“Soft bones” is the common way of describing a condition where your bones don’t harden properly. The medical term is osteomalacia in adults and rickets in children. In both cases, new bone tissue forms but fails to mineralize with calcium and phosphorus the way it should, leaving bones that are structurally weak, painful, and prone to fracturing or bending.
How Bones Become Soft
Your body is constantly building new bone tissue, a flexible protein framework called osteoid. Normally, calcium and phosphorus crystals deposit into that framework within about 9 to 20 days, hardening it into solid bone. In osteomalacia, that mineralization process stalls or never completes. The osteoid keeps accumulating without hardening, and the proportion of soft, unmineralized tissue in the bone can climb from a normal level of under 4% to over 10%.
This is fundamentally different from osteoporosis, which is the condition most people think of when they hear about weak bones. In osteoporosis, you lose bone mass overall, but the bone you still have is properly mineralized. In osteomalacia, you may have plenty of bone tissue, but it hasn’t hardened. The distinction matters because the two conditions require completely different treatments, and misdiagnosing soft bones as osteoporosis can actually make things worse.
What Causes It
The most common cause by far is vitamin D deficiency. Vitamin D is essential for absorbing calcium from your gut. Without enough of it, your body can’t supply the minerals your bones need to harden. Blood levels of vitamin D below 12 ng/mL are associated with osteomalacia in adults and rickets in children. Levels below 20 ng/mL are considered deficient.
Vitamin D deficiency itself can happen for several reasons. Limited sun exposure is one, since your skin produces vitamin D when exposed to ultraviolet light. Aging reduces that production. But the most common internal cause is malabsorption, where your digestive system can’t properly absorb vitamin D from food. Celiac disease is the leading culprit, followed by conditions like gastric bypass surgery, Crohn’s disease, pancreatic insufficiency, and liver disease.
Less commonly, soft bones result from problems with phosphorus rather than vitamin D. Certain kidney disorders cause your body to flush phosphorus out through urine faster than it can be replaced. Some medications can also interfere directly with the mineralization process. And in rare cases, a person may get adequate vitamin D but have a genetic condition that prevents their body from using it.
Symptoms in Adults
The hallmark of osteomalacia is a deep, aching bone pain that tends to settle in the lower back, pelvis, hips, and legs. It gets worse with activity and weight-bearing, which distinguishes it from joint pain or arthritis that may feel worst in the morning. The pain is often widespread and can be hard to pin down to one spot.
Muscle weakness is the other major symptom, particularly in the thighs and upper arms. You might notice difficulty climbing stairs, getting up from a chair, or walking without a waddling gait. This weakness increases the risk of falls, which is especially dangerous because osteomalacia also makes bones more likely to fracture. Some people experience fractures from minor impacts that wouldn’t normally cause injury, and this is sometimes the first sign that leads to a diagnosis.
How Rickets Looks in Children
In children, the consequences are more visible because bones are still growing. The growth plates at the ends of long bones are particularly affected, which can lead to a range of skeletal deformities. Swollen wrists and ankles are common early signs. As a child begins walking, the legs may bow outward or angle inward at the knees because the softened bones bend under body weight.
Other signs include a prominent forehead (called frontal bossing), which can appear as early as six months of age, delayed tooth eruption, and a distinctive bumpy pattern along the ribcage where cartilage meets bone, sometimes called a “rachitic rosary.” Children with rickets often have poor overall growth and end up with disproportionately short limbs relative to their torso. They also fracture more easily than healthy children and may have low muscle tone.
How Soft Bones Are Diagnosed
A blood test is usually the starting point. Your doctor will check your vitamin D level, along with calcium, phosphorus, and a marker of bone turnover called alkaline phosphatase, which tends to be elevated when mineralization is impaired. X-rays can reveal characteristic signs: bones may appear washed out or show partial fracture lines called pseudofractures, which are bands of unmineralized osteoid that look like cracks even though no actual break has occurred. These pseudofractures are a strong indicator of osteomalacia.
In ambiguous cases, a bone biopsy provides the definitive answer. A small sample of bone is examined under a microscope to measure how much unmineralized osteoid is present and how long mineralization is taking. This is rare in practice, though, because blood tests and imaging are usually enough.
Treatment and Recovery
When vitamin D deficiency is the cause, treatment is straightforward: high-dose vitamin D supplementation, often combined with calcium. The specific dose depends on how severe the deficiency is and whether malabsorption is involved. People with digestive conditions that block absorption may need higher doses or forms of vitamin D that bypass the gut.
Bone pain typically starts improving within weeks of starting supplementation, though full remineralization of the skeleton takes longer. Muscle weakness also gradually resolves. For children with rickets, correcting the deficiency early enough allows the growth plates to resume normal function, and mild bowing of the legs can straighten out over time as new, properly mineralized bone replaces the soft tissue.
When the cause is phosphorus wasting from a kidney disorder or a genetic condition, treatment is more complex and focuses on replacing phosphorus and addressing the underlying problem. These cases are less common but require specialist management.
Preventing Soft Bones
For most people, prevention comes down to maintaining adequate vitamin D and calcium intake. Adults up to age 70 need 600 IU of vitamin D daily, and those over 70 need 800 IU. Calcium needs range from 1,000 to 1,200 mg per day depending on age and sex. Fatty fish, fortified milk, and egg yolks are dietary sources of vitamin D, though it’s difficult to get enough from food alone if you have limited sun exposure.
People at higher risk include those who cover most of their skin, live at northern latitudes, have darker skin (which reduces UV-driven vitamin D production), or have any condition affecting nutrient absorption. If you fall into one of these groups, periodic blood testing of your vitamin D level is a simple way to catch a deficiency before it affects your bones.