Study Objectives. To determine whether orlistat causes fat-soluble vitamin deficiencies in African-American and Caucasian adolescents.

Design. Prospective, open-label pilot study.

Setting. Warren Grant Magnuson Clinical Center of the National Institutes of Health.

Patients. Seventeen adolescents with body mass indexes above the 95th percentile for age, race, and gender who also had at least one obesity-related comorbid condition.

Intervention. Subjects received orlistat 120 mg 3 times/day and a daily multivitamin supplement containing vitamin A 5000 IU, vitamin D 400 IU, vitamin E 300 IU, and vitamin K 25 μg.

Measurements and Main Results. During 3–6 months of orlistat treatment, acute absorption of retinol (vitamin A) was not significantly altered, but absorption of α-tocopherol (vitamin E) was significantly reduced compared with baseline levels (p<0.001). Serum levels of vitamins A and E did not change significantly; however, there was a nonsignificant decrease in vitamin K. Mean vitamin D levels were significantly reduced compared with baseline (p<0.02) after 1 month of orlistat, despite multivitamin supplementation.

Conclusion. It may be prudent to monitor vitamin D concentrations in adolescents who take orlistat, even when a multivitamin is prescribed.