What Happens if I Don't Take Vitamin D3?

October 14, 2025 •

4 min read

According to the NIH, nearly one-quarter of Americans have vitamin D levels that are too low for optimal health, largely from insufficient sun exposure and dietary intake. So, what happens if I don't take vitamin D3 and fall into this category?

Quick Summary

Not taking vitamin D3 can lead to serious health problems, including weakened bones, osteoporosis, and impaired immune function. Common symptoms can range from fatigue and muscle pain to more severe issues like osteomalacia and rickets.

Key Points

Fatigue and Weakness: A chronic lack of vitamin D3 can manifest as persistent fatigue, tiredness, and widespread muscle weakness.
Compromised Immune System: Insufficient vitamin D3 weakens the immune system, making the body more susceptible to frequent illnesses and infections.
Increased Fracture Risk: Deficiency leads to impaired calcium absorption, which over time can cause osteomalacia in adults and rickets in children, resulting in soft, weak, and brittle bones prone to fractures.
Mood Disorders: Low levels of vitamin D are linked to mood changes and an increased risk of depression, as the vitamin plays a role in brain function.
Risk of Chronic Conditions: Long-term deficiency is associated with a greater risk of developing chronic diseases, including autoimmune conditions, cardiovascular disease, and potentially certain types of cancer.
Need for Diagnosis: Diagnosis requires a blood test to measure 25-hydroxyvitamin D levels, as symptoms can be subtle and mimic other conditions.

Vitamin D3, or cholecalciferol, is a fat-soluble vitamin essential for numerous bodily functions, particularly calcium absorption for bone health. While sunlight is a primary source, factors like location, skin color, age, and sunscreen affect production, making diet and supplements crucial for many. Insufficient D3 can significantly impact various body systems.

The Immediate Consequences of Low Vitamin D3

Early signs of low vitamin D3 may be subtle. Fatigue and tiredness are common, often mistaken for other issues. Muscle weakness and pain can also occur due to D3's role in neuromuscular function.

Symptoms of a Developing Deficiency

Fatigue and tiredness: Persistent exhaustion.
Muscle weakness and pain: Aching muscles.
Bone or back pain: Reduced bone density causing discomfort.
Mood changes: Link to increased depression risk.
Compromised immune function: Frequent illness or infections.

Long-Term Health Risks Without Vitamin D3

Ignoring a D3 deficiency can lead to severe, chronic conditions affecting bone health and beyond.

Skeletal and Muscular Health Deterioration

Rickets in children: Improper bone mineralization causing deformities.
Osteomalacia in adults: Softening of bones, leading to pain and fracture risk.
Osteoporosis: Weakening of bones, increasing fragility and fracture susceptibility.

Increased Risk of Chronic Diseases

Research suggests a link between long-term low D3 and increased risk of chronic issues, though more studies are needed. These include:

Autoimmune diseases: Conditions like multiple sclerosis.
Cardiovascular disease: Potential link to heart problems.
Certain cancers: Some studies show a connection, with mixed findings.

Vitamin D3 vs. D2: Understanding the Difference

Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) are the main supplemental forms. D3 is generally more effective at raising blood levels for longer periods.


Feature	Vitamin D3 (Cholecalciferol)	Vitamin D2 (Ergocalciferol)
Source	Skin production from sun; fatty fish, egg yolks.	Plant sources like mushrooms; fortified foods.
Effectiveness	More potent for raising and maintaining levels.	Less effective than D3.
Availability	Over-the-counter supplements.	Often requires prescription for high doses.
Natural Production	Synthesized by the body from sunlight.	Not naturally produced by the human body.

How to Manage and Prevent Deficiency

Managing deficiency involves increasing vitamin D access. Mild cases may improve with lifestyle changes, while severe cases may need medical supervision and higher-dose supplements.

Lifestyle Adjustments

Safe sun exposure: 5-30 minutes of midday sun several times weekly (varies by factors).
Dietary intake: Consume D3-rich foods like fatty fish and egg yolks.
Fortified foods: Choose milk, cereals, or juice with added vitamin D.

Supplementation Options

If lifestyle changes are insufficient, a D3 supplement may be recommended by a healthcare provider based on a blood test.

Who is Most at Risk?

Certain groups have a higher risk of deficiency:

Older adults: Reduced skin synthesis from sun.
Individuals with darker skin: Higher melanin reduces D3 production from sun.
People with certain medical conditions: Conditions affecting fat absorption (e.g., Crohn's, celiac disease).
Breastfed infants: Breast milk is not a sufficient D3 source.
People with obesity: Body fat can store D3, making it less available.

Conclusion: The Critical Role of Vitamin D3

Not taking vitamin D3 can lead to various negative health outcomes, from fatigue to serious long-term bone and systemic issues. Adequate levels are crucial for bone health, immune function, and mood. Consult a healthcare professional for diagnosis and guidance if you are at risk or experiencing symptoms.

Visit the NIH Office of Dietary Supplements for more information on vitamin D.

The Risks of Forgoing Vitamin D3

How does not taking vitamin D3 affect bone density?

Vitamin D3 is essential for calcium absorption. A lack reduces calcium uptake, causing the body to take calcium from bones, weakening them and increasing the risk of osteoporosis and fractures.

Is it possible to get enough vitamin D3 from diet alone?

While some foods contain D3, meeting the recommended intake from diet alone is often difficult, especially without sufficient sun exposure, which is the body's primary source.

What are the early signs that I'm not getting enough vitamin D3?

Early signs can be subtle, including fatigue, general aches, muscle weakness, and potentially mood changes. These symptoms can worsen if the deficiency isn't corrected.

Does a lack of vitamin D3 only affect bone health?

No, vitamin D3 also impacts immune function, neuromuscular function, and mood. Deficiency can increase the risk of infection, muscle problems, and mood disorders.

Can I overdose on vitamin D3 if I take too much?

Yes, excessive supplement intake can cause vitamin D toxicity with symptoms like nausea and kidney issues. Follow recommended allowances and consult a doctor before high-dose supplements.

How is vitamin D3 deficiency typically diagnosed?

A blood test measuring 25-hydroxyvitamin D confirms deficiency. A doctor can interpret results and recommend action.

What is the difference between vitamin D3 and regular vitamin D?

Vitamin D is a group of compounds, including D3 and D2. D3 is sun-produced and in animal products, while D2 is plant-derived. D3 is generally more effective at raising blood levels.

Frequently Asked Questions

If you don't take vitamin D3, you can develop a deficiency that leads to weakened bones (osteoporosis or osteomalacia), fatigue, muscle weakness, mood changes, and a compromised immune system. In children, a severe lack can cause rickets.

Early signs are often subtle and can include fatigue, general tiredness, muscle weakness, and mild aches and pains in your bones or back. These symptoms can be easily overlooked or mistaken for other issues.

You can increase your vitamin D3 levels naturally by getting moderate, safe sun exposure, especially during midday, and by consuming foods rich in D3. Good dietary sources include fatty fish, egg yolks, and fortified foods like milk and cereal.

High-risk groups include older adults, people with darker skin pigmentation, those with medical conditions that affect nutrient absorption (e.g., Crohn's or Celiac disease), people with obesity, and breastfed infants.

Yes, vitamin D3 is the form produced by the skin in response to sunlight and is found in animal products. Vitamin D2 is derived from plant sources. Studies suggest that D3 is more effective than D2 at raising and maintaining vitamin D levels in the blood.

While diet is important, it is often difficult to get enough vitamin D from food alone. Supplementation may be necessary, especially for those with limited sun exposure, to reach and maintain adequate levels.

Diagnosis is confirmed with a blood test that measures the amount of 25-hydroxyvitamin D in your blood. This is the most reliable way to assess your vitamin D status.