What Happens if One Lacks Vitamin D?

October 31, 2025 •

4 min read

According to the National Institutes of Health, almost one out of four people in the United States have inadequate vitamin D blood levels. So, what happens if one lacks vitamin D and how does it affect the body? The consequences of low vitamin D can range from subtle fatigue and muscle weakness to severe bone disorders like osteoporosis and rickets.

Quick Summary

A lack of vitamin D can lead to serious health issues, impacting bone density, muscle function, and the immune system. Prolonged deficiency increases the risk of bone disorders such as osteoporosis and rickets, and is associated with fatigue, muscle weakness, and mood changes.

Key Points

Fatigue and Weakness: Persistent tiredness, muscle weakness, and pain are common early symptoms of vitamin D deficiency.
Bone Disorders: A long-term lack of vitamin D can cause rickets in children and osteomalacia and osteoporosis in adults, leading to weak, soft, and brittle bones.
Immune System Impact: Low vitamin D levels can weaken the immune system, making individuals more susceptible to infections and frequent illness.
Mood Regulation: Research has linked vitamin D deficiency to mood changes and an increased risk of depression.
Prevention and Treatment: The deficiency can be prevented or treated through sunlight exposure, consuming fortified and fatty foods, or taking supplements, with medical guidance.
D2 vs. D3: While both forms of vitamin D are effective, D3 is often considered slightly more potent and is widely available over-the-counter.

Understanding the Role of Vitamin D

Vitamin D, often called the "sunshine vitamin," is a vital nutrient that plays a crucial role in maintaining overall health. Its primary function is to help the body absorb calcium and phosphorus, two minerals essential for building and maintaining strong bones. Beyond bone health, vitamin D also supports the immune system, modulates cell growth, and aids in nerve and muscle function. The body primarily produces vitamin D through sun exposure, but it can also be obtained from certain foods and supplements.

Short-Term Effects of Lacking Vitamin D

In many cases, a mild deficiency may be asymptomatic or present with vague, non-specific symptoms that are easy to overlook. This makes it difficult for people to realize they have a problem until the deficiency becomes more severe.

Fatigue and Tiredness: One of the most common early signs is a persistent feeling of tiredness or fatigue, even after getting enough rest.
Muscle Weakness and Pain: Low vitamin D levels can lead to muscle pain, aches, and general muscle weakness, particularly in the upper arms and thighs. This can lead to a noticeable waddling gait in severe cases.
Bone and Back Pain: Vitamin D's role in calcium absorption means that a deficiency can cause a decrease in bone density, leading to pain in the bones and lower back.
Mood Changes: Research has indicated a link between low vitamin D levels and an increased risk of mood changes, anxiety, and depression.
Slow Wound Healing: A lack of vitamin D can also impair the body's healing process, causing wounds to take longer to recover.
Frequent Infections: Because vitamin D is crucial for a healthy immune system, its deficiency can lead to a weakened ability to fight off viruses and bacteria, resulting in more frequent illnesses.

Long-Term Health Consequences

If a vitamin D deficiency is left unaddressed over an extended period, the health consequences can become severe, impacting the skeletal system and overall well-being.

Rickets in Children: For children, severe vitamin D deficiency causes rickets, a rare condition where the bones become soft and bent. This can result in skeletal deformities, incorrect growth patterns, and bone pain.
Osteomalacia in Adults: In adults, severe deficiency leads to osteomalacia, a condition characterized by weak, soft bones that can cause significant bone pain and muscle weakness.
Osteoporosis: A chronic lack of vitamin D can lead to osteoporosis, a disease that thins and weakens the bones, making them fragile and more susceptible to fractures. This is particularly a risk for older adults.
Increased Risk of Falls: The muscle weakness and bone pain caused by low vitamin D levels can increase the risk of falls, especially in older adults, which in turn leads to a higher risk of fractures.
Association with Chronic Diseases: Long-term deficiency is also associated with an increased risk of developing other chronic conditions, including cardiovascular disease, type 2 diabetes, and certain autoimmune disorders.

Addressing and Preventing a Deficiency

Preventing or treating a vitamin D deficiency is often straightforward and can involve a combination of lifestyle changes and medical intervention. Consulting a healthcare provider for a blood test to determine your vitamin D status is the first step.

Methods for Prevention and Treatment

Sensible Sun Exposure: The most natural way to get vitamin D is through sunlight. Exposing bare skin to the sun for about 15–30 minutes, a few times a week, can be sufficient for most people. Factors like skin pigmentation and geographic location can affect the amount of vitamin D produced.
Dietary Sources: Incorporate foods rich in vitamin D into your diet. These include fatty fish like salmon and mackerel, cod liver oil, and egg yolks. Many foods, such as milk, cereals, and some orange juices, are also fortified with vitamin D.
Supplements: Many people require supplementation, especially during darker winter months or if they have limited sun exposure. Over-the-counter supplements are readily available, though a healthcare provider can recommend the appropriate dosage. High-dose supplements should only be taken under medical supervision.

Comparison of Vitamin D2 and D3

When choosing supplements or looking at food labels, you may encounter two forms of vitamin D: D2 (ergocalciferol) and D3 (cholecalciferol).


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Source	Plant sources, yeast.	Animal sources (fatty fish, lanolin), also produced by the skin from sunlight.
Availability	Prescription-strength doses and some supplements.	Widely available over-the-counter and often used for fortification.
Potency	Both forms increase vitamin D in the blood, but studies suggest D3 may raise levels higher and for a longer duration.	Considered slightly more potent and effective at raising blood levels.
Vegan Option	Yes, derived from plants.	Yes, a vegan version can be produced from lichen.

Conclusion

Lacking vitamin D can have a significant and wide-ranging impact on your health, affecting everything from your bone density and muscle function to your immune system and mental well-being. While the early signs can be subtle, prolonged deficiency can lead to serious conditions like rickets in children and osteomalacia or osteoporosis in adults. The good news is that preventing and treating a deficiency is manageable through sensible sun exposure, a balanced diet rich in fortified and natural sources, and supplementation when necessary. If you suspect you may have a deficiency, it is always best to consult a healthcare provider for an accurate diagnosis and a personalized treatment plan.

Visit the NIH Office of Dietary Supplements for more information.

Frequently Asked Questions

The initial signs can be subtle and include persistent fatigue, a general sense of not feeling well, muscle weakness, and bone or back pain. Some people may not experience any noticeable symptoms at all.

Yes, studies have shown an association between low vitamin D levels and an increased risk of mood changes, anxiety, and depression. The vitamin is essential for proper brain function and mood regulation.

Treatment typically involves increasing vitamin D intake through a combination of supplements, more dietary sources (like fortified foods and fatty fish), and sensible sun exposure. Your healthcare provider will determine the appropriate dosage for your specific needs.

It is difficult to get enough vitamin D from natural food sources alone, as very few foods contain it naturally. For most people, a combination of sun exposure, fortified foods, and sometimes supplements is necessary.

People with limited sun exposure, older adults, individuals with darker skin, people with malabsorption conditions (like celiac or Crohn's disease), and those who are obese are at higher risk.

Vitamin D2 comes from plant sources, while D3 is produced in the skin from sunlight and found in some animal products. D3 is generally considered more effective at raising and maintaining vitamin D blood levels.

Some studies suggest a link between vitamin D deficiency and hair loss, particularly a condition called alopecia areata. However, the relationship is complex, and more research is needed to fully understand the connection.