Anorexia nervosa can cause joint pain through several distinct pathways, from weakened bones and stress fractures to hormonal disruption, muscle wasting, and even an elevated risk of autoimmune arthritis. The connection is not as simple as “starving makes your joints hurt,” though. Some of the mechanisms are direct consequences of malnutrition, while others involve the immune system behaving in ways researchers are still working to understand. The result is that joint and bone pain are surprisingly common complaints among people with anorexia, and the underlying cause is not always obvious even to clinicians.
How Starvation Damages Bones
The most studied skeletal consequence of anorexia nervosa is bone loss. Prolonged caloric restriction starves the skeleton of the raw materials it needs to maintain itself, and the hormonal chaos that follows starvation accelerates the damage. A review of skeletal complications in eating disorders found that bone health is impacted by starvation and can be permanently impaired over the course of the illness.1Europe PMC. Skeletal complications of eating disorders That word “permanently” matters: unlike many of the body’s tissues, bone lost during severe malnutrition does not always fully recover, even after weight restoration.
Low bone mineral density is one of the most concerning complications because it changes the internal architecture of bone and makes fractures more likely.2PubMed Central. Endocrine consequences of anorexia nervosa For someone with anorexia, this can mean that everyday activities start producing pain in weight-bearing joints like the hips, knees, and feet, not because the joint itself is diseased but because the bone underneath is failing.
The Hormonal Chain Reaction
Bone loss in anorexia is not just about missing calories. The body’s hormonal system goes haywire in response to chronic starvation, and several of those hormonal shifts directly attack bone tissue. The hypothalamic-pituitary axis becomes dysfunctional, leading to low estrogen and androgen levels, growth hormone resistance, and elevated cortisol. Most of these changes reverse with weight recovery, but many contribute to impaired skeletal integrity while they persist.3Nature Reviews Endocrinology. The endocrine manifestations of anorexia nervosa: mechanisms and management
Cortisol deserves special attention here. In anorexia, cortisol levels run higher than in healthy people because the body clears cortisol more slowly and its half-life increases. That chronic excess damages bone from multiple directions at once: it reduces calcium absorption from food, suppresses the cells that build new bone, decreases the production of growth factors within bone tissue, and may increase bone breakdown by interfering with reproductive hormone signaling.4Endocrine Reviews. Effects of Anorexia Nervosa on Bone Metabolism This is essentially the same mechanism by which long-term steroid medications cause bone loss, except in anorexia the cortisol is the body’s own.
Estrogen deficiency adds another layer. When the body stops menstruating due to energy deficit, estrogen drops to levels similar to menopause. Estrogen normally acts as a brake on bone resorption, so losing that brake means bone is broken down faster than it can be rebuilt. For young women and adolescents, this is especially damaging because it occurs during the years when the skeleton should be reaching its peak density.
Vitamin D Deficiency and Bone Pain
Beyond the hormonal picture, severe nutritional deficiencies can produce their own brand of skeletal pain. Vitamin D deficiency is common in anorexia because of poor dietary intake, limited sun exposure, and impaired absorption of fat-soluble vitamins from a damaged gut. When vitamin D falls low enough, the result is osteomalacia, a condition in which bones soften because they cannot properly mineralize.
A case report illustrates how severe this can get: a 48-year-old woman with a nine-year history of anorexia was admitted with generalized bone pain. Her blood showed extremely low calcium, and imaging revealed multiple rib fractures. Her vitamin D level was below the detectable limit. Researchers noted that poor nutrition, lack of sunlight, intestinal malabsorption, and kidney phosphate loss all likely contributed.5PubMed Central. Vitamin D Deficiency-induced Osteomalacia in a Patient with Anorexia Nervosa The pain of osteomalacia often feels like a deep, diffuse ache in the bones and joints, and it can be mistaken for arthritis or fibromyalgia until bloodwork reveals the underlying deficiency.
Muscle Wasting Leaves Joints Unprotected
Muscles are not just for movement. They act as shock absorbers and stabilizers for the joints they cross. When anorexia strips away muscle mass, the joints lose that protective support. Starvation causes atrophy of muscle fibers, and work capacity declines dramatically. In semi-starvation experiments, work capacity in men dropped by about 70%, and in women with anorexia it fell by roughly 50%.6Europe PMC. Might Starvation-Induced Adaptations in Muscle Mass, Muscle Morphology and Muscle Function Contribute to the Increased Urge for Movement and to Spontaneous Physical Activity in Anorexia Nervosa?
Weak muscles mean that the force of walking, climbing stairs, or even standing shifts disproportionately onto cartilage, tendons, and ligaments. Over time this can produce pain in the knees, ankles, and hips that feels like a joint problem but is really a consequence of inadequate muscular support. It also makes the joints more vulnerable to injury during exercise, which is relevant because compulsive exercise is common in anorexia.
Stress Fractures That Masquerade as Joint Pain
One of the trickiest diagnostic challenges in anorexia is the stress fracture. These are tiny cracks in weakened bone caused by repetitive, ordinary forces like walking or light running. In someone with healthy bones, these forces are harmless. In someone with the bone density of a much older person, they can cause fractures that standard X-rays often miss entirely.
A case series described four women with anorexia, aged 22 to 34, who presented with skeletal pain and had X-rays that showed nothing abnormal. Their stress fractures were eventually identified only through bone scans.7PubMed. Osteoporotic stress fractures in anorexia nervosa: etiology, diagnosis, and review of four cases Another report described a patient with previously undiagnosed anorexia who first presented with foot pain that turned out to be a stress fracture, making it the initial sign of the eating disorder.8PubMed. Marrow changes in anorexia nervosa masking the presence of stress fractures on MR imaging
These cases matter because the pain from a stress fracture in the foot, shin, or hip feels a lot like joint pain to the person experiencing it. If a clinician is not thinking about anorexia as a risk factor for fragility fractures in a young person, the diagnosis can be delayed or missed. The bone marrow changes that occur in severe malnutrition can also alter how the fractures appear on MRI, further complicating imaging interpretation.8PubMed. Marrow changes in anorexia nervosa masking the presence of stress fractures on MR imaging
An Unexpected Inflammation Profile
Here is where the picture gets counterintuitive. You might expect that someone who is severely underweight and malnourished would have a suppressed immune system across the board. But research shows that certain inflammatory markers are actually elevated in anorexia. A meta-analysis found that people with anorexia had significantly higher levels of TNF-alpha, IL-1 beta, and IL-6 compared to healthy controls, while C-reactive protein was actually lower.9PubMed. Inflammatory cytokines and anorexia nervosa: A meta-analysis of cross-sectional and longitudinal studies
This profile is unusual. TNF-alpha, IL-1 beta, and IL-6 are the same inflammatory molecules that drive joint pain and damage in conditions like rheumatoid arthritis. Their elevation in anorexia suggests that chronic starvation triggers a low-grade inflammatory state, even in the absence of an infection or obvious autoimmune disease. Whether this inflammation directly causes joint pain in people with anorexia has not been definitively proven, but the biological plausibility is strong: these are molecules known to sensitize pain receptors and promote tissue breakdown in joints.
Eating Disorders and the Risk of Rheumatoid Arthritis
Beyond the indirect effects on bones and inflammation, there is emerging evidence that eating disorders may increase the risk of developing actual autoimmune arthritis. A large prospective study followed participants over a median of 12.5 years and found that individuals with a history of eating disorders had a 76% higher risk of developing rheumatoid arthritis compared to those without, even after adjusting for demographics, lifestyle, and genetic predisposition to RA.10PubMed. A prospective study of eating disorders and risk of rheumatoid arthritis
This finding is relatively new and should be interpreted with some caution as a single study, but it fits into a broader pattern. Research into the relationship between anorexia and autoimmune diseases points to a bidirectional connection built on shared immune dysfunction, including disrupted immune cell tolerance and the production of autoantibodies.11PubMed Central. Anorexia nervosa and autoimmune comorbidities: A bidirectional route? In other words, the same immune system disturbances that may predispose someone to an eating disorder could also predispose them to autoimmune conditions, and the malnutrition itself may further push the immune system toward self-attack.
The gut microbiome may be one link in this chain. Researchers have observed that patients with anorexia have a different composition of gut bacteria compared to healthy controls, with higher counts of certain bacteria and lower counts of others. One hypothesis is that these abnormal gut bacteria produce molecules that cross-react with the body’s own tissues, triggering autoantibodies that could contribute to autoimmune disease.12Central European Journal of Immunology. Anorexia nervosa and juvenile lupus erythematosus in a 16-year-old female patient – common disease origin or random coincidence? This is still at the hypothesis stage, but it offers a plausible biological route from starvation to joint inflammation.
Joint Hypermobility and Eating Disorders
An entirely separate source of joint pain in eating disorder populations involves joint hypermobility, where joints bend further than normal. A study comparing hypermobile and non-hypermobile eating disorder patients found that joint pain was reported by about 57% of the hypermobile group compared to 25% of the non-hypermobile group.13PubMed Central. Joint Hypermobility and Clinical Correlates in a Group of Patients With Eating Disorders
This overlap is not coincidental. Hypermobility syndromes and eating disorders appear to co-occur at rates higher than chance would predict, though the reasons are debated. One possibility is that both conditions share some connective tissue vulnerability. Another is that the gastrointestinal symptoms common in hypermobility syndromes, like early satiety and nausea, can mimic or trigger restrictive eating patterns. Whatever the mechanism, if you have an eating disorder and unusually flexible joints, the joint pain you experience may have roots in both conditions simultaneously, which complicates treatment.
Bone Marrow Changes and Diagnostic Confusion
Severe malnutrition can alter the bone marrow itself in ways that cause pain and confuse imaging. Gelatinous transformation of bone marrow is a condition where the fat cells in marrow atrophy and are replaced by a gel-like substance. A case report described a 20-year-old man with anorexia who developed heel pain without any trauma. His bone biopsy revealed this gelatinous transformation, and the condition resolved with nutritional rehabilitation. After six months of nutritional support, his blood counts normalized and the heel pain disappeared.14PubMed Central. Gelatinous Transformation of Bone Marrow in the Calcaneus, Diagnosed by Open Bone Biopsy in a Patient With Anorexia Nervosa: A Case Report
A related problem is that the unusual MRI appearance of malnourished bone marrow, sometimes called serous atrophy, can be misread by radiologists who are not expecting it. The signal changes can look like a tumor or infection, leading to unnecessary further imaging and biopsies. A review of imaging findings emphasized that it is important to differentiate these marrow changes from malignancy and technical artifacts.15Europe PMC. Recognising serous atrophy of bone marrow: a review of imaging findings For a patient with anorexia who is already anxious about medical procedures, unnecessary invasive workups can be deeply distressing.
Why Young People Are Especially Vulnerable
Anorexia most commonly develops during adolescence and young adulthood, which is precisely when the skeleton is supposed to be building its lifetime reserves of bone density. Peak bone mass is usually reached by the mid-to-late twenties, and the bone accumulated during those years serves as a kind of savings account that the body draws from for the rest of life. When anorexia interrupts this process, the person may never fully catch up, even after recovery.1Europe PMC. Skeletal complications of eating disorders
This means a person who had anorexia as a teenager may enter their thirties or forties with the bone density of someone decades older. Joint and bone pain that would not normally appear until much later in life can show up early, and the risk of fractures remains elevated long after the eating disorder itself has been treated. This is one of the strongest arguments for early and aggressive nutritional rehabilitation in young patients: the skeletal window does not stay open forever.
Safe Movement During and After Recovery
Exercise is a fraught topic in anorexia treatment because compulsive exercise is often part of the disorder itself, yet physical deconditioning during illness creates real musculoskeletal problems that benefit from rehabilitation. A systematic review of physical therapy interventions in anorexia found that supervised exercise programs could increase muscle strength and cardiovascular fitness. Muscle strength improved after structured training programs lasting two to three months, and supervised physical therapy was associated with improvements in overall physical condition.16PMC (Int J Environ Res Public Health). Physical Therapy Interventions in Patients with Anorexia Nervosa: A Systematic Review
The key word is “supervised.” Given the fragility of bones, the weakness of muscles, and the risk of stress fractures, unsupervised high-impact exercise in someone with active or recent anorexia can do more harm than good. Low-impact strength training under professional guidance rebuilds the muscular support system around joints while minimizing fracture risk. For anyone recovering from anorexia who is experiencing joint pain, a referral to a physical therapist familiar with eating disorders is more useful than a generic exercise prescription. The goal is rebuilding the body’s capacity to protect its own joints, which takes patience and the kind of graduated loading that accounts for bones that may not yet be ready for heavy demands.