What vitamin are you lacking if your joints hurt?

The base rate the question skips: what actually causes joint pain in UK adults, and why vitamin D and joint pain overlap by chance

What vitamin are you lacking if your joints hurt is a question with an assumption folded inside it, that joint pain is usually the body's way of reporting a vitamin deficiency, and the honest page answers it by unfolding the assumption and checking it against the base rate, because a question that asks which vitamin has already decided that the answer is a vitamin and the numbers say that it almost never is. In UK adults the causes of joint pain, in roughly the order a GP meets them, are four. Osteoarthritis, the wear of the joint surface and the bony response to it, which most knees, hips, hands and spines develop to some degree with age and which hurts on use, stiffens briefly in the morning and after sitting, and shows on X-ray. The soft tissue conditions around joints, tendinopathy where a tendon's capacity has fallen behind its load, bursitis where a fluid sac over a joint is inflamed, and enthesitis where a tendon or ligament meets bone, which hurt at the joint without being in it and which account for most of the shoulder, elbow, hip and heel pain a GP sees. Inflammatory arthritis, rheumatoid, psoriatic and reactive arthritis which inflame the joint lining and produce swelling, warmth and morning stiffness lasting past half an hour, and gout, in which uric acid crystallises in the joint fluid and produces a sudden hot, red, exquisitely tender joint, the big toe classically. And mechanical injury, the sprains, tears and cartilage injuries of sport and falls, and the aftermath of old ones. A nutritional deficiency is a rare primary cause of joint pain in a fed population, and the two that can be are specific. The joints are let answer for themselves on the joints hurt page, and the deficiencies are ranked by how common they are on the muscle and joint pain page; this page adds the arithmetic that sits under both. Vitamin D insufficiency is common in a British winter, with around one adult in five or six having a low blood level between October and March because the sun is too low for the skin to make any, and severe deficiency does cause symptoms, osteomalacia with bone and muscle aches, proximal weakness that makes stairs and rising from a chair hard, and tiredness, diagnosed by a blood test and treated on a doctor's dose. But the arithmetic is this: most people with a low vitamin D level have no joint symptoms at all, and most people with joint pain have one of the four diagnoses above, so that when a reader with a sore knee in January has their vitamin D measured and finds it low, the two findings have usually arrived together by chance rather than by cause, one in five people having the low level and most people over forty having some joint pain, and correcting the vitamin D, which is worthwhile for the bones and the muscle on the national advice, usually leaves the knee exactly where it was, because the knee's problem was its cartilage, its tendon or its load. The confusion is understandable, since the symptoms of severe deficiency do include aches, and it is encouraged by a shelf that benefits from it, but the base rate is the base rate: a vitamin is the explanation for a small minority of painful joints, and the joint is the explanation for the rest.

The one vitamin that does cause joint pain, the test worth doing and when, how the joint is examined for the four conditions, and the worked example

The one vitamin whose deficiency produces joint pain directly, rather than aches around joints, is vitamin C, and it does so in scurvy, where the failure of collagen stabilisation weakens the small blood vessels so that bleeding occurs into joints and under the skin, producing painful, swollen joints alongside the cluster that makes the diagnosis, bleeding and swollen gums, bruising, corkscrew body hairs with bleeding around them and wounds that will not heal; it is rare in the United Kingdom, needing months with almost no fruit or vegetables, and is seen in extreme diets, severe alcohol dependence, some eating disorders and isolated elderly people, and a reader eating any fruit or vegetables regularly does not have it. The other vitamins the shelf offers for joints, E, K and the B group, have no deficiency state that produces joint pain in a fed adult and no trial showing that any of them relieves it, and the minerals, magnesium above all, are sold on the same confusion between the cramps and aches of deficiency and the pain of a joint. So the test worth doing is one, and the honest page gives it its conditions: a vitamin D blood test in a British winter is worthwhile when the aches are diffuse, in the bones and muscles as much as the joints, on both sides and in several places rather than in one knee, with the proximal weakness and the tiredness that deficiency brings, in a reader with dark skin, little sun exposure, a covered body or an indoor life, and it is worth doing for the bones and muscle whatever it does for the joints; a reader with one painful joint and none of those features is more likely to spend the appointment better on the joint. How the joint is examined for the four conditions is a GP's or a physiotherapist's few minutes and a reader can rehearse it: where exactly it hurts, in the joint or beside it over a tendon or bursa; whether it is swollen, warm or red, which points to inflammation or infection; how long it is stiff in the morning, with under half an hour the osteoarthritis pattern and over half an hour the inflammatory one; whether it came on suddenly in one joint, which with heat and redness is gout until proven otherwise, or gradually in several; whether it hurts on use and eases with rest, the mechanical pattern, or hurts at rest and eases with movement, the inflammatory one; and whether a change in load or an injury preceded it by the twelve weeks a tendon runs behind. Each of the four conditions has a treatment that no vitamin replaces: load management, quadriceps strength and weight for osteoarthritis; progressive loading for tendinopathy; disease-modifying drugs for inflammatory arthritis, where delay costs joints; urate-lowering treatment for recurrent gout; and rehabilitation for injury. The coincidence audit, which does for a tub what this page does for a vitamin, is on the collagen and joint pain page. The worked example treats no joint condition and is stated on its true terms: two capsules, 1200mg hydrolysed type 1 marine collagen with 12mg vitamin C at 15% of its reference value plus zinc, 120 for £16.99 at 28p a day, lab tested and UK made, below the 10g dose at which the joint questionnaire trials found a point or two less pain, carrying vitamin C's collagen formation sentence for the normal function of cartilage, which is a maintenance sentence and not a treatment, and no joint claim of its own. What vitamin are you lacking if your joints hurt: probably none, by the base rate; vitamin D is worth testing in winter for diffuse aches with weakness and is worth correcting for bones and muscle; and the joint is examined for the four conditions that cause nearly all joint pain.

What to check on the label