that about 20% of Americans had levels between 12 and 19 ng/mL (at risk for inadequacy), and 5% fell below 12 ng/mL (at risk for outright deficiency).
The Endocrine Society notes that aiming for a level around 40 ng/mL provides a comfortable buffer. Given the variability between different lab tests, hitting 40 ng/mL on a blood draw ensures your true level is reliably above 30. This is well below the range where toxicity becomes a concern.
Capsules, Drops, or Sprays
The delivery method matters less than you might think. A randomized crossover study comparing D3 capsules to an oral spray found virtually identical increases in blood levels after four weeks of supplementation at the same dose. The spray raised levels by an average of 26.5 nmol/L and the capsules by 27.6 nmol/L, a difference that was not statistically meaningful.
Oral sprays do have one potential advantage: they’re absorbed through the membranes in your mouth rather than your intestines. This makes them a useful alternative for people with digestive conditions that impair fat absorption, such as Crohn’s disease, celiac disease, or a history of gastric bypass surgery. For everyone else, pick whichever form you’ll actually remember to take consistently.
Take It With Fat
Vitamin D is fat-soluble, meaning it absorbs best when there’s fat present in your digestive system. Taking your supplement with a meal that includes some dietary fat (eggs, avocado, nuts, olive oil, cheese) will improve absorption. Some vitamin D does get absorbed without fat, so taking it on an empty stomach isn’t useless, but pairing it with food is a simple way to get more out of each dose.
Vegan and Plant-Based Options
Most D3 supplements come from lanolin, a waxy substance in sheep’s wool. If you follow a vegan diet, look for D3 sourced from lichen, a slow-growing organism that naturally produces cholecalciferol. Lichen-derived D3 is chemically the same type of molecule, though it costs roughly three times more to produce than lanolin-based D3. The alternative is D2, which is always plant-derived (usually from UV-exposed mushrooms or yeast), but given D3’s superior performance at raising blood levels, lichen-based D3 is the better investment.
Signs You’re Taking Too Much
Vitamin D toxicity is rare from normal supplementation but does happen when people take extremely high doses for extended periods. The primary danger is a buildup of calcium in the blood, which can cause nausea, vomiting, weakness, frequent urination, bone pain, and kidney stones. This typically occurs at sustained daily intakes well above 10,000 IU over months. Staying at or below 4,000 IU daily (the commonly cited upper limit for adults) keeps the vast majority of people safely in range, though higher doses are sometimes used under medical supervision for people with confirmed deficiency or conditions affecting absorption.