During my routine physical, my doctor ordered the usual blood tests, including vitamin D levels.  When the results came back, I was told to reduce my intake because my blood levels of 70 ng/ml were too high…..really? Is there such a thing as too much vitamin D?

            During the past two years, we were told to increase vitamin D intake to improve immune function and avoid COVID infection and/or reduce its symptoms.  Supplement companies and health care practitioners suggested daily doses of 5000 and even 10000 IUs. Now the word is to back off and reduce the daily intake due to possible adverse effects. What is truth – and who to believe? I immediately took a deep dive into the research wanting to shed some light into the Vitamin D controversy.

            Lets’s start by clarifying that “ Vitamin D” is not really a vitamin but a pre-hormone. Unlike with other vitamins, there are few foods that offer only negligible amounts of “D” such as mushrooms, eggs and fish. “D” is produced in the skin under the influence of ultraviolet light and a steroid-like molecule in the skin. The activation of “D” is a complex biochemical process in which liver and kidneys play an important role.  This explains, why people with liver or kidney disease have difficulty absorbing it and can develop complications in the presence of too much vitamin D.

           However, vitamin D (let’s just stick with the term “vitamin”) does play an important role in keeping the body healthy and has many different functions:

  • Vitamin D is needed for proper cell function
  • It aids in the absorption of calcium and phosphorus, thereby
  • Keeping your bones and teeth strong and healthy
  • It supports muscles and nerve function
  • It supports the immune system

            While Deficiency of vitamin D can have serious consequences, too much of a good thing can also be detrimental to your health. During the COVID pandemic, we have been relying on the advice of medical practitioners (mainstream and alternative) to increase the intake of Vitamin D to protect ourselves from viral infection, to reduce the length and severity of the infection once contracted. I, too, have taken doses of 5000-10000 IUs for a long time and was surprised to learn, after much digging in to research studies, that high doses over a long time can lead to a serious complication called “hypercalcemia” .

            Hypercalcemia refers to a condition where there is too much calcium absorbed and present in the blood. As I mentioned earlier, Vitamin D is instrumental in absorbing calcium, therefore the more “D” you take,  the better calcium is absorbed. However when there is more calcium then needed to keep bones and teeth healthy, the excess is deposited in soft tissue, such as joints, skin, organs and blood vessels, where it has no place and can have negative effects on your health.

            A recent research study (Schuster and Goldfarb, May 2020) also found a causal relationship between too much vitamin D and the formation of kidney stones, despite the myriad of older studies that demonstrated the opposite. Doses exceeding 5000 IU’s daily over extended periods of time increase the risk of kidney stones, but even in moderate doses this risk increases for some people.


How much is too much?


  In general, levels greater than 90ng/ml have shown to have adverse effects. The very rare condition of Vitamin D toxicity which poses serious health risks, is observed at levels of greater than 150ng/ml. Most of us never reach these levels with the doses we take. High, therapeutic, doses may be appropriate in certain cases, but should be determined by a clinician.

In addition, there are numerous studies demonstrating that high doses of vitamin D are no better, and sometimes produce worse outcomes than lower doses.

Most of those studies show that levels of 800-1200 IU’s/ day are sufficient.

Lastly, lets not forget that our ancestors did not “supplement”, but relied on natural sources. Sunlight is still the best source for the production of vitamin D in the body. In fact it takes only 10-15 minutes of sunlight 2-3 days per week (without sunscreen) to produce the necessary vitamin D we need to thrive. Here in Arizona, that is easy and cheap to come by – so why not take advantage of it! 

Science is always striving to give us the most accurate information at a given time – however, as we know – it is not perfect and ever evolving.

Bart L. Clarke, MD, a professor of medicine in the division of endocrinology, metabolism, diabetes and nutrition at the Mayo Clinic College of Medicine in Rochester, Minnesota, and president of the American Society for Bone and Mineral Research, said it poignantly:

“Like most things in medicine, the pendulum swings from cynicism to enthusiasm, and over

time, as more data become available, things settle back down to some middle level, where it probably should have been all along.

If you want to do more of a deep dive into this subject, I recommend Dr. Alan Gaby’s website and research on vitamin D.