What Does a Lack of Vitamin D Cause in Adults?

January 4, 2026 •

4 min read

According to a 2011-2018 study using NHANES data, over 40% of adults in the United States have vitamin D insufficiency. This widespread issue means many are unaware of the significant health problems that a lack of vitamin D can cause in adults, extending beyond just bone health to affect mood, energy, and immunity.

Quick Summary

A lack of vitamin D in adults can lead to bone-softening disorders like osteomalacia and increase the risk of osteoporosis, fractures, and muscle weakness. Other symptoms include fatigue, frequent illness, and mood changes, highlighting its crucial role beyond just bone metabolism.

Key Points

Osteomalacia in Adults: A severe lack of vitamin D causes softening of the bones, leading to chronic bone pain and muscle weakness.
Increased Fracture Risk: A long-term deficiency contributes to osteoporosis, making bones brittle and significantly increasing the risk of fractures.
Neuromuscular Issues: Adults may experience persistent fatigue, muscle weakness, and cramps due to impaired nerve and muscle function.
Affects Mood and Immunity: Low vitamin D levels have been linked to an increased risk of depression and a weakened immune system, leading to more frequent infections.
Systemic Symptoms: Other signs include general tiredness, back pain, and slow wound healing, highlighting the vitamin's broad systemic impact.
At-Risk Populations: Older adults, individuals with darker skin, and those with malabsorption issues are at a higher risk of developing a deficiency.
Supplementation is Key: Correcting a deficiency often requires targeted supplementation, as dietary sources and sun exposure alone may not be sufficient.

The Core Role of Vitamin D

Vitamin D is a fat-soluble vitamin that plays a crucial, multifaceted role in adult health, most notably in regulating calcium and phosphate levels within the body. This regulation is essential for maintaining the strength and density of bones and teeth. However, the vitamin's influence extends far beyond the skeletal system, impacting neuromuscular function, immune response, and overall mood. When an adult experiences a deficiency, the body's ability to absorb these vital minerals from the intestine is compromised, triggering a cascade of health issues.

Bone and Musculoskeletal Complications

One of the most direct and serious consequences of a vitamin D deficiency is its impact on the bones. Without adequate vitamin D, the body struggles to maintain proper mineralization of the skeleton, leading to weak and soft bones.

Osteomalacia

In adults, a severe and prolonged lack of vitamin D can result in osteomalacia. This condition is characterized by a softening of the bones, which makes them prone to bending and fractures. The pain associated with osteomalacia is often described as a dull, aching sensation, particularly in the bones of the hips, lower back, legs, and ribs. Muscle weakness, especially in the limbs and back, is another common symptom that can contribute to a waddling gait and an increased risk of falls.

Osteoporosis

While different from osteomalacia, a long-term deficiency in vitamin D is a significant contributing factor to osteoporosis, a condition that causes bones to become fragile and brittle. Osteoporosis is a major cause of fractures, especially in older adults, who are already at a higher risk due to a natural decline in vitamin D synthesis. The reduced calcium absorption caused by insufficient vitamin D accelerates bone demineralization, making bones more susceptible to breaking from a minor fall or even a cough.

Systemic and Neuromuscular Symptoms

Beyond bone health, a deficit in this crucial nutrient can manifest in less obvious, but equally disruptive, systemic symptoms.

Fatigue and Weakness: Many adults with a deficiency report feeling chronically tired and lethargic, with a general feeling of low energy. This fatigue can be a result of impaired neuromuscular function, as vitamin D is vital for proper muscle contraction and strength.
Muscle Pain: Aches, cramps, and weakness in the muscles are frequently reported. This can range from mild discomfort to more severe myopathy, a condition causing muscle weakness.
Mood Changes: The link between vitamin D and mental health is an area of ongoing research, but some studies have shown an association between low levels and an increased risk of depressive episodes, anxiety, and irritability.
Frequent Infections: As vitamin D plays a key role in modulating the immune system, a lack of it can lead to a compromised immune response. This may result in frequent illnesses and a higher susceptibility to infections, particularly respiratory ones.

A Comparison of Deficiency Effects


Symptom Category	Mild to Moderate Deficiency	Severe to Chronic Deficiency
Musculoskeletal	Mild bone or muscle aches, general fatigue	Severe bone pain (osteomalacia), muscle weakness, increased fall risk
Skeletal Structure	Increased risk of bone density loss (osteopenia)	Weak, brittle bones (osteoporosis), increased fracture risk
Neuromuscular	Mild fatigue, generalized tiredness	Pronounced muscle weakness (myopathy), potential nerve-related sensations
Mood	Lowered mood, irritability	Increased risk of depressive episodes
Immunity	Increased susceptibility to common illnesses	Higher risk of severe infections due to compromised immune function

Who is at Risk?

Several factors increase an adult's risk of developing a deficiency. These include:

Limited Sun Exposure: People who are housebound, live in northern latitudes, or wear extensive clothing may not get enough UV-B radiation to synthesize sufficient vitamin D.
Darker Skin: Higher melanin content in the skin reduces its ability to produce vitamin D from sunlight.
Older Adults: As we age, the skin's efficiency in producing the vitamin decreases, and kidney function can decline, affecting the conversion to its active form.
Obesity: Fat cells sequester vitamin D, preventing its release into the blood, meaning individuals with a higher BMI may need more.
Malabsorption Conditions: Disorders like Crohn's, celiac disease, and cystic fibrosis can interfere with nutrient absorption in the gut.
Kidney and Liver Disease: These conditions can impair the body's ability to convert vitamin D to its active, usable form.

Conclusion

Addressing a vitamin D deficiency is crucial for mitigating risks to bone, muscle, and overall systemic health. For many adults, insufficient levels can cause chronic issues like osteomalacia and osteoporosis, alongside debilitating fatigue and mood disorders. While sun exposure and diet can help, many people, particularly those in high-risk groups, may require supplementation to restore adequate levels. The long-term consequences of an untreated deficiency underscore the importance of early diagnosis and proper management, often through simple and effective supplementation strategies determined in consultation with a healthcare provider.

What to Do Next

If you suspect you may have a vitamin D deficiency based on symptoms like persistent fatigue, muscle weakness, or bone pain, it is important to consult a healthcare provider. They can perform a blood test to measure your serum 25-hydroxyvitamin D levels, which is the most reliable indicator of your vitamin D status. Following diagnosis, a personalized treatment plan will be developed, which may include high-dose supplementation for a period followed by a lower maintenance dose. For more detailed information on dietary sources and daily requirements, the NIH Office of Dietary Supplements offers a comprehensive fact sheet on vitamin D.

Disclaimer: The information provided here is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before making any decisions about your health or treatment.

Frequently Asked Questions

While many adults with a deficiency may have no obvious symptoms, some of the most common signs include non-specific fatigue, general tiredness, and bone or muscle pain.

Yes, research indicates there is a link between low vitamin D levels and a higher risk of mood changes, including depression, anxiety, and irritability.

There is an association between low vitamin D levels and weight gain, as fat cells can sequester the vitamin and prevent its release into the bloodstream. People who are obese may require higher vitamin D intake to maintain normal levels.

Osteomalacia is the softening of bones due to defective bone mineralization caused by severe vitamin D deficiency. Osteoporosis is a condition of fragile, porous bones with low bone density, which a long-term deficiency can contribute to.

A blood test to measure the serum concentration of 25-hydroxyvitamin D is the most reliable way to diagnose a deficiency. You should consult your healthcare provider to arrange this test.

Treatment for a diagnosed deficiency typically involves taking vitamin D supplements. A doctor will determine the appropriate dosage, which may start high to correct the deficiency and then switch to a lower maintenance dose.

Prevention includes getting adequate sun exposure (5-30 minutes several times a week, depending on skin type and location), eating foods fortified with vitamin D, and consuming natural sources like fatty fish. Individuals in high-risk groups may need supplements.

Yes, older adults are at a higher risk because their skin's ability to produce vitamin D from sunlight declines with age. They also tend to spend more time indoors and may not consume enough through their diet.