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Vitamin D improves fatigue, according to new study

Posted on: January 6, 2017   by  Amber Tovey


A new randomized controlled trial published in the journal Medicine found that vitamin D supplementation significantly improved fatigue.

Fatigue characterizes unrelenting exhaustion that cannot be relieved by sleep. It reduces one’s motivation, concentration and energy, impacting both emotional and psychological health. It can lead to impaired quality of life and reduced productivity.

Most diagnoses of fatigue are idiopathic, meaning they have unknown causes. Researchers have suggested that vitamin D deficiency and fatigue are closely related. In fact, fatigue is considered a potential side effect of vitamin D deficiency.

A previous study found that vitamin D supplementation improved fatigue symptoms. However, the study lacked a control group, which greatly limited the strength of the results. Furthermore, the study used vitamin D2 opposed to D3, a less effective form of vitamin D.

Now, researchers have conducted a randomized controlled trial, a study that possesses both a control group and an experimental group, to determine the effects of vitamin D supplementation on fatigue.

The study included 120 adults with fatigue and vitamin D deficiency, 25(OH)D levels less than 20 ng/ml. Participants were randomized to receive a single oral dose of 100,000 IU vitamin D or placebo.

The researchers used the fatigue assessment scale (FAS) to evaluate the effects of vitamin D supplementation on fatigue symptoms. The FAS is a self-reported assessment with lower scores indicating less fatigue.

Average FAS decreased significantly more in the vitamin D group compared to the placebo (-3.3 vs -0.8, p = 0.01). Improvement of fatigue was reported more frequently in the vitamin D group than in the placebo group (72% vs. 50%, p = 0.01). The researchers also discovered that the improvement in fatigue scores was correlated with the rise in vitamin D level (p = 0.02).

The researchers concluded,

“Our study shows that a single dose of oral 100,000 IU vitamin D3 is an effective, well-tolerated, and economical treatment strategy for healthy adults who report fatigue.”

The study contained various strengths worth acknowledging. First, it followed the strongest study design, allowing it to prove causality. In addition, the sample size was adequate. The study enrolled participants with vitamin D deficiency and fatigue, which enabled the researchers to properly assess the effects of improving vitamin D status for the treatment of fatigue among vitamin D deficient subjects. Lastly, the participants were administered vitamin D3 rather than D2. The main limitation of the study was the use of bolus dosing opposed to daily dosing. (For information regarding the benefits of daily dosing, read this article.)


Tovey, A. & Cannell, JJ. Vitamin D improves fatigue, according to new study. The Vitamin D Council Blog & Newsletter, 2017.


Nowalk, A. et al. Effect of vitamin D3 on self-perceived fatigue: A double-blind randomized placebo-controlled trial. Medicine, 2016.

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