An estimated 30% of the global population suffers from iron deficiency anemia (IDA) and previous studies have suggested that iron deficiency (ID) and IDA are associated with adverse health outcomes. However, some research suggests that ID and IDA may be adaptive in areas with high levels of endemic infectious diseases. The present study examined the association between serum iron levels and four infectious diseases in a sample of 55,437 individuals in Calgary, Alberta. Associations between sociodemographic variables (SDVs) and iron and infection were also tested to explore ID’s complex etiology. This study evaluates two hypotheses: HA1: Low baseline serum iron predicts a lower risk of infection up to one year out, and HA2: Sociodemographic variables (higher median income, more postsecondary education, non-immigrant status, and non-Indigenous status) will be associated with higher serum iron levels. Cox regression analyses found that the lowest levels of iron were predictive of greater risk for infection in sepsis (blood) and urinary tract infections. Iron level was not associated with fungal sepsis and strep throat. Multiple regression analyses found no significant relationships between infection and SDVs and found that greater median household income and postsecondary education level were associated with higher mean serum iron levels. This research emphasizes the importance of context when evaluating the adaptiveness of a trait, in addition to calling for further investigation into individual-level associations of sociodemographic variables and infection throughout the city of Calgary.