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The Journal of the American Medical Association, in early 2015, published an editorial recommending that physicians “avoid overscreening and overprescribing supplemental vitamin D.” The JAMA authors argued that, given the “lack of convincing evidence for non-bone benefits of vitamin D,” doctors shouldn’t screen for vitamin D deficiency or recommend their patients take more than the current dietary allowance (RDA) for vitamin D: 600 IU per day for persons aged 1 to 70 years and 800 IU per day for those 71 years and older.
Around the same time this article was published, I went in for a visit with my primary care physician, a naturopathic doctor, to go over the results of some recent labs, one of which was my vitamin D levels. It had been over a year since I’d last had my levels checked.
“Your vitamin D levels are in the toilet,” said my doctor, who’s not one to mince words, as he pointed to my lab results. Sure enough, my level of 25-hydroxyvitamin D (abbreviated 25[OH]D), which is the compound that’s measured in the blood to check vitamin D status, was “low,” according to the lab’s (LabCorp) reference ranges, which reflect the Endocrine Society’s definition of vitamin D insufficiency.2,3
“But I take 5,000 IUs a day,” I replied. Even though I’d seen low vitamin D levels in some my own patients despite regular supplementation with 5,000 IUs or more, I was surprised at how much my own body seemed to require to maintain sufficient levels, let alone optimal ones.
“Well, you need to start taking 10,000 IUs,” said my doctor. I probably won’t need to take this dose forever, just until my levels come back up into a more optimal range. Once there, I can drop my dose back down. My goal is to find the dose that will keep my levels optimal but not too high, which can be dangerous. As with some of my patients, it seems as though I may need more than 5,000 IUs per day, especially during the winter months.
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Why Test Vitamin D Levels?
You’re likely aware of the huge surge in research showing that vitamin D plays a crucial role in a plethora of physiological and preventive functions. Not only does it regulate calcium and phosphate levels, as we thought, but vitamin D also has numerous extra-skeletal effects. Acting as a hormone, vitamin D significantly impacts the cardiovascular system, central nervous system, endocrine system, and immune system.4 Vitamin D receptors have now been found in most body cells. It is believed that when vitamin D binds to these receptors, it regulates a very large number of genes in the human genome.5
The research associates vitamin D deficiency with many acute and chronic illnesses, including autoimmune diseases,6 cancer,7 type 2 diabetes and insulin resistance,8 infectious diseases (including the common cold),9 cardiovascular disease,10 cognitive decline,11 and more.
While more research is needed, many vitamin D researchers and physicians, including Boston University’s Dr. Michael Holick, PhD, MD, one of the one of the world’s most prominent vitamin D researchers, disagree with the JAMA author’s stance on staying with low-dose vitamin D. Instead, they support increasing people’s vitamin D levels through high-dose supplementation.12
How to Get Tested
If your goal is to prevent these common conditions, achieve optimum health, or age more gracefully, you’ll want to regularly test your vitamin D levels and adjust your dose accordingly. Blood testing for 25(OH)D is only way to know if you’re getting enough or too much vitamin D. March or April (the end of winter) is an excellent time of the year to test.
You have three options for how to get the test: ask your doctor to order it; order it yourself online from a “direct-to-consumer” business like Request A Test or DirectLabs® and go to a local laboratory draw site for the blood draw; or order an in-home finger prick test from a website like the Vitamin D Council or ZRT Labs. Options two and three are not permitted in all states. Make sure the test is the correct one: even some doctors mistakenly order a 1,25(OH)₂D test instead of the correct 25(OH)D test.
What To Do Next
The optimal level and best dose for you depends on many factors, including your current levels, dietary intake, sun exposure, and health status. There is no universal agreement on what constitutes an ideal level. Different organizations recommend different ideal vitamin D levels. While the US Food and Nutrition Board believes 20 ng/ml is sufficient, the US Endocrine Society recommends staying above a level of 30 ng/ml. Many naturopathic doctors and practitioners of integrative, functional, or similar kinds nutrition-focused medicine suggests that a level closer to 50 ng/ml is more ideal. Make sure your levels do not go above 100 ng/ml.
The dose of vitamin D you’ll need to reach and maintain a level of 30 to 50 ng/ml cannot be exactly determined, which is why testing is so important. Generally, a dose of 3,000 to 5,000 IUs a day is required to maintain these levels. It is not recommended that you take more than 5,000 IUs a day unless under the direct supervision of a doctor.
1. JAMA. Published online February 19, 2015.
2. LabCorp Test Menu. Vitamin D, 25-hydroxy.
3. J Clin Endocrinol Metab. 2011 Jul;96(7):1911-30.
4. Dermatoendocrinol. 2013 Jun 1; 5(3): 331–347.
5. Best Pract Res Clin Endocrinol Metab. 2011 Aug;25
6. Autoimmun Rev. 2012 Dec;12(2):127-36.
7. Oncologist. 2011;16(9):1215-27.
8. Diabetologia. 2012 Aug;55(8):2173-82.
9. Inflamm Allergy Drug Targets. 2013 Aug;12(4):239-45.
10. Clin Endocrinol (Oxf). 2011 Nov;75(5):575-84.
11. Neurology. 2014 Dec 9;83(24):2292-8.
Originally published in February in 2016 and updated.