Serum Vitamin D

There are many misconceptions about vitamin D. Although the nutrition board still considers it a vitamin, it is actually a steroid hormone like testosterone or estrogen. Vitamins are considered essential to the diet but we can convert cholesterol in the skin to vitamin D when activated by sunlight. However, we also obtain vitamin D in our diet from eggs, fish, cheese, okra and kale.

Whether from the diet or the sun, vitamin D2 or D3 is transported to the liver. There a hydroxyl group is added to the twenty-fifth carbon on the cholesterol ring making 25-hydroxy vitamin D. This compound is released into the blood stream where it circulates in this inactive form.

This is the chemical we measure most frequently on laboratory testing. The normal range is 30-100, but I like to see levels of a least 40 for optimal health. Some physicians promote pushing the serum levels to a minimum of 80 with high supplementation.

The nutrition board allows me to supplement up to 5,000 IU of vitamin D per day with no laboratory testing to verify the need. However, supplements above 5,000 IU daily must have lab tests to document the need.

Vitamin D supplementation became very popular about 10 years ago following a study that showed significant health benefits from supplementation. Unfortunately, they used 50,000 IU, given once a week in that study and that has become the gold standard for prescribing vitamin D. The study used that format to verify compliance, having test subjects come to the facility once a week and watch them swallow the supplement. They also discarded data showing liver toxicity from the published report.



The inactive form of vitamin D (25 hydroxy vitamin D) is measured because it is stable. The kidneys convert it to the active form, 1,25-hydroxy vitamin D) by adding another hydroxyl group to the first carbon on the cholesterol ring. However, the active form is used immediately by the body so laboratory testing of the active form gives variable results by the minute.

All cells in the body can also take the inactive form of vitamin D and covert it to the active form for use within each cell. Scientists believe that measuring the active form of vitamin D within the cell reflects the best assessment of vitamin D status. However, that is not currently economically feasible. There is some correlation between the levels of inactive vitamin D in the blood stream and active vitamin D within the cell. For now, we use the serum test and extrapolate. Hopefully, someday soon, we will be able to measure the amount of active vitamin D in red blood cells at a reasonable cost.

Most of us know about vitamin D’s role in bone and calcium metabolism. However, its benefit goes way beyond building strong bones. Research indicates vitamin D may regulate DNA transcription at the cellular level. We think it acts much like a librarian, pulling the correct DNA like a book, to make it available for replication. This has far reaching applications for all chronic diseases, especially a large variety of cancers. Vitamin D may be an important factor in gene expression and balance of the immune system.

The Bottom Line:
I recommend a baseline test of vitamin D. If you’re levels are low (and often they will be) then supplement for three months and retest. Practicing in S. Florida, the sunshine state, I was amazed at how common vitamin D deficiency shows on laboratory testing. Even though we have plenty of sun, we hide indoors or lather on the sunscreen and are as deficient as the rest of the nation.