Can Vitamin D Deficiency Make You Feel Sick?

October 25, 2025 •

5 min read

According to the National Institutes of Health, nearly one in four Americans has vitamin D levels that are too low for optimal health. Many people wonder, 'Can vitamin D deficiency make you feel sick?' The answer is a resounding yes, as low levels can impact everything from your energy and mood to your immune system.

Quick Summary

A comprehensive guide explores how inadequate vitamin D levels can cause symptoms like fatigue, muscle weakness, bone pain, frequent infections, and mood changes. It details the underlying mechanisms, common causes, risk factors, and offers guidance on how to address a potential deficiency.

Key Points

Immune Function: Vitamin D activates immune cells, and a deficiency can lead to more frequent infections.
Common Symptoms: Fatigue, muscle weakness, and bone pain are key indicators that can be easily dismissed or misattributed.
Bone Health: Low vitamin D impairs calcium absorption, which can cause bone softening (osteomalacia) and increase fracture risk.
Mental Well-being: There is evidence linking low vitamin D levels to a higher risk of depression and mood swings.
Treatment: Addressing a deficiency typically involves a combination of supplements, targeted sun exposure, and dietary adjustments, guided by a medical professional.
Risk Factors: Older adults, people with darker skin, and individuals with obesity or certain gastrointestinal conditions are at a higher risk.

The Connection Between Vitamin D and Feeling Unwell

Vitamin D is a fat-soluble vitamin that the body can produce in response to sunlight and also absorb from certain foods and supplements. While famously essential for bone health by regulating calcium and phosphorus absorption, its role extends far beyond skeletal function. Vitamin D receptors are found throughout the body, including in cells related to the nervous and immune systems, suggesting its widespread importance. When levels are low, these systems can't function optimally, which can manifest in a variety of symptoms that leave you feeling under the weather.

How Low Vitamin D Affects Your Immune System

One of the most direct ways vitamin D deficiency can make you feel sick is by compromising your immune response. Vitamin D plays a crucial role in activating immune cells that fight off pathogens. When you're deficient, your immune system may be less effective at protecting you from viruses and bacteria, leading to more frequent and prolonged illnesses. Research has linked low vitamin D levels to a higher incidence of respiratory tract infections, including colds, bronchitis, and pneumonia.

Fatigue and Other Non-Specific Symptoms

Many people with a vitamin D deficiency experience non-specific symptoms that are often mistaken for other issues. These can be some of the most frustrating signs of low vitamin D because they are easy to overlook. Fatigue, for instance, is a very common complaint. Studies have found a clear link between low vitamin D levels and persistent tiredness, with some showing that supplementation can help reduce fatigue symptoms. Other vague but troubling symptoms can include general aches and pains, a low mood, and general malaise.

Understanding the Musculoskeletal Impact

Vitamin D's function in calcium absorption has a direct bearing on your muscular and skeletal systems. Without sufficient vitamin D, your body can't absorb calcium properly, and it may start taking calcium from your bones to maintain blood calcium levels. This process can lead to several problems:

Bone Pain: Many people with vitamin D deficiency experience bone pain, particularly in the lower back, hips, pelvis, and feet. The pain can be widespread and difficult to pinpoint.
Muscle Weakness: Beyond bone pain, low vitamin D levels can contribute to muscle weakness, aches, and cramps. This can make simple activities like climbing stairs or getting up from a chair feel difficult.
Increased Fracture Risk: In adults, chronic severe vitamin D deficiency can cause osteomalacia, a softening of the bones. This weakens the skeleton and increases the risk of fractures.

The Link to Mental Health and Mood

Growing research suggests a link between low vitamin D levels and certain mental health conditions. While not fully conclusive, some studies indicate that people with vitamin D deficiency may be at a higher risk of experiencing depressive episodes or mood changes. This might be because vitamin D receptors are present in the areas of the brain that regulate mood and behavior. For some individuals, maintaining healthy vitamin D levels can play a supporting role in managing overall mental well-being.

Causes of Vitamin D Deficiency

Vitamin D deficiency is a common global issue, affecting about 1 billion people worldwide. The primary cause is inadequate sunlight exposure, but several other factors can contribute.

Inadequate Sunlight Exposure: This is the most common cause. Your skin produces vitamin D from UVB rays, but sunscreens, living in northern latitudes, wearing covering clothing, or staying indoors frequently can all limit production.
Dietary Insufficiency: Few foods naturally contain vitamin D. Dietary sources include fatty fish, beef liver, egg yolks, and some fortified products like milk and cereals. Vegans, in particular, may struggle to get enough from diet alone.
Malabsorption Issues: Certain medical conditions, such as Crohn's disease, celiac disease, or cystic fibrosis, can prevent the intestines from properly absorbing vitamin D from food and supplements.
Age and Skin Color: As people age, their skin becomes less efficient at producing vitamin D. Additionally, higher melanin content in darker skin reduces the skin's ability to produce vitamin D from sunlight.
Obesity: Body fat can sequester vitamin D, preventing it from circulating in the blood. This means people with obesity may require higher doses to reach adequate levels.

Comparison of Low vs. Healthy Vitamin D Effects


Feature	Low Vitamin D Status	Healthy Vitamin D Status
Immune Response	Weakened, leading to more frequent infections like colds, flu, and respiratory illnesses.	Stronger, more effective immune system response and improved ability to fight off infections.
Energy Levels	Persistent fatigue, tiredness, and low energy levels, impacting daily activities.	Stable energy levels and reduced likelihood of experiencing unexplained chronic fatigue.
Musculoskeletal Health	Increased risk of bone pain, muscle weakness, cramps, and in severe cases, osteomalacia or rickets.	Proper calcium absorption, strong bones, and healthy muscle function, reducing pain and weakness.
Mood	Linked to mood changes and an increased risk of depression.	Supports brain function and mood regulation, contributing to better mental well-being.
Wound Healing	Impaired or slow wound healing, which can prolong recovery from injuries or surgery.	Proper wound healing, as vitamin D aids in inflammation control and skin regeneration.

How to Manage or Treat a Deficiency

If you suspect you have a vitamin D deficiency, a blood test (measuring 25-hydroxyvitamin D) is the most reliable way to confirm it. Always consult a healthcare professional for a diagnosis and treatment plan. A doctor may recommend one or more of the following:

Vitamin D Supplements: This is the most common and effective treatment. Vitamin D3 (cholecalciferol) is generally considered more easily absorbed than D2 (ergocalciferol). A doctor will advise on the correct dosage and duration.
Increased Sun Exposure: Sensible, short periods of sun exposure (5-30 minutes, several times a week) can help boost production. However, be mindful of skin cancer risks and wear sunscreen after a few minutes.
Dietary Changes: Incorporate more vitamin D-rich foods into your diet. This includes fatty fish like salmon and mackerel, fortified milk and cereals, and egg yolks.

Conclusion

Vitamin D deficiency is a surprisingly common and easily treatable condition that can have a profound impact on how you feel. It's not uncommon for the low-level, vague symptoms of feeling sick—fatigue, aches, and a compromised immune system—to be connected to insufficient vitamin D. By understanding its critical role in immune function, bone health, and mood regulation, you can recognize the signs and take proactive steps toward treatment. Proper diagnosis from a healthcare provider is the first step toward correcting a deficiency and improving your overall health and well-being.

Frequently Asked Questions

Some of the first and most common signs of a vitamin D deficiency are non-specific and subtle, such as fatigue, general tiredness, muscle weakness, aches, and a feeling of malaise. These symptoms are often mild at first and can be mistaken for general stress or lack of sleep.

Since fatigue has many causes, a blood test is the only definitive way to know if low vitamin D is the culprit. However, if your fatigue is accompanied by other symptoms like bone pain, muscle weakness, frequent infections, or mood changes, it may be worth discussing a vitamin D test with your doctor.

Yes, low vitamin D levels can contribute to frequent colds and other respiratory infections. Vitamin D is known to interact directly with the immune cells that are responsible for fighting off infections. When you're deficient, your immune system may be less effective at defending against invading pathogens.

While it's important to consult a doctor, methods to increase levels include taking a prescribed or recommended vitamin D3 supplement, getting safe, limited sun exposure (around 15-30 minutes a few times a week), and increasing dietary intake of vitamin D-rich or fortified foods.

Yes, many people with a vitamin D deficiency don't notice any obvious symptoms, and the condition is often clinically silent, especially in the early stages. For this reason, deficiencies can go undiagnosed until they become more severe or cause complications.

Several groups are at a higher risk, including older adults, breastfed infants, people with darker skin, individuals with obesity, those with limited sun exposure, and people with certain medical conditions like Crohn's disease or celiac disease.

Yes, muscle pain, aches, and weakness are well-documented symptoms of a vitamin D deficiency. This is due to vitamin D's role in supporting muscle function and helping the body absorb calcium, which is vital for muscle health.