Does my skin make enough Vitamin D?

Q: I have been following your advice on vitamin D, and as a result I took a vitamin D supplement during the winter months. When the summer came I stopped because I’m out in the sun a lot. Then, during my annual physical, I had them do a vitamin D level test. When I got the results back, my D level was 24 ng/ml. Is there something wrong with my skin that I don’t make enough vitamin D? I am going to start back on a supplement, but I thought that being out in the sun would give me enough D.

Thank you, Bob

Dr. Micozzi: First of all, congratulations, Bob, for keeping track of your vitamin D levels and for having your doctor perform a blood measurement of vitamin D during your annual physical exam. All doctors should perform this test, and all patients should request it.

But unfortunately, many mainstream doctors don’t believe this basic, simple test is necessary. During the depths of last winter, the British Medical Journal even told doctors “not to bother” measuring vitamin D levels, despite all of the growing evidence of its health benefits (some of which was published in the very same issue of that journal)!

Based on your test results, there is nothing wrong with your skin—or your vitamin D levels. Your level of 24 ng/ml is not at all bad, and certainly not deficient. In fact, a level of only 10 ng/ml is considered “low normal” (although the U.S. government’s dietary guidelines are not keeping up with the research about optimal levels).

Research consistently shows that people, like you, with levels in the 20s have much better health than those with levels in the teens. However, the ideal vitamin D level for optimal health is 30 ng/ml or more.  So your goal would be to achieve about 25 percent higher levels than you have now.

As you know, the sun helps your body create vitamin D, so spending 15 to 20 minutes a day in the sunshine without sunscreen during the summer months is a good first step to increase your vitamin D levels. But, as you’ve witnessed first-hand, most Americans can’t rely on summer sun alone to keep their D levels steady throughout the year.

If you live north of Atlanta, the sun does not get high enough in the sky from about November through March to activate the photosynthesis process that our skin uses to create vitamin D. Our bodies can store some leftover vitamin D from the summer, but only about a three-month supply.

Consequently, in order to maintain healthy vitamin D levels year-round, I recommend that no matter how much time you spend in the sun, you also take a vitamin D supplement every day. But keep in mind that not all dietary supplements are equal in terms of their quality, absorption, and bioavailability. Make sure you are using a high-quality supplement at all times.

Based on constantly increasing research about the benefits of vitamin D, and the growing worldwide epidemic of D deficiency, I recommend that everyone take 5,000 IU of vitamin D daily, year-round. You’ll find this amount in each dose of my Smart Science Core D Liquid Vitamin D3 (to learn more about Core D, visit my website  And I will keep you updated on all the exciting new research about the many health benefits of taking vitamin D.