Vitamin D3 is a key regulator of calcium and phosphorus in the body, and fulfills a key role in enabling the growth and strengthening of teeth and bones. The recommended daily intake of vitamin D3 rises from birth through infancy, and remains stable before rising again in old age. Certain medical conditions may justify temporarily increased doses of the vitamin.
Vitamin D Variants
Vitamin D exists in two forms. The most common, vitamin D3, is produced naturally by the human body, and some animals, in response to sunlight exposure.
The second variant, vitamin D2, is produced in plants. Both forms can be chemically synthesized in laboratories.
Formally known as cholecalciferol, D3 is generally considered a preferable form of the vitamin, with research in the "American Journal of Clinical Nutrition" concluding that it has greater biological efficacy than the D2 variant.
Vitamin D's Function in the Body
Vitamin D is the single most important chemical regulator of calcium and phosphorus in the bloodstream. Facilitating management of the blood levels of these minerals, vitamin D also enables their absorption and incorporation into bones and teeth.
While especially critical during childhood, the need for adequate vitamin D intake continues throughout life. Insufficient vitamin D at any stage in life can lead to osteopenia or osteoporosis, rickets and other serious disorders.
Common Vitamin D3 Sources
The simplest way to obtain vitamin D is to let the body produce it naturally. Exposing your skin to less than 30 minutes of sunlight, twice per week, activates the body's natural synthesis of vitamin D3.
Several foods are important sources of vitamin D as well. Pasteurized milk is the most common and important food source of vitamin D, with a single cup providing about 30 percent of the recommended daily intake. Sockeye salmon, tuna and mackerel also provide substantial levels of natural vitamin D3.
Many vitamin supplements also contain vitamin D, and can help people who don't receive sufficient vitamin D from sun exposure and food sources.
Vitamin D3 Recommended Intake
The Institute of Medicine recommends that newborn infants receive 400 international units, or IU, daily until 1 year old. From ages 1 to 70, the recommended daily intake increases to 600 IU, and increases again to 800 IU from age 70 onwards.
A study published in the "Journal of Steroid Biochemistry and Molecular Biology" suggests that a higher recommended daily intake of vitamin D may confer additional health benefits. Research into the vitamin's optimum daily dose remains ongoing.
Vitamin D3 Maximum Intake
The maximum tolerable daily intake of vitamin D starts at 1,000 IU from birth through 6 months. This level rises through early childhood until reaching 3,000 IU at 4 years. From age 9 onwards, the maximum daily intake remains at 4,000 IU.
Research cited by the National Institutes of Health has found that vitamin D toxicity is unlikely below 10,000 IU, though there may be a risk of long-term harmful effects.
Treatment of serious vitamin D deficiency may employ one or several "megadoses" that supply substantially more than the recommended daily intake, and may exceed the normal maximum tolerable dosage. Such treatment should only take place under medical supervision.
References
- Institute of Medicine: Dietary Reference Intakes for Calcium and Vitamin D
- "American Journal of Clinical Nutrition": The Case Against Ergocalciferol (Vitamin D2) as a Vitamin Supplement; Lisa Houghton, et al.; 2006
- "Journal of Steroid Biochemistry and Molecular Biology"; Why The Optimal Requirement For Vitamin D3 Is Probably Much Higher Than What Is Officially Recommended for Adults; Vieth R.; May 2004
- National Institutes of Health: Dietary Supplement Fact Sheet; Vitamin D
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