Could Low Vitamin D, Iron, B12, or Thyroid Problems Cause Anxiety, Depression, or Brain Fog?
- Ashley Hughes
- May 27
- 6 min read
Have you ever wondered why you feel exhausted, mentally foggy, or more anxious than usual—even when you're trying to take care of yourself?
Maybe you're sleeping enough but still wake up tired. Perhaps your concentration isn't what it used to be.
You find yourself rereading emails, forgetting simple tasks, or struggling to stay focused throughout the day.
You find yourself rereading emails, forgetting simple tasks, or struggling to stay focused throughout the day.
Maybe you've become more irritable, less motivated, or increasingly overwhelmed by responsibilities that once felt manageable.
It's easy to assume these symptoms are purely psychological. Sometimes they are. Anxiety, depression, ADHD, and chronic stress can absolutely affect energy, mood, and concentration. But sometimes there is more to the story.
Certain medical conditions and nutrient deficiencies can contribute to symptoms that closely resemble—or worsen—common mental health concerns. While they are rarely the sole cause of anxiety or depression, identifying and addressing underlying contributors can be an important part of comprehensive mental health care.
A Common Scenario
A woman in her late 30s schedules a psychiatric appointment because she thinks she's developing anxiety. She feels more overwhelmed than she used to. Her patience is shorter. She's exhausted despite getting what should be enough sleep.
Work feels harder. Concentration feels harder. Motivation feels harder.
She begins wondering if something is wrong emotionally. Sometimes the answer is anxiety. Sometimes it's depression. And occasionally, laboratory testing reveals a contributing factor such as iron deficiency, low vitamin D levels, vitamin B12 deficiency, or thyroid dysfunction. This is one reason I believe mental health care should consider the whole person—not just symptoms alone.
Why Physical Health Can Affect Mental Health
The brain is one of the most metabolically active organs in the body.
Every thought, emotion, memory, and decision relies on a constant supply of oxygen, hormones, vitamins, minerals, and neurotransmitters. When those systems are disrupted, the effects may show up not only physically, but emotionally and cognitively as well.
This can contribute to symptoms such as:
Fatigue
Brain fog
Difficulty concentrating
Low motivation
Irritability
Increased anxiety
Memory difficulties
Reduced stress tolerance
Low mood
Sleep disturbances
Because these symptoms overlap significantly with anxiety disorders, depression, ADHD, and burnout, it isn't always obvious when an underlying medical issue may also be contributing.
Symptoms That May Suggest an Underlying Medical Contributor
Not everyone with anxiety, depression, or fatigue has a vitamin deficiency or thyroid disorder. However, it may be worth discussing medical evaluation with your healthcare provider if you experience:
Fatigue despite adequate sleep
Brain fog
Difficulty concentrating
Hair thinning or increased hair shedding
New anxiety without a clear explanation
Worsening depression or loss of motivation
Dizziness or lightheadedness
Frequent headaches
Cold intolerance
Restless legs
Memory concerns
Reduced exercise tolerance
Feeling physically and mentally drained
These symptoms can occur for many reasons, but they sometimes warrant a closer look at potential biological contributors.
Iron Deficiency and Ferritin: Often Overlooked
One of the most commonly overlooked contributors to fatigue, brain fog, and reduced mental performance is low iron. Many people assume that if they are not anemic, their iron levels must be normal. However, iron stores can become depleted long before anemia develops.
What Is Ferritin?
Ferritin is a laboratory marker that reflects the body's stored iron supply. Think of ferritin as your body's iron savings account. Even when hemoglobin levels remain normal, low ferritin may indicate that iron reserves are running low.
Some individuals with low ferritin report symptoms such as:
Persistent fatigue
Poor concentration
Brain fog
Hair shedding or thinning
Reduced exercise tolerance
Irritability
Restless legs
Increased anxiety
Feeling mentally "slowed down"
Women with heavy menstrual cycles are particularly vulnerable to low iron stores, although iron deficiency can affect anyone. Because fatigue and difficulty concentrating are among the most common reasons people seek mental health treatment, iron status is sometimes worth considering when symptoms persist despite efforts to improve sleep, stress, and overall wellness.
Thyroid Function and Mental Health
The thyroid gland produces hormones that help regulate metabolism throughout the body—including the brain. When thyroid hormone levels become too low or too high, symptoms can closely resemble psychiatric conditions.
Hypothyroidism (Underactive Thyroid)
An underactive thyroid may contribute to:
Fatigue
Depression
Low motivation
Slowed thinking
Brain fog
Memory difficulties
Weight gain
Increased sensitivity to cold
Hyperthyroidism (Overactive Thyroid)
An overactive thyroid may contribute to:
Anxiety
Panic-like symptoms
Racing thoughts
Irritability
Restlessness
Sleep difficulties
Increased heart rate
Feeling constantly "on edge"
Because thyroid dysfunction can mimic anxiety and depression, thyroid screening is commonly considered when clinically appropriate.
Vitamin D: More Than Bone Health
Most people associate vitamin D with healthy bones, but vitamin D receptors are found throughout the brain and nervous system. Researchers continue to study how vitamin D may influence mood regulation, inflammation, stress response, and cognitive function. Low vitamin D levels have been associated with symptoms such as fatigue, low mood, reduced motivation, and increased stress sensitivity.
People at higher risk for deficiency include those who:
Spend most of their time indoors
Live in regions with limited winter sunlight
Consistently use sun protection
Have darker skin pigmentation
Have certain gastrointestinal or absorption disorders
Potential symptoms associated with low vitamin D include:
Fatigue
Low mood
Reduced motivation
Muscle aches
Poor stress tolerance
Feeling emotionally "flat"
Vitamin B12 and Brain Function/ Brain Fog
Vitamin B12 plays an important role in maintaining healthy nerve cells and supporting neurological function. When levels become low, symptoms can sometimes resemble anxiety, depression, ADHD, or simple mental exhaustion.
Possible symptoms include:
Brain fog
Difficulty concentrating
Memory concerns
Mental fatigue
Low energy
Tingling or numbness in the hands and feet
Mood changes
Increased anxiety
Individuals following vegetarian or vegan diets, older adults, and people with certain gastrointestinal conditions may have a higher risk of deficiency. Because symptoms often develop gradually, many people do not immediately recognize that low B12 levels could be affecting how they feel.
What Laboratory Tests Might Be Considered?
Depending on symptoms, medical history, medications, and individual risk factors, healthcare providers may sometimes consider laboratory testing such as:
Complete Blood Count (CBC)
Comprehensive Metabolic Panel (CMP)
Thyroid-Stimulating Hormone (TSH)
Free T4
Vitamin D
Vitamin B12
Folate
Ferritin
Iron studies
Hemoglobin A1c
Not every patient requires extensive laboratory testing, and evaluations should always be individualized. The goal is not to search endlessly for abnormalities, but rather to identify potentially treatable factors that may be contributing to symptoms.
Mental Health Isn't Always "Just Mental Health"
In psychiatric practice, it's important to recognize that emotional symptoms can sometimes have biological contributors. This does not mean every case of anxiety or depression is caused by a vitamin deficiency, hormone imbalance, or medical condition. Mental health disorders are complex and influenced by genetics, life experiences, relationships, stress, sleep, and many other factors. However, identifying and addressing underlying medical contributors may be an important piece of the puzzle for some individuals. Mental health treatment often works best when both physical and emotional health are considered together.
Looking Beyond Symptoms
Sometimes anxiety is anxiety.
Sometimes depression is depression.
And sometimes physical health factors may be contributing to how a person feels emotionally, mentally, and physically.
A comprehensive psychiatric assessment looks beyond symptoms alone and considers sleep, stress, medical history, medications, nutrition, lifestyle habits, and potential biological contributors. Understanding the full picture can help create a treatment plan that is more personalized, more targeted, and ultimately more effective.
Frequently Asked Questions
Can low iron cause anxiety?
Low iron and low ferritin levels may contribute to fatigue, irritability, poor concentration, and symptoms that overlap with anxiety in some individuals. Iron deficiency should be evaluated and treated under the guidance of a healthcare professional.
What is ferritin?
Ferritin is a blood test that measures the body's stored iron supply. Ferritin levels may be low before anemia develops, which is why some individuals experience symptoms such as fatigue, brain fog, hair shedding, or reduced exercise tolerance despite having a normal hemoglobin level.
Can low vitamin D cause depression?
Research has found an association between low vitamin D levels and depressive symptoms. However, vitamin D deficiency is rarely the sole cause of depression, and treatment should address all relevant contributing factors.
Can thyroid problems cause anxiety?
Yes. An overactive thyroid can contribute to symptoms such as anxiety, racing thoughts, restlessness, increased heart rate, and difficulty sleeping. An underactive thyroid may contribute to fatigue, low mood, and brain fog.
What blood tests may help evaluate fatigue and brain fog?
Depending on symptoms and medical history, healthcare providers may consider tests such as a CBC, ferritin, iron studies, vitamin D, vitamin B12, thyroid function tests, and other laboratory evaluations when clinically appropriate.
