Nutrition
Vitamin D, calcium, K2, protein — and the claims that do not hold.
6 guides · updated 4 Oct 2026 · every claim sourced
Calcium
How much calcium adults need, food first versus supplements, what calcium does and does not do for bones and back pain, and the risks of taking too much.
2 min read · Moderate evidenceConditionMagnesium
Magnesium matters for muscles and bone, but evidence for supplements in back pain is thin. How much adults need, best food sources, and safe supplement limits.
2 min read · Limited evidenceConditionVitamin D
Correcting a deficiency is justified. Taking vitamin D as a painkiller, with normal levels, is not supported by the pooled trials.
2 min read · Moderate evidenceMore in Nutrition
Vitamin K2
Vitamin K2 helps activate proteins that build bone. How much vitamin K you need, what trials show for bone health, and the warfarin warning.
2 min readHow-toSupplement safety
More is not better with supplements. Upper limits for calcium and magnesium, what high vitamin D doses did in trials, and warfarin interactions.
2 min readMythGlucosamine and chondroitin
Glucosamine is often taken for back and joint pain. A JAMA trial in chronic low back pain found no benefit over placebo. What to try instead.
2 min readAbout this topic
Vitamins and supplements are widely sold for bones, joints and backs. This section checks them against the evidence: vitamin D, calcium, vitamin K2, magnesium, glucosamine and more. It explains how much of each nutrient adults need, which foods provide it, what trials show for bone health and back pain, and where supplements can cause harm, from kidney stones to interactions with warfarin. The short version: correcting a deficiency matters, calcium and vitamin D help people at high fracture risk, and no supplement has good evidence for treating common back pain.
- Strong consistent results from trials and reviews
- Moderate good studies, some gaps
- Limited few or small studies
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Guides we are writing for this topic.