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"