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Dear Dr. Cannell: Vitamin D and fatigue

Posted on: November 5, 2015   by  John Cannell, MD


Dear Dr. Cannell:

My name is Diane, and for years I’ve struggled with fatigue. I could never explain why I always needed to take a nap on my lunch hour and after work. It was depressing, and it affected my quality of life. Despite the fact that I ate well, worked out and was in good shape, I still needed to take naps.

Finally, a few years ago, my doctor did a full panel blood test. He discovered that my Vitamin D level was 19 ng/ml, which is extremely low! He put me on 5,000 IU per day of vitamin D for a year. Now, I take 2,000 IU per day as maintenance. If I run out of my vitamins and miss a few days, I feel the effects on my energy immediately! For me, Vitamin D is the #1 vitamin to take.

Up here in Ohio, most people have vitamin D deficiencies and don’t even know it.

Thank you and have a great day!


Dear Diane:

In my experience, fatigue is a common symptom of vitamin D deficiency. Also, an open label trial consisting of 116 patients with fatigue who supplemented with 50,000 IU vitamin D 3 times per week for five weeks showed that ergocalciferol (D2) helped reduce fatigue (refer to the table) in medical outpatients (P<.001 on all fatigue subscales). In this study, mean 25(OH)D of the 116 subjects with vitamin D deficiency (< 30 ng/ml) went from 20 ng/ml to 52 ng/ml in five weeks.


We are still waiting for a randomized controlled trial of vitamin D deficient subjects with fatigue who are treated with therapeutic doses of vitamin D (10,000 IU/day). In the above open label trial, the authors believed it was unethical to identify, but not treat, anyone with vitamin D deficiency. This is the main reason why adequate randomized controlled trials can no longer be done with vitamin D.

Diane, I hope you get your vitamin D level checked to make sure 2,000 IU/day is adequate. In most adults, it is not. You want your 25(OH)D blood level to be in at least the “natural” range. “Natural” means the blood levels outdoor workers have, which are about 40 – 60 ng/ml. This usually takes at least 5,000 IU/day.


John Cannell, MD

1 Response to Dear Dr. Cannell: Vitamin D and fatigue

  1. [email protected]

    There have been many RCT with Fibro and pain and vitamin D – examples include:

    Fibromyalgia pain reduced with vitamin D intervention that achieved 30-48 ng – RCT Feb 2014

    7 improvements in lives of veterans with chronic pain with 50,000 IU vitamin D weekly – June 2012

    Musculoskeletal pain reduced with 4,000 IU of vitamin D – RCT April 2015

    High dose vitamin reduced pain of fibromyalgia, osteoarthritis, and rheumatoid arthritis – July 2015

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