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.
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.
The study, published in Nutrition Reviews, analyzed data from randomized controlled trials and found that vitamin D2 supplementation resulted in a reduction in vitamin D3 levels compared to those not taking a vitamin D2 supplement. In many of the studies, the vitamin D3 levels went lower than in the control group.
Emily Brown, PhD Research Fellow and Lead Researcher of the study from the University of Surrey's Nutrition, Exercise, Chronobiology & Sleep Discipline, said:
"Vitamin D supplements are important, especially between October and March, when our bodies cannot make vitamin D from sunlight in the UK. However, we discovered that vitamin D2 supplements can actually decrease levels of vitamin D3 in the body, which is a previously unknown effect of taking these supplements. This study suggests that subject to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2."
This research supports a previous study published in Frontiers in Immunology, led by Professor Colin Smith from the University of Surrey, which suggests that vitamin D2 and D3 do not have identical roles in supporting immune function. Vitamin D3 has a modifying effect on the immune system that could fortify the body against viral and bacterial diseases.
Professor Colin Smith said: “We have shown that vitamin D3, but not vitamin D2, appears to stimulate the type I interferon signalling system in the body - a key part of the immune system that provides a first line of defence against bacteria and viruses. Thus, a healthy vitamin D3 status may help prevent viruses and bacteria from gaining a foothold in the body.”