6 Symptoms of Vitamin D Deficiency

Vitamin D deficiency is becoming increasingly prevalent. With reasons including low dietary intake, reduced sun exposure, too much time spent indoors, and higher body weight, vitamin D deficiency is now thought to affect 1 billion people.¹  

Although the bone-deforming disease of rickets is mostly a thing of the past, approximately half of the global population has vitamin D insufficiency that may cause both skeletal and non-skeletal symptoms.¹

While not all vitamin D deficiencies produce symptoms—you should test your blood vitamin D levels regularly to check your status—there are some potential things to look out for, including bone and muscle pain, getting sick frequently, fatigue, poor wound healing, and mood changes.

Symptoms of Vitamin D Deficiency

Vitamin D deficiency has been linked to bone-related symptoms for about a century, but we now also know that inadequate vitamin D is linked to several other non-skeletal issues.

1. Fatigue

Fatigue is more than just feeling sleepy—it’s typically a chronic condition that significantly impacts work, social life, and daily activities. 

Although chronic fatigue has many causes, one might be vitamin D deficiency. 

One study found that the prevalence of low vitamin D was 77.2% in patients with complaints of fatigue. After 5 weeks of vitamin D supplementation, there was a significant improvement in all five categories of fatigue assessment (general fatigue, physical fatigue, emotional fatigue, mental fatigue, and vigor).² Another study—this time a randomized controlled trial—found that high-dose vitamin D supplementation (a single dose of 100,000 IU) significantly reduced fatigue more than a placebo in people with vitamin D deficiency.³

2. Getting Sick Often

Vitamin D deficiency may cause you to get sick more frequently because vitamin D plays a role in our innate and adaptive immune responses.⁴

The innate immune system is the first line of defense against invading bacteria or pathogens. In contrast, the adaptive immune system is more specialized, targeting specific invaders and adapting to previous infections.

Vitamin D facilitates innate immunity by enhancing the production of the antimicrobial molecule cathelicidin and defensive immune cells. It also strengthens the physical barrier function of epithelial cells, helping to keep pathogens out. 

It modulates the adaptive immune system by supporting the differentiation of naive T cells into immune-benefiting regulatory T cells and reducing the secretion of pro-inflammatory cytokines.

Therefore, insufficient vitamin D weakens your immune system, potentially leading to more frequent infections or illnesses.

Research has shown that vitamin D supplementation (4,000 IU of vitamin D daily for one year) reduced the prevalence of respiratory tract infections (RTIs) in people prone to illness who typically get four or more RTIs per year.⁵

3. Soft, Weak Bones

Vitamin D deficiency first became well-known when it was discovered as a cure for rickets around the 1930s. 

The disease of rickets causes bowed legs and stunted growth in children because vitamin D is needed for your body to absorb calcium, which induces proper bone mineralization and normal bone development. 

In adults, vitamin D deficiency can cause a loss of bone mineral density, bone fractures, osteomalacia (softening of bones), and eventual osteoporosis if untreated.⁶ 

Vitamin D increases calcium absorption in the intestines, so low vitamin D levels lead to decreased blood calcium levels.

Low blood calcium increases the activity of a hormone called PTH (parathyroid hormone). PTH attempts to get more calcium into your bloodstream, but it does this by taking it from the bones, leading to too much bone turnover and weaker bones.⁷ 

Conversely, healthy vitamin D levels will regulate PTH activity, promoting normal rates of bone resorption and remineralization. 

4. Bone and Muscle Pain

Vitamin D deficiency can cause musculoskeletal pain (muscle and bone pain) for similar reasons to its link to weak bones: the relationship between vitamin D and calcium (as well as phosphate). 

Deficient or inadequate vitamin D status may increase the risk of myalgia—muscle pain. One study found vitamin D deficiency to be present in 93% of adults who went to a clinic with musculoskeletal pain, myalgias, or muscle weakness.⁸ 

One mechanism behind this is the presence of vitamin D receptors in nerve cells called nociceptors, which sense pain. This may mean that vitamin D is involved in pain signaling pathways.⁹

Another reason why vitamin D deficiency can cause musculoskeletal pain is because low vitamin D increases the production and secretion of parathyroid hormone (PTH).¹⁰

Excess PTH induces phosphaturia (high phosphate in the urine), which leads to hypophosphatemia (low phosphate in the blood). When phosphate (and calcium) in the blood are lower, bone mineralization is inadequate.

However, bone-building cells called osteoblasts still try to deposit collagen into the bones, but without proper mineralization, it becomes a rubbery, low-support structure. 

This insufficient structural support expands the sheath outside your bones—called the periosteal covering—putting outward pressure on areas of the periosteal covering that contain sensory pain nerve fibers.

The end result? A dull, aching sensation in the bones and muscles. 

5. Poor Wound Healing

Slow wound healing after an injury can be a sign of inadequate vitamin D.

Some studies have found that people with vitamin D deficiency have compromised healing or outcomes after dental surgery.¹¹ 

This may be because vitamin D promotes the production of compounds (including connective tissue growth factor) that form new skin when wounds heal.¹² Another potential reason is due to vitamin D’s anti-inflammatory and antibacterial effects.¹³

6. Mental Health Disorders

Vitamin D is linked to mood and mental health. Some potential mechanisms behind vitamin D’s impact on mood include:¹⁴

• There is an increased expression of vitamin D receptors in areas of the brain known to play a role in mood regulation, including the limbic system, cerebellum, and cortex. 
• Vitamin D modulates the link between depression and inflammation. 
• Vitamin D has anti-inflammatory effects that may be neuroprotective and positively impact mood.

One small study of 100 people found that those who were diagnosed with depression were more likely to be vitamin D deficient than non-depressed people.¹⁵

However, studies like these cannot determine cause and effect, meaning it’s possible that depression led to vitamin D deficiency (by staying indoors more often, for example) and not the other way around. 

That said, some research has shown promise for using vitamin D to improve symptoms of depression, suggesting a more causal effect.

In this meta-analysis, researchers found that people who took vitamin D supplements had significant improvements in their depressive symptoms that were comparable to anti-depressant medication.¹⁶

Risk Factors for Vitamin D Deficiency

Many factors play a role in the development of vitamin D deficiency, including:

• Having darker skin
• Living at a more northern latitude
• Spending most of your time indoors
• Limited skin exposure to the sun (i.e., wearing clothing with maximum skin coverage or wearing high SPF sunscreen always)
• Older age (65+)
• Being overweight or obese
• Chronic kidney disease or liver disease
• Gut conditions that affect nutrient absorption, like celiac disease, Crohn’s disease, or ulcerative colitis 
• Taking some medications that impact vitamin D metabolism, including statins, laxatives, steroid medications, seizure drugs, and orlistat (a weight loss drug)

Weight loss surgery (like gastric bypass)¹⁷

Defining Vitamin D Deficiency

Although the statistics on deficiency vary, researchers estimate that up to 50% of the world has deficient or inadequate vitamin D levels.¹⁸ 

Subclinical vitamin D inadequacy—meaning, your levels aren’t quite low enough to cause severe bone-related problems—is more prevalent than overt vitamin D deficiency, but both can cause health issues. 

Vitamin D deficiency is the highest in older adults (especially those in senior care facilities), people with obesity, and those who are in long-term hospitalizations.¹

Vitamin D levels are checked by a serum (blood) test of 25-hydroxyvitamin D, or 25(OH)D. However, optimal blood vitamin D levels are controversial and debated often. 

Many health organizations recommend optimal 25(OH)D levels between 20 and 40 ng/mL. However, other vitamin D researchers promote levels between 30 and 50 ng/mL.

As a quick aside, you may also see 25(OH)D measured in nmol/L. One nmol/L is equal to 0.4 ng/mL, and 1 ng/mL is equal to 2.5 nmol/L. For example, 20 ng/mL is equal to 50 nmol/L. 

According to the Food and Nutrition Board (FNB), people have vitamin D deficiency at serum 25(OH)D concentrations less than 12 ng/mL, and vitamin D inadequacy is between 12 to 20 ng/mL. The FNB states that vitamin D levels above 20 ng/mL are likely adequate for the general population.¹⁹ 

That said, other research has found optimal vitamin D to be 30 ng/mL or higher, with others claiming up to 50-80 ng/mL is healthiest.^20,21

Although there are controversies about what the optimal level is, many vitamin D experts agree that using <12 ng/mL as a deficiency marker is much too low and should instead indicate very severe vitamin D deficiency. They state that “a serum level of 30 ng/mL is closer to the bottom end of the acceptable range for skeletal health.”²² 

If you get your serum vitamin D checked, your doctor can help you better understand the results and determine the best course of action needed, if any. 

Vitamin D Deficiency FAQs