Plasma levels of nitrate and risk of prostate cancer: a prospective study
Cette étude prospective cas-témoins (630 cas et 630 témoins) évalue l'association entre des niveaux plasmatiques de nitrate, mesurés en 1994, et le risque de cancer de la prostate (diagnostic entre 1997 et 2005)
Background : Nitrate and nitrite supplements have recently been shown to improve cardiovascular health, but there is concern that these supplements could contribute to the development of cancer. Previous small, cross-sectional studies reported positive associations between circulating nitrate/nitrite levels and cancer. Prospective studies examining the association between plasma nitrate and cancer, especially prostate cancer (PCa), are lacking. Methods : We conducted a nested case-control study within the Health Professionals Follow-up Study. Baseline blood samples were collected in 1994, and incident cases of PCa were identified from 1997-2005. Baseline plasma levels of nitrate were measured in the 630 cases and 630 matched controls. Results : We have found that baseline levels of plasma nitrate were not associated with risk of PCa. Compared to quintile 1, the relative risk from quintiles 2-5 were 1.13 (95% CI 0.78-1.63), 0.93 (95% CI 0.63-1.38), 0.95 (95% CI 0.65-1.39), and 0.99 (95% CI 0.68-1.48); p for trend was 0.9 after adjustment of multivariate risk factors. Further, plasma nitrate appeared to be inversely associated with advanced-stage PCa. The relative risk across extreme quartiles was 0.44 (95% CI 0.17-1.12; p for trend = 0.07) for the whole data set and 0.30 (95% CI 0.09-0.99; p for trend = 0.05) for the fasting data set. Conclusions : We did not find an increased risk of PCa associated with higher plasma nitrate levels. A potential protective association between nitrate and aggressive forms of PCa requires confirmation. Impact:Nitrate-nitrite-nitric oxide pathway has emerged as a new therapeutic pathway for chronic diseases. The results of this study certainly merit replications.