Exploring What Deficiency Causes Knock Knees and Bow Legs

October 15, 2025 •

4 min read

According to the Cleveland Clinic, a lack of vitamin D is the most common nutritional cause of rickets, a condition that can lead to bone deformities like knock knees and bowed legs. Understanding what deficiency causes knock knees and bow legs is crucial for addressing bone health issues, particularly during childhood and adolescence.

Quick Summary

The nutritional conditions that cause knock knees and bow legs are primarily vitamin D and calcium deficiencies, which lead to rickets in children. This bone-softening disorder impairs proper bone mineralization and can cause skeletal deformities.

Key Points

Vitamin D Deficiency: The most common nutritional cause of rickets, a bone-softening disease that can lead to knock knees and bow legs in children.
Rickets vs. Osteomalacia: Rickets affects growing bones in children, while osteomalacia is the adult equivalent, causing bone pain and weakness but typically not leg deformities.
Calcium is Key: Vitamin D is necessary for the body to absorb calcium, the primary mineral for building and maintaining strong bones.
Beyond Nutrition: While diet is a major factor, conditions like Blount's disease, skeletal dysplasia, and obesity can also cause leg deformities.
Dietary Prevention: Ensuring adequate intake of Vitamin D and calcium through fortified foods, dairy, leafy greens, and safe sun exposure is crucial for preventing nutritional rickets.
Signs to Watch For: Persistent or worsening leg deformities in children over age three, especially with symptoms like bone pain or muscle weakness, require a medical evaluation.

The Critical Role of Vitamin D and Calcium

Proper bone development and structure are highly dependent on a diet rich in specific vitamins and minerals, most notably vitamin D and calcium. While a balanced diet is important for overall health, deficiencies in these key nutrients can have a profound and lasting impact on the skeleton. Bone is a living, dynamic tissue that undergoes constant remodeling throughout a person's life, and this process relies on a steady supply of nutrients. When this supply is interrupted, especially during formative years, bones can weaken, soften, and fail to mineralize correctly, leading to deformities.

Rickets: The Primary Culprit for Knock Knees and Bow Legs

Rickets is a bone disease in children caused by a severe deficiency of vitamin D, calcium, or phosphate. Vitamin D's primary function related to bone health is to help the body absorb calcium from the intestines. Without enough vitamin D, calcium absorption is compromised, and the body can't deposit enough mineral into the developing cartilage at the ends of growing bones. This results in soft, pliable bones that are unable to support a child's weight, causing them to bend and warp.

The resulting deformities often manifest as either bowed legs (genu varum) or knock knees (genu valgum). In cases of rickets, the bone structure is compromised on both sides, and the legs can appear misaligned. While children under the age of two often experience some degree of natural bowing that corrects itself, a persistent or worsening condition, especially beyond age three, warrants medical attention to rule out rickets. Osteomalacia is the adult form of this bone-softening condition, and while it doesn't typically cause the pronounced deformities seen in children, it results in bone pain and a higher risk of fractures.

Beyond Rickets: Other Factors Affecting Leg Alignment

While nutritional rickets is a significant cause of knock knees and bow legs, other factors can also contribute to these conditions. It is important for a proper diagnosis to differentiate between these and nutritional deficiencies. Some conditions may require different treatment approaches than simple dietary correction.

Non-Nutritional Causes of Bow Legs and Knock Knees:

Blount's disease: A growth disorder of the shinbone (tibia) that causes it to curve outwards. It can affect toddlers and overweight adolescents and often requires bracing or surgery for correction.
Skeletal dysplasias: A group of genetic disorders that cause abnormal bone growth and development.
Obesity: Excess weight places significant stress on the growing knee joints, increasing the risk of deformities.
Trauma or injury: A fracture or injury to the leg can disrupt the growth plate and lead to improper bone alignment.

Nutritional Strategies for Bone Health

To prevent nutritional deficiencies that can lead to rickets and other bone problems, a diet rich in essential nutrients is vital. The following nutrients are crucial for strong, healthy bones:

Vitamin D: Helps the body absorb calcium. Sources include safe sun exposure, fortified milk, cereals, and fatty fish like salmon and mackerel.
Calcium: The primary mineral component of bone. Found in dairy products, green leafy vegetables (like kale), fortified juices, and sardines.
Phosphorus: Works with calcium to build bone mineral. Found in dairy products, meat, and nuts.
Magnesium: Aids in calcium absorption and retention. Rich sources include spinach, nuts, and avocado.
Vitamin K: Important for bone formation and mineralization. Found in leafy greens like spinach and kale.

Comparison of Knock Knees vs. Bow Legs

To better understand the deformities, here is a comparison of their key characteristics:


Feature	Knock Knees (Genu Valgum)	Bow Legs (Genu Varum)
Appearance	Knees curve inward, touching or "knocking" when the feet are apart.	Legs curve outward, with a wide gap between the knees when the ankles are together.
Typical Age	Most common in children aged 3-5 years, often developing after a period of being bow-legged.	Normal for most children aged 18 months to 2 years, often resolving by age 3 or 4.
Underlying Cause	Often part of normal growth, but persistent cases can be due to nutritional rickets, injury, or obesity.	Typically normal developmental stage, but persistent cases may indicate nutritional rickets or Blount's disease.

Conclusion: Nutrition is Key, But So is Medical Oversight

While most cases of mild bow legs and knock knees in young children are a normal part of development that resolves with time, persistent or severe cases can be a clear indicator of an underlying issue, such as nutritional rickets. For this reason, a balanced diet rich in vitamin D, calcium, and other essential nutrients is critical for healthy bone formation. Prevention through a healthy diet and adequate sunlight is the first line of defense. However, if deformities persist or worsen, consulting a healthcare provider is essential for proper diagnosis and a comprehensive treatment plan. With early intervention, many cases of rickets can be effectively managed with dietary changes and supplementation, often reversing the bone deformities over time.

For more detailed information on nutrition and bone health, consult reliable sources like the American Academy of Orthopaedic Surgeons (AAOS): Calcium, Nutrition, and Bone Health.

Frequently Asked Questions

The primary nutritional cause is a deficiency of vitamin D and calcium, which leads to rickets in children. Vitamin D is essential for the body to absorb calcium, which is needed for strong bone mineralization.

Rickets is a bone disease in children that causes soft and weakened bones due to inadequate calcium absorption. Since the bones cannot support the child's weight, they bend and warp, leading to conditions like bowed legs (genu varum) or knock knees (genu valgum).

While adults can develop osteomalacia from a vitamin D deficiency, causing soft bones and pain, it does not typically lead to the leg deformities seen in children because their bones have finished growing.

To prevent rickets, ensure your child gets enough vitamin D from sunlight and fortified foods like milk and cereals, and has sufficient calcium from dairy products or leafy greens. In some cases, supplements may be recommended.

Yes, other causes include Blount's disease (a growth disorder of the shinbone), genetic conditions, obesity, and traumatic injuries to the legs.

Knock knees (genu valgum) is when the knees angle inwards toward each other, while bow legs (genu varum) is when the legs curve outwards, with a gap between the knees. Both can be caused by rickets.

Consult a doctor if a child over age three has persistent or worsening bow legs, if knock knees persist beyond age seven or eight, or if the child experiences pain, limping, or has a deformity on only one side.