Complex sentence: The USPHS continued to study the Uranium miners, eventually including four-thousand American Indian and non-Indian underground uranium miners; new miners were added to the study in 1951,1953,1954,1957 and 1960.
Split into simpler sentences: The USPHS continued to study the uranium miners, eventually including 4,000 American Indian and non-Indian underground uranium miners. They added miners in 1951,1953,1954,1957 and 1960.