Vitamin D Deficiency—How Can You Tell If You Have One?

The Importance Of Vitamin D

Vitamin D is a fat-soluble vitamin that is probably most well-known for 2 things: 1) it’s important for bone health and 2) it’s sometimes referred to as the sunshine vitamin because our body (our skin to be more specific) produces it with exposure to sunlight. Vitamin D is important in the body for MANY more reasons than just bone health. There are receptors for vitamin D in nearly every type of tissue and cell in the body including our brain, heart, stomach, pancreas, skin and immune system. In addition to its role in bone health, vitamin D also reduces inflammation, regulates cell growth, regulates immune function and also regulates glucose metabolism²—and that’s just scratching the surface. Being that vitamin D’s functions are so broad, it’s not surprising that vitamin D deficiency is associated with many health conditions including certain types of cancer, cardiovascular disease, diabetes, autoimmune diseases, and respiratory tract infections. Please note that these associations do not necessarily mean that vitamin D deficiency causes these conditions, it could also be that these conditions cause a vitamin D deficiency. Related Reading: CAN YOU TAKE VITAMIN C AND VITAMIN D TOGETHER?

Vitamin D Testing

The only way to know for sure if you are vitamin D deficient is for your doctor to order a blood test. Most expert groups recommend a specific test called a “serum circulating 25-hydroxyvitamin D level”. If your doctor orders a test, here’s what you should focus on: ➔ Optimal levels of vitamin D appear to be in the range of 30-100ng/mL, but there is not a consensus in the scientific community on this point. ➔ The Endocrine Society Clinical Practice Guidelines divide vitamin D levels into categories of deficiency (25-hydroxyvitamin D level less than 20 ng/mL (50 nmol/L)) and insufficiency/inadequacy (25-hydroxyvitamin D level 21-29ng/mL (525-725 nmol/L)). The distinction between a vitamin D deficiency and a vitamin D insufficiency is important. A vitamin D deficiency can result in overt symptoms like bone and muscle weakness and cause reduced bone mineral density.⁵ Vitamin D insufficiency may cause more general symptoms like tiredness or fatigue, reduced immune function, impaired focus or impaired mood.⁶ If you’re wondering what the likelihood is that you are vitamin D deficient, more recent estimates of how many people in the United States are vitamin D deficient show that around 6% of the population is probably deficient and about 24% have inadequate vitamin D status.⁷ But, some researchers estimate go as far as to say that 40-100% of the U.S. population is vitamin D deficient⁸—so, it’s plain to see that the verdict is still out on exactly how common this problem is and what to do about it.

How Do I Know If I Should Ask For A Vitamin D Test?

While the scientists figure it out, you may be thinking about asking your doctor about your vitamin D status. What are some signs of a vitamin D deficiency—or insufficiency? Here are a few things to watch out for:

1. Fatigue

In general, most nutrient deficiencies can lead to fatigue. Specific to vitamin D, there is research to suggest that vitamin D is inversely related to fatigue severity, which means that some studies have found that people with lower vitamin D levels report greater levels of fatigue.^{9, 10} Remember, anytime you have unexpected or unexplained fatigue, it should prompt a conversation with your doctor to make sure that everything is okay in there!

2. Feeling Run Down Often?

We’ve already talked about how important vitamin D is for immune health, but we can take it a step further and say that vitamin D is crucial for two really important facets of the immune response—the innate and adaptive.¹¹ A 2013 systematic review and meta-analysis found that vitamin D supplementation appeared to have a protective effect on respiratory tract infections.¹² There are also associations found between vitamin D deficiency and upper respiratory tract infections.¹³ If you’re feeling so fatigued that even binge watching your latest Netflix addiction feels like too much effort, you might consider checking your vitamin D levels to see if you could use a little support in the sunshine vitamin department.

3. Muscle Pain, Weakness Or Slow Recovery After Workouts

Vitamin D is also important for muscle function (add it to the list of the things vitamin D does), and insufficiency or deficiency can lead to declining muscle mass and strength. These effects are especially prominent in older individuals.^{14, 15} Apart from older individuals, research in elite athletes has shown that lower vitamin D levels were associated with lower extremity muscle strains and injuries to muscles of the core.¹⁶ Vitamin D supplements were also shown to have a positive effect on muscle function and risk for injury.¹⁷

4. Depression Or Cognitive Changes

Vitamin D deficiency and insufficiency have been linked to cognitive decline in elderly people¹⁸ and also risk for depression.¹⁹ Like many of the potential signs of a vitamin D deficiency, depression or cognitive changes should always prompt a convo with your doctor. It’s important to keep the lines of communication open with a trusted medical provider, as it’s always better to identify a potential issue before things progress! After your vitamin D test, your doctor may recommend a vitamin D supplement to help get your vitamin D status on the right track. Also, remember that just getting more sun exposure can help you to improve your levels. If you do have a deficiency, it’s pretty easy to fix and the health benefits are worth it!