Percentage of fat in milk consumption and risk of six cancers: a Mendelian randomization study

Background: The causal relationship between percentage of fat in milk consumption and cancer risk lacks sufficient investigation. The purpose of this study was to explore whether the percentage of fat in milk consumption is a factor that affects the risk variation of several common types of cancer.

Methods: Mendelian randomization (MR) was performed to estimate the unconfounded causal relationship between the percentage of fat in milk consumption and the risk of six cancers related to milk intake, as well as to assess the associations between body fat percentage and these cancers. Data corresponding to the percentage of fat in milk consumption (n=411,503), body fat percentage (n=401,772), breast cancer (n=139,274), ovarian cancer (n=66,450), endometrial cancer (n=121,885), colorectal cancer (n=32,072), prostate cancer (n=140,254), and bladder cancer (n=373,295) were obtained from the Integrative Epidemiology Unit (IEU) or the genome-wide association study (GWAS) Catalog databases. The primary analytical strategy employed the inverse-variance weighted (IVW) method. Sensitivity analysis, including assessments of heterogeneity and pleiotropy, was conducted to assess the robustness of the findings.

Results: The percentage of fat in milk consumption only exhibited a causal relationship with breast cancer (β=2.993, P=0.01). The study identified significant causal effects of body fat percentage on the risk of several cancers, including ovarian cancer (β=0.225, P=0.002), endometrial cancer (β=0.669, P<0.001), and colorectal cancer (β=0.344, P<0.001), as well as a protective effect on prostate cancer (β=-0.104, P=0.046). Sensitivity analysis demonstrated that the findings were robust.

Conclusions: Our study findings indicated that a higher percentage of fat in milk consumption was associated with an increased risk of breast cancer, providing valuable insights for cancer prevention strategies among the European population.