Brian MacMahon (23 August 1923 – 5 December 2007) was a British-born American epidemiologist who chaired the Department of Epidemiology of the Harvard School of Public Health from 1958 until 1988.

[1] Enrolment in a course in public health at the University of Birmingham brought him into contact with epidemiologists Thomas McKeown, Ronald Lowe and Reginald Record, who became his supervisors in a PhD in "social medicine" (as epidemiology was then known) studying infantile pyloric stenosis.

[3] MacMahon built the Harvard School of Public Health into a world-class research institution; he particularly prided himself, however, on nurturing students, many of whom went on to become leaders in the field of epidemiology.

[4][7] Subsequent work by MacMahon's group showed that every year a woman delays giving birth after the age of eighteen increases her risk of developing breast cancer by 3.5%.

[1][3] MacMahon's group also studied other factors associated with breast cancer risk, including age at menarche[9] and menopause,[10] lactation,[11] alcohol consumption[12] and diet.

[4] Their study showed that non-smoking women whose husbands smoked heavily (more than a pack per day) had a greater than threefold increased risk of developing lung cancer.

[4] This research was not without controversy: a case-control study which unexpectedly linked coffee drinking with increased risk of pancreatic cancer[15] provoked a storm of protest from coffee drinkers and industry groups, with coverage in the New York Times, Time magazine and Newsweek.

[1][3] Despite developing Dupuytren's contracture in his hands, which hindered computer use,[1] MacMahon remained active in research long after his official retirement, for example, contributing a final review on pyloric stenosis in 2006.