Vitamin D deficiency
Also called: low vitamin D, vitamin D insufficiency, vitamin D deficiency risk factors, low vitamin D causes, sun exposure bone health
What it means
Vitamin D deficiency means your body doesn't have enough vitamin D, which is needed to absorb calcium and keep bones strong. It can come from too little sun exposure, certain health conditions, or poor diet.
Without enough vitamin D, your body struggles to absorb calcium, which can weaken bones over time and raise fracture risk.
Vitamin D deficiency happens when your body doesn't have enough of this vitamin to work properly. Vitamin D helps your gut absorb calcium from food, and it supports the hormone signals that keep calcium levels steady in your blood. Your skin makes it when exposed to sunlight, and it's also found in some foods and supplements. As people age, skin becomes less efficient at making vitamin D, and many older adults spend less time outdoors, both of which raise the risk.
When vitamin D stays very low for a long time, bones can't mineralize properly. The bone-building cells still lay down the soft protein framework (osteoid), but without enough vitamin D to help absorb calcium, that framework doesn't harden the way it should. This is different from osteoporosis, where the bone mineral is normal but there's simply less bone overall. Severe, long-standing deficiency in adults is called osteomalacia and can cause diffuse bone pain and muscle weakness; in children it's called rickets.
Low vitamin D is common with limited sun exposure, darker skin, obesity, older age, certain digestive conditions like celiac or Crohn's disease, and malabsorption after bariatric surgery. A simple blood test, the 25-hydroxy vitamin D test, checks your levels, and your doctor can also check parathyroid hormone, calcium, and other markers if a deeper cause needs to be ruled out. A doctor is the right person to decide whether supplementation or further testing makes sense for you.
Low vitamin D blocks calcium absorption, which can weaken bones and raise fracture risk over time.
Where this leads
WordYou just read how deficiency weakens bones. Curious exactly how vitamin D helps your gut absorb calcium in the first place?
Where the Academy teaches it
This page is the short version. The lessons teach it in full, with the context around it and a quiz to lock it in.
Related words
Vitamin D is a nutrient that helps your gut absorb calcium so it can be used to build and maintain bone.
A 25-hydroxy vitamin D test is a blood test that checks how much vitamin D you have in your body, which is important…
Osteomalacia is softening of the bones caused by severe, long-term vitamin D deficiency, which prevents bone from…
Rickets is a childhood bone disease where bones stay soft and weak because of a lack of vitamin D, calcium, or…
Calcium is the main building-block mineral in bone, and since your body can't make it, you need to get it from food…
Celiac disease is an autoimmune condition that damages the small intestine, often reducing absorption of calcium,…
Education only, not medical advice. Decisions about tests, medications and treatment belong with your own doctor. OsteoStrong does not diagnose, treat or cure any disease.
