The Who, Why, and When of Vitamin D Screening

Story at-a-glance -

  • I recommend getting your vitamin D level tested at least once per year, when your levels are likely to be at its lowest. For people in the northern hemisphere, this would be around January or February
  • Vitamin D has a number of potent anticancer effects, including the promotion of cancer cell death, known as apoptosis, and the inhibition of angiogenesis (the growth of blood vessels that feed a tumor)
  • A recent study links vitamin D optimization to improved cancer prognosis among those with a family history of cancer—regardless of the type of cancer involved—and a reduced risk of death from any cause
  • An Indian study found that vitamin D and calcium supplementation in combination with exercise can aid prediabetic individuals by preventing the progression into full blown diabetes
  • Other research has shown that vitamin D may be the single most important nutrient to address the complications of pregnancy such as preeclampsia and premature delivery

By Dr. Mercola

A robust and rapidly growing body of research clearly shows that vitamin D is absolutely essential for good health and disease prevention, in part due to the fact that it influences about 10 percent of all your genes.

The US Preventive Services Task Force recently proposed new guidelines for vitamin D screening,1 which can be crucial for a number of different health conditions.

Unfortunately, the task force claims there's "inadequate evidence" to make a determination about the value of routine vitamin D screening for people with asymptomatic vitamin D deficiency. As reported by CBS News:2

"Normally, our bodies make all of the vitamin D that we need by being out in the sun. However, the sunscreen that is used to protect us from skin cancer can also prevent us from getting enough vitamin D, especially during the winter.

...Vitamin D is a nutrient that helps your body absorb calcium for healthy bones. The greatest source is sun exposure... The panel agreed that vitamin D is important, but how much is needed remains unclear.

'What we don't know is exactly what levels really would classify someone as being deficient in vitamin D,' Dr. Bibbins-Domingo explained."

My Recommendation: Get Tested at Least Once a Year

In the end, the task force is leaving it up to individual doctors to make their own determinations as to whether a patient may benefit from vitamin D testing. My recommendation is to get your vitamin D level tested at least once per year, when your levels are likely to be at its lowest.

For people in the northern hemisphere, this would be around January or February. In the southern hemisphere, it would be around June or July. This is particularly important if you're pregnant or planning a pregnancy, or if you have cancer.

From my perspective, it is simply reprehensible malpractice for a health care professional to fail to address your vitamin D level if you're pregnant or undergoing cancer treatment—it's just that important. For pregnant women, optimizing your vitamin D is more important for your child's health and development than folate, which is routinely recommended for pregnant women.

Recent Studies Confirm Vitamin D's Importance for Cancer Prevention

As for cancer, there are well over 800 references in the medical literature showing vitamin D's effectiveness—both for the prevention and treatment of cancer.

Vitamin D has a number of potent anticancer effects, including the promotion of cancer cell death, known as apoptosis, and the inhibition of angiogenesis (the growth of blood vessels that feed a tumor).

Carole Baggerly, founder of the vitamin D research group GrassrootsHealth, believes that as much as 90 percent of ordinary breast cancer may in fact be related to vitamin D deficiency.

According to a meta-analysis published in the March 2014 issue of Anticancer Research,3 patients diagnosed with breast cancer who had high vitamin D levels were twice as likely to survive compared to women with low levels.4, 5, 6

The high serum group had an average vitamin D level of 30 nanograms per milliliter (ng/ml). Women in the low serum group averaged 17 ng/ml, which is in fact the average vitamin D level found in American breast cancer patients.7

These findings indicate you need at least 30 ng/ml of serum 25-hydroxyvitamin D (25(OH)D) to prevent cancer from spreading. Other research suggests you'd be better off with levels as high as 80 ng/ml.

An even more recent study,8, 9 published in the British Medical Journal on June 17, links vitamin D optimization to improved cancer prognosis among those with a family history of cancer—regardless of the type of cancer involved—and a reduced risk of death from any cause, courtesy of its multi-varied influence on your health.

Here, data from eight population-based studies were analyzed. All in all, the studies followed more than 26,000 Europeans and Americans, aged 50 to 79, over the course of a 16-year period.

The data showed a clear pattern: those with consistently lower vitamin D levels were more likely to die from various health problems, including cancer, compared to those with higher levels. According to the authors:

"Despite levels of 25(OH)D strongly varying with country, sex, and season, the association between 25(OH)D level and all-cause and cause-specific mortality was remarkably consistent."

Optimizing Your Vitamin D Also Reduces Your Risk of Diabetes, New Study Suggests

In related news, an Indian study found that vitamin D and calcium supplementation in combination with exercise can aid prediabetic individuals by preventing the progression into full blown diabetes. Since exercise is one of the most effective ways to improve your insulin and leptin sensitivity, this certainly makes sense. As noted by Nephrology News:10

"Vitamin D deficiency has been linked to prediabetes, which is a blood glucose, or sugar, level that is too high but not high enough to be considered diabetes. It is unclear, however, if bringing low vitamin D blood levels to normal through supplementation will affect progression to diabetes.

In the new study, every unit increase in vitamin D level after supplementation of the vitamin decreased the risk of progression to diabetes by eight percent...

'Without healthy lifestyle changes, nothing works to prevent diabetes in at-risk individuals,' said the lead author, Deep Dutta, MD, DM... 'However, our results are encouraging because the addition of vitamin D and calcium supplements is easy and low in cost.'"

Here, a vitamin D level below 30 ng/ml was considered insufficient. All participants in the study were prediabetic.

The treatment group received a once-weekly dose of 60,000 IUs of vitamin D3, along with 1,250 milligrams (mg) of calcium carbonate daily, for eight weeks. A second group received only the calcium supplement. Both groups were advised to get 30 minutes of daily exercise. More than two years' worth of follow-up revealed that:

  • Just under 11 percent of those receiving both vitamin D3 and calcium became diabetic, while 26.5 percent of the calcium-only group developed diabetes
  • Blood sugar levels normalized in over twice as many of those in the vitamin D/calcium group, compared to the calcium-only group (41.8 percent versus 20.4 percent respectively)

Calcium/Vitamin D Supplementation Also Helpful for Gestational Diabetes

Similar results11 were found in another recent randomized placebo-controlled trial12 investigating the effect of calcium and vitamin D supplementation on the metabolic status of pregnant women with gestational diabetes (GDM).  The test group received 1,000 mg calcium daily. They also received 50,000 IUs of vitamin D3 at the outset of the study, and another 50,000 IUs three weeks later. The control group received placebos. After six weeks, the treatment group had "significant reductions" in fasting plasma glucose, insulin, and LDL cholesterol compared to the placebo group. The treatment group also showed improved insulin sensitivity, and had higher HDL cholesterol. According to the authors:

"Calcium plus vitamin D supplementation in GDM women had beneficial effects on metabolic profile... This is important because elevated circulating levels of inflammatory markers and impaired insulin metabolism in GDM can predict the progression to type 2 diabetes later in life and neonatal complications... In addition, increased inflammatory markers in GDM might predict the future development of both metabolic and cardiovascular disease."

The Importance of Optimizing Your Vitamin D Level During Pregnancy Cannot Be Overstated

Optimizing your vitamin D levels prior to, or at the very least during, pregnancy is important for other reasons besides protecting against gestational diabetes. Previous research has shown that your levels need to be above 50 ng/ml to protect you and your baby from even more serious complications such as premature delivery and preeclampsia. So please, if you're pregnant, make sure to get your 25 hydroxy D levels checked.

Previous research by Drs. Hollis and Wagner reveals even more reasons for addressing any vitamin D insufficiency during pregnancy. Their preliminary findings were discussed at a 2009 international vitamin D research conference in Brugge, Belgium,13 and included the following (the study was eventually published in 201114):

Mothers who took 4,000 IUs (10 times the RDA of 400 IU) of vitamin D daily during pregnancy decreased their risk of premature birth by half Women taking high doses of vitamin D had a 25 percent reduction in infections, particularly respiratory infections such as colds and flu, as well as fewer infections of the vagina and the gums
Women taking high doses of vitamin D reduced their chances by half of delivering their babies prematurely at both 32 and 37 weeks The "core morbidities of pregnancy" were reduced by 30 percent in the women who took the high-dose vitamin D. (Including diabetes, high blood pressure, and preeclampsia -- a potentially deadly increase in blood pressure and fluid accompanied by low platelets)
Fewer babies were born "small for dates" Babies getting the highest amounts of vitamin D after birth had fewer colds and less eczema


According to Dr. Hollis: "I'm telling every pregnant mother I see to take 4,000 IUs and every nursing mother to take 6,400 IUs of vitamin D a day. I think it is medical malpractice for obstetricians not to know what the vitamin D level of their patients is. This study will put them on notice."

How to Optimize Your Vitamin D Level

When it comes to vitamin D, you don't want to be in the "average" or "normal" range, you want to be in the "optimal" range. Based on the evaluation of healthy populations that get plenty of natural sun exposure, the optimal range for general health appears to be somewhere between 50 and 70 ng/ml. 

vitamin d levels

As for HOW to optimize your vitamin D levels, I firmly believe that appropriate sun exposure is the best way. In fact, I personally have not taken a vitamin D supplement for over four years, yet my levels are in the 70 ng/ml range. There's a handy smartphone app called DMinder ( that will tell you how much UV radiation you're getting and how many IUs of vitamin D you're making based on your local weather conditions (reported from the weather service) and other individual parameters such as your skin tone and age. It will also tell you when to get out of the sun, to protect yourself from sunburn.

If you can't get enough sunshine, then a safe tanning bed would be your next best option. Most tanning equipment use magnetic ballasts to generate light. These magnetic ballasts are well known sources of EMF fields that can contribute to cancer. If you hear a loud buzzing noise while in a tanning bed, it has a magnetic ballast system. I strongly recommend you avoid these types of beds and restrict your use of tanning beds to those that use electronic ballasts.

If your circumstances don't allow you to access the sun or a safe tanning bed, then you really only have one option if you want to raise your vitamin D, and that is to take a vitamin D supplement. GrassrootsHealth has a helpful chart showing the average adult dose required to reach healthy vitamin D levels based upon your measured starting point. Many experts agree that 35 IUs of vitamin D per pound of body weight could be used as an estimate for your ideal dose.

If You Opt for Oral Vitamin D, Remember Vitamin K2

Keep in mind that if you opt for a vitamin D supplement, you also need to take vitamin K2. The biological role of vitamin K2 is to help move calcium into the proper areas in your body, such as your bones and teeth. It also helps remove calcium from areas where it shouldn't be, such as in your arteries and soft tissues.

Vitamin K2 deficiency is actually what produces the consequences similar to vitamin D toxicity, which includes inappropriate calcification that can lead to hardening of your arteries. The reason for this is because when you take vitamin D, your body creates more vitamin K2-dependent proteins that move calcium around in your body. Without vitamin K2, those proteins remain inactivated, so the benefits of those proteins remain unrealized. So remember, if you take supplemental vitamin D, you're creating an increased demand for K2. Together, these two nutrients help strengthen your bones and improve your heart health.

Test Your Levels at Least Once a Year—Even if You're Healthy

While the US Preventive Services Task Force may be unclear on whether otherwise healthy people need to test their vitamin D levels, I believe the evidence is overwhelmingly clear: if your levels are consistently low, you will eventually suffer some kind of consequence. And when you consider how inexpensive vitamin D testing is becoming, there's little financial disincentive to get tested at least once a year, in the middle of the winter when your level would be at its lowest.

This will at least give you an idea of the extent of your insufficiency. Ideally, I recommend getting your level tested several times a year, at regular intervals, to ensure you're continuously staying within the ideal range. Once you know your pattern and can comfortably predict that you will not fall below 60 ng/ml, then it would be fine to shift to annual testing.

A Wired15 article published earlier this year discusses the revolutionary work of Elizabeth Holmes, a woman who invented a way to run 30 different lab tests on a single drop of blood. The pricing of these tests are as groundbreaking as the technology itself. For example, a cholesterol test costs less than $3. Her company, Theranos, rolled out its blood testing service in a Walgreens pharmacy in Palo Alto, California in the fall of last year. As reported by Wired:

"Theranos requires only a pinprick and a drop of blood. With that they can perform hundreds of tests, from standard cholesterol checks to sophisticated genetic analyses. The results are faster, more accurate, and far cheaper than conventional methods. The implications are mind-blowing. With inexpensive and easy access to the infor­mation running through their veins, people will have an unprecedented window on their own health. And a new generation of diagnostic tests could allow them to head off serious afflictions..."

I believe vitamin D testing should be at the top of virtually everyone's list—but especially pregnant women and cancer patients. It's important to remember that optimal vitamin D levels appear to offer powerful PREVENTION of a whole host of chronic diseases, so please, do not wait for a problem to appear before addressing your vitamin D status.