The severe joint pain of gout, most often felt in the big toe, is caused by the deposition of

Explanation

Gout follows a raised blood level of uric acid, the end product of purine breakdown, which crystallises as sodium urate in a cool peripheral joint and provokes intense inflammation. This is why treatment lowers uric acid production or increases its excretion and why purine rich foods such as red meat and organ meat are restricted. Calcium salts harden bone rather than inflame joints.