Impact of birth season on second-to-fourth digit ratio, prostate volume, and prostate cancer

The second-to-fourth digit ratio (digit ratio), which is determined in utero, is associated with exposure to visible sunlight during early pregnancy and the season of birth. The digit ratio is also associated with benign prostatic hyperplasia (BPH) and prostate cancer. This suggests that BPH and prostate cancer may be related to the birth season. Therefore, this study aimed to determine whether prostate volume and prostate cancer were related to the birth season.

A total of 858 male patients with lower urinary tract symptoms were enrolled. The right digit ratio was measured, and the month of birth was surveyed. Serum prostate-specific antigen (PSA) levels were measured, and prostate volumes were measured by transrectal ultrasonography. Patients with suspected prostate cancer underwent prostate biopsy.

The mean age, digit ratio, prostate volume, and serum PSA level of 858 patients were 61.6 years, 0.947, 36.2 mL, and 4.24 ng/mL, respectively. Age, serum PSA levels, prostate biopsy rates, and cancer detection rates did not differ significantly according to the birth season. However, compared with the summer birth group, the winter birth group had lower digit ratios (0.951±0.040 vs. 0.941±0.040; p=0.014), larger prostate volumes (33.4±14.9 mL vs. 38.2±20.7 mL; p=0.008), and more prostate cancer (5.3% vs. 11.3%; p=0.031). Multivariate analysis showed that birth season independently predicted prostate cancer.

The relationships of birth season with prostate volume and prostate cancer may be due to differences in the amount of light exposure during early pregnancy.