Vitamin D Deficiency: Symptoms, Risk Factors & Research

Vitamin D deficiency is quite common and can affect far more than just your bones. Healthy vitamin D levels are also important for your immune system, muscles, nerves, brain, and mood.

This post is one part of my vitamin D series. Throughout the article, you'll find links to related posts that explore vitamin D food sources, how to safely get vitamin D from sun exposure, supplements, dosage, and other topics in more detail.

What's in This Post

• Who is most at risk: The most common causes and risk factors for vitamin D deficiency
• Mental health effects: What research says about vitamin D's connection to anxiety and depression
• GLP-1 medications: Why drugs such as Ozempic and Wegovy may increase deficiency risk
• What to do next: Practical guidance on improving low vitamin D levels and when supplementation may help

Notes: The contents of this post are not intended to be medical advice. It is always advisable to consult with your personal medical professionals for individualized recommendations. I may receive a small commission for sales made through links on this post, but it doesn't affect your cost.

Be Careful About Over-Supplementing Vitamin D

Before we talk about vitamin D deficiency symptoms, I just want to point out that vitamin D supplementation is a situation where too much of a good thing can be dangerous. 

You might recognize yourself in the deficiency symptoms, but I caution you against mega-dosing supplements without consulting with a medical professional. 

Unlike water-soluble vitamins like B and C, vitamin D is fat-soluble. If you take more water-soluble vitamins than your body needs, your body will release the excess in your urine. If you take more vitamin D than your body needs, you store it in your fat cells. That excess vitamin D can have negative side effects. 

🟢 ➜ I get into vitamin D supplementation safety precautions more in this post: The Sunshine Vitamin: D3 Benefits, Sources, and Dosage

How Common is Vitamin D Deficiency?

Vitamin D deficiency is far too common.

According to the Cleveland Clinic website, approximately:

• 1 billion people worldwide have vitamin D deficiency
• 35% of adults in the United States have vitamin D deficiency

Vitamin D Deficiency Symptoms

Many people with low vitamin D don't realize it unless they get a blood test to assess their level.

When symptoms do occur, they often develop gradually and may include:

• Fatigue or low energy
• Muscle weakness
• Bone or back pain
• Frequent illness or infections
• Brain fog or difficulty concentrating
• Low mood or depression
• Anxiety
• Hair loss (more on this in a minute)

More severe vitamin D deficiency is associated with more severe symptoms, including: 

• Rickets in children
• Bone loss in adults (osteopenia and osteoporosis)
• Increased risk of fractures
• Difficulty walking because of muscle weakness

These symptoms and conditions can have many possible causes. A blood test is the only way to know for certain whether your vitamin D level is low and may therefore be a contributing factor. I talk about testing vitamin D levels in this post: The Sunshine Vitamin: D3 Benefits, Sources, and Dosage.

Can Vitamin D Deficiency Cause Hair Loss?

One of my counseling clients who came in with anxiety had also been experiencing hair loss for quite a while. Testing her vitamin D revealed very low levels. Under medical supervision, she started on large-dose supplementation. Both her anxiety and hair loss quickly subsided. 

A 2021 review of 13 studies looked at vitamin D levels and androgenetic alopecia (also known as AGA, male pattern baldness, and female pattern hair loss). Their findings included:

• "serum vitamin D might be a possible parameter for diagnosing the onset and severity of AGA"
• "Vitamin D supplementation has proven to be useful in the regrowth of hair in non-human subjects"
• "Vitamin D could be a valid therapeutic approach, such as topical vitamin D (calcipotriol) seems to be a good treatment option to regrow hair follicles and prevent miniaturization of follicles due to androgenetic alopecia."

Another 2021 review of the literature found that lower blood vitamin D levels were associated with increased incidence of non-scarring alopecias, such as telogen effluvium, androgenetic alopecia, alopecia areata, and trichotillomania.

10 Vitamin D Deficiency Risk Factors

Many people don't get enough vitamin D, but some groups are at particular risk of deficiency.

Your risk of vitamin D deficiency is higher if you:

1. Get little sun exposure because of an indoor job, or by keeping your skin covered with sunscreen or clothing outdoors
2. Live in a northern or cloudy climate
3. Have darker skin
4. Are over age 65
5. Are obese
6. Have kidney or liver disease
7. Follow a vegan diet
8. Have a condition that interferes with nutrient absorption, such as Crohn's or celiac disease
9. Have had bariatric surgery
10. Are on GLP-1 drugs, such as Ozempic or Wegovy

January, 2026 study in Clinical Obesity about the GLP-1 connection to vitamin D deficiency: A review of six large studies with a total of almost 500,000 subjects found that "Vitamin D deficiency was the most common abnormality, occurring in 7.5% at 6 months and 13.6% at 12 months."

Can Low Vitamin D Contribute to Anxiety? What the Research Says

Data collected on 7,500 British people who were followed for fifty years found a strong correlation between low vitamin D and both depression and panic. (1)

A study by the Institute of Endocrinology and the National Institute of Mental Health in the Czech Republic compared vitamin D levels in three groups: forty men and women with depression, forty with an anxiety disorder, and healthy counterparts. Those with depression and those with anxiety had similarly low vitamin D levels when compared to the healthy control subjects. (2)

Low vitamin D levels corresponded with both depression and anxiety in seventy-five fibromyalgia patients. (3)

When 200 stroke patients were followed for a month, low vitamin D levels were associated with the development of post-stroke anxiety. (4)

Studies with rodents have shown an increase in anxiety behaviors when the vitamin D receptor gene is absent (5) and reduced anxiety-related behaviors with vitamin D supplementation. (6)

Vitamin D Deficiency and Depression: Scientific Evidence

This is just a small sample of vitamin D depression research:

Examination of data collected on 8,000 US residents between the ages of 15 and 39 showed that people with low vitamin D were much more likely to have depression than people with higher levels of the vitamin. (7)

A couple thousand people in the Netherlands, divided into three groups (current diagnosis of depression, past diagnosis of depression, and non-depression), were compared for vitamin D levels. The comparisons were controlled for lifestyle—including sunlight exposure—to eliminate confounding factors. Low vitamin D levels were associated with both the presence of depression and the severity of symptoms. (8)

600 young adults in New Zealand from the general population were tested for depression symptoms and vitamin D levels. Results—adjusted for time spent outdoors, etc.—showed that those whose vitamin D fell in the lowest quarter of the values had more depression symptoms than those whose values fell in the highest quarter of the values. (9)

Many studies show that vitamin D supplementation may help alleviate depression. In his 2014 examination of previous studies regarding vitamin D and depression, Simon Spelding concluded that vitamin D had a similar effect to antidepressant medication. (10)

What to Do About Vitamin D Deficiency

The best way to get vitamin D is from the sun, but if cloudy weather or other conditions get in the way of you achieving enough sun exposure, you may benefit from supplementing with vitamin D3 because food sources of the vitamin are not thought to be adequate to get you to optimal levels. (11)

Your need to supplement may change throughout the year as your sun exposure changes.

For more on getting enough vitamin D, check out these posts:

🟢 ➜ The Sunshine Vitamin: D3 Benefits, Sources, and Dosage

🟢 ➜ Tips for How to Get Vitamin D from the Sun

🟢 ➜ What Foods Have Vitamin D? Separating Myth from Reality

References: Vitamin D Deficiency Research

1. Jane Maddock et al., “Vitamin D and Common Mental Disorders in Mid-Life: Cross-Sectional and Prospective Findings,” Clinical Nutrition 32, no. 5 (2013): 758–764, https://doi.org/10.1016/j.clnu.2013.01.006.

2. M. Bičíková et al., “Vitamin D in Anxiety and Affective Disorders,” Physiological Research 64, Supplement 2 (2015): S101–S103.

3. D. J. Armstrong et al., “Vitamin D Deficiency Is Associated with Anxiety and Depression in Fibromyalgia,” Clinical Rheumatology 26, no. 4 (2006): 551–554, https://doi.org/10.1007/s10067-006-0348-5.

4. Chaowen Wu et al., “Association between Serum Levels of Vitamin D and the Risk of Post-Stroke Anxiety,” Medicine 95, no. 18 (2016): e3566, https://doi.org/10.1097/md.0000000000003566.

5. Allan V. Kalueff et al., “Increased Anxiety in Mice Lacking Vitamin D Receptor Gene,” NeuroReport 15, no. 8 (2004): 1271–1274, https://doi.org/10.1097/01.wnr.0000129370.04248.92.

6. Julia Fedotova, Svetlana Pivina, and Anastasia Sushko, “Effects of Chronic Vitamin D3 Hormone Administration on Anxiety-Like Behavior in Adult Female Rats after Long-Term Ovariectomy,” Nutrients 9, no. 1 (2017): 28, https://doi.org/10.3390/nu9010028.

7. Vijay Ganji et al., “Serum Vitamin D Concentrations Are Related to Depression in Young Adult US Population: The Third National Health and Nutrition Examination Survey,” International Archives of Medicine 3, no. 1 (2010): 29, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2996356/.

8. Y. Milaneschi et al., “The Association between Low Vitamin D and Depressive Disorders,” Molecular Psychiatry 19, no. 4 (2013): 444–451, https://doi.org/10.1038/mp.2013.36.

9. Maria Polak et al., “Serum 25-Hydroxyvitamin D Concentrations and Depressive Symptoms among Young Adult Men and Women,” Nutrients 6, no. 11 (2014): 4720–4730, https://doi.org/10.3390/nu6114720.

10. Simon Spedding, “Vitamin D and Depression: A Systematic Review and Meta-Analysis Comparing Studies with and without Biological Flaws,” Nutrients 6, no. 4 (2014): 1501–1518, https://doi.org/10.3390/nu6041501.

11. Ulrike Lehmann et al., “Efficacy of Fish Intake on Vitamin D Status: A Meta-Analysis of Randomized Controlled Trials,” American Journal of Clinical Nutrition 102, no. 4 (2015): 837–847, https://doi.org/10.3945/ajcn.114.105395.

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