What Can a Vitamin D Deficiency Cause in Adults?

October 20, 2025 •

3 min read

According to the National Institutes of Health, almost 1 in 4 US adults are considered to have low levels of vitamin D. A vitamin D deficiency can cause a wide range of health issues in adults, from common symptoms like fatigue and bone pain to more serious, long-term complications.

Quick Summary

This article explores the numerous health problems, from musculoskeletal issues to immune system dysfunction, that a lack of vitamin D can cause in adults. It covers symptoms, long-term effects, and treatment options to help improve overall health.

Key Points

Osteomalacia: A severe and prolonged vitamin D deficiency can cause the bones to soften, leading to a condition called osteomalacia in adults.
Fatigue and Weakness: Common symptoms of a deficiency include persistent tiredness, muscle pain, and muscle weakness.
Increased Fracture Risk: A long-term shortage of vitamin D can contribute to osteoporosis, which weakens bones and increases the risk of fractures.
Mood and Mental Health: Low vitamin D levels have been associated with mood changes and a higher risk of depression.
Compromised Immunity: A deficiency can weaken the immune system, making adults more susceptible to frequent infections and illnesses.
Diet and Sun Exposure: The primary causes of deficiency are insufficient sun exposure and a lack of dietary intake from fortified foods.
Diagnosis and Treatment: A blood test can diagnose the deficiency, which is typically treated with supplements and dietary changes under medical supervision.

Understanding Vitamin D's Crucial Role

Vitamin D is a fat-soluble nutrient essential for overall health. It's crucial for strong bones and teeth, helping regulate calcium and phosphate absorption. While the body produces it upon sun exposure, it can also be obtained from certain foods and supplements. Insufficient levels can lead to health issues.

Short-Term Symptoms of Deficiency

A mild vitamin D deficiency may show no symptoms, but some adults experience subtle signs often mistaken for other problems.

Common signs of low vitamin D:

Fatigue: Persistent tiredness is a common symptom.
Bone and Joint Pain: Deficiency can cause bone pain, particularly in the lower back.
Muscle Weakness: Low levels can lead to muscle pain, weakness, and cramps.
Mood Changes: Some studies link low vitamin D to increased depression risk.
Impaired Wound Healing: Slow healing may indicate inadequate vitamin D.
Frequent Infections: A weakened immune system due to low vitamin D can lead to more frequent illnesses.

Long-Term Complications of Vitamin D Deficiency

Untreated chronic deficiency can cause serious complications, particularly affecting bone health.

Bone and Musculoskeletal Disorders

Osteomalacia: Severe deficiency causes osteomalacia, a softening of the bones in adults due to poor mineralization.
Osteoporosis: Long-term deficiency can contribute to bone density loss and osteoporosis, increasing fracture risk.
Increased Risk of Falls: Older adults with low vitamin D are more prone to falls and fractures.

Potential Links to Chronic Diseases

Research suggests deficiency may increase the risk of certain chronic conditions.

Cardiovascular Disease: Some studies associate low vitamin D with higher risk of heart issues.
Autoimmune Diseases: Inadequate vitamin D is linked to increased risk of autoimmune disorders.
Type 2 Diabetes: Research indicates a potential link between deficiency and higher type 2 diabetes risk.

Comparison of Bone Health Conditions in Adults


Feature	Osteomalacia	Osteoporosis
Problem	Defective mineralization of bone.	Reduced bone mass and density.
Cause	Primarily severe vitamin D deficiency.	Long-term shortages of vitamin D and calcium.
Key Symptom	Bone pain, muscle weakness, soft bones.	Increased fracture risk due to brittle bones.
Underlying Mechanism	Inefficient absorption of calcium and phosphorus.	Accelerated bone turnover.
Result	Bones become weak and soft.	Bones become fragile and porous.

Causes of Vitamin D Deficiency

Several factors contribute to deficiency, including insufficient sun exposure, diet, age, skin pigmentation, obesity, and certain medical conditions.

Lack of Sunlight: The most common cause, especially in winter or for those mostly indoors.
Dietary Factors: Not consuming enough vitamin D-rich or fortified foods contributes.
Age: Skin produces less vitamin D from sun as people age.
Skin Pigmentation: Darker skin reduces vitamin D production from sun.
Obesity: Higher BMI is linked to lower vitamin D levels.
Medical Conditions: Conditions affecting absorption, like Crohn's, can prevent sufficient vitamin D uptake.

Conclusion: Taking Action Against Deficiency

Understanding what a vitamin D deficiency can cause in adults is vital. Effects range from fatigue to serious chronic conditions. Deficiency is treatable and preventable through increased sun exposure, dietary changes, and supplements. High-risk individuals should monitor their levels. Proactive steps can reduce risks and improve health.

How to Manage Your Vitamin D Levels

Consult a healthcare professional if you suspect a deficiency. Diagnosis is via a blood test. Treatment often includes:

Supplements: Vitamin D supplements are effective; a doctor will advise on dosage.
Dietary Adjustments: Increase intake of fatty fish, fortified foods, and egg yolks.
Safe Sun Exposure: Controlled time outdoors with sun exposure can help, mindful of skin cancer risks.

For more information, the NIH Office of Dietary Supplements is a resource. Always consult your doctor before supplements.

Frequently Asked Questions

The initial signs can be subtle, including fatigue, general tiredness, and mild bone or muscle pain. Many adults may not even notice symptoms in the early stages.

Yes, research suggests a link between low vitamin D levels and hair loss, particularly in cases of alopecia areata, an autoimmune disease.

A vitamin D deficiency is diagnosed with a simple blood test that measures the concentration of 25-hydroxyvitamin D in the body.

The time it takes to correct a deficiency varies based on the severity and treatment plan, but it can often be addressed with a course of high-dose supplements over several weeks or months.

Yes, older adults are at a higher risk because the skin's ability to synthesize vitamin D from sunlight decreases with age.

Yes, people with a higher BMI are at greater risk because vitamin D is stored in fat cells, making it less available for the body to use.

Osteomalacia is a condition where bones soften due to a defect in mineralization, whereas osteoporosis is the loss of bone mass that makes bones brittle and prone to fracture.