TPN and Vitamin D

Thompson P, Duerksen DR. Vitamin D deficiency in patients receiving home parenteral nutrition. JPEN. 2011;35:499-504.

Vitamin D is obtained through oral ingestion and by conversion of vitamin D in the skin from exposure to sunlight. Recently, it has been demonstrated that the daily recommendation for vitamin D intake is low for the general population. Patients on home parenteral nutrition (HPN) have very limited oral vitamin D intake or absorption. These patients often do not get outside into the sun for the time period necessary for adequate ultraviolet light exposure. They obtain most of their vitamin D (200 IU) from the multivitamin supplementation they receive in their PN prescription. The accepted method for monitoring a patient’s vitamin D status is through serum 25(OH)D serum levels.

Twenty-two long-term HPN patients had their vitamin D levels checked by 25(OH)D status. Most of the patients had been on HPN for >1 year. Their most common diagnosis for receiving HPN was gastrointestinal dysmotility (45%), malabsorption (36%), and GI obstruction (18%).Vitamin D insufficiency was defined as a serum level of 25(OH)D between 50 and 75 nmol/L, and deficiency was defined as a serum level <50 nmol/L. The mean 25(OH)D level was 42+/-22 nmol/l. Sixty-eight percent of the patients in this study had vitamin D insufficiency, and 27% had vitamin D deficiency. There did not appear to be a seasonal variation in vitamin D status. There appeared to be no correlation of small intestinal length and vitamin D status in patients with a diagnosis of short bowel syndrome.

One complication of patients on long-term HPN is metabolic bone disease (MBD). The etiology of this complication is multifactorial, with vitamin D as only one component of this complex problem. Intake of calcium, magnesium, and phosphorous, in addition to fluoride exposure, aluminum exposure, metabolic acidosis, and other factors, plays a role in the development of MBD. More work needs to be done to understand the optimal IV dose of vitamin D that is required in patients on long-term HPN. In addition, consideration needs to be given to the other factors listed previously as to their role in causing or worsening MBD in long-term HPN patients.