There are decreases in bone mineral density in drug naive individuals with bipolar disorder compared to age- and gender-matched healthy controls. Individuals with bipolar I disorder have have high homocysteine levels. High homocysteine levels in individuals with bipolar disorder point to the transsulfuration pathway being dysregulated. Via the transsulfuration pathway L-cysteine is synthesized from homocysteine. L-taurine is synthesized from L-cysteine.
Taurine is required for calcium homeostasis. Taurine, also, is conjugated to various bile acids. Bile acids are are required for absorption of fat-soluble vitamins. Vitamin D and vitamin K are fat-soluble vitamins. Individuals with bipolar disorder are 4.7 times more likely to be vitamin D deficient than individuals amongst the general population of the Netherlands, however, deficient levels of vitamin D are not specific to bipolar disorder but are also present in individuals with schizophrenia. The taurine transporter is present in osteoblasts. Osteoblasts synthesize bone.
With taurine metabolism dysregulated calcium homeostasis is dysregulated and absorption of vitamin D and vitamin K is decreased. Decreases in bone mineral density in bipolar disorder could be due to dysregulation of the transsulfuration pathway which dysregulates calcium homeostasis and vitamin D and vitamin K absorption resulting in low bone mineral density.