Vitamin D deficiency is the most common micronutrient deficiency in the United States. According to the Linus Pauling Institute Micronutrient Information Center at Oregon State University, a whopping 94.3% of the U.S. population does not meet the daily intake requirement for vitamin D. If you suspect that you fall into this group, being able to recognize the number-one sign of a vitamin D deficiency can help prompt a conversation with your healthcare provider about ways to get more vitamin D in your diet and possible supplementation.
Meet the expert: Michael Holick, M.D., Ph.D., an endocrinologist and vitamin D expert.
Vitamin D is important for maintaining strong, healthy bones, helping your body absorb calcium, supporting your immune system, regulating cell growth, and fighting inflammation, according to Michael Holick, M.D., Ph.D., an endocrinologist and vitamin D expert. And yet, the telltale sign of vitamin D deficiency is constant exhaustion, especially fatigue that persists even after getting enough sleep.
A review published in the journal Nutrients explains that vitamin D influences numerous factors that contribute to fatigue, including regulating production of the neurotransmitters dopamine and serotonin, controlling levels of oxidative stress and inflammatory cytokines, and maintaining electrolyte balance. Furthermore, studies have shown benefits of supplementing with vitamin D for improving fatigue in different groups of people, including those with multiple sclerosis and those with post-COVID syndrome.
In addition to fatigue, other symptoms of vitamin D deficiency include increased sweating, joint pain, muscle aches, and anxiety or depression. If you experience chronic fatigue alongside one or more of these other symptoms, it’s worth getting your vitamin D levels checked and talking to your doctor about supplementation.
While the National Institutes of Health (NIH) recommends that adults get 600 to 800 IU (or 15 to 20 micrograms) of vitamin D per day, Dr. Holick suggested taking 1,500 to 2,000 IU (or 37.5 to 50 micrograms) a day. It is possible to take too much vitamin D, but you would need to take more than 10,000 IU every day to reach those dangerous levels, according to the National Library of Medicine. Still, getting a personalized recommendation from a doctor or dietitian will ensure you’re getting all the vitamin D you need.
Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing. Also, be careful about giving supplements to a child, unless recommended by their healthcare provider.
