Low levels of vitamin D often produce subtle symptoms that can be mistaken for other conditions. Research led by Michael F. Holick, Boston University School of Medicine, and clinical guidance from the Endocrine Society describe several consistent clinical features that clinicians look for when evaluating possible deficiency. The National Institutes of Health Office of Dietary Supplements and the Mayo Clinic identify overlapping signs rooted in vitamin D’s role in bone metabolism, muscle function, immune regulation, and mood.
Bone and muscle signs
The most characteristic manifestations are related to impaired bone mineralization. People may experience bone pain and diffuse aching, often reported in the lower back, hips, pelvis, and legs. In adults, prolonged deficiency can lead to osteomalacia, a softening of bones that produces persistent discomfort and increases the risk of fractures. Children with severe deficiency can develop rickets, which causes bone deformities and delayed growth. Muscle symptoms include muscle weakness and difficulty rising from a chair or climbing stairs, reflecting vitamin D’s role in muscle strength. These symptoms can be subtle at first and may progress slowly, so they are sometimes attributed to aging or inactivity.Systemic and neuropsychiatric signs
Vitamin D influences immune responses and brain chemistry, so deficiency can present beyond the musculoskeletal system. Chronic fatigue and generalized low energy are commonly reported by patients and noted in clinical reviews. Mood disturbances including depressive symptoms have been associated with low vitamin D levels in observational studies, though causality remains an area of active research. Recurrent upper respiratory infections and slower wound healing are also described, aligning with vitamin D’s modulatory effects on immune cells and inflammation.Causes of deficiency are multifactorial. Reduced ultraviolet B exposure because of high latitude, winter season, heavy air pollution, or extensive skin covering for cultural or occupational reasons lowers cutaneous vitamin D synthesis. Darker skin pigmentation diminishes ultraviolet-driven vitamin D production, making individuals of African, South Asian, or Middle Eastern descent more vulnerable in low-sun environments. Older adults synthesize vitamin D less efficiently and often spend more time indoors. Malabsorption conditions such as celiac disease, inflammatory bowel disease, and certain surgeries that bypass the small intestine impair dietary uptake. Some medications alter vitamin D metabolism and storage.
Consequences of unrecognized deficiency extend beyond immediate symptoms. Chronic insufficiency contributes to bone fragility and higher fracture risk, with public health implications in aging populations. In children, untreated deficiency can impair development and cause lasting skeletal abnormalities. Sociocultural patterns that limit sun exposure interact with territorial and environmental factors to create localized high-risk groups, highlighting health equity concerns.
Diagnosis relies on blood measurement of 25-hydroxyvitamin D and clinical judgment informed by guidance from the Endocrine Society and public health agencies such as the National Institutes of Health Office of Dietary Supplements. Treatment typically includes thoughtful supplementation and addressing underlying causes, with follow-up testing to ensure adequacy. Because many signs overlap with other disorders, medical evaluation is important to confirm deficiency and tailor care to the individual’s cultural and environmental context.