Vitamin D is important for the maintenance of health because it plays many roles in the human body. But there is more than one form of vitamin D, and recent research suggests these forms may have different effects. So what are the different types of vitamin D, and is one really more beneficial than the other?
Although the medical conditions later associated with vitamin D deficiency, such as rickets, have been known since the 17th century, vitamin D itself was not identified until the early 20th century. This discovery led to Adolf Windaus won the Nobel Prize in Chemistry in 1928.
The vitamin D family actually includes five molecules, the two most important being vitamins D2 and D3. These molecules are also known as ergocalciferol and cholecalciferol, respectively. Although both of these types of vitamin D contribute to our health, they differ in how we get them.
Dietary vitamin D2 usually comes from plants, especially mushrooms and yeastwhile we get vitamin D3 from animal sources, like fatty fish, liver and eggs. Both forms of vitamin D are also available in dietary supplements.
What most people probably don’t know is that most of our vitamin D comes from expose our skin to the sun. When our skin is exposed to the sun, ultraviolet rays convert a precursor molecule called 7-dehydrocholesterol into vitamin D3. This strong effect of sun exposure explains why people living in more extreme latitudes, or people with darker skin, are more prone to vitamin D deficiency. Melanin, a skin pigment, prevents ultraviolet rays from activating 7-dehydrocholesterol, thus limiting the production of D3. Wearing clothing or sunscreen has a similar effect.
Vitamins D2 and D3 are essentially inactive until they go through two processes in the body. First the the liver changes its chemical structure to form a molecule known as calcidiol. This is the form in which vitamin D is stored in the body. Calcidiol is then further altered in the kidneys form calcitriol, the active form of the hormone. It is calcitriol that is responsible for the biological actions of vitamin D, including helping to build bone, metabolizing calcium, and supporting the way our the immune system works.
Technically, vitamin D is not a vitamin at all, but a pro-hormone. This means that the body converts it into an active hormone. All hormones have receptors (on bone cells, muscle cells, white blood cells) that they bind and activate, like a key unlocking a lock. Vitamin D2 has the same affinity for vitamin D receptor like vitamin D3meaning that neither form is better at binding to its receptor.
Different effects on the immune system
A recent study found that vitamin D2 and D3 supplementation had different effects on genes important for immune function. These results are significant because most previous research has failed to find a big difference in the effect of vitamin D2 or D3 supplementation.
Most research published to date suggests that the main difference between vitamin D2 and D3 supplementation is the effect on circulating vitamin D levels in the blood. Studies have repeatedly shown that vitamin D3 is superior increase vitamin D levels in the body. These results were supported by a recent review of the evidence which found that vitamin D3 supplementation increased vitamin D levels in the body. better than vitamin D2. But not all studies I agree.
Very few studies support that vitamin D2 supplementation is superior to vitamin D3. A trial showed that vitamin D2 was more effective in treating immune problems in patients on corticosteroid therapy. However, other than increasing vitamin D levels in the body, there is not much evidence that vitamin D3 supplements are better than vitamin D2 supplements. A study found that vitamin D3 improved calcium levels more than vitamin D2. But we need more research to provide definitive answers.
So which one should I take?
Vitamin D deficiency is now more present than everwith about a billion people in the world being deficient in vitamin D. It is important that people at risk of vitamin D deficiency – the elderly, people living in less sunny climates and people with darker skin – take vitamin D supplements .
Health professionals recommend that most people take 10 micrograms of vitamin D per dayabove all in winter. It would seem that vitamin D3 supplements are the best option for maintaining vitamin D levels, but short exposure of the skin to sunlight, even on cloudy days, will also help you maintain healthy vitamin D levels.