Vitamin D3 by the numbers

By Jim Catano

In the sun:

The best time of day to tan is 1 p.m., typically, at our edge of the Mountain Time Zone during Standard Time. Look for shadows pointing north to know when UVB is at its highest concentration.

To calculate how much sun exposure you need to generate enough D3 on any given day, check out: Salt Lake’s latitude is 40.78 and altitude, in kilometers, is about 1.4. (Don’t worry about longitude.) Estimate cloud thickness on the 1-20 scale. Set ozone thickness as medium.

What to ask a tanning salon:

“What kind of beds do you use?” You’ll want a standard type (not a pressure bed) that puts out at least 3% and ideally 5% UVB.

“How old are your bulbs?” Less than 3 years old is best.

Buying supplements:

For most people who get little sun, take daily 1,000 IU per 25 pounds of body weight. Most children are OK with 2,000 IU. D2 is in most prescription supplements and is the “vegan” variety derived from yeast. D3 comes from the lanolin in sheep’s wool and is more potent. If you take D2, multiply the amount above by 2.5.

Ideal D3 blood levels:

Bring your D3 blood level, if possible, to 50-60 ng/ml (nanograms per milliliter). To see the blood levels needed for maximum protections against several diseases see:

Getting tested:

A blood test is the only sure way to know if your D levels are where they should be. Make sure the test you’re getting is for 25-OHD, not for 1,25-OHD. That little “1” makes a big difference. Some results from Quest Labs have been misleadingly high; several lawsuits are pending.

Most clinics charge $100 or more for testing. A national study on Vitamin D is being conducted and offers testing for only $40 every six months. See:



This article was originally published on November 6, 2009.