Why would I have a low vitamin D level despite taking 8000 IU daily?

Anthony L. Komaroff, MD
Internal Medicine
Not getting enough vitamin D can have a long-term effect on bone health and may be associated with other health problems.

Get a copy of the actual laboratory report. It will show what that lab considers as the normal vitamin D level. Your level may be adequate. The Institute of Medicine has defined new normal ranges for vitamin D. A level of 20 ng/mL or higher is considered adequate for bone and overall health. But some labs have not adjusted their normal ranges to reflect these new guidelines.

If your vitamin D level is below 20 ng/mL, there are a few reasons why you might be low in vitamin D -- even when taking 8000 IUs of vitamin D daily. You could be:
  • Unable to absorb vitamin D. This is often seen in patients who have had gastric bypass surgery. It's also common in patients with celiac disease. If you have any symptoms of celiac disease, it's a good idea to get tested.
  • Secreting too much vitamin D in your urine. People with nephrotic syndrome secrete large amounts of protein in their urine. Vitamin D binds to protein. So excess loss of protein in the urine lowers vitamin D levels.
  • Breaking down vitamin D quickly. Many medicines can cause this, including those for seizures and migraines. Even some antibiotics. So you should carefully review the medicines you take.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.