Primary prevention
It is difficult to obtain an adequate amount of vitamin D from dietary sources alone (both natural sources and vitamin D-fortified foods); dietary vitamin D intake is often low in older people in particular.[16] Dietary sources of vitamin D include wild caught salmon, sun-dried mushrooms, cod liver oil, and vitamin D-fortified foods (e.g., milk, margarine, and orange juice in the US).
A combination of sensible sun exposure along with adequate vitamin D supplementation for all children and adults will prevent vitamin D deficiency/insufficiency in the general population. However, for a variety of reasons, even in the sunniest parts of the globe, including the Middle East, India, Colombia, Mexico, Brazil, and Australia, vitamin D deficiency and insufficiency is common because of inadequate sun exposure.[3][15]
Vitamin D supplementation is the most effective method for preventing deficiency, particularly for those at high risk. Recommendations on daily intake to prevent deficiency vary between guideline providers, and depend in part on sun exposure and the standards used to define a deficient state. A summary of international guideline recommendations is provided here.
Pregnancy and lactation
Due to uncertainties regarding safety for both mother and fetus, it is advisable to seek specialist advice when starting vitamin D supplementation during pregnancy.
The National Academy of Medicine recommends that an adequate intake (Recommended Dietary Intake or RDI) of vitamin D during pregnancy and lactation is 600 IU/day.[79]
Although the World Health Organization (WHO) does not recommend supplementation for all pregnant women, if vitamin D deficiency is suspected (such as women in populations where sun exposure and dietary vitamin D is limited), vitamin D supplements may be given at the current recommended nutrient intake of 200 IU/day.[80]
Unlike WHO guidance, the Endocrine Society recommends empirical vitamin D supplementation during pregnancy due to its potential to reduce the risk of pre-eclampsia, intrauterine mortality, preterm birth, and other adverse fetal outcomes. Recommended strategies include fortified foods, antenatal vitamins containing vitamin D, or supplements (pills or drops), although the Endocrine Society does not specify dosing for this group.[4]
In the UK, the National Institute for Health and Care Excellence (NICE) recommends that pregnant and lactating women, particularly teenagers and young women, receive 400 IU/day of vitamin D supplementation.[81]
Although vitamin D concentrations can be increased in milk of lactating women by using large doses of vitamin D supplements, there is currently insufficient evidence as to the safety and efficacy of this approach for the prevention of vitamin D deficiency in babies.
Infants and children
The National Academy of Medicine recommends infants 0-12 months receive 400 IU/day of vitamin D and children ≥1 year receive 600 IU/ day.[79] Furthermore, based on the literature available, they recommended the upper limit of vitamin D for infants 0-6 months and 6-12 months at 1000 and 1500 IU/day, respectively. The upper limit was increased to 2500 IU/day for children aged 1-3 years, and 3000 IU/day for 4-8 years. For children aged >8 years, the upper limit was raised to 4000 IU/day.[79]
The Endocrine Society recommends empirical vitamin D supplementation in children and adolescents aged 1-18 years, including intake of fortified foods, antenatal vitamin formulations containing vitamin D and/or a vitamin D supplement (pills or drops); the Endocrine Society in 2024 does not provide clear guidance on dosing for this age group, and does not offer guidance on vitamin D supplementation for infants <1 year, in spite of this being a key group which may experience vitamin D deficiency.[4] However, in its 2011 guidance it recommended vitamin D supplementation for infants on the basis that there is little if any vitamin D in human breast milk.[82]
In the UK, the National Institute for Health and Care Excellence (NICE) recommends that all infants and young children aged 6 months to 3 years take a daily supplement containing vitamin D in the form of vitamin drops. They advise that infants who are fed infant formula will not need them until they have less than 500 mL/day of infant formula, because these products are fortified with vitamin D. Breastfed infants may need drops containing vitamin D from 1 month of age if their mother has not taken vitamin D supplements throughout pregnancy.[81] NICE recommends a ‘safe intake’ of 340-400 IU/day for infants <1 year, and 400 IU/day for children aged 1-4 years. For children aged 4 years and older, NICE recommends a reference nutrient intake of 400 IU/day.[81]
Adults
In the US, the Recommended Dietary Allowance (RDA) for vitamin D is 600 IU/day for non-pregnant adults up to 70 years of age, and 800 IU/day for those >70 years, according to the National Academy of Medicine.[79] For adults the safe upper limit is 4000 IU/day.[79]
The Endocrine Society in 2024 does not recommend empirical vitamin D supplementation in the general adult population younger than aged 75 years, beyond the RDA established by the National Academy of Medicine.[4] An exception to this is adults with high-risk prediabetes; empirical vitamin D supplementation is recommended by the Endocrine Society for this patient group, in addition to lifestyle modification, to reduce the risk of progression to diabetes. However, the Endocrine Society does not provide clear guidance on dosing for this patient group.[4]
Older adults, particularly those who are confined indoors or belong to high-risk groups, may have lower serum levels of 25-hydroxyvitamin D at this intake level and may need higher amounts.[79]
The American Geriatrics Society (AGS) and the National Osteoporosis Foundation (NOF) recommend slightly higher doses of vitamin D for older adults to help reduce the risk of fractures and falls; the AGS advises at least 1000 IU/day for adults aged 65 years and older, while the NOF recommends 800-1000 IU/day for adults aged 50 years and older.[83][84] Both AGS and NOF recommend maintaining serum 25-hydroxyvitamin D concentrations ≥75 nanomoles/L (≥30 nanograms/mL).[83][84]
For those aged ≥75 years, the Endocrine Society in 2024 recommends empirical vitamin D supplementation because of its potential to lower mortality; however, although the Endocrine Society does not provide clear guidance on dosing for this age group they describe evidence which suggests that this age group may benefit by taking 900 IU/day.[4]
In the UK, adults who are at risk of vitamin D deficiency are advised to take 400 IU/day.[21] Specific populations at risk of vitamin D deficiency are: those with limited exposure to the sun (e.g., if they cover their skin for cultural reasons or are housebound); and women and children of Asian origin.[81]
Current uncertainties: supplementation for prevention of vitamin D deficiency exceeding recommended daily intake guidelines
Uncertainties exist regarding supplementation above the recommended daily intake for preventing vitamin D deficiency. While most guidelines suggest 600-800 IU/day for adults and 400-600 IU/day for children, some studies indicate that higher doses (1500-2000 IU/day) may be beneficial for prevention, especially for high-risk populations.[17][85][86]
The 2024 Endocrine Society guidelines focus on using vitamin D to reduce disease risk in those without indications for treatment or 25-hydroxyvitamin D testing, while the 2011 guidelines had a broader goal and emphasised preventing and treating vitamin D deficiency more generally, recommending daily doses of 400-1000 IU/day for infants, 600-1000 IU/day for children aged ≥1 years, and 1500-2000 IU/day for adults to maintain a 25-hydroxyvitamin D level >75 nanomoles/L (>30 nanograms/mL).[4][82] The 2011 guidelines also noted that adults with a BMI of 30 kg/m² or higher require 2-3 times more vitamin D than the standard dose.[82]
There is minimal evidence of any significant adverse effects from doses up to 2000 IU/day in the general population, and so it may be reasonable for healthy adults without obesity to take this amount daily, following shared decision-making.[17] A 100 IU/day increase in vitamin D raises serum 25-hydroxyvitamin D by about 2.5 nanomoles/L (1 nanogram/mL) in a normal weight adult, and an intake of 2000-3000 IU/day is needed to achieve a serum concentration >75 nanomoles/L (>30 nanograms/mL). Adults with obesity may need higher doses to reach the same levels. Higher doses may benefit older adults or those with limited sun exposure.[85][86]
Clinicians should consider specialist referral if considering a higher dose of vitamin D than the recommended daily intake as outlined in their relevant clinical practice guidance, especially in complex cases. Special consideration and caution is recommended during pregnancy. The 2024 Endocrine Society guidelines recommend vitamin D during pregnancy to reduce risks like pre-eclampsia and preterm birth. The guidelines suggested that the estimated weighted average from the various studies was approximately 2500 IU/day, quoting a wide range of vitamin D doses within studies, and did not specify a recommended dose.[4]
Safety issues, including increased risks of falls and fractures with high doses (e.g., a single dose of 500,000 IU/year), suggest daily or weekly supplementation may be safer for older adults.[87]
Retesting serum 25-hydroxyvitamin D concentrations (e.g., after 2-3 months) is typical to assess effectiveness and adjust doses as needed.
[Figure caption and citation for the preceding image starts]: Sources of vitamin DCreated by M.F. Holick, PhD, MD; used with permission [Citation ends].
Secondary prevention
Once the desired serum concentration of 25-hydroxyvitamin D is obtained, daily oral vitamin D maintenance dose is initiated and is typically continued for life to prevent recurrence.
Although vitamin D concentrations can be increased in milk of lactating women by using large vitamin D supplements, there is currently insufficient evidence as to the safety and efficacy of this approach for the prevention of vitamin D deficiency in babies.
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