IU/d = international units per day (a measure of vitamin D intake) nmol/L = nanomoles per litre (a measure of resultant blood concentration of vitamin D) The

IU/d = international units per day (a measure of vitamin D intake) nmol/L = nanomoles per litre (a measure of resultant blood concentration of vitamin D) The ELI5 is: 1. Trials indicate that vitamin D deficiency (possibly below a blood concentration of 75 nmol/L) is a bad thing and is associated with a higher risk of death (from any cause) and also other health problems (risk of development of type I diabetes is given as an example) 2. The current recommended daily allowance (RDA) of vitamin D (https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessiona...) is currently lower than the intakes that studies have found are needed for most people to provide the blood concentrations which may be needed for good health (possibly due to a previous calculation error in determining the RDA) 3. Therefore, the author recommends to increase the RDA for vitamin D