Vitamin D3 Fast Absorb

Choosing D3 over D2 is usually the easy part. The questions worth asking are about the source, the units on the label and what else you already take.

A good fit if

• You want the form of vitamin D with the best evidence for raising your levels and keeping them up
• You're vegan or vegetarian and need D3 from lichen rather than sheep-wool lanolin
• You're comparing labels in micrograms and IU and want to convert properly before choosing
• Your doctor has set a dose after a blood test and you want a product that matches it
• You'll take it with a meal that has some fat in it, and want a format designed for that

Check with us first if

• You take thiazide diuretics (water tablets). Combined with vitamin D, they raise the risk of high blood calcium.
• You take digoxin or another cardiac glycoside (a type of heart medicine). Its effects may be stronger when vitamin D is taken with calcium.
• You take anticonvulsants, barbiturates, corticosteroids, orlistat or a statin. Each can change your vitamin D levels or be changed by them.
• You have coeliac disease, Crohn's disease, cystic fibrosis or untreated malabsorption, or have had bariatric surgery. Absorbing a fat-soluble vitamin can be unpredictable.
• You have kidney disease or a history of kidney stones. Dose and monitoring are a decision for your doctor.
• You're pregnant or breastfeeding. Set the dose with your midwife or doctor.
• You're buying for a baby or child. The upper limit under 12 months is 25 µg a day, which one adult capsule reaches on its own.
• You already take a multivitamin, calcium, fish oil, bone formula or immune formula. Check every label before adding more D3.
• You're looking at a 2,000 IU or 5,000 IU product from an overseas website. Those aren't listed in Australia and aren't regulated by the TGA for quality.
• You take any prescription medicine. A quick check with your doctor, pharmacist or our naturopaths first is the sensible step.

• Lanolin-derived D3 in an oil-filled capsule. Best known for: The usual Australian product: colecalciferol suspended in an oil such as olive or sunflower. Absorption: Fat-soluble and already dissolved in oil, which is the simplest way to take a fat-soluble vitamin. Typical use: One capsule a day, most often 1,000 IU (25 µg), with a meal.
• Lichen-derived (animal-free) D3. Best known for: The vegan and vegetarian option, and the choice if you avoid lanolin from sheep's wool. Absorption: The same colecalciferol molecule. Lichens have been shown to contain genuine vitamin D3, not only D2. Typical use: Capsules and drops at the same strengths as lanolin-derived products.
• Oral spray or liquid drops. Best known for: Flexible dosing, and an option if swallowing a capsule is hard. Absorption: Still needs fat to be absorbed. The oil or emulsifier base matters more than the spray. Typical use: One to a few sprays or drops a day. Check the label for IU per spray, not IU per bottle.
• Dry D3 powder in a tablet or blend. Best known for: D3 built into calcium tablets, multivitamins, immune formulas and bone products. Absorption: Absorbed less predictably than an oil-based capsule if there's no fat in the meal. Typical use: Often a small dose you didn't go looking for. Add up every product you take.
• High-strength D3 above 1,000 IU. Best known for: 5,000 IU and similar strengths, common overseas and on international websites. Absorption: No different, microgram for microgram. The issue is the total daily amount, not how well it's absorbed. Typical use: Can't be sold as an Australian listed medicine at that strength. It's one to discuss with your doctor after a blood test.

Reference values. Australia's recommended intakes are set for vitamin D overall, not D3 specifically. They're published in micrograms, but almost every Australian label uses international units (IU), which is where most dosing confusion starts. The conversion is simple: 1 µg = 40 IU. So the adult Adequate Intake of 5 µg is 200 IU, the 10 µg figure for ages 51–70 is 400 IU, and the 15 µg figure from age 71 is 600 IU.

Typical supplemental range. Australian D3 products usually come in three strengths. 400 IU (10 µg) is the usual drop for babies and children. 1,000 IU (25 µg) is the standard adult capsule, and also the legal maximum for a listed medicine, which is why so many products sit at exactly that number. Anything labelled 2,000 IU or 5,000 IU isn't listed in Australia at that strength.

Upper level. The NHMRC upper limit for vitamin D is 80 µg a day (3,200 IU) from age one, including during pregnancy and breastfeeding. For babies under 12 months it's 25 µg a day (1,000 IU), so a single adult capsule already reaches the infant limit. According to the NIH, vitamin D toxicity typically involves blood levels of 25-hydroxyvitamin D above 375 nmol/L.

Worth knowing. The simple rule: convert before you compare. A 1,000 IU capsule, a 25 µg capsule and a 0.025 mg capsule are the same dose written three ways, so a label that mixes units is worth a second look. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Cod liver oil and oily fish such as salmon, trout and herring: the main dietary sources of D3 specifically (vitamin D in animal foods is D3, not D2)
• Egg yolk and liver: small amounts of D3; the yolk carries it, the white does not
• Mushrooms exposed to ultraviolet light: a useful vitamin D source, but it supplies D2, not D3 (relevant if the D3-versus-D2 difference matters to you)
• Fortified milks, plant milks, margarines and cereals: may be fortified with either D3 or D2 (the ingredient list will say colecalciferol or ergocalciferol)
• Sunlight on bare skin: not a food, but it is the body's own D3 route and the reason the Australian intake figures are set low

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• You have high calcium in your blood or urine (hypercalcaemia or hypercalciuria), or a condition that causes them. Don't take it.
• You have vitamin D toxicity (hypervitaminosis D). Don't take it.
• You have kidney stones (nephrolithiasis) or severe kidney impairment. Don't take it unless your doctor directs you to.
• You're allergic to any ingredient in the product. Don't take it.
• You take more than 1,000 IU a day long term. Your blood calcium, urine calcium and kidney function should be monitored.
• You mix up the units. 25 µg equals 1,000 IU, and reading a label in the wrong unit is a 40-fold dosing error either way.
• Babies under 12 months. Their Upper Level is 25 µg (1,000 IU) a day, the same as one standard adult capsule.
• You take thiazide diuretics. They increase the risk of high blood calcium.
• You take digoxin or other cardiac glycosides. Their effects may be stronger with vitamin D plus calcium.
• You take anticonvulsants or barbiturates. They may make vitamin D less effective.
• You take corticosteroids. They impair vitamin D metabolism and calcium absorption.
• You take orlistat. It reduces absorption of fat-soluble vitamins.
• You take statins. An interaction in both directions has been reported, through shared metabolic pathways.
• You have a condition that affects absorption: coeliac disease, Crohn's, cystic fibrosis, liver disease or bariatric surgery.
• You're pregnant or breastfeeding. Set your dose with your midwife or doctor.
• You take several products. D3 also turns up in multivitamins, calcium tablets, fish oils, and bone and immune formulas.
• You have nausea, vomiting, constipation, thirst, frequent urination, weakness, apathy or confusion. These could be signs of high blood calcium, so get advice.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before you start.