Relationship between prostate-specific antigen levels and ambient temperature

We examined the association between prostate-specific antigen (PSA) and daily mean ambient temperature on the day of the test in healthy men who had three annual checkups. We investigated 9,694 men who visited a hospital for routine health checkups in 2007, 2008, and 2009. Although the means and medians of ambient temperature for the three years were similar, the mode in 2008 (15.8 A degrees C) was very different from those in 2007 and 2009 (22.4 A degrees C and 23.2 A degrees C). After controlling for age, body mass index, and hematocrit, a multiple regression analysis revealed a U-shaped relationship between ambient temperature and PSA in 2007 and 2009 (P < 0.001 and P = 0.004, respectively), but not in 2008 (P = 0.779). In 2007, PSA was 13.5 % higher at 5 A degrees C and 10.0 % higher at 30 A degrees C than that at 18.4 A degrees C (nadir). In 2009, PSA was 7.3 % higher at 5 A degrees C and 6.8 % at 30 A degrees C compared with the level at 17.7 A degrees C (nadir). In logistic regression analysis, a U-shaped relationship was found for the prevalence of a higher PSA (> 2.5 ng/mL) by ambient temperature, with the lowest likelihood of having a high PSA at 17.8 A degrees C in 2007 (P = 0.038) and 15.5 A degrees C in 2009 (P = 0.033). When tested at 30 A degrees C, there was a 57 % excess risk of having a high PSA in 2007 and a 61 % higher risk in 2009 compared with those at each nadir temperature. We found a U-shaped relationship between PSA and ambient temperature with the lowest level of PSA at 15-20 A degrees C.