What deficiency causes bow leggedness?

October 18, 2025 •

4 min read

According to the Cleveland Clinic, the most common cause of rickets, a condition leading to softened and weakened bones, is a vitamin D deficiency. This nutritional deficiency is the primary cause for what deficiency causes bow leggedness in children, though a lack of calcium and phosphorus can also contribute. While many infants are naturally bow legged and grow out of it, persistence can signal an underlying problem that requires treatment.

Quick Summary

This article explains how deficiencies in Vitamin D, calcium, and phosphorus can lead to rickets and subsequent bow leggedness. It also covers other medical conditions, hereditary factors, and environmental influences that can cause this deformity. An overview of symptoms, diagnosis, treatment options, and prevention strategies is included.

Key Points

Rickets is the main cause: The primary nutritional cause of bow leggedness is rickets, which results from a severe deficiency of Vitamin D, calcium, or phosphorus.
Vitamin D is crucial: Vitamin D deficiency is the most common nutritional cause of rickets because it impairs the body's ability to absorb calcium and phosphorus for bone mineralization.
Physiologic bowing is normal: Many infants are born with bowed legs that naturally correct themselves by age 2 or 3; this is called physiologic genu varum.
Blount's disease is another cause: Pathologic bowing can be caused by Blount's disease, a growth disorder of the shin bone that worsens over time.
Dark skin is a risk factor: Children with darker skin have a higher risk of Vitamin D deficiency and subsequent rickets because more melanin reduces skin's ability to produce Vitamin D from sunlight.
Treatment depends on the cause: Treatment for bow leggedness varies based on the cause, ranging from supplements and dietary changes for rickets to bracing or surgery for more severe conditions like Blount's disease.
Early intervention is important: For pathologic bowing, early diagnosis and treatment are essential to prevent worsening deformities and long-term complications.

Understanding Rickets: The Primary Nutritional Cause of Bow Leggedness

When addressing the question of what deficiency causes bow leggedness, rickets is the most common answer. Rickets is a condition affecting children, where their bones become soft and weak, which can lead to skeletal deformities like bowed legs, also known as genu varum. The root cause of nutritional rickets is a deficit of key minerals required for proper bone mineralization. The primary players in this process are Vitamin D, calcium, and phosphorus.

The Role of Vitamin D, Calcium, and Phosphorus

Vitamin D Deficiency: The most common culprit, a lack of Vitamin D directly impacts the body's ability to absorb calcium and phosphorus from food. Without enough Vitamin D, bones cannot harden properly, leading them to become soft and pliable. Sources include sunlight exposure, fortified foods like milk and cereal, and some fatty fish.
Calcium Deficiency: As a fundamental building block of bone, insufficient calcium intake can lead to softened bones and, consequently, rickets. This can occur due to inadequate dietary intake from sources like dairy products and leafy greens.
Phosphorus Deficiency: Less common than Vitamin D or calcium issues, a deficit in phosphorus can also impede proper bone development. This can be influenced by diet, but also by rare genetic disorders affecting mineral absorption.

Factors Increasing the Risk of Nutritional Deficiencies

Several factors can heighten a child's risk of developing the deficiencies that cause bow leggedness:

Limited Sun Exposure: Children who spend most of their time indoors or live in northern latitudes receive less sunlight, hindering their skin's natural Vitamin D production.
Dietary Restrictions: Vegan or vegetarian diets, as well as lactose intolerance, can reduce intake of vital nutrients like Vitamin D and calcium, unless properly supplemented.
Exclusive Breastfeeding: Breast milk contains limited Vitamin D, so exclusively breastfed infants, especially those with darker skin, need supplements to prevent rickets.
Malabsorption Issues: Certain underlying health conditions like celiac disease, inflammatory bowel disease, or cystic fibrosis can affect nutrient absorption.
Darker Skin Pigmentation: Higher levels of melanin reduce the skin's ability to produce Vitamin D from sunlight, increasing risk.

Other Medical Causes of Bow Leggedness

While nutritional deficiencies are a major cause, particularly in developing countries, other medical conditions can also result in bow leggedness.

Blount's Disease

This growth disorder affects the growth plates of the shin bone (tibia), causing the legs to bow. Unlike physiologic bowing, which corrects itself, Blount's disease worsens over time.

Skeletal Dysplasias

This group of genetic disorders affects bone growth, with conditions like achondroplasia (a form of dwarfism) being a known cause of bow legs.

Chronic Health Conditions

Issues with the liver or kidneys can interfere with the body's metabolism of Vitamin D and phosphorus, leading to a form of rickets even with adequate dietary intake.

The Difference Between Normal and Pathologic Bowing

It's crucial to distinguish between normal, or physiologic, genu varum and pathologic bowing. Most infants are born with bowed legs due to their position in the womb, and the condition naturally corrects itself by the age of 2 or 3. Pathologic bowing, however, persists, worsens, or is asymmetrical, necessitating medical evaluation.

Comparison: Physiologic Bowing vs. Pathologic Genu Varum


Feature	Physiologic Bowing (Normal)	Pathologic Genu Varum (Requires Attention)
Onset	Present at birth or early infancy.	Can develop at any age, often noticed after 2 years old.
Progression	Self-corrects by age 2-4.	Worsens over time or fails to improve.
Symmetry	Symmetrical (affects both legs equally).	Often asymmetrical (one leg may be more bowed).
Pain	Typically painless.	May cause pain, instability, or difficulty walking, especially in older children.
Associated Signs	None, other than the bowing itself.	Widened wrists/ankles, delayed growth, muscle weakness (often seen with rickets).
Underlying Cause	Position in the womb.	Nutritional deficiency (rickets), Blount's disease, or other bone disorders.

Diagnosis, Treatment, and Prevention

For a proper diagnosis, a doctor will conduct a physical exam and may order X-rays to assess bone alignment. Blood tests can also confirm underlying nutritional deficiencies.

Treatment

Nutritional Rickets: In cases of Vitamin D or calcium deficiency, treatment involves supplements and dietary changes. Increased sun exposure may also be recommended.
Blount's Disease: Bracing can be effective in young children with less severe cases. For more advanced or persistent cases, surgery may be necessary to realign the bone.
Other Conditions: Treatment addresses the underlying cause, such as managing kidney or liver disease.

Prevention

Adequate Nutrition: Ensuring sufficient intake of Vitamin D, calcium, and phosphorus through a balanced diet is crucial.
Supplementation: High-risk infants, such as those exclusively breastfed or with darker skin, should receive Vitamin D supplements as recommended by a pediatrician.
Sunlight Exposure: Safe, moderate sun exposure can help the body produce Vitamin D.

Conclusion

In conclusion, the most common deficiency causing bow leggedness is a lack of Vitamin D, calcium, or phosphorus, which results in rickets in children. However, it is vital to remember that not all cases are due to nutritional issues. Conditions like Blount's disease, skeletal dysplasias, and other metabolic problems can also lead to genu varum. While physiologic bowing in infants often resolves on its own, persistent or worsening bowing should be evaluated by a healthcare professional. Early diagnosis and treatment are essential for managing the condition and preventing long-term complications. A balanced diet, appropriate supplementation, and safe sun exposure are key preventative measures against nutritional rickets.

Resources

For more detailed information, the Nemours KidsHealth page on Bow Legs provides comprehensive information on the causes, symptoms, and treatment options for both normal and more serious forms of the condition, including those related to nutrient deficiencies.

Frequently Asked Questions

The primary vitamin deficiency that causes bow leggedness is a lack of Vitamin D, which leads to the bone disease rickets.

Yes, a deficiency in calcium, often linked with Vitamin D deficiency, can also cause rickets, which results in softened bones and bowed legs.

No, it is not always a sign of a deficiency. Many infants are born with physiologic bowed legs due to their position in the womb and will outgrow it naturally by age 2 or 3.

Doctors may order X-rays and blood tests if a child's bowing is severe, asymmetrical, worsening after age 2, or accompanied by other symptoms like pain or growth issues.

Other conditions include Blount's disease, which affects the shin bone's growth plate, skeletal dysplasias, and improperly healed fractures.

The adult equivalent of rickets, also caused by a Vitamin D deficiency, is osteomalacia. While it causes bone pain and weakness, it does not typically lead to bowed legs as adult bones are fully formed.

Bow leggedness caused by a nutritional deficiency is typically treated with Vitamin D and calcium supplements, dietary adjustments, and increased safe sun exposure.

Surgery may be an option for severe cases of bow leggedness, especially those caused by Blount's disease that don't respond to bracing.