Age at first sexual intercourse and pan- cancers: Mendelian Randomization Study

Abstract Background Whether the age of first sexual intercourse increases the risk of cancer has attracted widespread attention, but the conclusion is still controversial. It is unclear whether the age of first sexual intercourse has a definite causal effect on pan- cancers. Methods Based on the Genome-Wide Association Study (GWAS) dataset from the large prospective UK Biobank and other alliance databases, two sample mendelian randomization (MR) analysis was used to explore the causal impact of age at first sexual intercourse on cancer risk in different regions. Five MR methods were applied to to investigate the causality. The stability, heterogeneity, and pleiotropy of MR results were also evaluated. Results 196 SNPs were selected as instrumental variables in the population of the age of first sexual intercourse, which satisfies the local wide significance level (p < 5*10 − 8). the age of first sexual intercourse has a significant causal effect on the risk of head and neck cancer(OR = 0.997, 95%CI:0.9955–0.9984, p < 0.0001) and lung cancer(OR = 0.9928, 95%CI:0.9903–0.9954, p < 0.0001). And there is a slight causal relationship between the age of first sexual intercourse and the liver cell cancer(OR = 0.9993, 95%CI:0.9988–0.9999, p = 0.0260) and cervical cancer(OR = 0.9979, 95%CI:0.9960–0.9998, p = 0.0366). At the same time, the age of first sexual intercourse has a slight causal effect on breast cancer(OR = 1.005, 95%CI:1.0009–1.0092,p = 0.0175) and prostate cancer(OR = 1.1732, 95%CI:1.0118–1.3604, p = 0.0344). Conclusion This study explored the causal relationship between the age of first sexual intercourse and pan-cancer, and found that the age of first sexual intercourse has a significant protective effect on head and neck cancer and lung cancer, a slight protective effect on liver cell cancer and cervical cancer, and a slight promoting effect on breast cancer cancer and prostate cancer. However, more rigorous research is still needed to explore the relationship between first sexual intercourse and pan-cancer.