Vitamin D-2 vs. vitamin D-3: Are they one and the same?

It is firmly established that humans need to obtain sufficient vitamin D in order to optimise calcium absorption and thus ensure robust skeletal health throughout the life stages. Vitamin D research is rapidly expanding, with significant interest in the potential health benefits to conditions such as diabetes, multiple sclerosis, tuberculosis and dementia. Yet, as the field has expanded, gaps in knowledge have emerged. One of the most pertinent questions at present is whether the two forms of vitamin D (vitamin D-2 and D-3) are equal in their physiological effect. Emerging evidence challenges this long-held assumption and raises the possibility that there may in fact be a distinct and significant difference between the efficacy of vitamins D-2 and D-3 that could have substantial impact in terms of vitamin D status.