Rotimi investigates genetics and health disparities, ensuring that African genomes are represented in genome databases.[5][6] He was appointed as an epidemiologist at Loyola University Chicago, where he worked on cardiovascular disease and obesity in people in the African diaspora.[2] Together with his colleague Richard Cooper, Rotimi recruited 10,000 people to study the prevalence of hypertension in populations of West African descent.[5] He found that hypertension and diabetes rates are significantly higher in African-American populations in Chicago than they are in rural Africa. He attributed this to lifestyle factors, including weight, salt consumption and levels of physical activity.[5]
Rotimi moved to Howard University in 1990, where he worked with Georgia M. Dunston at the National Human Genome Center. Rotimi was promoted[when?] to head of genetic epidemiology.[2] Here he studied the impact of the underrepresentation of African and African-American data in genomic datasets.[2] He argued for the use of genomic tools to understand variation in human biology, but pointed out that it is not possible to use genetics to define race; the variation in genomes do not account for the socially defined racial groups and racial self-identity.[7][8] He compiled genomic data from 6,000 people in 13 language families, identifying 21 global genetic ancestries.[2] The study established that 97 % of people have mixed ancestry, emphasising the problems with labels such as hispanic, black and white.[9][10] In an interview with The Lancet, Rotimi described inequality as "one of the most outrageous aspects of society".[3]
Rotimi led the African component of the International HapMap Project, which contributed to the 1000 Genomes Project.[2] He recruited three African communities in Kenya and Nigeria, ensuring that African genomes were part of the record.[2] It is understood that homo sapiens originated in Africa, leaving after 100,000 years.[2] During this time much of the genetic evolution had already occurred, and those that emigrated carried a subset of the original genetic diversity. African genomes are the most ancient.[2]
Rotimi looks at the heritability of complex disease.[11] He began to work with Kári Stefánsson in 2007, studying the diabetes risk variant TCF7L2 in West African populations.[12] He demonstrated that both TCF7L2 and its genetic variant HapA increase the risk of diabetes due to their function in energy metabolism. To determine the origins of the sickle cell disease mutation, Rotimi studied the genomes of 3,000 people.[2] He identified that sickle cell emerged around 7,000 years ago in Africa.[2]