Protect bones and joints

That 35g went to ten men on one occasion, with no long-term follow-up. All ten were men, so nothing here speaks to anyone else. And no formal ceiling means nobody has set one, which is not the same as evidence that any dose is safe indefinitely.

This is a strong recommendation resting on an absence of benefit rather than on demonstrated harm, and the guideline notes glucosamine's toxicity is low. It hardened from a conditional recommendation against glucosamine in 2012, so a reader may still meet the older advice. The search closed in 2018.

None was designed to detect rare harm, and the participants were people with knee osteoarthritis, not the general population. The chondroitin review's finding of fewer serious events on treatment than on placebo more likely reflects sparse, inconsistently reported data than a real effect.

The 0.9 cm threshold is these authors' own choice rather than an agreed one, and a reader accepting a smaller threshold would read some of these intervals differently. Restricting by trial size excludes most of the older positive literature, so this is not the body of trials other reviews pool.

A placebo response of six in ten leaves very little room for a supplement to show a difference, and every arm could take up to 4,000 mg of paracetamol a day as rescue, narrowing the gaps further. The trial used glucosamine hydrochloride, not the sulfate salt sold in Europe as a medicine.

This is a continuation in the participants who met stricter X-ray criteria, not a fresh randomisation, so it carries the parent trial's high placebo response with it. Two years of dropout leaves less power, not more. The authors call the trends beneficial but not significant, which describes a null.

The result is fragile: its interval reaches to 0.002 mm, its p value is 0.046, and it survives only after adjustment for sex, weight and baseline severity. It is one of several comparisons, so a multiple-testing correction would likely remove it. Whether a tenth of a millimetre is felt is untested.

The subgroup was one of two specified in advance, but was never powered as a test of its own and no independent trial has repeated it. The Spanish trial is small, at 164 people, and its placebo group's larger improvement appears only when everyone randomised is counted, vanishing among completers.

Risk of bias was the second-largest explanation, cutting the disagreement by a further 32%, so brand and how well a trial was run stay entangled. The shrunken estimate rests on three trials, and even after both factors the trials still disagree substantially. Pain only, nothing on joint structure.

Which preparation a trial used and how rigorously it was designed cannot be separated either: the older, weaker trials are also that manufacturer's. On the standard osteoarthritis questionnaire, pain, function and stiffness reached significance for neither preparation. Its search closed in 2005.

Manufacturer involvement, the salt used and whether allocation was concealed are almost perfectly entangled here, so this cannot say which explains the gap. These are comparisons across trials, not a randomised contrast, so sponsorship is associated with the result, not shown to cause it.

All five datasets shared were independently funded, so the form distinction is tested only inside independent trials, and no dataset from the manufacturer whose product the argument is about was contributed. In the published record, form, sponsorship and concealment cannot be separated.

The five contributed trials still cover 55% of everyone ever randomised in a published placebo-controlled glucosamine trial, so the gap is in which trials are represented, not in people. Because no manufacturer-sponsored dataset arrived, the reanalysis cannot answer those trials on their own data.

A guideline grades other people's evidence rather than producing any, and most of its positions are worded as suggestions, which is how low certainty gets expressed. It sets aside anyone with an established medical reason to be tested or treated, so it speaks only about people without one. Two corrections to it were published in 2025 and its paediatric advice has drawn published rebuttals.

The outcome in both studies is a blood level; neither measured whether anyone felt or functioned better. The 87 percent figure comes from 33 people on a single-blind protocol at a weekly dose, which makes it a statement about that regimen rather than about a daily D3 tablet against a daily D2 one. The pooled comparison searched the literature only to July 2011.

Nobody was recruited for having low vitamin D, low bone mass or osteoporosis, which is exactly the group the supplement is normally prescribed to. Fractures were reported by participants once a year and then checked against medical records. Hip fractures were few enough that their estimate spans a 30 percent reduction to a 47 percent increase.

Both trials gave very large intermittent doses, so nothing here suggests a daily tablet carries the same risk. The falls trial enrolled 200 people and had no placebo group, comparing one dose against another rather than against nothing. The annual-dose trial's fracture interval starts at exactly no effect, and its explanation for the timing, a spike in blood levels just after each dose, is a hypothesis it raises rather than one it tests.

The over-75 recommendation rests on a very small reduction in deaths, graded as high certainty but never translated into a number of lives. Most of the guideline's positions are worded as suggestions rather than recommendations, the wording used when certainty is low. The trials behind it used widely varying doses and often let participants keep taking their own vitamin D, so the right dose is left unresolved.

The joint trial tested one branded product, and two of its authors work for the manufacturer and for the contract firm that ran it, so an independent repeat is still missing. Several outcomes in the largest synthesis, skin roughness among them, came out flat.

Finding the fragment in blood shows it survives digestion; it does not show it did anything afterwards. The signalling step rests on animal and cell-dish work rather than on the human trials the reviews cover. That headline pools 113 trials through 16 earlier reviews, so its precision is theirs rather than its own, and several outcomes within it, including skin roughness and two joint sub-scores, came out flat. The peptide work came from a research institute owned by a collagen manufacturer.

These are absorption curves for a few marker fragments, not a clearance time for the ingredient as a whole. Collagen from different animal sources may behave differently. And finding the tough fragment in blood shows it lasts, not that it does anything while it is there.

Milder knees showed a trend toward benefit with no significance test attached to it, so it is not a result and should not be reported as one. The trial used glucosamine hydrochloride rather than the sulfate salt, which is one of the two ways it differs from the three-year trials reporting a benefit.

This is one manufacturer's label, so its choices are evidence about this product rather than about US labelling rules in general. The document also disagrees with itself: the index title says tablet where the Drug Facts panel and carton say capsule, and three different effective dates appear in it.

Three in ten had knee pain without X-ray-confirmed osteoarthritis, so this is not purely a trial in established disease. Twenty-four weeks is short for a structural endpoint when the trials reporting benefit ran three years. It used a hydrochloride drink, which sulfate proponents reject.

Fifteen people and a single dose cannot rule out rare reactions, and the authors limit their conclusion to the manufacturers' products they tested rather than to glucosamine in general. Nothing here tests a poorly purified product or daily use. Chondroitin comes from cattle or shark cartilage.

Opioids showed a similar association, at 1.69, with no proposed bone-healing mechanism at all, which points at more painful or more severe fractures attracting stronger prescriptions rather than at the drugs themselves. Prescriptions filled stand in for drugs actually swallowed, and anything bought over the counter is invisible, which weakens the non-selective comparison specifically. Nonunion was rare, following 0.9% of episodes, so these odds sit on small absolute numbers.

Bone turnover chemistry is a surrogate: it is neither bone density nor fracture. The temptation is to lead with pyridinoline at 12 percent lower, and its interval runs from 25 percent lower to 1 percent higher. Doses across the pooled trials ranged nearly tenfold, from 30.9 to 300 mg a day.

These are standing pharmacological facts from a clinical reference chapter rather than findings from a trial. The chapter does not say how long supplementation takes to raise a level, or the dose at which toxicity begins. Nothing in it settles what level to aim for, which is a separate and open question.

This is a snapshot of two existing groups at one research unit, so it shows which mathematical curve fits best rather than testing the mechanism directly. Ruling out fat trapping the vitamin rests on that better fit, which is suggestive rather than conclusive. The advice to scale a dose by body weight follows from the model and was not itself tested here.

The 10-percentage-point figure usually quoted from it is the one it rates low quality, with high bias risk and heavy disagreement. The benefit became uncertain whenever the analysis narrowed to trials that concealed allocation properly, to large trials, or to independently funded ones.

Chondroitin's knee-pain benefit is small, and whether it is worth having is unsettled. The largest trials put it below the smallest change a patient would notice, while Cochrane counts six people in a hundred helped.

This is diet recall at a single point in time, so daily cola drinkers may differ from occasional ones in ways nobody recorded, including what they were drinking instead. The difference showed at the hip and not the spine. Daily cola drinkers were not taking in more phosphorus overall, which makes phosphoric acid the authors' inference rather than something they measured.

The bar for counting as no worse was 40 points on a 0-to-500 pain scale, which is wide. The pair used glucosamine hydrochloride, the salt an earlier analysis concluded was ineffective, which makes matching a prescription drug harder to square with the rest of this literature rather than easier.

This review does not separate trials by manufacturer, by funder, or by how well allocation was concealed, the three things earlier analyses of this literature found decide the answer. Its combination conclusion rests on three trials. It reports direction and significance, no effect sizes.

Whether chondroitin and glucosamine ease pain turns on method, not data. Analyses splitting trials by funder, brand and trial quality find no difference a patient would notice; the review finding a benefit did not split them.

People who choose supplements differ from people who do not in ways no adjustment removes, and a modest reduction turning up in every outcome at once is what that difference usually produces. Preparation and amount went unrecorded. No randomised trial has tested glucosamine against heart outcomes.

The reviewers work for a consultancy that carries out safety assessments for industry clients, and the paper names no client. In the same passage where they set aside the studies reporting a glucose effect, they acknowledge that no long-term trial exists in people with pre-diabetes.

A one-dose glucose challenge and months of resting glucose measure different things, so both results can stand. What neither covers is years of glucosamine in someone who is already glucose intolerant.

The two arms' confidence intervals overlap substantially, so the striking loss-versus-no-loss framing compares each arm against zero rather than against the other. Around 200 people is small for a three-year X-ray endpoint. Both sit in the stratum later analyses found produces larger effects.

Every trial measuring joint structure independently of the manufacturer found nothing, but those ran shorter and used another salt. Nobody has repeated the three-year sulfate trial without its manufacturer.

The abstract gives p values and directions but no effect sizes, so how much bone was saved cannot be stated. Whole-body density is the weakest endpoint measured, and the sites where people actually fracture were null. The 80 mg arm showed nothing, so two doses do not make a dose-response.

This is a snapshot of blood levels taken in 2005 and 2006, so it shows who sits below a line and never what being below it does to them. Race here stands in for skin pigmentation, sun exposure, diet and income all at once, rather than for anything measured biologically. Black Americans measure lowest without correspondingly worse bone density or fracture rates, which is the part the number does not explain.

The 20 nanogram figure was set as a population planning number covering the needs of nearly everyone, not as a line for diagnosing one person, and the committee that set it has said so in print. The Institute of Medicine derived it from bone health alone, having found the evidence on cancer, heart disease, diabetes and infection too thin to set requirements on. Which number a person is measured against decides whether they are told they have a problem.

Where vitamin D deficiency begins is unsettled: expert lines sit at 30, 20 and 12 nanograms per millilitre. Evidence cannot choose between them, because no trial has tested whether measuring a level and acting on it does anyone good.

Three people identified after the study began is a hypothesis rather than a finding, and the authors hedge their own conclusion accordingly. It was one dose alongside a 75 g glucose load, with no placebo group described. Larger reviews of fasting glucose over months and years find no such effect.