Science & Technology: Best Source Of Vitamin D (What Do You Do When The Sun Isn't Shining)

We find it fascinating and frustrating to watch both the scientific and mainstream media acknowledge that UVR is the primary source of our daily vitamin D requirement but then fail to mention that the best place to get a controlled dose of vitamin D-effective ultraviolet radiation is at your professional neighborhood indoor tanning salon—especially when the sun isn’t shining.

Consider the following facts:

1. There is no such thing as “artificial UVR” or “artificial vitamin D-effective UVR.” UVR is UVR. It is the amount of vitamin D-effective irradiance, i.e., the energy between 250 nm and 320 nm, that is important, not the source.

2. Diffey’s “Law of Reciprocity” clearly and unambiguously states that it is dose—not dose rate—that determines the biological activity of UVR. Thus, a 0.⁶ W/m^2 dose of UVR for 10 minutes is biologically the same as a 0.³ W/m^2 dose for 20 minutes.

3. Sunlight only can strike one side of the body at a time. This is a fact of photobiology and physics. The belief that 15 minutes of sunlight exposure to the face and hands is sufficient to produce an adequate amount of vitamin D is mistaken. In fact, it takes 30 minutes of whole body exposure per side—a total exposure time of 60 minutes—at noon on a typical Midwestern summer day to accomplish this goal.

4. Age and skin type/subtype must be taken into consideration when determining how long it takes to stimulate vitamin D. Older people and those with darker pigment require more frequent or longer exposure times to stimulate the same amount of vitamin D as younger or lighter-skinned individuals.

5. The use of a sunscreen containing UVB filters with an SPF of 8 or higher prevents the skin from producing vitamin D. In addition, the use of a sunscreen containing UVA filters prevents the development of facultative pigmentation (a.k.a., a tan). Thus, using a sunscreen containing both UVB and UVA filters prevents the production of vitamin D and the development of a photoprotective tan.

6. A recent study showed that eight weeks after vitamin D-deficient subjects were given a 60,000 IU vitamin D supplement, their vitamin D levels increased from 13.⁵ nmol/L to 82.⁴ nmol/L. However, after one year, that level had dropped back to 24.⁷ nmol/L. This shows that continued high-dosage supplementation—far higher than is being recommended in the United States because of concerns about toxicity—is necessary.

7. Another recent study showed that the average person must take a 2,600 IU supplement each day in order to maintain 75 nmol/L to 80 nmol/L or a 10,000 IU supplement daily in order to attain/maintain a blood level greater than 120 nmol/L. Unfortunately, 10,000 IUs is a level that most physicians are reluctant to prescribe because of the danger of vitamin D toxicity.