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Are Americans Taking Too Much Vitamin D?

Many people have become aware of the importance of vitamin D and are taking supplements; experts worried about overdose, but found that it is rare.

Many studies have revealed that a surprisingly high proportion of Americans have low levels of vitamin D circulating in their blood stream. (We have written about this observation previously.) Research repeatedly confirms that low levels of 25-hydroxyvitamin D are strongly associated with increased risks of cancer, diabetes, depression, high blood pressure and joint pain. Not only that, a recent publication warns that heavy individuals are often low in this vitamin. This may lead to inflammation and make the lungs more susceptible to damage from the SARS-CoV-2 virus (Obesity, April 16, 2020). 

It’s not clear, however, that taking supplements will prevent such conditions. So many people have begun taking supplements that experts worry Americans may be overdosing on this fat soluble vitamin.

Few Are Overdosing:

A study published in the Mayo Clinic Proceedings concluded that very few people take enough vitamin D to reach toxic levels (Mayo Clinic Proceedings, May, 2015). Out of more than 20,000 blood tests, only 8 percent measured in the high range of 50 ng/mL. Fewer than 1 percent were in the dangerous range of over 100 ng/mL. The researchers found few or no symptoms of toxicity even among those with high blood levels.

Symptoms of vitamin D toxicity include constipation, digestive distress and muscle weakness. Elevated calcium levels usually accompany vitamin D toxicity and can lead to kidney stones. In the Mayo Clinic study, one person had a 25-hydroxyvitamin D level over 300 and severe toxicity. That individual had taken 50,000 IU daily for three months. This is a blatant overdose.

Consequences of 50,000 IU Daily:

We heard recently from another person taking 50,000 IU of vitamin D daily.

Q. My doctor prescribed 50,000 units of vitamin D daily because my lab work showed low vitamin D levels. I have developed pain in my right arm and shoulder so severe that I can’t put on a long-sleeved top without help. Also, I have severe restless legs every night, plus terrible insomnia. I am going to stop the vitamin D to see if that is causing all my problems.

A. The dose of vitamin D you are taking is very high. You should definitely check back with your doctor and schedule another blood test as soon as that is feasible.

In addition, it would make sense to request a lower dose. Vitamin D is fat-soluble, which means that it is stored in the body. As a result, such a high dose over time could lead to an excessive level. Symptoms could include muscle pain and weakness. Loss of appetite, digestive upset and fatigue have also been reported.

You can learn more about interpreting lab results, the pros and cons of various vitamin D formulations and the hazards of too much of this supplement in our eGuide to Vitamin D for Optimal Health

A more recent review concluded that taking high doses of the vitamin can result in toxicity (Nutrients, July 24, 2018). They note that such cases are rare but may result from manufacturing errors, prescribing too high a dose or patients independently taking an overdose. A different review identified inappropriate prescribing or overuse of high-potency OTC preparations as a potentially serious problem (British Journal of Clinical Pharmacology, June 2019). Occasionally, a person may get far too much of the vitamin inadvertently and doesn’t develop symptoms (Proceedings [Baylor University Medical Center], Oct. 8, 2019). 

Stories from Other Readers:

Pro Vitamin D:

Noel says:

“For over five years, I’ve been taking 4,000 IU of vitamin D3 per day in the form of supplements. I rarely get sick except for a cold or bout of flu about once per year. I also get more vitamin D from food sources. While this is just one of many supplements I take, it is probably of greater importance to overall health than many of the others.”

Susan offers:

“I  have been on a prescription for 50,000 units of vitamin D every other week for several years. I stay out of the sun due to rosacea. I was getting sick all the time, but since going on the supplement my blood level has gone from 18 to 50. That seems to be the magic number to keep me free of illness. My doctor tests my blood every three months to track things.”

Missy shares:

“I take 400 units of vitamin D daily. My physicians say I shouldn’t exceed that. In the past, I took 1000 units of D, and it solved all my skin problems. Now they are back!”


Con Vitamin D:

Sandy says:

“I have been low in vitamin D at every yearly physical for several years. However, when I begin taking the D3/Calcium supplements my doctor recommends, my chronic reflux flairs up quite badly and my usual medication doesn’t seem to help. Consequently, I take the supplement for a few days until I can’t stand the reflux any more and then I quit.

“Of course, my levels are still low. My doctor doesn’t seem to believe that the supplement is causing the reflux, but the reaction has been pretty consistent for at least 3 years.”

Penny offers this caution:

“Before taking massive doses of any supplement you should check out possible side effects. I’ve been taking a 5,000 IU Vitamin D-3 supplement and having severe dizzy spells for several months. Yesterday I decided to look up the side effects and, you guessed it, dizziness is a side effect. Not good for a senior who also has back problems from falling too many times.”

Jen relates:

“I was prescribed 10,000 IU of vitamin D for six weeks after I had a stress fracture and my blood work showed a low level (21) of vitamin D.

“I have had severe reflux since I started taking it. The reflux is causing a nagging cough. I have not had a problem with my reflux in over three years. The doctor said she doesn’t think it’s the vitamin D but nothing else has changed in my diet except that.”

Share your own vitamin D story below in the comment section. You will find more information about the pros and cons of vitamin D in our Guide.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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  • Carter SJ et al, "Considerations for obesity, vitamin D, and physical activity amidst the COVID-19 pandemic." Obesity, April 16, 2020. DOI: 10.1002/oby.22838
  • Dudenkov DV et al, "Changing incidence of serum 25-Hydroxyvitamin D values above 50 ng/mL: A 10-year population-based study." Mayo Clinic Proceedings, May, 2015. DOI: https://doi.org/10.1016/j.mayocp.2015.02.012
  • Galior K et al, "Development of vitamin D toxicity from overcorrection of vitamin D deficiency: A review of case reports." Nutrients, July 24, 2018. DOI: 10.3390/nu10080953
  • Taylor PN & Davies JS, "A review of the growing risk of vitamin D toxicity from inappropriate practice." British Journal of Clinical Pharmacology, June 2018. DOI: 10.1111/bcp.13573
  • Rahesh J et al, "Hypervitaminosis D without toxicity." Proceedings [Baylor University Medical Center], Oct. 8, 2019. DOI: 10.1080/08998280.2019.1674052
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