The excitement over the health benefits of vitamin D have, not unexpectedly, generated lots and lots of questions about how, why, and when to best use it.

Let's review some of the most frequent questions and answers about vitamin D.

Now, please keep in mind that much of this is my opinion, based on clinical experience replacing vitamin D in over 1000 patients. I've learned a lot of lessons along the way, and I'm still learning new lessons and making new observations. But this is the approach I have applied successfully and safely. (Please, always consult your doctor to discuss your unique health situation.)

My starting level of vitamin D was 19.4 ng/ml. I took 6000 units of vitamin D (yes, a gelcap!) and my level increased to 59.8 ng/ml. My doctor then said it was okay to stop it.

Do you agree with stopping vitamin D?

No. I absolutely do not agree with stopping your vitamin D, unless of course you have reason to believe you will be obtaining vitamin D from substantial sun exposure. But, if not, it is clear that once you stop supplementing vitamin D, your blood level will drift right back down to the prior level, since your body is not making it.

How often should vitamin D blood levels be checked?

There are no hard and fast rules to go by, but I have found every 6 months to work well. Ideally, the two blood levels are in mid-summer and mid-winter, giving you and your doctor an idea of the fluctuations of your vitamin D level. Contrary to what you hear in the media, I find that the majority of adults, particularly those over 40 years old, fail to activate much vitamin D on sun exposure. Most adults do not raise their blood level much more than 10-15 ng/ml even with summer sun exposure. However, there are occasional exceptions. That's why it's important to know your individual level of fluctuation.

I'm 56 years old and I like to get a tan in summer and occasionally use a tanning parlor in the winter months. Though my doctor is not wild about the tanning, he said that it was not necessary to check my blood level of vitamin D and I shouldn't add any additional vitamin D. Does that sound correct?

I disagree with this advice. A tan does not equal vitamin D activation, particularly as we age. I have had many patients with dark Caribbean tans from extended vacations have blood levels of vitamin D clearly in the deficient range, occasionally <20 ng/ml.
The only confident way to know your vitamin D level, tan or no, is to check a blood level.

My doctor said that vitamin D might interfere with my cholesterol drug and other medications. Why is that?

Well, for the vast majority, it's not true.

With rare exceptions, taking vitamin D is no more likely to interfere with medications than getting a tan (should you retain the ability to activate vitamin D). The only exceptions that I am aware of would be thyroid medication, which shouldn't be taken at the very same time as vitamin D; the old-fashioned cholesterol drug, cholestyramine, can prevent vitamin D from being absorbed, as can weight-loss fat-blocker, Xenical®, or its over-the-counter equivalent, Alli®. Rarely, thiazide diuretics can raise blood calcium and vitamin D can exaggerate this effect. (This may be a reason to have an occasional calcium level checked by your doctor.) There are also special issues if you are receiving treatment for cancer or have cancer; however, since some of the most exciting new developments for vitamin D have been in the world of cancer prevention and treatment, this is worth a serious conversation with your doctor or oncologist.