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How long does it take for vitamin D to work?

Medically reviewed by Sally Chao, MD. Last updated on Feb 2, 2021.

Official Answer


It varies. It could take weeks or months, depending on where your levels are now.

Vitamin D deficiency and the impact of getting enough or too much of the nutrient have been the topic of numerous studies.

That includes variations in how much vitamin D people should take or doctors should prescribe and for how long. One 2011 protocol from the Endocrine Society suggests a very high dose of vitamin D3: 50,000 IU, once a week for two to three months or three times a week for one month to restore the nutrient in the body to above 30 ng/mL for those who are deficient. That would be followed by a specific maintenance dose or a variable dose based on a person’s weight.

Therefore, it may take up to 2 to 3 months to bring levels of vitamin D up, depending on how deficient you are.

Yet, the recommended daily allowance of vitamin D in the United States is 600 IUs for adults up to age 70 and 800 IUs after age 70. People at high risk of vitamin D deficiency may need more, but how much and for how long can be determined by your doctor.

The National Institutes of Health acknowledges that even with these guidelines, there is no international agreement on vitamin D intake, and some professional organizations also disagree. It notes for instance that the Endocrine Society recommends about 1,500 to 2,000 IU per day for the average adult. And the United Kingdom’s government suggests 400 IU per day for everyone ages four and up.

More certain is that vitamin D deficiency is common. It affects almost half of all people in the United States. People with darker skin are at higher risk of being deficient in the vitamin, as are those who live in higher latitudes in winter, nursing home residents and healthcare workers.

The nutrient is considered to be important for a variety of health reasons, including:

  • Maintaining strong bones
  • Helping the body absorb calcium
  • Helping nerves carry messages between the brain and body parts
  • Reducing inflammation
  • Helping the immune system fight bacteria and viruses

In addition to taking supplements of vitamin D2 (ergocalciferol) or D3 (cholecalciferol), you can increase your vitamin intake by eating a small number of foods that naturally contain it, eating fortified foods or through sunlight. Consuming vitamin D with food that contains fat aids in absorption of the nutrient.

Foods that naturally contain vitamin D are:

  • Fatty fish
  • Beef liver
  • Cheese
  • Mushrooms
  • Egg yolks

Foods commonly fortified with vitamin D include:

  • Milk and some other dairy products
  • Breakfast cereals
  • Orange juice
  • Soy drinks

Excess amounts of vitamin D can be toxic, resulting in renal failure, calcification of soft tissues, cardiac arrhythmias and death.

  1. Sadat-Ali, Mir, et al. Maintenance Dose of Vitamin D: How Much Is Enough? Journal of Bone Metabolism. 2018 Aug; 25(3): 161-164. doi: 10.11005/jbm.2018.25.3.161. Available at: [Accessed November 19, 2020].
  2. Endocrine Society. Evaluation, Treatment, and Prevention of Vitamin D Deficiency. July 19, 2011. Available at: [Accessed November 19, 2020].
  3. National Institutes of Health. Vitamin D Fact Sheet for Professionals. October 9, 2020. Available at: [Accessed November 19, 2020].
  4. U.S. National Library of Medicine MedlinePlus. Vitamin D Deficiency. June 12, 2020. Available at: [Accessed November 19, 2020].
  5. Meltzer, David O., et al. Association of Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results. JAMA Network Open. 2020; 3(9): e2019722. doi:10.1001/jamanetworkopen.2020.19722. Available at: [Accessed November 19, 2020].

  6. Office of Dietary Supplements. Vitamin D Fact Sheet for Consumers. March 24, 2020. Available at: [Accessed November 19, 2020].

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