Consequently, much of the U.S population is considered vitamin D deficient. Knowing this, you may have looked into supplementing your own vitamin D needs, only to be stonewalled by which is best: vitamin D2 or vitamin D3.
But before discussing which form of vitamin D is best, it’s important to understand the role of vitamin D in the body.
What Does Vitamin D Do?
Despite its name, vitamin D is more of a hormone.
In the liver, vitamin D is converted to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol. This is the body’s storage form of the vitamin and the best indicator of vitamin D status.
It is then converted in the kidneys to its active, hormone form, 1,25-dihyroxyvitamin D [1,25(OH)2D], also known as calcitriol.
Calcitriol circulates around the body, entering the nuclei of cells. There it binds with vitamin D receptors (VDR), which are found in over 30 organs, including the bone, intestines, kidneys, lungs, muscle and skin.
As a hormone, vitamin D then acts as a messenger, signaling the body to carry out specific tasks. For example, vitamin D plays a role in bone health by signaling the intestines to absorb calcium.
Vitamin D also plays a role in neuromuscular and immune function, cell growth regulation, and inflammation reduction.
Vitamin D2 vs Vitamin D3
Vitamin D is unique because it can be made in the skin from exposure to sunlight.
The two main forms of the vitamin are D2 (ergocalciferol) and D3 (cholecalciferol).
Vitamin D2 is sourced from the ultraviolet (UV) irradiation of ergosterol, a steroid found in fungi, like mushrooms.
Vitamin D3 is naturally found in few foods. Fatty fish including herring, salmon, tuna, and sardines, and fish liver oils are the best sources. Liver, egg yolks, and cheese also contain vitamin D3 but in small amounts.
Because food sources of vitamin D are limited, selected foods, including milk, yogurt, orange juice, and breakfast cereals are fortified with the vitamin, usually as D3 but sometimes as D2.
The two forms are also available as a supplement. They differ in their chemical structure, but not in their general metabolism or functions in the body.
At nutritional doses vitamins D2 and D3 are equivalent. At high doses, however, vitamin D3 is more effective in increasing and maintaining concentrations of 25(OH)D — the body’s storage form of the vitamin.
Vitamin D3 is therefore the preferred choice.
How Much Vitamin D Do You Need?
A blood level of 25(OH)D less than 20 nanograms per milliliter (ng/mL) or 50 nanomoles per liter (nmol/L) is generally accepted as a vitamin D deficiency.
As with other vitamins and minerals, the National Academies of Sciences established recommendations for the dietary intake of vitamin D to prevent a deficiency.
The current Recommended Dietary Allowance (RDA) for vitamin D is 600 International Units (IU) for both children and adults up to age 70.
This amount is the estimated daily level of intake needed to meet the nutrient requirements of nearly all (97.5%) healthy people.
The current RDA for vitamin D, however, may be largely underestimated and greater intakes may be needed to maximize the effect of vitamin D on calcium, bone, and muscle metabolism.
Older adults in particular at an increased risk of vitamin D deficiency (Click here to learn more).
Still, the majority of people struggle to meet the current RDA for vitamin D intakes. Due to limited food sources of vitamin D and sunlight exposure, taking vitamin D supplements may be the most viable option for getting additional amounts.