The Pharmacokinetics of a Single Large Dose of Vitamin D3

The Pharmacokinetics of a Single Large Dose of Vitamin D3

When people eat a meal, some, but not all of the calcium in that meal is absorbed, that is, moved into the bloodstream. When the skin is exposed to sunlight during summer months, Vitamin D is made there and then modified into more active forms by the liver and kidneys. These more active forms of Vitamin D improve calcium absorption. Many adults living in the U.S. have little or no sun exposure and are low in Vitamin D. A single dose of 100,000 IU of Vitamin D3 has been used both as empiric treatment for Vitamin D deficiency as well as in controlled trials without risk of raising blood calcium to dangerous levels.This study is to determine the serum levels of Vitamin D and 25-hydroxyvitamin D (vitamin D after it has been modified by the liver) that can be expected when Vitamin D3 is given as a single oral dose of 100,000 IU.

The group receiving the supplement will be scheduled for short visits to our research center at baseline and days 1,3,5,7 and then weekly for 3 weeks and then every other week for 6 visits (total 14 visits in 4 months). The group not receiving supplement will be scheduled for short visits at baseline and in 4 months. At the beginning of the study we will measure your height, weight, skin color, and draw blood to measure your blood levels of Vitamin D, 25-hydroxyvitamin D, calcium and parathyroid hormone. At each visit we will draw blood to measure your blood levels of Vitamin D and 25-hydroxyvitamin D. There will be fourteen blood draws for a total of 280 cc of blood drawn (about 4 teaspoons drawn each time) in the supplemented group. There will be 2 blood draws in the group not receiving supplements for a total of 60 cc of blood drawn (about 4 teaspoons drawn each time).

Inclusion Criteria:

• healthy with limited sun exposure of less than 10 hours per week and daily milk consumption of less than 0.47 L (16 oz.).

Exclusion Criteria:

• those with granulomatous conditions, liver disease, kidney disease, or diabetes and those taking anticonvulsants, barbiturates, or steroids in any form.