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Vitamin D supplements are available in both D2 and D3 form. Research has long supported that it's vitamin D3 that has health benefits, and that vitamin D2 doesn't do anything. Well... a recent study found that vitamin D2 actually has a negative effect - that it lowers how much vitamin D3 the body absorbs.

Ingesting vitamin D2 supplements results in lower levels of vitamin D3 in the blood - measured as  serum vitamin 25(OH)D3 concentrations.  Note that Vitamin D3 is the form of vitamin D synthesized in human and animals skin upon exposure to ultraviolet B (UVB) radiation from sunlight. Thus, vitamin D3 is the form of vitamin D that our body naturally produces from sunlight and then use.

All the more reason to avoid vitamin D2 (ergocalciferol), and instead only take vitamin D3 (cholecalciferol). Read the ingredients list on the bottle!

From Science Daily: Scientists warn popular vitamin D supplement may have a “previously unknown” downside

Taking vitamin D2 might lower the body's levels of the more efficient form of vitamin D, vitamin D3, according to new research from the University of Surrey, John Innes Centre and Quadram Institute Bioscience. Many people take vitamin D supplements to support their bone and immune health and meet the UK government recommendation of 10 micrograms (µg) each day, especially during the winter months. ...continue reading "Research Finds Vitamin D3 to Be Beneficial, But Not Vitamin D2"

For years the medical advice has been that when taking vitamin D supplements, make sure it is the vitamin D3 form and not vitamin D2. The reasons given are that vitamin D3 is absorbed better and has more health benefits. A recent study found that there is an even better reason for taking vitamin D3 and not vitamin D2. It's because vitamin D2 actually lowers vitamin D levels in the blood.

From Medical Xpress: Vitamin D3 concentrations are lowered by a common vitamin D supplement

Taking vitamin D2 might lower the body's levels of the more efficient form of vitamin D, vitamin D3, according to new research from the University of Surrey, John Innes Center and Quadram Institute Bioscience. Many people take vitamin D supplements to support their bone and immune health and meet the UK government recommendation of 10 micrograms (µg) each day, especially during the winter months.

There are two forms of vitamin D supplements available: vitamin D2 and vitamin D3. Researchers have found that taking vitamin D2 supplements can lead to a drop in the body's concentration of vitamin D3, which is the form our bodies naturally produce from sunlight and use most effectively to raise overall vitamin D levels. ...continue reading "Study Finds Reason To Take Vitamin D3 and Not Vitamin D2"

For years it has been generally accepted that vitamin D3 is superior to vitamin D2 when taken as a supplement. Another recent study confirms that they are not equivalent in their effects in the human body, and that vitamin D3 is far superior.

Vitamin D2 (ergocalciferol) is plant and fungus-derived, and vitamin D3 (cholecalciferol) is animal-derived. Vitamin D3 is also naturally produced in the skin when exposed to sunlight, which is why it is frequently called the "sunshine vitamin".

From Science Daily: Study questions the role of vitamin D2 in human health but its sibling, vitamin D3, could be important for fighting infections

New research has found significant differences between the two types of vitamin D, with vitamin D2 having a questionable impact on human health. However, the study found that vitamin D3 could balance people's immune systems and help strengthen defences against viral infections such as Covid-19.

In a collaborative study by the Universities of Surrey and Brighton, researchers investigated the impact of vitamin D supplements -- D2 and D3 -- taken daily over a 12-week period on the activity of genes in people's blood. ...continue reading "All Vitamin D Supplements Are Not The Same"

I've frequently mentioned that when taking vitamin D supplements, the one to take is vitamin D3, and not D2. Medscape (the medical site) has an article explaining that results of a recent study showed that vitamin D3 is twice as effective as D2 in raising blood levels of vitamin D. The vitamin D3 form is derived from animal products, while vitamin D2 is plant-based. So check any supplements you purchase because many contain the vitamin D2 form of vitamin D.

Of course, sunlight is the best because it has more benefits than vitamin D - such as also having low levels of "blue light" which energizes T cells (which are part of the immune system). From Medscape:

Vitamin D3, Not D2, Is Key to Tackling Vitamin D Deficiency

Vitamin D3 is significantly more effective at raising the serum biological marker of vitamin D status than vitamin D2 when given at standard doses in everyday food and drink, say UK researchers — findings that could have major implications for both current guidelines and the supplement industry.

In a randomized controlled trial of vitamin D supplements, vitamin D3, which is derived from animal products, was associated with significantly higher serum total 25-hydroxyvitamin D [25(OH)D] levels after 12 weeks than vitamin D2, which is plant-based and currently used in the vast majority of vitamin D supplements.

"The importance of vitamin D in our bodies is not to be underestimated, but living in the UK it is very difficult to get sufficient levels from its natural source, the sun, so we know it has to be supplemented through our diet," explained lead author Laura Tripkovic, PhD, department of nutritional sciences, University of Surrey, Guildford, United Kingdom, in a press release.

She added, "Our findings show that vitamin D3 is twice as effective as D2 in raising vitamin D levels in the body, which turns current thinking about the two types of vitamin D on its head." "Those who consume D3 through fish, eggs, or vitamin D3-containing supplements are twice as likely to raise their vitamin D status [compared with those] consuming vitamin Drich foods, such as mushrooms, vitamin Dfortified bread, or vitamin Dcontaining supplements, helping to improve their long-term health." [Original study.]