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Promotes calcium absorption from the gut and calcium balance in the body
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Supports bone health
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Supports immune function
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Involved in cell growth Involved in the expression of hundreds of genes
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Involved in regulating blood phosphorus levels
How it works
Recommended daily amount
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Sunlight Fortified plant milks
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Fortified 100% fruit juices
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Fortified breakfast cereals
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Mushrooms (UV light exposed)
Animal-sourced foods: fatty fish, fish oil, egg yolk (from fortified hens) [2,5]
Sources of nutrient
Daily upper limits
Prolonged exposure to sunlight cannot cause toxic levels of vitamin D. [2] Little is known about the effects of chronic excess intake of vitamin D below the tolerable upper limit values shown above.[2]
Vitamin D
Many people do not consume adequate vitamin D, and some people do not produce enough vitamin D from sunlight due to darker skin, living in higher latitudes, and spending much time indoors.
Vitamin D is a fat-soluble vitamin absorbed primarily in the upper part of the small intestine and stored in the liver and adipose tissue. [1] Thus, fat malabsorption conditions can interfere with vitamin D absorption (e.g., cystic fibrosis, Crohn’s, gastric bypass). [1,2]
Supplements and fortified foods often have the inactive forms of vitamin D (D2 and D3). Both tend to raise vitamin D levels similarly in the body except at high doses where D3 may be more effective in raising and/or sustaining serum vitamin D levels than D2. [1,2,5]
Animal studies suggest that D2 may be less toxic than D3. It may be due to the high pharmacological doses and frequencies of the vitamin used in animal studies, as this has not been clearly documented in humans. [2]
Bioavailability
Examples of nutrient-rich foods
Assays used to measure vitamin D may have large variations in accuracy, [1,2] and may have values corresponding to status that are different than those presented here due to the type of test used. A false high or low result may occur. [1]
Note that serum concentrations of 75 to 120 nmol/mL (30 to 48 ng/mL) have been linked with an increased risk for all-cause mortality, cardiovascular events, some cancers (pancreas), and fractures in the elderly. [1] (Intake of 5000 IU/day has resulted in serum levels of 100 - 150 nmol/mL. [1])
Note 1,25-dihydroxyvitamin D (calcitriol, the active form of vitamin D) is not a good indicator of status since it has a short half-life of 15 hours, is regulated by PTH, calcium and phosphate, and does not decrease until severe deficiency occurs. [1,2]
Caution, there is no universal consensus on cut-off values defining vitamin D status, particularly for insufficiency;[2] values should be interpreted with caution for diagnostic purposes. [2,5,6]
Serum 25-hydroxyvitamin D is considered a good indicator of status. [1,2,6 ]Although it does not measure vitamin D stores, [1] it reflects endogenous and ingested vitamin D [1,2,6] and has a 15-day half-life. [1]
Measures of adequate status
Infants born to mothers with low/insufficient vitamin D intake/status [1,2,5]
Exclusively breastfed infants who do not receive vitamin D supplements and receive little sun exposure or infants with darker skin tones [1,2,5]
Those living in higher latitudes (far north/south, particularly in winter months) [1,2,5]
Persons that spend much time indoors (limited sun exposure), who wear clothing that covers a large majority of the body, or who regularly and effectively use sunscreen [1,2,5]
Persons with darker skin tones [1,2,5]
Obese individuals since vitamin D may be sequestered as stored fat [2] Persons with gastric bypass surgery [1]
Those with chronic kidney disease or with fat-malabsorption (cystic fibrosis, Crohn’s, celiac disease, IBS, gastric bypass) [1,2,5]
The elderly, since the capacity to produce the vitamin D precursor in the skin is reduced,2 and they may be more likely to spend more time indoors and wear sunscreen [1]
Potentially those with magnesium deficiency (it is needed for enzymes in vitamin D metabolism) [5]
Populations at risk for deficiency
Deficiency signs and symptoms
Low calcium status
Poor bone growth and development
Rickets, osteomalacia, and osteoporosis
Soft tissue calcification [1,2]
Hypercalciuria and increased risk of kidney stones [2]
Hypercalcemia (nausea, vomiting, fatigue, diarrhea, headache, confusion, tremor) [1]
Anorexia, weight loss, polyuria, heart arrhythmias [1]
Acute vitamin D toxicity has been reported at 10,000 IU/day or more. [6]
Toxicity signs and symptoms
The content provided is for informational purposes only and may not be an exhaustive list of potential interactions.
Drugs that may decrease vitamin D absorption (take separately):
cholestyramine (Questran)
colestipol (Colestid)
orlistat (Xenical) mineral oil
Drugs that increase the metabolism of vitamin D (and may lower serum 25(OH)D):
phenytoin (Dilantin)
fosphenytoin (Cerebyx)
phenobarbital (Luminal)
carbamazepine (Tegretol)
rifampin (Rimactane)
Cimetidine (H2 blocker) prevents hydroxylation of vitamin D in the liver
Ketoconazole has been shown to inhibit the enzyme that converts vitamin D to its active form in healthy men
Glucocorticoids and HIV treatment drugs can increase the catabolism of 25-OH-vitamin D; thus, the patient’s vitamin D status should be monitored
Some chemotherapy agents (cytostatic agents or cell growth inhibitors) may decrease vitamin D levels
Potential drug-nutrient interactions
Exposure to UVB light stimulates the precursor of vitamin D (7-dehydrocholesterol) in the skin to create vitamin D3 (cholecalciferol) where it travels to the liver and then kidneys to be hydroxylated into 25-hydroxyvitamin D (calcidiol) and the active form of vitamin D (1,25-dihydroxyvitamin D, or calcitriol), respectively.
The active form of vitamin D (1,25OH-vitamin D, calcitriol) is regulated by its concentration in serum, as well as serum calcium, phosphorus, PTH, and fibroblast growth factor-23. [5] When calcium blood levels drop, PTH is secreted, which stimulates enzymes to convert 25(OH)-vitamin D to the active form of vitamin D (1,25(OH)-vitamin D). This, in turn, increases calcium resorption and excretion of phosphorus in the kidneys, increases absorption of calcium and phosphorus in the gut, and stimulates calcium and phosphorus release from the bone. A negative feedback loop stops the conversion of active vitamin D and the release of PTH. [5]
Vitamin D is needed for calcium absorption in the gut and calcium balance in the body (maintains adequate calcium and phosphate blood concentrations).
Vitamin D and Metabolism
The American College of Obstetrics and Gynecology recommends the following for vitamin D and pregnancy: [7]
There is insufficient evidence to support a recommendation for screening all pregnant women for vitamin D deficiency. Recommendations concerning routine vitamin D supplementation during pregnancy beyond that contained in a prenatal vitamin should await the completion of ongoing randomized clinical trials.
For pregnant women with an increased risk of vitamin D deficiency, serum 25-OH-D levels “can be considered and should be interpreted in the context of the individual clinical circumstance.” When vitamin D deficiency is identified during pregnancy, “most experts agree that 1,000–2,000 international units per day of vitamin D are safe. Higher dose regimens used to treat vitamin D deficiency have not been studied during pregnancy.”
There is insufficient evidence to recommend vitamin D supplementation to prevent preterm birth or preeclampsia.
The WHO does not recommend routine vitamin D supplementation during pregnancy to improve pregnancy outcomes. [8]
Vitamin D and Pregnancy
Heading 3
Notes
Vitamin D is a fat-soluble vitamin found in only a few foods. Most vitamin D intake is from fortified food in the diet in the U.S. and Canada. [1,6]
Supplements may be needed for children and adults, including pregnant and breastfeeding moms depending on diet, sun exposure, vitamin D status, and other factors. [3]
Many countries recommend that babies, especially if breastfed, be given vitamin D drops (400 IU) starting shortly after birth. [3]
Breast milk is typically low in vitamin D (~10 – 80 IU/L). [5] Although breast milk remained unchanged with supplementation up to at least 2000 IU, [2] high maternal intake has the capacity to increase milk concentrations.[3,5] Breastfeeding mothers may consider 6400 IU/d to increase milk amounts. [9]
There is a non-linear effect of vitamin D intake on serum 25-vitamin D concentrations, and it can depend on baseline concentration, supplement dose, and duration. [2] Clinical use of high-dose supplements to treat vitamin D deficiency (i.e., 15000 IU/week for 4 – 8 weeks) needs careful monitoring. [6]
Notes
1. Vitamin D. Fact Sheet for Health Professionals. Office of Dietary Supplements. National Institutes of Health. Updated Mar 2020. Accessed Sept 2020. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
2. Institute of Medicine 2011. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press. https://doi.org/10.17226/13050.
3. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at https://DietaryGuidelines.gov.
4. FoodData Central Database. United States Department of Agriculture. Accessed Oct 2021. https://fdc.nal.usda.gov.
5. Vitamin D. Linus Pauling Institute Micronutrient Information Center, Oregon State University. Updated Sept 2017. Accessed Sept 2020. https://lpi.oregonstate.edu/mic/vitamins/vitamin-D.
6. Brannon PM, Fleet JC. Vitamin D. Adv. Nutr. 2011; (2): 365–367.
7. The American College of Obstetricians and Gynecologists. Vitamin D: Screening and Supplementation During Pregnancy. Committee Opinion. CO Number 495. July 2011. Reaffirmed 2017 (on website Reaffirmed 2021). Obstet Gynecol 2011; 118:197-8.
8. WHO recommendation on antenatal care for a positive pregnancy experience. Nov 2016. https://www.who.int/publications/i/item/9789241549912. 9. Meek, J. Y., Noble, L., & Section on Breastfeeding. Policy Statement: Breastfeeding and the Use of Human Milk. Pediatrics 150, e2022057988 (2022).