What is vitamin D, and why is it important?
Best dietary sources of vitamin D
Vitamin D content of selected foods
Health benefits of vitamin D
Recommended intake and deficiency risks
Safety and excess intake
References
Further reading
Vitamin D is essential for maintaining bone health, immunity, and muscle function; however, deficiency affects approximately one billion people worldwide. Few foods naturally contain vitamin D, making fortified foods and supplements crucial for maintaining adequate levels.
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The most clinically established and studied function of vitamin D is its role in maintaining skeletal integrity through the dynamic modulation of calcium and phosphorus absorption.2 In addition to supporting bone and teeth health, vitamin D is a key immune system modulator, as it influences both innate and adaptive responses.3
Despite the human body's ability to synthesize vitamin D from sunlight, vitamin D deficiency remains a global public health issue affecting approximately one billion people.2 This article discusses the physiological benefits of vitamin D, as well as its metabolic functions, optimal dietary sources, and clinical safety and dosage recommendations.
What is vitamin D, and why is it important?
Vitamin D is a unique fat-soluble nutrient that functions as a pro-hormone, as it is a precursor to the steroid hormone calcitriol.1 Vitamin D can exist as either ergocalciferol (vitamin D2), obtained from plants and fungi, or cholecalciferol (vitamin D3), produced in mammalian skin following ultraviolet B (UVB) exposure and the consumption of animal-based foods.4
In the liver, vitamin D is converted to calcidiol, the primary circulating form, which is measured in laboratory assays. In the kidneys, calcidiol is converted to calcitriol, the biologically active hormone responsible for systemic effects.1,2,6
The actions of calcitriol are mediated through the vitamin D receptor (VDR), which is present in nearly all cells. Key functions include facilitating bone mineralization, enhancing intestinal absorption of calcium and phosphorus, regulating immune responses, and maintaining muscle strength and function.2,3,6
Best dietary sources of vitamin D
Although sunlight is the primary natural source of vitamin D, dietary intake is essential where sunlight exposure is limited. Few foods are naturally rich in vitamin D, with many potent sources being animal-derived.3,4
A three-ounce serving of cooked sockeye salmon provides 570 IU, whereas a tablespoon of cod liver oil offers about 1,360 IU. Smaller amounts are in beef liver (42 IU) and egg yolks (44 IU).3,4
Fortified foods are the largest dietary source in the U.S. and many countries. Almost all cow’s milk and many plant-based alternatives provide about 120 IU per cup. Fortified orange juice and cereals add ~100 IU and 80 IU per serving, respectively. Some yogurts and margarines are also fortified.4,8
The main non-animal source is mushrooms. UV-exposed mushrooms can contain up to 366 IU per half cup, but vitamin D levels are negligible in unexposed varieties.3
Vitamins D2 and D3 differ in bioavailability: both are absorbed, but D3 is more effective at sustaining serum 25(OH)D levels and is the preferred supplement form.1,7
Vitamin D content of selected foods
| Food |
Micrograms
(mcg) per
serving |
International
Units (IU)
per serving |
Percent DV* |
| Cod liver oil, 1 tablespoon |
34.0 |
1,360 |
170 |
| Trout (rainbow), farmed, cooked, 3 ounces |
16.2 |
645 |
81 |
| Salmon (sockeye), cooked, 3 ounces |
14.2 |
570 |
71 |
| Mushrooms, white, raw, sliced, exposed to UV light, ½ cup |
9.2 |
366 |
46 |
| Milk, 2% milkfat, vitamin D fortified, 1 cup |
2.9 |
120 |
15 |
| Soy, almond, and oat milks, vitamin D fortified, 1 cup |
2.5–3.6 |
100–144 |
13–18 |
| Ready-to-eat cereal, fortified with 10% DV vitamin D, 1 serving |
2.0 |
80 |
10 |
| Sardines (Atlantic), canned in oil, 2 sardines |
1.2 |
46 |
6 |
| Egg, 1 large, scrambled** |
1.1 |
44 |
6 |
| Liver, beef, braised, 3 ounces |
1.0 |
42 |
5 |
| Tuna fish (light), canned in water, 3 ounces |
1.0 |
40 |
5 |
| Cheese, cheddar, 1.5 ounce |
0.4 |
17 |
2 |
| Mushrooms, portabella, raw, diced, ½ cup |
0.1 |
4 |
1 |
| Chicken breast, roasted, 3 ounces |
0.1 |
4 |
1 |
| Beef, ground, 90% lean, broiled, 3 ounces |
0 |
1.7 |
0 |
| Broccoli, raw, chopped, ½ cup |
0 |
0 |
0 |
| Carrots, raw, chopped, ½ cup |
0 |
0 |
0 |
| Almonds, dry roasted, 1 ounce |
0 |
0 |
0 |
| Apple, large |
0 |
0 |
0 |
| Banana, large |
0 |
0 |
0 |
| Rice, brown, long-grain, cooked, 1 cup |
0 |
0 |
0 |
| Whole wheat bread, 1 slice |
0 |
0 |
0 |
| Lentils, boiled, ½ cup |
0 |
0 |
0 |
| Sunflower seeds, roasted, ½ cup |
0 |
0 |
0 |
| Edamame, shelled, cooked, ½ cup |
0 |
0 |
0 |
| *DV = Daily Value. The FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for vitamin D is 20 mcg (800 IU) for adults and children age 4 years and older. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet. |
Health benefits of vitamin D
Vitamin D and calcium, when taken together, reduce the risk of fractures in older adults.5 However, supplementation with vitamin D alone does not prevent fractures.5
Severe deficiency causes rickets in children and osteomalacia in adults, while chronic insufficiency increases the risk of osteoporosis.2 Low vitamin D also raises the risk of acute respiratory infections (ARIs).3
Recent meta-analyses have shown a modest protective effect against ARIs when vitamin D is taken daily in moderate doses (400–1000 IU), particularly in children, but not when administered in large boluses.3
Evidence for the prevention of depression, cardiovascular disease, or cancer remains inconsistent. Large trials, such as VITAL, found no general benefit in preventing falls or chronic diseases.6
Recommended intake and deficiency risks
The U.S. NIH recommends 600 IU daily for adults aged 19–70 years and 800 IU for those over 70 years. Infants require 400 IU, and pregnant or breastfeeding women 600 IU.4
Deficiency may cause fatigue, bone pain, muscle weakness, and an increased risk of infection. At-risk groups include older adults, people with darker skin, those in northern latitudes, obese individuals, and patients with malabsorption or chronic conditions.2
Safety and excess intake
Dietary sources of vitamin D are limited, thus emphasizing the need for fortified foods and a balanced approach to diet. Sufficient exposure to sunlight, particularly in the morning, and targeted supplementation are crucial for preventing the consequences of widespread vitamin D deficiency.
While essential at optimal dosages, excessive intake of vitamin D from supplements can be toxic and lead to hypercalcemia, which can cause nausea, weakness, confusion, and, in severe cases, kidney damage and cardiovascular complications. Notably, this condition does not occur from sun exposure or diet.4,9
References
- Borel, P., Caillaud, D., & Cano, N. J. (2013). Vitamin D Bioavailability: State of the Art. Critical Reviews in Food Science and Nutrition 55(9); 1193-1205. DOI:10.1080/10408398.2012.688897, https://www.tandfonline.com/doi/full/10.1080/10408398.2012.688897.
- Kaur, J., Khare, S., Sizar, O., & Zulfiqar, H. (2025). Vitamin D deficiency. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK532266/
- Jolliffe, D. A., Camargo, C. A., Sluyter, J. D., et al. (2021). Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials. The Lancet Diabetes & Endocrinology 9(5); 276-292. DOI:10.1016/S2213-8587(21)00051-6, https://www.thelancet.com/journals/landia/article/PIIS2213-8587(21)00051-6/fulltext.
- National Institutes of Health, Office of Dietary Supplements. (08 November 2022). Vitamin D: Fact Sheet for Consumers. https://ods.od.nih.gov/factsheets/VitaminD-Consumer/. Accessed on 19 September 2025.
- Chakhtoura, M., Bacha, D. S., Gharios, C., et al. (2021). Vitamin D Supplementation and Fractures in Adults: A Systematic Umbrella Review of Meta-Analyses of Controlled Trials. The Journal of Clinical Endocrinology & Metabolism 107(3); 882-898. DOI:10.1210/clinem/dgab742, https://academic.oup.com/jcem/article/107/3/882/6431451.
- LeBoff, M. S., Murata, E. M., Cook, N. R., et al. (2020). VITamin D and OmegA-3 TriaL (VITAL): Effects of Vitamin D Supplements on Risk of Falls in the U.S. Population. The Journal of Clinical Endocrinology & Metabolism 105(9); 2929-2938. DOI:10.1210/clinem/dgaa311, https://academic.oup.com/jcem/article/105/9/2929/5850900.
- Lehmann, U., Hirche, F., Stangl, G. I., et al. (2013). Bioavailability of Vitamin D2 and D3 in Healthy Volunteers, a Randomized Placebo-Controlled Trial. The Journal of Clinical Endocrinology & Metabolism 98(11); 4339-4345. DOI:10.1210/jc.2012-4287, https://academic.oup.com/jcem/article/98/11/4339/2536636.
- U.S. Department of Agriculture & U.S. Department of Health and Human Services. (2020). Food Sources of Vitamin D. Nutrition and Your Health: Dietary Guidelines for Americans, 2020-2025. https://health.gov/sites/default/files/2020-01/DGA2000.pdf. Accessed 19 September 2025.
Further Reading
Last Updated: Sep 30, 2025