The three major bone diseases are osteoporosis, osteomalacia (called rickets in children), and Paget’s disease of bone. Each one disrupts bone in a different way: osteoporosis thins it, osteomalacia softens it, and Paget’s disease deforms it. Together, these conditions affect tens of millions of people and account for the vast majority of non-cancer-related bone problems worldwide.
Osteoporosis: Thinning, Fragile Bones
Osteoporosis is by far the most common of the three. In the United States alone, roughly 10 million people over age 50 have it, and another 43 million have low bone mass that puts them on the path toward it. Most of those affected are women, though about 2 million men also carry the diagnosis.
Healthy bone is constantly being recycled. Specialized cells break down old bone while other cells build new bone in its place. Osteoporosis develops when the breakdown side of this cycle outpaces the rebuilding side. Over time, bones lose density and develop a porous, honeycomb-like internal structure that fractures far more easily than normal bone. A stumble that would bruise a healthy person can snap the hip or wrist of someone with advanced osteoporosis.
The disease is diagnosed with a bone density scan, which produces a number called a T-score. A score of negative 1 or higher is normal. Between negative 1 and negative 2.5 indicates osteopenia, a milder form of bone loss. A score at or below negative 2.5 points to osteoporosis. There are no symptoms in the early stages, which is why many people don’t find out until they break a bone or lose noticeable height from compressed vertebrae.
Hip fractures are the most dangerous consequence. One-year mortality after a hip fracture ranges between 17% and 25%, and survivors face a three- to four-fold higher risk of death compared to peers of the same age who haven’t fractured. Those numbers have improved over the decades, dropping from around 27% in the 1960s to about 20% by the 2010s, but the risk remains serious.
Who Is Most at Risk
Postmenopausal women face the highest risk because the drop in estrogen accelerates bone loss. Other risk factors include a small body frame, family history of fractures, smoking, excessive alcohol use, low calcium intake, and long-term use of corticosteroid medications. Men over 70 are also at significant risk, though the condition is often underdiagnosed in men.
Osteomalacia and Rickets: Soft, Poorly Mineralized Bones
Osteomalacia literally means “soft bone.” While osteoporosis involves losing bone tissue altogether, osteomalacia is a mineralization problem. The body builds new bone normally, but it fails to harden that bone with enough calcium and phosphate. The result is a skeleton that bends and aches under everyday stress. When this same process happens in children whose bones are still growing, it’s called rickets.
The most common cause is vitamin D deficiency. Vitamin D is essential for absorbing calcium from food. Without enough of it, even a calcium-rich diet won’t supply the minerals your bones need. People who get very little sun exposure, have darker skin (which produces less vitamin D from sunlight), live at northern latitudes, or have digestive conditions that interfere with nutrient absorption are all at higher risk. Certain kidney and liver disorders can also block the body’s ability to activate vitamin D.
Symptoms of osteomalacia include widespread bone pain, particularly in the hips, legs, and lower back, along with muscle weakness that can make it hard to climb stairs or get up from a chair. In children with rickets, the softened bones can produce visible deformities: bowed legs, a protruding breastbone, thickened wrists and ankles, and delayed growth. Adults don’t typically develop visible deformities, but they do fracture more easily.
The key distinction from osteoporosis matters for treatment. Osteoporosis requires medications that slow bone breakdown or stimulate new bone growth. Osteomalacia often improves significantly with vitamin D and calcium supplementation alone, because the underlying bone structure is intact. It just needs the raw materials to mineralize properly.
Paget’s Disease: Enlarged, Misshapen Bones
Paget’s disease of bone is a disorder of bone recycling where the body breaks down and rebuilds bone far too quickly. The replacement bone forms incorrectly, producing larger bones that are misshapen, weaker, and softer than they should be. It most commonly affects the pelvis, spine, skull, and leg bones, and it tends to appear after age 50.
Many people with Paget’s disease have no symptoms at all. The condition is often discovered incidentally when a blood test reveals an elevated level of alkaline phosphatase, an enzyme that spikes when bone turnover is abnormally high. In one documented case, a 65-year-old man had an alkaline phosphatase level nearly three times the upper limit of normal before any symptoms appeared. X-rays and bone scans then confirm the diagnosis by showing characteristic thickening and deformity of the affected bones.
When symptoms do develop, bone pain is the most common complaint and is frequently mistaken for arthritis. As the disease progresses, it can cause visible changes depending on which bones are involved. An enlarged skull may lead to headaches and hearing loss if the growing bone compresses nerves. A bowed tibia or femur can change the way you walk. Spinal curvature can develop if vertebrae are affected. Joints near the abnormal bone often develop arthritis from the altered mechanical stress.
People with mild disease and only slightly elevated enzyme levels can often be monitored with yearly blood tests and no active treatment. When treatment is needed, medications that slow bone breakdown are the standard approach, and they work well for both Paget’s disease and osteoporosis since both conditions involve excessive bone resorption.
How These Diseases Differ at the Bone Level
A useful way to remember the three diseases is by what goes wrong in each one. Osteoporosis is a quantity problem: you lose too much bone and don’t build enough back. Osteomalacia is a quality problem: you build enough bone, but it doesn’t harden properly. Paget’s disease is a remodeling problem: bone is recycled too fast and the replacement bone is structurally abnormal.
These distinctions matter because they lead to different symptoms and different treatments. Someone with osteoporosis may feel perfectly fine until a fracture occurs. Someone with osteomalacia typically has chronic aching pain and muscle weakness. Someone with Paget’s disease may notice that a limb is changing shape or that their hat size is increasing.
Protecting Your Bones
Calcium and vitamin D are the foundation of bone health for all three conditions. Adults aged 19 to 50 need about 1,000 mg of calcium and 600 IU of vitamin D daily. Women over 50 and anyone over 70 need more: 1,200 mg of calcium, and 800 IU of vitamin D after age 70. These nutrients come from dairy products, fortified foods, fatty fish, egg yolks, and sunlight exposure.
Weight-bearing exercise, including walking, jogging, dancing, and resistance training, stimulates bone-building cells and helps maintain density throughout life. Avoiding smoking and limiting alcohol also reduce bone loss. For people already diagnosed with one of these conditions, the specifics of treatment vary, but the nutritional and lifestyle basics remain the same across all three.
Osteogenesis Imperfecta: A Notable Fourth Condition
While not always grouped with the “big three” metabolic bone diseases, osteogenesis imperfecta (commonly called brittle bone disease) deserves mention because it’s the most well-known genetic bone disorder. It’s caused by mutations in the genes responsible for producing collagen, the protein that gives bone its flexibility and strength. These mutations account for about 90% of all cases.
At least 19 types have been identified, ranging from mild to fatal. The mildest form (type I) causes bones that break more easily than normal, mostly before puberty, along with loose joints and a blue or purple tint to the whites of the eyes. The most severe form (type II) is lethal around the time of birth due to underdeveloped lungs and extreme skeletal fragility. Types III and IV fall between these extremes, with progressive bone deformity, short stature, curved spines, and barrel-shaped rib cages among the more visible features.
Unlike osteoporosis, osteomalacia, and Paget’s disease, osteogenesis imperfecta is present from birth and cannot be prevented through diet or lifestyle. Treatment focuses on strengthening existing bone, preventing fractures, and managing symptoms throughout life.