“…We have recently shown in four studies in children, adolescents and adults, that a history of iron deficiency is associated, probably causally, with multiple pain conditions [66] (see Supplementary Information). Other shared risk factors for multiple pain conditions include some bidirectional factors such as impaired sleep [67][68][69], restless legs syndrome [56,70], early childhood adversity [71,72], although bias [73] is acknowledged, and anxiety and depression [74][75][76][77]. Consistent with the anxiety and depression studies cited, both categories of back pain were associated with the measure of anxious depression.…”