More proof that there is no “one size fits all” dose of vitamin D that will work for everyone, and that different individuals achieve different blood levels of 25-hydroxy D on similar doses of supplements. 25-hydroxy D is a reliable marker of vitamin D status and higher blood levels help protect against numerous serious diseases, including many types of cancer, autoimmune diseases like multiple sclerosis, rheumatoid arthritis and Crohn’s disease, heart disease and stroke. Researchers at the University of Toronto gave 98 adults 600 or 4000 IU of vitamin D(3) per day and checked their 25-hydroxy D serum levels after one year.

Before any supplementation, genetic variations (polymorphisms) in the vitamin D binding protein (DBP), the main carrier protein for vitamin D in serum, predicted 25-hydroxy D serum levels. After 1 year’s supplementation with vitamin D, those with variations in DBP associated with lower starting blood levels of 25-hydroxy D had the poorest response to supplementation.

This paper underscores the importance of the 25-hydroxy D blood test in establishing individual requirement for vitamin D supplements.

Reference Common genetic variants of the vitamin D binding protein (DBP) predict differences in response of serum 25-hydroxyvitamin D [25(OH)D] to vitamin D supplementation. Fu LYun FOczak MWong BYVieth RCole DEFu L, Oczak M, Wong BY, Veith R, Cole DE. Clin Biochem. 2009 Jul;42(10-11):1174-7