Transparency data

TOX/2026/20 Draft Position statement on the effects of calcidiol in the maternal diet

Published 25 June 2026

This is a paper for discussion. This does not represent the views of the Committee and should not be cited.

Introduction

1.       In 2019, the Scientific Advisory Committee on Nutrition (SACN) agreed to conduct a risk assessment on nutrition and maternal health, focusing on maternal outcomes during pregnancy, childbirth and up to 24 months after delivery; this would include the effects of chemical contaminants and excess nutrients in the diet.

2.       SACN agreed that, where appropriate, other expert committees such as COT would be consulted to carry out relevant risk assessments. Following publication of the 2022 Statement on the potential effects of excess vitamin D intake during preconception, pregnancy and lactation, SACN asked COT to also review the risks of calcidiol supplementation in the maternal diet. This was on the basis that calcidiol is a more bioavailable form of vitamin D2 and D3 and its availability on the market is increasing.

3.       The Committee was subsequently presented with a discussion paper oncalcidiol supplementation during preconception, pregnancy and lactation in May 2025 (TOX/2025/21). It concluded that there was no substantive difference between EFSA and ACNFP advice, with both identifying a safe intake level of 10 µg/day, and ACNFP additionally proposing a conservative upper intake level of 40 µg/day to account for potential misuse. Members agreed that estimated intakes did not reach levels of toxicological concern and were therefore not considered a risk Draft Minutes of the 20th May 2025 COT Meeting Committee on Toxicity. However, a number of limitations were noted, including that women during preconception, pregnancy and lactation are underrepresented in the evidence base, and further clarification and revisions were requested.

4.       Members also raised several methodological and presentational issues. These included ensuring consistent reporting of dose units, providing the duration of all human studies cited, and clearly setting out the limitations of key studies (for example where data were unpublished or based on limited clinical observations).

5.       In relation to exposure assessment, Members agreed with the overall conclusion that exposures were below levels of concern. However, they asked whether the assessment should include all forms of vitamin D to better reflect total intake, and whether scenarios could consider NHS dietary advice for pregnant women. Following discussion between the Secretariat, Chair and Deputy Chair, it was agreed that the assessment should remain focused on orally consumed calcidiol, as requested by SACN. While the implications of following NHS advice on exposure was considered, it was not taken forward, as many recommendations cannot be reflected in the available NDNS data (for example cooking practices, portion limits or product-specific distinctions). In addition, modifying or removing food groups could introduce bias and additional uncertainty without significantly affecting exposure estimates, particularly as dietary sources contribute only a small proportion of overall calcidiol exposure compared with supplements. It was therefore considered unlikely that such refinements would change the overall conclusions.

6.       Following an auxiliary meeting with the COT Chair, Secretariat and rapporteurs, it was agreed that a position statement, supported by a supplementary report, should be developed. These documents would summarise the Committee’s conclusions and provide a clear account of the evidence base and key data gaps.

7.       The draft position statement sets out the Committee’s overall conclusions on calcidiol and vitamin D in the maternal diet, drawing on previous COT outputs and the 2024 ACNFP assessment. It is intended to provide a concise, standalone summary of the Committees current position on the effects of calcidiol and vitamin D, including key considerations on risk, exposure and data gaps.

8.       The supplementary report supports the position statement by setting out the underlying evidence on calcidiol. It provides a more detailed assessment of toxicology, exposure and risk characterisation, including human and animal data, derivation of health-based guidance values, and a summary of uncertainties.

9.       Members are asked to consider both documents together. In particular, views are sought on whether the position statement accurately reflects the Committee’s conclusions, and whether the supplementary report provides sufficient supporting detail.

10.      The position statement (Annex A) has been prepared incorporating Members’ comments and suggested revisions.

Questions on which the views of the Committee are sought

a)       Are Members content with the content and structure of the position statement?

Secretariat

May 2026

TOX/2026/20 Annex A

Introduction

1.       As part of the Scientific Advisory Committee on Nutrition (SACN) risk assessment on nutrition and maternal health, the Committee on Toxicity (COT) reviewed vitamin D and whether excess exposure would pose a risk to maternal health. Following publication of the Statement on the potential effects of excess vitamin D intake during preconception, pregnancy and lactation a request from SACN was made for the COT to also consider risk from a vitamin D derivative called calcidiol and whether this also poses a risk to maternal health. The request was made by SACN on the basis that calcidiol is a more potent form of vitamin D than vitamin D2 (ergocalciferol) and D3 (cholecalciferol), and its availability is increasing on the market.

2.       The COT previously reviewed vitamin D in the maternal diet (COT, 2022) and a discussion paper on calcidiol in the maternal diet was last presented to the Committee in May 2025 (COT, 2025). Following an auxiliary meeting with the COT chair, Secretariat and rapporteurs for the discussion paper it was agreed that a position statement as well as a supplementary report providing brief overview of calcidiol in the maternal diet that summarises the conclusions of the discussion paper and highlights the exiting data gaps would be presented to the Committee.

3.       This position statement provides an overview of the COTs work on calcidiol, with a focus on its presence in the maternal diet and the potential implications for maternal and infant health. It summarises the evidence considered by the COT and their conclusions across its published opinions on calcidiol and vitamin D (where contextually relevant to the calcidiol assessment), including evidence of adverse effects, exposure assessments, tolerable upper intake levels, vulnerable groups, and highlights evidence gaps relevant to risks from calcidiol. In addition, the statement takes account of conclusions from the UK Advisory Committee for Novel Foods and Processes (ACNFP) regarding calcidiol as a novel food. The paper is structured to consider each relevant publication in turn, followed by a synthesis of the COT’s overall views and final conclusions.

Background

4.       Vitamin D refers to two lipid-soluble substances termed seco-steroids. One of these (vitamin D2 or ergocalciferol) is of plant and fungal origin and thus is only available to humans via the diet. The other seco-steroid (vitamin D3 or cholecalciferol) is synthesised in mammalian skin via ultraviolet-B radiation from sunlight, which induces photolysis of the steroid 7-dehydroxycholesterol (7-DHC). Vitamin D3 may also be acquired through the consumption of oil rich foods or supplements of animal origin such as cod liver oil (COT, 2022).

5.       Vitamin D is important for musculoskeletal health as it regulates calcium and phosphorous metabolism, which is required for normal bone mineralisation, muscle contraction, nerve conduction and general cellular function in all cells in the body. Other possible functions involve a role in immunoprotection due to the wide distribution of vitamin D receptors on various cells of the immune system. Vitamin D may also play a role in regulation of cell proliferation, cell differentiation and apoptosis as vitamin D-responsive elements are present in a large number of genes associated with these cellular processes (COT., 2014).

6.       Vitamin D is lipid soluble, and adipose tissue in the body is the major site of vitamin D storage. Excess vitamin D consumption can lead to elevated circulating concentrations and possible toxicity (Holick et al., 1981).

7.       When absorbed or released into the systemic circulation, both forms of vitamin D are transported to the liver by Vitamin D Binding Protein (DBP), where they are hydroxylated by P450 (CYP) 2R1 to 25-hydroxyvitamin D (25(OH)D) (COT, 2014). The 25(OH)D is then secreted from the liver into the systemic circulation, where it binds to DBP. When the bound 25(OH)D reaches the kidneys, it is further hydroxylated, following facilitated uptake, to the hormonally active product 1,25-dihydroxyvitamin D (1,25(OH)2D) by CYP27B1. Both 25(OH)D and 1,25(OH)2D are inactivated by CYP24A1-mediated hydroxylation.

8.       Calcidiol is a naturally occurring metabolite of vitamin D. It is an inactive precursor to the biologically active hormone 1,25-dihydroxyvitamin D (1,25(OH)2D) (Vieth, 2020). In the context of supplementation, however, calcidiol is considered a novel source of vitamin D3 (ACNFP, 2024). The supplemental form is chemically synthesised from cholestatrienol and is identical to endogenous 25-hydroxyvitamin D (25(OH)D) (Vieth, 2020; ACNFP, 2024). Calcidiol is marketed under several names, including calcidiol monohydrate, 25-hydroxycholecalciferol monohydrate (25(OH)D3 monohydrate) (EFSA, 2023), calcifediol or 25(OH)D; the latter two terms are most used in the context of supplementation (Biondi et al., 2017).

9.       Calcidiol is generally assumed to be approximately 2.5 times more bioavailable than cholecalciferol (vitamin D3) (EFSA, 2023; ACNFP, 2024). Compared with cholecalciferol, calcidiol is more hydrophilic and has a shorter half-life (Navarro-valverde et al., 2016; Henríquez and Gómez de Tejada Romero, 2020; Donati et al., 2023). Supplementation with calcidiol results in a more rapid increase in circulating serum 25(OH)D levels (Navarro-Valverde et al., 2016; Maghbooli et al., 2021). This effect is attributed to differences in absorption and metabolism. Unlike vitamin D3, calcidiol does not require bile acids for intestinal absorption nor hepatic 25-hydroxylation, leading to faster and more efficient entry into the systemic circulation (EFSA, 2022).

10.      Consistent with its higher bioavailability, calcidiol has been reported to be more effective than vitamin D3 at increasing serum 25(OH)D levels, such that lower doses are required to achieve equivalent circulating levels (Vieth., 2020; Pereda and Nishishinya., 2022; Stamp et al., 1977). However, the COT does not consider calcidiol to be intrinsically more potent than vitamin D3 as neither are the active form of vitamin D (i.e. 1,25(OH)2D). However, the COT does recognise that calcidiol’s greater bioavailability, means that an equivalent oral dose can result in higher serum 25(OH)D concentrations compared with vitamin D3 (COT., 2025).

11.      Consideration of vitamin D opinions is included within this position statement insofar as it is directly relevant to maternal and infant dietary exposures. Calcidiol (25(OH)D) is the primary circulating metabolite of vitamin D and an established biomarker of vitamin D status; therefore, discussion of calcidiol necessarily requires reference to vitamin D intake.

COT Statement on adverse effects of high levels of vitamin D (2014)

12.      In 2014 the COT published a Statement on the possible harmful effects of high intakes of vitamin D . The SACN asked the COT to advise on the possible adverse effects of high vitamin D intakes and which population groups might be unusually vulnerable to adverse effects of vitamin D.

13.      The COT concluded that excessive vitamin D increases calcium absorption and mobilisation, which can lead to hypercalcaemia and associated harms such as soft tissue calcification, bone demineralisation, and kidney damage. These effects can occur with both short- and long-term high exposure, and hypercalcaemia was identified as the most appropriate endpoint for setting safe limits.

14.      Based on the evidence, the COT concluded that the existing EFSA Tolerable Upper Levels (TULs) were appropriate: 100 µg/day for adults and children aged 11-17 years, 50 µg/day for children aged 1-10 years and 25 µg/day for infants. Furthermore, the COT found no evidence that pregnant women or older adults are unusually sensitive to vitamin D and considered the adult TUL of 100 µg/day to be appropriate for these groups. These limits applied to total intake, as vitamin D from food contributes little compared with supplements.

15.      The COT noted that these TULs may not adequately protect people with conditions that predispose them to hypercalcaemia, such as certain parathyroid disorders, granulomatous diseases (e.g., sarcoidosis or tuberculosis), or specific genetic conditions.

16.      The COT advised that occasional high single doses of vitamin D (up to 7,500 µg or 300,000 IU given no more frequently than once every three months) are unlikely to cause harm in adults, though uncertainty remains for larger doses. There was insufficient evidence to define a safe single-dose limit for children, but limited data suggest that toxicity (hypercalcaemia) could occur in infants at doses around 15,000 µg.

COT Statement on vitamin D Exposure Levels in Formula Fed Infants and Children (2024)

17.      The FSA received a request from the Nutrition, Labelling, Composition and Standards (NLCS) seeking a view on the potential risk of vitamin D toxicity in infants and children up to 4 years old, consuming infant and follow-on formula as a result of the increase in the minimum vitamin D content of both due to a change in regulations. The maximum vitamin D content for both remained the same.

18.      The COT subsequently published a Statement considering vitamin D exposure in infants (0-12 months) and young children (1-4 years) (COT., 2024). Exposure was estimated from dietary sources, including breast milk, infant and follow‑on formulae, and vitamin D supplements.

19.      In line with EFSA, the COT were in agreement with the TULs of 50 µg/day for children aged 1-10 years, 35 µg/day for infants aged 6-12 months old and 25 µg/day for infants up to 6 months old (COT., 2014, 2024; EFSA., 2023).

20.      For infants under one year of age, estimated vitamin D intakes from food and formula alone were generally below established TULs. Potential exceedances of these TULs were identified only in specific, high‑intake scenarios, most notably when infants consumed large volumes of formula in addition to vitamin D supplements, which does not align with current NHS guidance. When existing advice is followed, exceedance of safe intake levels is not expected.

21.      Adding the maximum recommended supplement dose could lead to TUL exceedances at the highest exposure levels in both younger (4-6 months) and older (6-12 months) infants, but these were limited to extreme or worst‑case exposure scenarios rather than typical intakes.

22.      Overall, the Committee concluded that the mandatory increase in minimum vitamin D content in infant and follow‑on formulae does not raise toxicological concerns, and that current UK supplementation guidance remains appropriate. The assessment also supported the revised EFSA TUL for infants aged 6-12 months (EFSA., 2018), reflecting updated evidence on vitamin D requirements in this age group.

COT Statement on the potential effects of excess vitamin D intake during preconception, pregnancy and lactation (2022)

23.      In 2022 the COT published a Statement on the potential effects of excess vitamin D intake during preconception, pregnancy and lactation . The statement specifically reviewed the effects of vitamin D in the form of vitamin D2 and D3 in the maternal diet and outlined the available evidence on the toxicological effects of vitamin D during preconception, pregnancy and lactation.

24.      The COT agreed that dietary exposure to vitamin D (i.e. from food) and not including supplements) in women attempting conception, and pregnant and lactating women were unlikely to be at risk of adverse effects such as hypercalcemia and hypercalciuria as exposure estimates for women in this category are below the TUL for vitamin D of 100 µg/day.

25.      Mean exposure estimates from all dietary sources (including supplements) for women of childbearing age, mean and total intakes did not exceed the TUL set for vitamin D of 100 µg/day. As for 97.5th percentile exposure estimates for vitamin D from all dietary sources, the TUL was exceeded up to 2-fold. However, it was noted that the supplement use was “the biggest driver of exposure from all dietary intakes at the 97.5th percentile and is only likely to be of concern if exposures at the 97.5th percentile were sustained long term”. Nevertheless, the risk of hypercalcemia and hypercalciuria in the maternal diet “cannot be completely excluded, especially in a few sensitive individuals who may have loss of function mutations in CYP24A1, responsible for vitamin D inactivation”.

26.      The COT further noted that the contribution of vitamin D from the diet (i.e. food sources) is much lower than from supplements and “the major risk of excess vitamin D exposure is in relation to supplement consumption rather than consumption of vitamin D containing foods”.

27.      Regarding vitamin D synthesis via UVB radiation the COT concluded that “topical UV radiation is unable to increase systemic exposure to vitamin D sufficiently to cause toxicity, due to the inbuilt mechanisms for degradation of excess vitamin D in the skin”.

28.      Ultimately, the COT concluded that dietary exposure to vitamin D from consumption of foods (excluding supplements), is very unlikely to result in sufficiently high levels of intake of the vitamin to be any cause for concern. Consumption of higher strength vitamin D supplements (>10 µg/day), either alone or in combination with dietary intake, may result in exposure levels that exceed the TUL and would therefore be of potential health concern. Consumption of lower strength supplements aimed at pregnant and breast-feeding women (≤10 µg/day), either alone or in combination with dietary intake, is very unlikely to result in excessive exposure to vitamin D.

ACNFP safety assessment on calcidiol as a novel food (2024)

29.      In 2021 the FSA and FSS received an application from DSM Nutritional Products Ltd for the authorisation of Calcidiol, 25-hydroxycholecalciferol monohydrate as a novel food. The novel food is intended as a new source of vitamin D3 for use as a food supplement targeted at a generally healthy population including pregnant and lactating women, except children under 3 years. To support the FSA and FSS in their evaluation of the application, the UK Advisory Committee for Novel Foods and Processes (ACNFP) were asked to review the safety dossier.

30.      The risk assessment approach taken by the ACNFP largely followed the approach taken by EFSA in their own assessment on the Safety of calcidiol monohydrate (EFSA, 2021). The ACNFP agreed with the level of 10 µg/day calcidiol which EFSA established as safe. The ACNFP also established an adjusted upper intake level of 40 µg/day for adults which was calculated by applying a 2.5 conversion factor to the TUL of 100 µg/day for vitamin D. The conversion factor was derived by EFSA for converting calcidiol to vitamin D3 to account for its greater ability to increase serum 25(OH)D concentrations compared to vitamin D3 (EFSA., 2023). The ACNFP agreed with EFSA’s conversion factor of 2.5 (ACNFP, 2024). The adjusted upper intake level was calculated to account for foreseeable misuse by consumers, which was considered a possibility by the ACNFP as the product is available over the counter and would be used without medical supervision (ACNFP, 2024).

31.      The ACNFP also considered whether administration of calcidiol might alter downstream metabolic pathways or interfere with the homeostatic regulation of circulating vitamin D metabolites. Based on data submitted by DSM Nutrition Ltd, the ACNFP concluded that there was no evidence to suggest that supplemental 25‑hydroxycholecalciferol would be metabolised differently from endogenous calcidiol derived from dietary vitamin D or cutaneous synthesis, nor that it would exert wider effects on feedback regulation, related metabolic pathways, or vitamin D homeostasis.

32.      Based on the ACNFP review of a calcidiol application submitted by DSM Nutritional Products Ltd the FSA and FSS concluded calcidiol does not pose a toxicological concern and is safe under the proposed conditions of use (ACNFP, 2024).

COT Evaluation of calcidiol supplementation during pregnancy, childbirth and lactation (2025)

33.      A discussion paper on the effects of calcidiol supplementation during pregnancy, childbirth and lactation was last presented to the COT in May 2025. This paper followed the 2022 Statement on the potential effects of excess vitamin D intake during preconception, pregnancy and lactation at the request of the SACN. The request was made on the basis that calcidiol is a more bioavailable form of vitamin D2 (ergocalciferol) and D3 (cholecalciferol), and its availability is increasing on the market.

34.      The discussion paper reviewed the toxicological effects of calcidiol on the maternal diet during preconception, pregnancy and lactation. In line with the ACNFP and EFSA, the COT were in agreement with the proposed safe level of intake of 10 µg/day calcidiol for adults. The COT were also in agreement with the additional TUL of 40 µg/day proposed by the ACNFP, in order to identify a level of intake that would be safe if consumers were to exceed the proposed intake of 10 µg/day. This was considered a possibility by the ACNFP as the product is available over the counter and would be used without medical supervision.

35.      An exposure assessment was performed to estimate the total dietary intake of two forms of calcidiol, 25-hydroxycholecalciferiol (25(OH)D3) and 25-hydroxyergocalciferol (25(OH)D2). For women of childbearing age whose only exposure to calcidiol is from food sources (excluding supplements), their intake did not exceed the ACNFP TUL of 40 µg/day or the level EFSA established as safe i.e., up to 10 μg/day. When considering exposure estimates from food and supplements combined, maximum mean exposures of calcidiol exceeded the level EFSA established as safe (i.e., up to 10 μg/day) by 2-fold. The minimum 97.5th percentile intake marginally exceeded the level EFSA established as safe (i.e., up to 10 μg/day), whereas the maximum 97.5th percentile intake exceeded the level EFSA established as safe by 2.1-fold.  However, all mean and 97.5th percentile chronic intakes of calcidiol from food and supplements combined were below the ACNFP TUL of 40 µg/day. Supplements are the greatest contributor to calcidiol exposure in these population groups. The COT concluded that exposure from calcidiol supplements and calcidiol from food sources in healthy pregnant and lactating women is unlikely to result in significant exceedances of the ACNFP TUL and the level EFSA established as safe. However, sensitive individuals with loss of function mutations in CYP24A1 would be more susceptible to the effects of calcidiol.

36.      The Committee agreed that estimated intakes of calcidiol were not reaching threshold levels and therefore were not of risk (COT, 2025). However, Members identified several uncertainties and data limitations with the assessment. Most notably, data on the population of interest (i.e., women during preconception, pregnancy or lactation) is underrepresented, with most toxicological data being insufficient and not relevant. To date there are no published human studies on the safety of calcidiol during preconception, pregnancy and lactation. Most of the clinical trials published are in individuals with vitamin D deficiency, in older men or in post-menopausal women (Quesada-Gomez, et al., 2023).

Conclusions

37.      Overall, the risks to infants and women of childbearing age from dietary intake of vitamin D or calcidiol were considered to be low and unlikely to raise concern. Exceedances of health-based guidance values (HBGVs) were observed only at high‑end (97.5th percentile) or maximum estimated mean intakes, with supplements accounting for the majority of total exposure. Risk cannot be excluded in women who are sensitive to vitamin D toxicity and may develop hypercalcaemia at lower vitamin D intakes than the general population.

38.      The COT acknowledged that there are gaps in the toxicological evidence base for calcidiol, most notably the limited availability of data directly relevant to the population of interest. To date, there are no published human studies specifically designed to assess the safety of calcidiol during preconception, pregnancy or lactation. Consequently, risk assessment for these life stages necessarily relies on data from other adult populations and established understanding of vitamin D metabolism, and would benefit from additional relevant data should such information become available in the future.

Questions on which the views of the Committee are sought

a)       Are Members content with the content and structure of the position statement?

List of Abbreviations and Technical terms

Abbreviation / Term	Definition
1,25(OH)2D	1,25-dihydroxyvitamin D
25(OH)D	25-hydroxyvitamin D
25(OH)D2	25-hydroxyergocalciferol
25(OH)D3	25-hydroxycholecalciferiol
ACNFP	Advisory Committee on Novel Foods and Processes
DBP	Vitamin D Binding Protein
COT	Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment
EFSA	European Food Safety Authority
FSA	Food Standards Agency
FSS	Food Standards Scotland
HBGV	Health Based Guidance Value
SACN	Scientific Advisory Committee on Nutrition
TUL	Tolerable Upper Intake Level

References

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Biondi, P., Pepe, J., Biamonte, F., Occhiuto, M., Parisi, M., Demofonti, C., Baffa, V., Minisola, S. and Cipriani, C. (2017). Oral calcidiol is a good form of vitamin D supplementation. Clinical Cases in Mineral and Bone Metabolism, 14(2), p.207. Oral calcidiol is a good form of vitamin D supplementation - PubMed

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Secretariat

May 2026