What part of the body would be most affected by vitamin D deficiency?

November 13, 2025 •

4 min read

According to the National Institutes of Health, almost one out of four people in the United States have vitamin D blood levels that are too low or inadequate. When considering what part of the body would be most affected by vitamin D deficiency, the skeletal system and associated muscles are the primary areas of concern due to the vitamin's critical role in mineral absorption.

Quick Summary

The skeletal system and muscles are the most affected areas due to vitamin D deficiency, which impairs the body's ability to absorb calcium and phosphate. This leads to softened bones (osteomalacia/rickets) and significant muscle weakness. Secondary impacts can affect the nervous system and mood.

Key Points

Skeletal System: The bones are the most significantly impacted part of the body due to vitamin D's role in calcium and phosphate absorption.
Rickets and Osteomalacia: Severe deficiency in children causes rickets (soft, bent bones), while adults develop osteomalacia (softening of bones).
Muscles: Impaired muscle function is a major consequence, leading to pain, weakness, cramps, and an increased risk of falls.
Mineral Balance: Low vitamin D impairs mineral absorption, causing the body to pull calcium from bones to maintain blood levels, which degrades bone density.
Immune and Nervous Systems: Secondary effects include weakened immunity, increased susceptibility to infection, fatigue, mood changes, and potential links to neurological disorders.
Treatment and Prevention: Correcting deficiency involves increasing sun exposure, consuming fortified foods, and often taking supplements under a doctor's guidance.

The Most Affected Body Part: The Skeletal System

The skeletal system, consisting of bones and teeth, is unequivocally the part of the body most profoundly affected by vitamin D deficiency. Vitamin D is crucial for the regulation of calcium and phosphate in the body. When levels are low, the intestines absorb less of these minerals from food. To compensate for falling blood calcium levels, the body increases parathyroid hormone (PTH), which draws calcium from the bones to keep blood levels stable. This process, if prolonged, leads to a significant weakening of the bone structure. The primary conditions manifesting this are rickets in children and osteomalacia in adults.

In children, whose bones are still growing, this lack of mineralization can cause:

Softening and weakening of bones, leading to deformities such as bowed legs.
Delayed or incorrect growth patterns.
Bone pain and joint deformities.

In adults, the condition is known as osteomalacia and can cause:

General bone pain, particularly in the lower back, hips, and legs.
Increased risk of fractures from minor falls or slight jarring.
Muscle weakness and stiffness.

Another condition closely linked to vitamin D deficiency is osteoporosis, which causes bones to become weak and brittle. While the two disorders can coexist, osteomalacia is a problem of soft bones due to poor mineralization, whereas osteoporosis is a problem of low bone mass density. Severe vitamin D deficiency, combined with low calcium absorption, can contribute significantly to bone loss and a higher fracture risk in those with osteoporosis.

The Critical Impact on Muscle Function

While bones may be the most severely impacted, muscles are a very close second, with significant consequences for mobility and daily function. Vitamin D is directly involved in muscle contraction and repair. The presence of vitamin D receptors (VDR) in skeletal muscle tissue confirms its direct role in muscle health. A deficiency can lead to a condition known as myopathy, characterized by muscle weakness, aches, and pain.

Symptoms of muscle-related issues include:

Generalized muscle weakness, especially in the hips, upper arms, and thighs.
Aches and cramping.
Increased risk of falls, particularly in older adults, due to reduced muscle strength.
A 'waddling' gait caused by weakened leg and hip muscles.

Severe deficiency can lead to low blood calcium levels (hypocalcemia), which can trigger muscle spasms and cramps, known as tetany. This demonstrates the strong link between calcium regulation, controlled by vitamin D, and proper muscle function. Studies in athletes have also shown that inadequate vitamin D levels are linked to a higher prevalence of muscle injuries and longer recovery times.

Secondary Effects on Other Body Systems

Beyond the musculoskeletal system, vitamin D deficiency has secondary, widespread effects on other body systems, including the immune and nervous systems.

Immune System: Vitamin D plays a crucial role in regulating immune responses. Low levels can compromise the immune system's ability to fight off infections, leading to more frequent illnesses like colds and flu.
Nervous System and Mood: Vitamin D receptors are present in many areas of the brain. Low levels have been associated with neurological and neuropsychiatric disorders, including fatigue, depression, and mood changes. Some research suggests a link between deficiency and a higher risk of conditions like multiple sclerosis, Parkinson's, and Alzheimer's disease, though more study is needed.
Other Symptoms: General fatigue, hair loss, and slow wound healing are also commonly reported signs of low vitamin D levels.

Rickets vs. Osteomalacia: A Comparison


Feature	Rickets (Children)	Osteomalacia (Adults)
Affected Population	Infants and growing children, primarily between 6 and 36 months of age.	Adults, whose bones have finished growing.
Primary Cause	Impaired mineralization of the growth plate and new bone tissue.	Impaired mineralization of new bone tissue, causing existing bones to soften.
Skeletal Deformities	Common, including bowed legs, enlarged wrists and ankles, and an oddly shaped skull.	Deformities are less common, but pelvic bones can flatten in severe cases.
Key Symptoms	Painful or tender bones, muscle weakness, stunted growth, and developmental delays.	Generalized bone pain, muscle weakness, and increased risk of fractures.
Fracture Risk	Increased due to weakened, pliable bones.	Increased, particularly in weight-bearing areas like the hips and spine.
Reversibility	Generally curable with treatment, though severe deformities may be permanent.	Usually curable with appropriate supplementation.

Addressing Vitamin D Deficiency

For those who are deficient, treatment typically involves lifestyle changes and supplementation under medical guidance.

Sunlight Exposure: Sensible sun exposure is a primary way for the body to produce vitamin D naturally. However, factors like skin pigmentation, latitude, season, and sunscreen use can limit its effectiveness.
Dietary Intake: Include vitamin D-rich foods such as fatty fish, fortified milk and cereals, and egg yolks.
Supplements: Vitamin D supplements are often necessary, especially for those with severe deficiency. Dosages can vary, and it is important to follow a healthcare provider's recommendations.

For more information on supplements and bone health, consult the Bone Health & Osteoporosis Foundation's recommendations.

Conclusion

While vitamin D deficiency can cause a wide array of non-specific symptoms like fatigue and mood changes, its most direct and significant impact is on the musculoskeletal system. Bones suffer from improper mineralization, leading to conditions like osteomalacia and rickets, and muscles lose strength and function. The cascade of effects stems from the body's impaired ability to absorb vital minerals, underscoring vitamin D's central role in maintaining strong bones and functional muscles. Identifying and addressing a deficiency early is critical for preventing long-term damage and improving overall health.

Frequently Asked Questions

The primary sign of severe vitamin D deficiency in children is rickets, a condition that causes bones to soften and weaken, leading to deformities such as bowed legs.

Vitamin D deficiency leads to muscle weakness because the vitamin is essential for regulating calcium, which is required for proper muscle contraction. Low calcium levels disrupt this process, causing weakness, pain, and cramps.

Yes, low vitamin D levels can contribute to osteoporosis by inhibiting calcium absorption. The body then leaches calcium from the bones to maintain blood levels, leading to a loss of bone mineral density over time.

Osteomalacia is the softening of bones due to impaired mineralization, while osteoporosis involves a loss of bone tissue, making bones brittle and weak. Both can occur due to vitamin D deficiency.

Yes, chronic fatigue and a general sense of not feeling well are common, but non-specific, symptoms associated with low vitamin D levels.

You can increase your vitamin D levels through a combination of sensible sun exposure, eating fortified foods and natural sources like fatty fish, and taking supplements as recommended by a healthcare professional.

Yes, low levels of vitamin D are linked to mood changes, including depression and anxiety, as the vitamin is involved in brain function and mood regulation.