Vitamin D and Fatigue

By Charles Li, MD
December 21, 2020

Why Vitamin D Matters

Vitamin D is most commonly associated with bone health. But, research has recently shown links between vitamin D and mental health.

Unlike most vitamins which only come from food, your body can make its own Vitamin D with the help of sunlight. Sunlight catalyzes a key reaction in creating Vitamin D.

How Vitamin D Is Made

Cases of Vitamin D and Fatigue

One of the more interesting effects of Vitamin D may be its protective effect against fatigue.

While there has not been a ton of research on Vitamin D and fatigue, the research that we do have suggests that there may be a link.

There have been at least two published case studies of patients with severe fatigue that have gotten better when they were given vitamin D.

In one case, a woman who had daytime sleepiness and fatigue got better after she was given vitamin D supplements to treat her low vitamin D levels.

Case Study
Vitamin D and Fatigue

"A 28-year-old woman was evaluated for 4 months of excessive daytime sleepiness (EDS), after an overnight polysomnogram (PSG) revealed neither sleep disordered breathing nor a sleep related movement disorder. A full sleep evaluation revealed the presence of heavy daytime napping and pervasive fatigue...Vitamin D supplementation was initiated at a dose of 50,000 IU once weekly, and EDS improved within 2 weeks. One week later, a PSG with next-day multiple sleep latency testing (MSLT) failed to show significant pathology. At follow-up, she reported resolution of thigh pain and headaches, with a significant improvement in her low back pain syndrome. EDS had resolved, and her ESS score was 1/24. Follow-up 25-hydroxyvitamin D level was normal at 39 ng/mL."

Resolution of hypersomnia following identification and treatment of vitamin d deficiency

In a second case study, is 61-year-old man with daytime fatigue was also found to have low vitamin D. His daytime fatigue resolved when doctors treated his low vitamin D levels.

Case Study
Vitamin D and Fatigue

"A 61-year-old man was evaluated for excessive daytime fatigue. No features characteristic for depression, sleep apnea, or narcolepsy were present. A comprehensive work-up, including thyroid function tests and testosterone levels, did not reveal any abnormalities. However, serum 25-hydroxyvitamin D level was low, at 18.4 ng/mL. Vitamin D supplementation was initiated. At follow-up in 3 and 12 months, the patient reported complete resolution of daytime fatigue, corresponding to an increase in his vitamin D levels."

Vitamin D deficiency and fatigue: an unusual presentation

These case studies don’t tell us much about how common fatigue caused by vitamin D levels might be, but they do suggest that at least in some people with fatigue, treating their low vitamin D levels may be a good place to start.

Studies on Vitamin D and Fatigue

So far, studies on vitamin D and fatigue have focused mostly on younger woman.

One study in pre-menopausal women with fatigue found that generally, those with enough vitamin D also had a better quality of life. They had more vitality, mental health, and better physical health.

Cross Sectional Study on Vitamin D in Pre-menopausal Women
Vitamin D & Quality of Life
Cross sectional study
n=80 premenopausal women
Methods: SF-36 and 25-hydroxyvitamin D levels
Those with higher Vitamin D also had:
Mental Health
Mental component of quality of life
A measure of energy and fatigue
Physical Functioning
Physical health
Much Better
Ecemis et al
A cross-sectional study on Vitamin D in pre-menopausal women found that those with more Vitamin D had better mental health, more vitality, and much better physical functioning.

A second study on nurses in Iran found that vitamin D deficiency was extremely common and strongly correlated with their risk of having fatigue.

Cross Sectional Study on Vitamin D in Iranian Nurses
Vitamin D & Fatigue
Cross sectional study
n=200 female nurses
Methods: Visual analogue scale, 25-hydroxyvitamin D levels
Those with higher Vitamin D also had:
Lower Fatigue
As measured by the visual analogue scale
Ecemis et al
Cross Sectional Study on Vitamin D in Iranian Nurses

Research on Vitamin D and fatigue is still in the early stages. We will need clinical trials in order to confirm the link.

However given Vitamin D’s importance and how common Vitamin D deficiency is, it’s safe to say that treating Vitamin D Deficiency when you do have fatigue may not be a bad thing to try.