Body size, age at shaving initiation, and prostate cancer in a large, multiracial cohort.

BACKGROUND: The purpose of this study was to examine the potential relationship between body size, self-reported age at initiation of shaving, and subsequent risk of prostate cancer in a large, racially diverse cohort of men followed for up to 32 years.
METHODS: The study population included 70,712 male subscribers to the Kaiser Permanente Medical Care Program who had received a multiphasic health checkup between 1964-1973. This general health checkup consisted of a number of laboratory tests and physical measurements, as well as a self-completed health questionnaire that included a request for men to record the age when they began shaving. Subjects were followed for the development of prostate cancer, using the local tumor registry. Cox regression was used to estimate relative risks (RR) and 95% confidence intervals (CI).
RESULTS: Altogether, 2, 079 men in the study cohort were diagnosed with prostate cancer. There was a very strong positive association between prostate cancer risk and birth cohort. After adjusting for race, age, and birth year, there was no association between height, weight, body mass index, or several other anthropometric measures and prostate cancer risk in the full cohort. There was a suggestion of a very weak positive association between height and prostate cancer risk among white men. There also was no overall association between age at shaving initiation and prostate cancer risk, although nonwhite men who started shaving at a young age (</=14 years) appeared to be at somewhat elevated risk (RR = 1.49; 95% CI, 1.01-2.22). Relative risks associated with anthropometry and age at shaving did not vary consistently by decade of life, age at health checkup, or stage of prostate cancer at diagnosis.
CONCLUSIONS: Results from our large, multiracial cohort study do not support a relationship between several measures of adult body size and prostate cancer risk. There was a suggestion of a weak association between height and age at shaving initiation and prostate cancer risk, but only among some racial subgroups. Copyright 2000 Wiley-Liss, Inc.