How Do You Feel When Your Vitamin D Is Really Low?

According to a 2025 StatPearls article on the NCBI Bookshelf, vitamin D deficiency is a frequently overlooked issue that can lead to significant health complications if left untreated. When your vitamin D is really low, it can manifest in a surprising range of symptoms that impact your physical and mental well-being.

Quick Summary

Severe vitamin D deficiency manifests through a variety of subtle and noticeable symptoms, including fatigue, bone pain, muscle weakness, frequent infections, and mood changes. A blood test is necessary for proper diagnosis, which then guides treatment involving supplements, sunlight, and dietary changes.

Key Points

• Fatigue: Chronic, unexplained tiredness is a primary indicator of very low vitamin D levels.

• Pain: Widespread muscle weakness, bone aches, and joint pain are common due to poor calcium absorption.

• Mood Changes: Low vitamin D is linked to mood disorders, including depression and anxiety.

• Weakened Immunity: A severely low level can make you more susceptible to frequent illnesses and infections.

• Hair Loss: Significant hair loss has been associated with severe deficiency, particularly in women.

• Impaired Healing: Wounds may take longer to heal, as vitamin D aids in the skin's repair process.

• Professional Diagnosis: A blood test ordered by a healthcare provider is the only way to confirm a deficiency.

• Safe Treatment: A doctor can recommend safe approaches including supplements, sun exposure, and dietary changes to correct levels.

The Surprising Signs and Symptoms of Really Low Vitamin D

Before taking any supplement or making changes to your diet or sun exposure for low vitamin D, it is important to consult with a healthcare professional. Information provided here is for general knowledge and should not be taken as medical advice.

When your vitamin D levels are extremely low, the effects can be widespread and often go unnoticed because the symptoms can be vague or attributed to other causes. While many associate this nutrient primarily with bone health, its role in regulating calcium absorption and supporting the immune and nervous systems means a profound deficiency can affect your entire body. It's not just about fragile bones; it's about a fundamental disruption to your body's systems.

Physical Manifestations of Severe Vitamin D Deficiency

• Chronic Fatigue and Tiredness: One of the most common and persistent signs is a feeling of being constantly tired, even with adequate sleep. This is often the first symptom to appear and can significantly impact daily life.
• Bone and Joint Pain: Vitamin D is crucial for absorbing calcium, so a lack of it leads to bone and back pain. This can be mild initially but worsens over time, sometimes leading to more serious bone conditions.
• Muscle Aches, Weakness, or Cramps: Low levels can affect muscle function and lead to widespread muscle pain, weakness, and persistent cramps. This can increase the risk of falls, especially in older adults.
• Impaired Wound Healing: Studies have found that vitamin D deficiency can compromise the healing process after an injury or surgery. This is because the nutrient is involved in creating compounds critical for new skin formation.
• Hair Loss: Severe hair loss, particularly in women, has been linked to low vitamin D levels. The nutrient plays a role in hair follicle health, and deficiency can contribute to conditions like alopecia areata.
• Frequent Illness or Infection: Vitamin D directly interacts with the cells responsible for fighting infection. If you find yourself getting sick often with colds or other infections, very low vitamin D could be a contributing factor.

Psychological and Mood-Related Symptoms

Beyond physical discomfort, a significant vitamin D deficit can have a notable impact on mental health.

• Depression and Mood Changes: Low vitamin D is associated with mood changes, including depression and anxiety. The vitamin is thought to play a role in regulating mood and serotonin levels.
• Poor Sleep Quality: A 2020 study in children found that low vitamin D levels were associated with poor sleep quality and duration, suggesting a link that may contribute to fatigue.

Comparison of Low vs. Very Low Vitamin D Symptoms

Recognizing the difference between general insufficiency and severe deficiency can be difficult, as symptoms overlap. The severity of your symptoms often correlates directly with the level of deficiency.

Symptom	Low Vitamin D (Insufficiency)	Really Low Vitamin D (Severe Deficiency)
Fatigue	Mild, occasional tiredness; feeling of low energy.	Persistent, chronic, and debilitating fatigue that is not relieved by rest.
Bone Pain	Subtle aches and discomfort, particularly in the lower back or legs.	Pronounced and widespread bone and joint pain, potentially leading to weakened bones and fractures.
Muscle Weakness	Minor weakness or soreness after physical activity.	Significant muscle weakness, aches, cramps, and an increased risk of falls.
Immune Health	More frequent illnesses like colds.	Recurrent or prolonged infections, indicating a seriously compromised immune response.
Mood	General feelings of sluggishness or malaise; potentially mild mood shifts.	Clinically relevant mood disorders like depression and anxiety.
Other Signs	May be asymptomatic or have very subtle, hard-to-pinpoint issues.	May include more advanced symptoms like impaired wound healing, hair loss, and potentially other serious complications.

Diagnosis and Treatment Options

If you suspect you have very low vitamin D, it's essential to get a blood test to confirm. The 25-hydroxyvitamin D test is the most common and accurate way to determine your levels. If a deficiency is found, a doctor will recommend a treatment plan, which is often a combination of approaches.

The Road to Recovery

1. Supplementation: This is the most common treatment for clinically low levels. Your doctor may recommend vitamin D supplements to rapidly restore levels, followed by a maintenance plan. The D3 form (cholecalciferol) is often more easily absorbed than D2.
2. Increased Sun Exposure: The body naturally produces vitamin D from sunlight. A doctor may recommend getting safe sun exposure on your skin regularly, while being mindful of skin cancer risks.
3. Dietary Changes: While often not enough to correct a significant deficiency alone, incorporating more vitamin D-rich foods can help with maintenance. These include fatty fish (salmon, mackerel), fortified milk and cereals, and egg yolks.

A Note on Safety

It is crucial to follow a doctor's guidance on dosage, as excessive vitamin D intake can lead to toxicity, which has its own set of unpleasant symptoms like nausea, vomiting, and confusion. A blood test is the only way to know for certain what your levels are and what treatment is needed.

Conclusion: Don't Ignore the Signs

Low vitamin D can cause a multitude of seemingly unrelated symptoms, making it an easy condition to overlook. The feeling of persistent fatigue, unexplained muscle or bone pain, frequent illnesses, and shifts in mood should not be dismissed as simply part of daily life. If you're experiencing these signs, understanding how you feel when your vitamin D is really low is the first step toward getting a diagnosis. Consulting a healthcare professional for a simple blood test can provide clarity and set you on the path to effective treatment through supplements, dietary adjustments, and safe sun exposure. Taking these steps can lead to a significant improvement in both your physical health and overall well-being. A 2025 review in StatPearls emphasizes that with proper supplementation, most individuals can restore normal vitamin D levels and prevent serious complications.

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What to Do If You Suspect a Deficiency

• Consult a Doctor: The first and most important step is to talk to a healthcare provider. They can order the necessary blood test to determine your exact vitamin D levels and rule out other potential causes for your symptoms.
• Request the Right Test: Ensure your doctor orders a 25-hydroxyvitamin D (25(OH)D) test, as this is the most accurate measure of the vitamin D in your blood.
• Discuss Treatment Options: Based on your test results, your doctor will advise on the best course of action. Do not self-prescribe supplements, as this can be dangerous.
• Track Your Progress: Follow your doctor's recommendations for re-testing to ensure your levels are improving and to establish a long-term maintenance plan.

Frequently Asked Questions

What are the first signs that your vitamin D is really low?

The initial signs of very low vitamin D are often subtle but include persistent and chronic fatigue, general tiredness, and vague aches and pains in your muscles and bones.

Can low vitamin D cause mood swings and depression?

Yes, low vitamin D levels have been associated with mood changes, including feelings of depression and anxiety. The nutrient is involved in regulating mood, so a deficiency can impact mental well-being.

How do you test for a severe vitamin D deficiency?

A severe vitamin D deficiency is diagnosed with a blood test, specifically the 25-hydroxyvitamin D (25(OH)D) test, which measures the level of vitamin D in your blood. Your doctor will order this test if they suspect a deficiency based on your symptoms or risk factors.

How can you tell the difference between low and very low vitamin D symptoms?

While symptoms overlap, the key difference is severity. Very low levels often result in chronic, debilitating fatigue; widespread and intense bone pain; significant muscle weakness; and a seriously weakened immune system, compared to the milder versions seen in insufficiency.

What is the fastest way to increase vitamin D levels?

The fastest way to increase vitamin D levels, especially for a severe deficiency, is through vitamin D supplements prescribed and monitored by a healthcare professional. This is often more effective than diet or sun exposure alone for correcting a significant deficit.

Can very low vitamin D cause serious health problems?

Yes, prolonged and untreated severe vitamin D deficiency can lead to serious health problems. These include bone disorders like osteoporosis and osteomalacia, an increased risk of fractures, and potentially contributing to other chronic conditions.

Is it possible to have low vitamin D and not know it?

Yes, it is very common to have low vitamin D and be unaware of it, as the symptoms are often non-specific or mild. Many people don't realize they have a deficiency until it is discovered through routine lab work or they develop health problems.