# How to Know If You're Vitamin D Deficient (And What to Do About It) Vitamin D is essential for bone health, muscle function, and immune support. Despite its importance, many people worldwide have insufficient vitamin D levels. Symptoms can be subtle or overlap with other health issues, so awareness of causes, signs, and testing options helps with early detection and management. ## What is vitamin D deficiency? Vitamin D deficiency means circulating levels of 25-hydroxyvitamin D are too low to meet physiological needs. This impairs calcium and phosphorus absorption, increasing the risk of weak or brittle bones. In children, severe deficiency can cause rickets; in adults, it can lead to osteomalacia and contribute to osteoporosis. ## Common causes - Limited sun exposure: UVB radiation triggers vitamin D synthesis in skin. People who live at higher latitudes, spend most time indoors, or regularly use sun protection may make less vitamin D. - Diet: Few foods naturally contain vitamin D—fatty fish, egg yolks, and some mushrooms. Many countries fortify milk and cereals, but dietary intake alone may be insufficient. - Malabsorption and medical conditions: Disorders such as celiac disease, Crohn’s disease, and bariatric surgery can reduce vitamin D absorption. - Medications and age: Certain drugs (e.g., anticonvulsants, glucocorticoids) affect vitamin D metabolism. Older adults synthesize vitamin D less efficiently. ## Symptoms to watch for Symptoms are often nonspecific. Common signs include persistent fatigue, muscle weakness, bone pain, and increased susceptibility to infections. In more severe cases, adults may experience diffuse bone pain and difficulty walking; children can show delayed growth and skeletal deformities. ## Health effects beyond bones Low vitamin D primarily affects skeletal integrity and muscle strength, raising fracture and fall risk. Observational studies have associated low vitamin D with higher incidence of some chronic conditions, including cardiovascular disease and insulin resistance, but causality has not been firmly established and research is ongoing. ## How to check your vitamin D status The most reliable test measures serum 25-hydroxyvitamin D. Levels under about 20 ng/mL (50 nmol/L) are commonly considered deficient; some guidelines define sufficiency at higher concentrations. Testing is recommended when symptoms or risk factors are present, or when medical conditions or medications may affect vitamin D levels. ## Managing and preventing deficiency If tests indicate deficiency, supervised supplementation and follow-up testing can restore levels. Safe sun exposure—short periods several times per week—plus dietary sources such as fatty fish and fortified foods can help maintain adequate status. Discuss any supplementation, dose, and monitoring plan with a healthcare professional, particularly if you have chronic conditions or take interacting medications. For practical guidance and a concise overview, see the article [How to Know If You're Vitamin D Deficient (And What to Do About It)](https://www.topvitamine.com/blogs/news/how-to-know-if-you-re-vitamin-d-deficient-and-what-to-do-about-it-topvitamine). Further reading and resources: How to Know If You're Vitamin D Deficient (detailed guide) Related reading on supplements and nutrient context Topvitamine home