Drops, capsules, tablets, ampoules, D2 or D3, daily or once a month: the vitamin D aisle is one of the least transparent. And the question matters: among 55,844 Europeans with standardized dosages, 40.4% were below 50 nmol/L of 25(OH)D, the blood marker for vitamin D, and 13% below 30 nmol/L, peaking at 17.7% from October to March.
This comparison answers the question "what is the best vitamin D?" using studies identified via PubMed: D2 or D3, intake frequency, form and meals, origin, dose, overdose, prescription or over-the-counter, then the best vitamin D profile by profile, with a chart of forms and a chart of doses.
The form : vitamin D3 raises 25(OH)D more than D2, by an average of 15.7 nmol/L in a meta-analysis of 24 studies, and the gap widens with a single dose. The molecule is the same, lanolin or lichen. In a trial of 66 adults, oily drops produced a greater increase per µg than a tablet, though fewer participants reached 30 ng/mL, and a meal containing fat increases absorption by 32%.
Frequency and dose : daily intake reduced respiratory infections where bolus dosing failed, and high monthly or annual doses increased falls in seniors in two trials. 600 to 800 IU per day covers bone needs for the majority, a total intake of 1,120 IU per day, according to modeling from one trial, maintains above 50 nmol/L throughout winter in 97.5% of young adults, and overweight or obese individuals need 1.5 to 3 times more. At 4,000 and 10,000 IU per day over three years, one trial measured lower radius bone density than at 400 IU, with no benefit.
- Why the question arises: deficiency in numbers
- D2 or D3: the first answer from studies
- Daily or as a bolus: frequency changes the outcome
- Drops, capsules, tablets, ampoules: form and meals
- Lanolin or lichen: the same molecule
- How many IU: the dose according to age, weight, and status
- Blood thresholds, overdose, and hypercalcemia
- What vitamin D does, and does not do, according to major trials
- Over-the-counter or by prescription: what really differs
- Vitamin D, vitamin K2, and magnesium
- The best vitamin D by profile
- Frequently asked questions
Why the question matters: deficiency by the numbers
Vitamin D is measured in blood by 25-hydroxyvitamin D, or 25(OH)D, in nmol/L or ng/mL (1 ng/mL = 2.5 nmol/L), with two thresholds: deficiency below 50 nmol/L (20 ng/mL), severe deficiency below 30 nmol/L (12 ng/mL). The most robust figures come from 55,844 samples from 18 European studies, remeasured or recalibrated by mass spectrometry: 13.0% of people below 30 nmol/L over the year, 17.7% from October to March versus 8.3% in summer, and 40.4% below 50 nmol/L. Subgroups with darker skin had severe deficiency 3 to 71 times more frequently.
In France, a study conducted in 20 cities between November and April among 1,569 healthy adults found 14% of values at or below 30 nmol/L, with a clear gradient from North to South, correlated with sunshine exposure. Parathyroid hormone increased as soon as 25(OH)D fell below 78 nmol/L, a sign of insufficient intake. Our guide vitamin D deficiency details symptoms and causes.
D2 or D3: the first answer from research
<<<22>>> Vitamin D2 vitamine D2, or ergocalciferol, comes from mushrooms and yeast exposed to UV; vitamin D3, or cholecalciferol, is what the skin produces, derived from lanolin or lichen as a supplement. The 2012 meta-analysis of randomized trials concludes that D3 raises 25(OH)D significantly more (P = 0.001), with a net advantage in bolus dosing that diminished with daily intake. A 2024 meta-analysis, limited to daily or weekly doses, nevertheless finds a difference: among 12 comparisons at daily doses measured by mass spectrometry, the increase in total 25(OH)D was 10.39 nmol/L, or 40%, lower under D2 than under D3, body mass index explaining most of the differences.
Among 1,277 healthy participants, cholecalciferol (D3) raised total 25(OH)D by 15.69 nmol/L more than ergocalciferol (D2) (95% CI: 9.46 to 21.93) and lowered parathyroid hormone more, regardless of age, dose, or vehicle. Average daily dose was the only predictor of the difference, smaller at low doses.
Balachandar R, Pullakhandam R, Kulkarni B, Sachdev HS. Nutrients 2021;13(10):3328. DOI: 10.3390/nu13103328
Individual trials explain this: in 20 men receiving a single dose of 50,000 IU, 25(OH)D continued to rise 14 days under D3 and had returned to its initial value on day 14 under D2; the area under the curve at 28 days was 60.2 ng.d/mL for D2 versus 204.7 for D3, and the time-extrapolated area gave a relative potency of 9.5 to 1 in favor of D3. At low daily dose, the difference narrows: at 1,000 IU per day for 11 weeks, D2 and D3 raised 25(OH)D similarly (from 16.9 to 26.8 and from 19.6 to 28.9 ng/mL).
D3 is thus the best-documented form, the one in our Plant-Based Vitamin D3, lichen-derived cholecalciferol dosed at 1,000 IU per drop.
Every day or in bolus: frequency changes the result
On blood level first: among 338 nursing home residents aged 84, of which 98% started below 50 nmol/L, 600 IU per day performed better after four months than the equivalent weekly and especially monthly: 69.9 versus 67.2 and 53.1 nmol/L.
On clinical criteria, the difference widens: in 2,256 women aged 70 and over followed for 3 to 5 years, an annual dose of 500,000 IU increased the rate of falls by 15% (83.4 versus 72.7 per 100 person-years) and fractures by 26%, with excess falls concentrated in the three months following administration, when 25(OH)D peaked around 120 nmol/L.
In 200 people aged 70 and over who had already fallen, 60,000 IU of vitamin D3 per month, or 24,000 IU plus 300 µg of calciferol, more often raised 25(OH)D above 30 ng/mL than 24,000 IU per month, without improving lower limb function. However, 66.9% and 66.1% of participants in these two groups fell within the year, compared to 47.9% under 24,000 IU.
Bischoff-Ferrari HA, Dawson-Hughes B, Orav EJ, et al. JAMA Intern Med 2016;176(2):175-183. DOI: 10.1001/jamainternmed.2015.7148
High daily doses are not spared: in women aged 66 starting at 20 ng/mL, a 12-month trial showed a U-shaped curve, with fewer falls at 1,600, 2,400, and 3,200 IU per day (p = 0.020), no decrease at 400 and 800 IU nor at 4,000 and 4,800 IU. At 12 months, 21% of women had fallen with a 25(OH)D of 32 to 38 ng/mL, compared to 60% below 25 ng/mL and 72% between 38 and 46 ng/mL.
For immunity, the schedule matters even more. A meta-analysis of individual data from 25 trials (11,321 participants) found a reduced risk of acute respiratory infection (adjusted odds ratio 0.88) driven by daily or weekly doses without bolus (0.81) and absent with bolus (0.97); in the most deficient (less than 25 nmol/L) under regular supplementation, the odds ratio dropped to 0.30. The 2021 update (46 trials, 75,541 participants) confirms: modest overall effect (0.92), more marked with daily dosing (0.78), at 400 to 1,000 IU per day (0.70), and in ages 1 to 16 years (0.71). Our article vitamin D and immunity details these findings. The Endocrine Society has recommended since 2024 daily administration rather than high intermittent doses after age 50.
60,000 IU per month and 500,000 IU per year increased falls in seniors in two randomized trials, without functional benefit. Very high-dose vials require a prescription (documented severe deficiency, malabsorption). If such a dose is prescribed to you, do not add a daily supplement without consulting your prescriber.
Drops, capsules, tablets, ampoules: form and meals
Vitamin D is fat-soluble: it crosses the intestinal wall with fats. In four studies from a systematic review, an oily vehicle raised 25(OH)D more than powder or alcohol. A 12-week trial in 66 adults at 33 ng/mL compared three D3 supplements at the same stated dose: oil-emulsified drops produced a higher increase in 25(OH)D per µg than a chewable tablet (P < 0.05), with no significant difference from a powder capsule; however, 80% of drop users reached 30 ng/mL, versus 100%. In two out of three products, the content measured by a third-party lab significantly deviated from the label.
Fifty older men and women took 50,000 IU of vitamin D3 with a fat-free breakfast or one providing 30% of its calories as fat. The plasma vitamin D3 peak measured 12 hours later was 32% higher (95% CI: 11 to 52%) with the fatty meal, whether fats were primarily monounsaturated or polyunsaturated.
Dawson-Hughes B, Harris SS, Lichtenstein AH, et al. J Acad Nutr Diet 2015;115(2):225-230. DOI: 10.1016/j.jand.2014.09.014
Meals therefore matter as much as form. Our Plant-based Vitamin D3 combines both tested conditions: D3 dissolved in organic virgin rapeseed oil, taken with a meal, ideally at breakfast. Our guide when and how to take vitamin D details the timing of administration.
| Form | What studies show | For whom |
|---|---|---|
| Oily drops | Oil superior to powder and alcohol in 4 studies; drops superior to tablet per µg in a trial of 66 adults | Adults and children, dose adjusted according to weight |
| Capsules | Powder capsule no different from oily drops in the 2014 trial; fixed dose | Adults who prefer a fixed daily dose |
| Tablets | Increase per µg lower than oily drops in the 2014 trial; to be taken with a fatty meal | Low-dose maintenance, often with calcium |
| High-dose ampoules | More falls in seniors at 60,000 IU per month and 500,000 IU per year; no effect on respiratory infections | On prescription: severe deficiency, malabsorption |
| Multivitamins | 5 µg (200 IU) per day, including diet, approach the total intake of 8.7 µg that maintains above 25 nmol/L in 97.5% of young adults in winter, far from the 28 µg modeled for 50 nmol/L | Basic intake, to be supplemented with dedicated D3 in winter |
Lanolin or lichen: the same molecule
Almost all vitamin D3 in supplements comes from lanolin, the fat from sheep's wool, whose 7-dehydrocholesterol is converted to cholecalciferol under UV. The plant-based source is lichen, an association of a fungus and an algae: a 2018 biochemistry review describes, in the lichen Cladonia rangiferina, the conversion of 7-dehydrocholesterol and ergosterol into vitamins D3 and D2, even at low temperature.
The decisive point: the final molecule is the same. Cholecalciferol from lichen has the same formula and the same hepatic metabolism as that from lanolin, and meta-analyses comparing D3 and D2 do not distinguish the source of D3. To our knowledge, no randomized trial has compared lichen D3 and lanolin D3, and no biochemical reason suggests expecting a difference at equal dose and vehicle. The source is an ethical choice, not an efficacy criterion: our Plant-based Vitamin D3 is thus suitable for vegetarians and vegans without compromise on form. Our article Plant-based D3 from lichen or lanolin explores the topic in depth.
Some plant-based products contain vitamin D2 derived from fungi or yeasts. It is also vegan, but raises 25(OH)D less than D3, by 15.7 nmol/L on average, and its effect is exhausted more quickly after a dose. For the most effective form, a vegan will choose lichen D3.
How many IU: the dose according to age, weight, and status
The units first: 1 µg of vitamin D = 40 IU, therefore 1,000 IU = 25 µg and 2,000 IU = 50 µg. The Institute of Medicine set in 2011 recommended intakes of 600 IU per day from 1 to 70 years and 800 IU from 71 years, which cover the bone needs of at least 97.5% of the population at minimal sun exposure, i.e., a 25(OH)D of at least 20 ng/mL (50 nmol/L).
Dose-response trials translate these benchmarks. In 238 adults aged 20 to 40 years who received 0, 5, 10 or 15 µg per day throughout winter, the authors calculated the total daily intake (including diet) maintaining 97.5% of participants above each threshold: 8.7 µg for 25 nmol/L, 28.0 µg (1,120 IU) for 50 nmol/L and 41.1 µg (1,644 IU) for 80 nmol/L, these last two values being extrapolated beyond the tested doses. In 17,614 volunteers, the response followed an exponential curve (+12.0 nmol/L per 1,000 IU between 0 and 1,000 IU per day); obese individuals had a 25(OH)D lower by 19.8 nmol/L and overweight individuals by 8.0 nmol/L, hence the proposal for a dose multiplied by 2 to 3 in case of obesity and by 1.5 in case of overweight, with no observed increase in hypercalcemia (observational data).
| Profile | Daily dose benchmark | Source |
|---|---|---|
| Breastfed infant | 400 IU: +22.63 nmol/L of 25(OH)D (6 studies, 334 infants) and less insufficiency (RR 0.57, 4 studies), low certainty | Cochrane 2020, 19 studies, 2,837 mother-child pairs |
| Child and adolescent | 600 IU; supplementation suggested from 1 to 18 years; respiratory infections: 0.71 between 1 and 16 years | Institute of Medicine 2011; Endocrine Society 2024; Jolliffe 2021 |
| Adult aged 19 to 70 years | 600 IU for bone requirements; total modeled intake of 1,120 IU to remain above 50 nmol/L throughout winter, 1,644 IU for 80 nmol/L | Institute of Medicine 2011; Cashman 2008 |
| 71 years and older | 800 IU, taken daily; fewer falls between 1,600 and 3,200 IU in one trial, no decrease at 4,000 IU and above | Institute of Medicine 2011; Endocrine Society 2024; Smith 2017 |
| Overweight or obesity | 1.5 times (overweight) to 2 or 3 times (obesity) the dose of a normal-weight person | Ekwaru 2014, 17,614 volunteers (observational) |
| Pregnancy | On medical advice; less pre-eclampsia (RR 0.48, 4 trials, 499 women) and gestational diabetes (RR 0.51, 4 trials, 446 women) with vitamin D alone, moderate certainty | Cochrane 2019, 3,725 women |
With our Plant-based Vitamin D3, one drop provides 1,000 IU: two drops per day equal 2,000 IU (50 µg), above the total intake of 41.1 µg modeled to maintain over 80 nmol/L in 97.5% of young adults in winter, and at the dose tested for 5.3 years in the 25,871 adults in VITAL without excess adverse effects. One drop (1,000 IU) is sufficient for many normal-weight adults and is the indicated dose before age 10. Our guide vitamin D: how many IU per day details the calculation based on weight.
Blood thresholds, overdose, and hypercalcemia
A clinical review notes that toxicity is rare, almost always results from very high and prolonged pharmacological doses, and a 25(OH)D above 150 ng/mL (375 nmol/L) is its signature. Symptoms are those of hypercalcemia: confusion, repeated vomiting, abdominal pain, excessive thirst and urination. In rare individuals with dysregulated metabolism (sarcoidosis, other granulomatoses, genetic abnormalities), hypercalcemia can occur even at doses safe for the general population.
At usual doses, a meta-analysis of 48 trials of 24 weeks or longer (19,833 participants) quantifies the risk: hypercalcemia 1.54 times more frequent under vitamin D than placebo, hypercalciuria 1.64 times, with no link to dose, duration, or associated calcium, and no increase in kidney stones (RR 0.66, not significant). Calcium measurement is justified with high long-term doses. High doses provide nothing for bone: in 311 adults aged 55 to 70 followed for 3 years, 4,000 and 10,000 IU per day raised 25(OH)D to 132 and 144 nmol/L versus 77 with 400 IU, and radial bone density decreased by 2.4% and 3.5% versus 1.2%, with no difference in bone strength.
Starting at 4,000 IU per day over months, without medical advice, the benefit-risk ratio deteriorates: no bone gain, more falls at 4,000 and 4,800 IU per day than at 1,600 to 3,200 IU in deficient elderly women, and increased hypercalcemia risk. Combined products (multivitamins, calcium-vitamin D, cod liver oil, ampoules) add their doses. Our article dangers and contraindications of vitamin D details at-risk situations.
What vitamin D does, and does not do, according to major trials
On bone, in unselected adults without deficit, the meta-analysis of 81 randomized trials (53,537 participants) finds no effect on fractures (relative risk 1.00), hip fractures (1.11), or falls (0.97). The VITAL trial, in 25,871 adults aged 50 and older receiving 2,000 IU of D3 daily for 5.3 years, did not reduce fractures (hazard ratio 0.98). These populations were mostly well-supplied initially: these results say nothing about correcting true deficiency.
On respiratory infections, the effect is real but modest: in the meta-analysis of 46 trials, 61.3% of supplemented participants had at least one infection, compared to 62.3% on placebo. The Endocrine Society drew conclusions in 2024: supplementation suggested from 1 to 18 years, after 75 years (possible mortality reduction), during pregnancy and in high-risk prediabetes, without exceeding reference intakes in healthy adults under 75 years. See also our guide winter immunity: vitamin D, zinc, vitamin C.
Without prescription or by prescription: what really differs
Three points answer the question "best vitamin D without prescription." First, the molecule is the same : the cholecalciferol in a prescribed ampoule and that in a drops bottle are identical; only the dose per intake changes: tens of thousands of IU at once on one hand, a few hundred to a few thousand IU daily on the other. Yet section 3 shows the advantage of daily intake over blood levels and respiratory infections, and excess falls from high spaced doses in two trials.
Next, prescription provides monitoring. A survey of 966 French pediatricians and general practitioners after the 2022 pediatric recommendations shows it: over 90% prescribe supplementation at all ages, daily until age 2 (97%), then every three months; only 5% still prescribe loading doses of 200,000 IU, contrary to recommendations.
Finally, blood vitamin D testing is only useful in certain cases. The Endocrine Society does not recommend systematic screening in 2024, even in cases of obesity or dark skin, due to lack of evidence that it improves outcomes. Testing remains worthwhile when it changes the decision: symptoms of severe deficiency, malabsorption, kidney or liver disease, high-risk pregnancy, long-term high-dose use. For a healthy adult wanting to cover the winter months, daily D3 without a prescription, taken with meals, aligns with research findings.
Where you buy says nothing about effectiveness. The criteria from studies: the form (D3), the vehicle (oil), precise dosing per drop or capsule, a daily dose adapted to body weight, clear labeling in IU and µg, and a manufacturer that controls its batches, as a 2014 trial found contents far from label claims in two out of three products.
Vitamin D, vitamin K2 and magnesium
Many products combine D3 and vitamin K2, on the grounds that vitamin D increases the production of vitamin K-dependent proteins. A 2017 narrative review summarizes: D + K trials mainly focused on bone health in postmenopausal women, few examined cardiovascular outcomes, and the authors write that the combination "could" be more effective than each vitamin alone, without concluding. None of the studies cited here show that K2 increases the 25(OH)D elevation achieved with vitamin D.
The magnesium is a better documented cofactor: the enzymes that convert vitamin D into 25(OH)D and then into active form depend on it. In a randomized trial of 180 adults aged 40 to 85, magnesium supplementation increased 25(OH)D3 in people starting around 30 ng/mL and lowered it between 30 and 50 ng/mL, suggesting a regulatory role. Our article magnesium and vitamin D details this data; our Magnesium+ combines Magshape, malate, taurine and vitamin B6, at 4 capsules per day.
The best vitamin D by profile
Healthy adult. Daily D3, in oily drops or capsule form, 1,000 to 2,000 IU per day depending on body weight, with meals containing fats, from October to March at minimum.
Senior. Daily dosing rather than bolus: 800 IU per day according to the Institute of Medicine, fewer falls between 1,600 and 3,200 IU per day in deficient 66-year-old women, never more than 4,000 IU. The Endocrine Society suggests daily supplementation after age 75.
Child. In breastfed infants, 400 IU per day increased 25(OH)D by 22.63 nmol/L (6 studies, 334 infants) and reduced insufficiency by 43% (RR 0.57, 4 studies), with low certainty (Cochrane 2020); prescription is the pediatrician's responsibility. From 1 to 18 years, the Endocrine Society suggests supplementation. One drop of our Plant-Based Vitamin D3 (1,000 IU) is the recommended dose before age 10, two drops from age 10 onwards.
Pregnancy and breastfeeding. Medical advice only. The 2019 Cochrane review (comparing vitamin D alone: 22 trials, 3,725 women, but 4 to 5 trials per outcome) reports less pre-eclampsia (RR 0.48), gestational diabetes (RR 0.51) and low birth weight (RR 0.55), with moderate certainty.
Vegetarian or vegan. D3 from lichen rather than D2 from mushrooms: same molecule as D3 from lanolin, 15.7 nmol/L ahead of D2.
Dark skin. Melanin filters UVB: after the same UV dose, in a landmark 1982 study of five volunteers, blood vitamin D was multiplied up to 60-fold in two light-skinned individuals and did not change in three dark-skinned individuals; one of them, re-exposed to a dose six times stronger, reached comparable values. Daily D3 compensates.
Overweight and obesity. At equal doses, obese individuals had 25(OH)D that was 19.8 nmol/L lower, hence a dose 2 to 3 times higher proposed from observation, 1.5 times in case of overweight.
What about multivitamins? They often contain 5 µg (200 IU) of D3, 100% of the reference daily intake. Added to diet, this dose can approach the total intake of 8.7 µg that maintains over 25 nmol/L in 97.5% of young adults in winter, but falls far short of the 28 µg modeled to exceed 50 nmol/L: baseline intake, yes, but not enough to replace dedicated D3 from October to March.
Cholecalciferol extracted from boreal lichen, 100% plant-based, in organic virgin rapeseed oil, in a 20 ml dropper bottle. One drop provides 1,000 IU (25 µg): two drops per day with meals for adults and children over 10 years, one drop before age 10, allowing you to adjust the dose to weight and season, without prescription.
View Vitamin D3For a complete vitamin foundation, discover our Multivitamins, 12 vitamins and minerals in two capsules per day.
Frequently Asked Questions
What is the best vitamin D?
A D3 taken daily with meals containing fats, at a dose adapted to body weight. D3 raises 25(OH)D by 15.7 nmol/L more than D2, oily drops performed better than a tablet per µg in a trial of 66 adults, and daily intake provided better protection against respiratory infections than single doses, whose high doses increased falls in seniors.
What is the best vitamin D without a prescription?
A daily D3 in oily drops or capsules, precisely dosed, 1,000 or 2,000 IU per day depending on weight and season. The molecule is the same as in prescribed ampoules; only the dose per intake changes; moderate daily intakes performed better for infections, and high spaced doses increased falls in seniors.
What is the best vitamin D at the pharmacy?
The place of purchase does not change effectiveness. The criteria are the same everywhere: D3 form, oil-based vehicle, precise dosing per drop or capsule, daily dose adapted to weight, clear label in IU and µg. High-dose ampoules require a prescription.
Vitamin D2 or D3: which to choose?
D3. In the 2021 meta-analysis, it raised 25(OH)D by 15.69 nmol/L more than D2; after a single dose of 50,000 IU, the area under the curve extrapolated over time gave it a relative potency of 9.5 to 1. At 1,000 IU per day, the two forms converge, but D3 remains the best documented.
Vitamin D in drops or capsules: what's the difference?
In a 12-week trial in 66 adults, oily drops gave a 25(OH)D increase per µg greater than a chewable tablet, with no significant difference from a powder capsule. Drops adjust to weight, capsules offer a fixed dose; in both cases, a meal with fats increases absorption.
Vitamin D every day or once a month?
Every day. At equal cumulative dose, daily intake gave a higher blood level than monthly bolus in a nursing home, reduced respiratory infections where boluses failed, and high spaced doses (60,000 IU per month, 500,000 IU per year) increased falls whereas moderate daily doses reduced them in another trial. The Endocrine Society recommends daily intake after age 50.
How many IU of vitamin D per day?
600 IU from ages 1 to 70 and 800 IU after age 71 meet the bone health needs of 97.5% of the population according to the Institute of Medicine. To stay above 50 nmol/L throughout the winter, a study in young adults modeled a total daily intake of 1,120 IU, including dietary sources, for 97.5% of participants. In case of overweight, count 1.5 times more; 2 to 3 times more in case of obesity, without exceeding 4,000 IU without medical advice.
Is lichen-derived vitamin D3 as effective as lanolin-derived vitamin D3?
The molecule is identical: cholecalciferol, with the same structure and metabolism. Meta-analyses comparing D3 and D2 do not distinguish the source of D3, and there is no biochemical reason to expect a difference at equal doses and delivery vehicles.
What are the signs of vitamin D overdose?
Those of hypercalcemia: repeated vomiting, abdominal pain, intense thirst, abundant urination, confusion. They occur after very high and prolonged doses, with 25(OH)D greater than 150 ng/mL (375 nmol/L). At common doses, a meta-analysis of 48 trials found hypercalcemia 1.54 times more frequent than with placebo.
Is a multivitamin with 5 µg of vitamin D sufficient?
As a baseline intake, yes; to cover winter or correct a deficiency, no. Based on modeling from a winter study, a total daily intake of 8.7 µg, including dietary sources, maintains over 25 nmol/L in 97.5% of young adults, and 28 µg is needed to stay above 50 nmol/L. A multivitamin should therefore be combined with a dedicated D3 supplement.
Sources
The studies cited below were identified via PubMed.
- Cashman KD, Dowling KG, Škrabáková Z, et al. Vitamin D deficiency in Europe: a pandemic? The American Journal of Clinical Nutrition, 2016;103(4):1033-1044. DOI
- Chapuy MC, Preziosi P, Maamer M, et al. Prevalence of vitamin D insufficiency in a normal adult population. Osteoporosis International, 1997;7(5):439-443. DOI
- Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and D3 for raising serum 25-hydroxyvitamin D: systematic review and meta-analysis. The American Journal of Clinical Nutrition, 2012;95(6):1357-1364. DOI
- van den Heuvel EG, Lips P, Schoonmade LJ, et al. Comparison of the effect of daily vitamin D2 and D3 on serum 25-hydroxyvitamin D and importance of body mass index: systematic review and meta-analysis. Advances in Nutrition, 2024;15(1):100133. DOI
- Balachandar R, Pullakhandam R, Kulkarni B, Sachdev HS. Relative efficacy of vitamins D2 and D3 for improving vitamin D status: systematic review and meta-analysis. Nutrients, 2021;13(10):3328. DOI
- Armas LA, Hollis BW, Heaney RP. Vitamin D2 is much less effective than vitamin D3 in humans. The Journal of Clinical Endocrinology and Metabolism, 2004;89(11):5387-5391. DOI
- Holick MF, Biancuzzo RM, Chen TC, et al. Vitamin D2 is as effective as vitamin D3 in maintaining circulating 25-hydroxyvitamin D concentrations. The Journal of Clinical Endocrinology and Metabolism, 2008;93(3):677-681. DOI
- Chel V, Wijnhoven HA, Smit JH, et al. Efficacy of different doses and intervals of oral vitamin D supplementation with or without calcium in elderly nursing home residents. Osteoporosis International, 2008;19(5):663-671. DOI
- Sanders KM, Stuart AL, Williamson EJ, et al. High-dose annual oral vitamin D, falls and fractures in older women: a randomized controlled trial. JAMA, 2010;303(18):1815-1822. DOI
- Bischoff-Ferrari HA, Dawson-Hughes B, Orav EJ, et al. Monthly high-dose vitamin D treatment to prevent functional decline: a randomized clinical trial. JAMA Internal Medicine, 2016;176(2):175-183. DOI
- Smith LM, Gallagher JC, Suiter C. Average daily vitamin D doses reduce falls and higher daily vitamin D3 doses increase them: a randomized clinical trial. The Journal of Steroid Biochemistry and Molecular Biology, 2017;173:317-322. DOI
- Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of individual participant data. BMJ, 2017;356:i6583. DOI
- Jolliffe DA, Camargo CA, Sluyter JD, et al. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of aggregate data from randomized trials. The Lancet Diabetes and Endocrinology, 2021;9(5):276-292. DOI
- Demay MB, Pittas AG, Bikle DD, et al. Vitamin D for disease prevention: clinical practice recommendation from the Endocrine Society. The Journal of Clinical Endocrinology and Metabolism, 2024;109(8):1907-1947. DOI
- Grossmann RE, Tangpricha V. Evaluation of vehicle substances on vitamin D bioavailability: systematic review. Molecular Nutrition and Food Research, 2010;54(8):1055-1061. DOI
- Traub ML, Finnell JS, Bhandiwad A, et al. Impact of the vitamin D3 supplement matrix on clinical response. The Journal of Clinical Endocrinology and Metabolism, 2014;99(8):2720-2728. DOI
- Dawson-Hughes B, Harris SS, Lichtenstein AH, et al. Dietary fats increase vitamin D3 absorption. Journal of the Academy of Nutrition and Dietetics, 2015;115(2):225-230. DOI
- Cashman KD, Hill TR, Lucey AJ, et al. Estimation of dietary vitamin D requirements in healthy adults. The American Journal of Clinical Nutrition, 2008;88(6):1535-1542. DOI
- Göring H. Vitamin D in nature: a product of synthesis and/or degradation of membrane components. Biochemistry (Moscow), 2018;83(11):1350-1357. DOI
- Ross AC, Manson JE, Abrams SA, et al. The 2011 Institute of Medicine report on dietary reference intakes for calcium and vitamin D: what clinicians need to know. The Journal of Clinical Endocrinology and Metabolism, 2011;96(1):53-58. DOI
- Ekwaru JP, Zwicker JD, Holick MF, et al. The importance of body weight in the dose-response relationship between oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers. PLoS One, 2014;9(11):e111265. DOI
- Tan ML, Abrams SA, Osborn DA. Vitamin D supplementation for term-born breastfed infants to prevent deficiency and improve bone health. Cochrane Database of Systematic Reviews, 2020;12(12):CD013046. DOI
- Palacios C, Kostiuk LK, Peña-Rosas JP. Vitamin D supplementation for women during pregnancy. Cochrane Database of Systematic Reviews, 2019;7(7):CD008873. DOI
- LeBoff MS, Chou SH, Ratliff KA, et al. Supplemental vitamin D and incident fractures in middle-aged and older adults. The New England Journal of Medicine, 2022;387(4):299-309. DOI
- Marcinowska-Suchowierska E, Kupisz-Urbańska M, Łukaszkiewicz J, et al. Vitamin D toxicity: a clinical perspective. Frontiers in Endocrinology, 2018;9:550. DOI
- Malihi Z, Wu Z, Stewart AW, et al. Hypercalcemia, hypercalciuria, and kidney stones in long-term vitamin D supplementation studies: systematic review and meta-analysis. The American Journal of Clinical Nutrition, 2016;104(4):1039-1051. DOI
- Burt LA, Billington EO, Rose MS, et al. Effect of high-dose vitamin D supplementation on volumetric bone density and bone strength: randomized clinical trial. JAMA, 2019;322(8):736-745. DOI
- Bolland MJ, Grey A, Avenell A. Effects of vitamin D supplementation on musculoskeletal health: systematic review, meta-analysis and sequential analysis. The Lancet Diabetes and Endocrinology, 2018;6(11):847-858. DOI
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