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How long does it take for vitamin D to work?

Medically reviewed by Carmen Pope, BPharm. Last updated on March 8, 2023.

Official answer


Generally, it takes a few weeks of taking daily vitamin D supplements for vitamin D levels in the body to rise. Each 1,000 IU of vitamin D3 taken daily is expected to raise blood levels of 25(OH)D by 10 ng/ml after a few weeks. But it may take months to resolve symptoms of severe vitamin D deficiency such as rickets in children. It depends on how low your vitamin D levels were in the first place and some individual factors. Obesity, polluted environments, and malabsorption syndromes (such as Crohn’s disease) are just some factors that can increase the time it takes for vitamin D supplements to increase vitamin D levels.

Research has found that vitamin D insufficiency resolved with 12 weeks of weekly high-dose vitamin D.

How much vitamin D should I take daily?

Guidelines in the United States and internationally vary as to how much vitamin D you should ingest daily to maintain good health or resolve a deficiency. The recommended dietary allowance for Vitamin D recommended by the Institute of Medicine, Food and Nutrition Board depends on age and is as follows:

  • 0-12 months: 400IU (10mcg)
  • 1 to 70 years: 600IU (15mcg)
  • Over 70 years: 800IU (20mcg).

People who are vitamin D deficient will need more than this. Dosages vary depending on the level of deficiency, but one source recommended 2000 IU daily for a person with vitamin D insufficiency with higher dosages recommended for those diagnosed vitamin D deficient. Talk to your doctor about this.

What does it mean to be vitamin D deficient?

The definition of vitamin D deficiency varies among professional bodies because levels of the main indicator of vitamin D status, serum concentration of 25(OH)D, have not been definitely correlated with deficiency (such as that causing rickets), adequacy for bone health, and overall health. In addition, there can be variation in the available assays used to conduct the analysis depending on laboratory. The Institute of Medicine, Food and Nutrition Board defines the following according to 25(OH)D levels:

  • More than 125 nmol/L (50 ng/mL): Considered potentially toxic, could lead to detrimental effects
  • At least 50 nmol/L (20 ng/mL): Considered adequate for bone and overall health in most people
  • 30 to <50 nmol/L (12-<20 ng/mL): Considered inadequate for bone and overall health (Vitamin D insufficiency)
  • Less than 30 nmol/L (12 ng/mL): Associated with vitamin D deficiency (symptoms may include rickets in children and osteomalacia in adults).

Who is at risk of vitamin D deficiency?

Vitamin D deficiency is estimated to affect approximately 25% of men and 35% of women in the United States. Risk factors for vitamin D deficiency include:

  • Dark (pigmented) skin
  • Fat malabsorption conditions such as Crohn’s disease
  • Highly polluted environments
  • Lack of sun exposure without sunscreen
  • Lack of vitamin D supplementation
  • Obesity
  • Older age
  • Osteopenia
  • Osteoporosis
  • Postmenopausal
  • Previous gastric bypass surgery
  • Wearing head coverings.

What are the symptoms of vitamin D deficiency?

Symptoms of vitamin D deficiency are generally nonspecific and may include:

  • Back or joint pain
  • Hair loss
  • Headache
  • Fatigue
  • Low mood and depression
  • Muscle weakness
  • Sleep disturbances

Symptoms are uncommon unless 25(OH)D levels fall below 50 nmol/mL (20 ng/mL).

Can vitamin D be toxic?

Excess amounts of vitamin D can be toxic and because vitamin D increases calcium absorption, vitamin D toxicity causes high blood calcium levels, which can lead to nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, polyuria, excessive thirst, and kidney stones. Rarely, renal failure, calcification of soft tissues, cardiac arrhythmias, and death may occur.

Why is vitamin D important?

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 infection.

What foods contain vitamin D?

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 high amounts of vitamin D are:

  • Cod liver oil
  • Fatty fish (eg, salmon, sardines, tuna, trout)
  • 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.
  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 August 19, 2022].
  2. Endocrine Society. Evaluation, Treatment, and Prevention of Vitamin D Deficiency. July 19, 2011. Available at: [Accessed August 19, 2022].
  3. U.S. National Library of Medicine MedlinePlus. Vitamin D Deficiency. August 19, 2022. Available at: [Accessed November 19, 2020].
  4. Khan QJ and Fabian CJ. How I Treat Vitamin D Deficiency
    Journal of Oncology Practice 2010 6:2, 97-101
  5. Vitamin D. National Institutes of Health. Office of Dietary Supplements. Updated Aug 12, 2022.
  6. Zeratsky K. Nutrition and Healthy Eating. Mayo Clinic. 2022,are%20rich%20in%20vitamin%20D.

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