Abstract 5312: No association between vitamin K intake and prostate cancer risk in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO)

Prostate cancer is one of the most common cancers worldwide. The etiology of prostate cancer largely remains unclear, with almost all established risk factors (e.g. age, race, family history) being not modifiable. Ecological, migrant, and temporal trend studies suggest that diet plays role in the occurrence of prostate cancer, but few nutrients that alter its risk have been identified from case-control and cohort studies. Vitamin K has two forms that naturally occur in foods, i.e., phylloquinone (vitamin K1) and menaquinone (vitamin K2). While phylloquinone is abundant in green leafy vegetables and some vegetable oils, menaquinone is primarily derived from fermented food products (e.g. cheese). Although experimental studies have shown that vitamin K inhibits the growth of various cancer cell lines (including prostate cancer cells), only one epidemiologic study has investigated the association between vitamin K intake and prostate cancer risk. In that German study, a significant inverse association with advanced prostate cancer was observed for menaquinone intake. The present study thus sought to investigate the associations between intake of vitamin K (from both dietary and supplemental sources) and the risk of total and advanced prostate cancer among 28,356 PLCO participants. A total of 2978 cases of prostate cancer (including 490 advanced cases) have been documented during a median follow up of 11.8 years. Advanced prostate cancer were defined as disease in stage II with a Gleason score of 8-10, stage III, or stage IV. Usual dietary intake among study subjects was assessed with Dietary Questionnaire (DQX) at baseline and Dietary History questionnaire (DHQ) at year 3, both of which were developed and validated by the National Cancer Institute. Dietary intake of phylloquinone and menaquinones were calculated using the USDA National Nutrient Database for Standard Reference (Release 23), supplemented with menaquinone data from published studies. Cox proportional hazards regression was performed to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for dietary intake of phylloquinone and menaquinones in relation to prostate cancer risk. After adjustment for confounders, no statistically significant associations were found between vitamin K intake estimated from the DQX and prostate cancer risk [HR (95% CI) for the highest quintile vs. the lowest quintile: 0.99 (0.87, 1.13) for total vitamin K, 0.99 (0.87, 1.12) for phylloquinone, and 1.02 (0.87,