In premature infants with low vitamin D, taking 1,000 IU of vitamin D3 by mouth every day for 15 days leads to higher blood levels of vitamin D than receiving one 15,000 IU injection, even when...
Mechanism
Synthesis from 1 study
Giving vitamin D3 every day by mouth keeps the liver supplied with material to make the active form, so blood levels keep rising. A single big shot gives all the material at once, but the liver runs out after converting it once, so blood levels don't go as high.
Most probable mechanism
When vitamin D3 is given daily by mouth, the body slowly absorbs it and turns it into its active form in the liver over time, leading to higher levels in the blood. When it is given as one big shot into the muscle, the body absorbs it quickly but then runs out of material to keep making the active form, so blood levels don't rise as high.
Vitamin D3 is absorbed from the gastrointestinal tract after oral administration or from muscle tissue after intramuscular injection
Absorbed vitamin D3 enters the bloodstream and is transported to the liver
In the liver, vitamin D3 is converted to 25-hydroxyvitamin D3 by the enzyme 25-hydroxylase
Oral administration provides repeated daily doses of vitamin D3, sustaining substrate availability for continuous hepatic conversion over 15 days
A single intramuscular dose delivers a large bolus that is rapidly absorbed and converted, but substrate depletion occurs after initial conversion, limiting sustained production of 25-hydroxyvitamin D3
Continuous hepatic conversion from daily oral dosing results in higher cumulative serum concentrations of 25-hydroxyvitamin D3 compared to a single intramuscular dose
Evidence from Studies
Supporting (1)
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Contradicting (0)
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