How to test for collagen deficiency?

The test menu: the vitamin C test, the turnover markers, and what each actually measures

How to test for collagen deficiency is a question the honest page has to answer with an awkward preliminary, which is that there is no such test because there is no such condition: collagen deficiency is not a diagnosis in any medical classification, no laboratory offers a validated measure of it, and the phrase is a marketing construction that bundles together three real things and a great deal of ordinary ageing. The useful answer is therefore the test menu, each test that actually exists and what it actually measures, so that a reader can find which real question they are asking. The first test on the menu is a blood vitamin C level, and it is the only test that detects a deficiency which fails collagen. Vitamin C is the cofactor for the prolyl and lysyl hydroxylases that fold collagen chains into their triple helix, and without it the body cannot make functional collagen anywhere, which is scurvy: bleeding and swollen gums, easy bruising, tiny bleeds around hair follicles with corkscrew hairs, wounds that will not heal, fatigue, and joint pain from bleeding into joints, a general connective tissue failure that appears after weeks to months of very low intake. It is rare in the UK, confined to very restricted diets, alcohol dependence, some eating disorders and some older people living alone on tea and toast, and it is diagnosed by a doctor from the symptoms and a plasma vitamin C level, then treated with vitamin C and a changed diet, after which the collagen enzymes work again and the connective tissue repairs; a reader with any fruit or vegetables in their week is not short of vitamin C and does not need the test, and a reader with the symptoms needs a doctor and not a supplement. The second item on the menu is the set of collagen turnover markers, which sound like what the reader wants and are not. The amino-terminal propeptide of type I procollagen, P1NP, is a fragment released into the blood each time a type I collagen molecule is made, so it measures the rate of collagen synthesis; the carboxy-terminal telopeptide, CTX, is a fragment released each time mature type I collagen is broken down, so it measures the rate of breakdown; and urinary hydroxyproline is an older, non-specific breakdown marker affected by what was eaten. These markers are used by clinicians to assess bone turnover, since bone is the body's largest type I collagen store and remodels constantly, and by researchers, the collagen pre-loading trial having measured P1NP to show synthesis doubling after gelatin and vitamin C before loading. What they do not measure is how much collagen a body has, whether its tendons, skin or joints are short of it, or whether a person needs a supplement, since a high P1NP can mean growth, healing or bone disease and a low one can mean a quiet, healthy adult skeleton, and no marker value has been validated against any collagen-related outcome in a consumer; a reader sold a P1NP test as a collagen check has bought a bone turnover number they cannot interpret.

Genetic testing, the online kits, and the question the reader is really asking

The third item on the menu is genetic testing, and it detects the one group of conditions in which a person's collagen is genuinely abnormal, the heritable connective tissue disorders. The Ehlers-Danlos syndromes, osteogenesis imperfecta, Marfan syndrome and their relatives arise from variants in the genes for particular collagens or for the enzymes that process them, and they produce collagen of the wrong structure rather than the wrong quantity: hypermobile and dislocating joints, stretchy or fragile skin, poor wound healing with wide scars, easy bruising, fragile bones or blood vessels, depending on the type. They are assessed by specialists, rheumatologists, clinical geneticists and others, against published diagnostic criteria that begin with the history and examination, and are confirmed for most types by sequencing the relevant genes, with the commonest hypermobile type still diagnosed clinically because its gene has not been identified. A reader whose joints have always dislocated, whose skin has always stretched and whose scars have always spread has a reason to ask a doctor about these criteria; a reader with sore knees at fifty does not, and dietary collagen does not address a structural gene variant in either case, since the fibroblast builds the collagen its genes specify from whatever amino acids it is given. The fourth item is the one the reader most likely met first, the collagen tests sold online: finger-prick kits that report a collagen score, skin-pinch and wrinkle quizzes, and app-based photo assessments. None of these measures anything validated against a collagen outcome; a finger-prick kit can at most measure a turnover marker, which as above does not mean what the kit says it means, and a skin quiz measures the appearance of ageing, which is a mix of sun exposure, genetics, fat and bone change beneath the skin, and dermal collagen loss, with no way to separate them and no action that follows from the score except the purchase the site is built around. Having laid out the menu, the honest page can name the question the reader is really asking, which is one of three. If the question is whether a cofactor deficiency is failing their collagen, the answer is a vitamin C test from a doctor when the symptoms of scurvy are present, and a varied diet otherwise. If the question is whether their collagen is structurally abnormal, the answer is a specialist's assessment against the heritable disorder criteria when the lifelong signs are present. And if the question is what most readers mean, whether ageing skin, thinning hair, brittle nails or aching joints indicate a collagen shortfall that a supplement would fix, the answer is that those are not a deficiency and have no test, that each has its own causes, sun and smoking for skin, the hair cycle for hair, trauma and water for nails, load and wear for joints, and that the oral collagen trials address them at the margin, with a few percent by instrument in skin at 2.5g and above and modest joint questionnaire gains at 5 to 10g, which a reader can try with a diary and without a test. The worked example claims no test and needs none, 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 2.5 to 15g research band, carrying vitamin C's collagen formation sentence and no collagen claim. How to test for collagen deficiency: you cannot, because it is not a condition; you can test for the cofactor, the gene or nothing, and a doctor decides which, if any, your symptoms call for.

What to check on the label