Perhaps the most common question asked by people who supplement with vitamin D is “How much should I take?” Unfortunately, there is no single answer that applies to everyone. Vitamin D dose should be individualized, and the only way to do so is by measuring a blood level. Ideally, you should have your blood level of 25-hydroxy-vitamin D [25(OH)D] tested regularly. This level should then be used to determine the amount of supplementation needed to maintain optimal vitamin D status.

What is an optimal blood level?

To begin receiving the multitude of health benefits offered by vitamin D, a minimum level of 30 ng/mL is necessary. Yet, even higher levels are likely required in order to take full advantage of vitamin D. The most recent numbers indicate that 50-65 ng/ml is the optimal value to aim for.

Without regular testing to measure 25(OH)D, you should choose a dose great enough to provide some benefit, while also being safe for virtually all adults. Keep in mind that there is considerable benefit to be gained, and no established risk of adverse effects for an intake less than 10,000 IU daily. Also, be sure that you are taking vitamin D3, or cholecalciferol, as studies show it to be much more effective and safer compared to vitamin D2.

Below you will find recommendations on vitamin D dosing from multiple sources to help you make an informed decision:

Vitamin D Monograph. Alternative Medicine Review Volume 13, Number 2 2008

According to data examined from a large number of studies, supplementation with 2,000 IU daily, for three months, increased blood levels to an average of 35ng/mL. However, only 60 percent of individuals achieved a level greater than 30 ng/mL.

Cannell JJ, Hollis BW. Use of vitamin D in clinical practice. Altern Med Rev 2008;13:6-20

Treatment of vitamin D deficiency in otherwise healthy patients with 2,000-7,000 IU vitamin D3 per day should be sufficient to maintain year round 25(OH)D levels between 40-70 ng/mL.

Linus Pauling Institute

The Linus Pauling Institute recommends that generally healthy adults take 2,000 IU of supplemental vitamin D daily. Most multivitamins contain 400 IU of vitamin D, and single ingredient vitamin D supplements are available for additional supplementation. Sun exposure, diet, skin color, and obesity have variable, substantial impact on body vitamin D levels. To adjust for individual differences and ensure adequate body vitamin D status, the Linus Pauling Institute recommends aiming for a serum 25-hydroxyvitamin D level of at least 32 ng/mL. Numerous observational studies have found that serum 25-hydroxyvitamin D levels of 32 ng/mL and above are associated with reduced risk of bone fractures, several cancers, multiple sclerosis, and type 1 (insulin-dependent) diabetes. Infants, children, and adolescents should have a minimum daily intake of 400 IU of vitamin D, a recommendation set by the American Academy of Pediatrics in 2008.

Older adults (> 50 years)

Daily supplementation with 2,000 IU of vitamin D is especially important for older adults because aging is associated with a reduced capacity to synthesize vitamin D in the skin upon sun exposure.

Scientists’ Call to Action Statement, GrassrootsHealth

Intake of 2000 IU/day is the current upper limit of the National Academy of Sciences, Institute of Medicine, Food and Nutrition Board. New evidence indicates that the upper limit should be raised substantially. The levels that are needed to prevent a substantial proportion of cancer would also be effective in substantially reducing risk of fractures, Type I childhood diabetes and multiple sclerosis. Greater oral intakes of vitamin D3 may be needed in the aged and in individuals who spend little time outdoors, because of reduced cutaneous synthesis. Choice of a larger dose may be based on the individual’s wintertime serum 25(OH)D level. Any risks of vitamin D inadequacy considerably exceed any risks of taking 2000 IU/day of vitamin D3, which the NAS-IOM regards as having no adverse health effect.

Creighton University Osteoporosis Research Center

The body needs about 4000 IU per day in order to maintain a healthy concentration of 25(OH)D in the blood. Most of us don’t get that much; even so, most of what we do get seems to come from casual exposure of the skin to sunlight. The foods, fortified foods, and supplements we typically consume generally provide no more than 150–250 IU each day, on average. Because most of us don’t get enough sun exposure, the combination of what sun we do get, plus the vitamin D that we take by mouth, generally totals no more than 2000–3000 IU/day. Thus, in order to meet the body’s need for about 4000 IU/day, most adults in North America need to take a supplement providing somewhere in the range of 800–2000 IU/day. Current best estimates indicate that doses of up to 10,000 IU/day are safe for virtually all adults. Very few individuals need anything remotely close to that dose, so it is comforting to know that there is a margin of safety between what we ought to be taking by mouth, and the level that might produce harmful effects.