Nitrate exposure and cancer risk : evidence from European case-control studies

Ingested nitrate is a precursor of N-nitroso compounds that are carcinogens in animals, with limited evidence in humans. The main objective of this thesis was to evaluate whether the exposure to nitrate through drinking water and diet is associated with carcinogenic effects in humans. This thesis has been conducted in the Centre for Research in Environmental Epidemiology (CREAL) from 2011 to 2015, under the supervision of Cristina M. Villanueva Belmonte PhD. The results of this thesis consists of a compilation of four scientific papers including: a) a descriptive study of nitrate levels in drinking water in Spain (paper I), and b) three large European case-control studies evaluating the risk of prevalent tumors (bladder, breast and colorectal) associated with nitrate exposure through drinking water and diet (papers II, III and IV). This document also includes a general introduction, a description of the methodology, an overall discussion of the results, conclusions and an appendix section.El nitrato ingerido es un precursor de compuestos N-nitroso, que son carcinógenos en animales, con poca evidencia en humanos. El objetivo principal de esta tesis fue evaluar si la exposición a nitrato a través del agua de consumo y la dieta está asociada a efectos carcinogénicos en humanos. Esta tesis fue llevada a cabo en el Centro de Investigación en Epidemiología Ambiental (CREAL) entre 2011 y 2015, bajo la supervisión de Cristina M. Villanueva Belmonte PhD. La parte principal de esta tesis es una compilación de cuatro artículos científicos, que incluyen: a) un estudio descriptivo de los niveles de nitrato en agua de consumo en España (artículo I) y b) tres estudios caso-control que evaluaron el riesgo de tres tumores prevalentes (vejiga, mama y colorrectal), asociados con la exposición a nitrato a través del agua de consumo y la dieta (artículos II, III and IV). Este documento incluye también una introducción general, una descripción de los métodos, una discusión y conclusiones generales y una sección de anexos

Ingested Nitrate and Breast Cancer in the Spanish Multicase-Control Study on Cancer (MCC-Spain).

BACKGROUND: Ingested nitrate leads to endogenous formation of N-nitroso compounds that are breast carcinogens in animals, but human evidence is limited. OBJECTIVE: We evaluated ingested nitrate as a risk factor for breast cancer (BC) in a multicase-control study. METHODS: Hospital-based incident BC cases and population-based controls were recruited in eight Spanish regions in 2008-2013; participants provided residential and water consumption from 18 years of age and information on known BC risk factors. Long-term nitrate levels (1940-2010) were estimated and linked with residential histories and water consumption to calculate waterborne ingested nitrate (milligrams/day). Dietary ingested nitrate (milligrams/day) was calculated using food frequency questionnaires and published dietary nitrate contents. Interactions with endogenous nitrosation factors and other variables were evaluated. A total of 1,245 cases and 1,520 controls were included in the statistical analysis. RESULTS: Among the study regions, average ± SD waterborne ingested nitrate ranged from 2.9 ± 1.9 to 13.5 ± 7.5 mg/day, and dietary ingested nitrate ranged from 88.5 ± 48.7 to 154 ± 87.8 mg/day. Waterborne ingested nitrate was not associated with BC overall, but among postmenopausal women, those with both high nitrate (> 6 vs. < 2.6 mg/day) and high red meat intake (≥ 20 vs. < 20 g/day) were more likely to be cases than women with low nitrate and low red meat intake (adjusted odds ratio = 1.64; 95% confidence interval: 1.08, 2.49; overall interaction p-value = 0.17). No association was found with dietary nitrate. CONCLUSIONS: Waterborne ingested nitrate was associated with BC only among postmenopausal women with high red meat consumption. Dietary nitrate was not associated with BC regardless of the animal or vegetable source or of menopausal status.This study was funded by the “Acción Transversal del Cáncer del Consejo de Ministros del 11/10/2007” from the “Instituto de Salud Carlos III-FEDER” (PI08/1770, PI08/0533, PI11/00226), ISCIII FIS grants. N.E.H. received financial support for the Ph.D. program from the “Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR FI-DGR 2013) Generalitat de Cataluña.

Colorectal cancer risk and nitrate exposure through drinking water and diet

Ingested nitrate leads to the endogenous synthesis of N-nitroso compounds (NOCs), animal carcinogens with limited human evidence. We aimed to evaluate the risk of colorectal cancer (CRC) associated with nitrate exposure in drinking water and diet. A case-control study in Spain and Italy during 2008-2013 was conducted. Hospital-based incident cases and population-based (Spain) or hospital-based (Italy) controls were interviewed on residential history, water consumption since age 18, and dietary information. Long-term waterborne ingested nitrate was derived from routine monitoring records, linked to subjects' residential histories and water consumption habits. Dietary nitrate intake was estimated from food frequency questionnaires and published food composition databases. Odd ratios (OR) were calculated using mixed models with area as random effect, adjusted for CRC risk factors and other covariables. Generalized additive models (GAMs) were used to analyze exposure-response relationships. Interaction with endogenous nitrosation factors and other covariables was also evaluated. In total 1,869 cases and 3,530 controls were analyzed. Average waterborne ingested nitrate ranged from 3.4 to 19.7 mg/day, among areas. OR (95% CIs) of CRC was 1.49 (1.24, 1.78) for >10 versus ≤5 mg/day, overall. Associations were larger among men versus women, and among subjects with high red meat intake. GAMs showed increasing exposure-response relationship among men. Animal-derived dietary nitrate was associated with rectal, but not with colon cancer risk. In conclusion, a positive association between CRC risk and waterborne ingested nitrate is suggested, mainly among subgroups with other risk factors. Heterogeneous effects of nitrate from different sources (water, animal and vegetables) warrant further research.This study was funded by the “Acción Transversal del Cáncer del Consejo de Ministros del 11/10/2007”, from the “Instituto de Salud Carlos III-FEDER” (PI08/1770, PI08/0533, PI11/00226), ISCIII FIS grants, and HIWATE-EU project (036224). NEH receives funding for the PhD program in Biomedicine from the “Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR FI-DGR 2013) Generalitat de Cataluña

Colorectal Cancer and Long-Term Exposure to Trihalomethanes in Drinking Water: A Multicenter Case-Control Study in Spain and Italy.

BACKGROUND: Evidence on the association between colorectal cancer and exposure to disinfection by-products in drinking water is inconsistent. OBJECTIVES: We assessed long-term exposure to trihalomethanes (THMs), the most prevalent group of chlorination by-products, to evaluate the association with colorectal cancer. METHODS: A multicenter case-control study was conducted in Spain and Italy in 2008-2013. Hospital-based incident cases and population-based (Spain) and hospital-based (Italy) controls were interviewed to ascertain residential histories, type of water consumed in each residence, frequency and duration of showering/bathing, and major recognized risk factors for colorectal cancer. We estimated adjusted odds ratios (OR) for colorectal cancer in association with quartiles of estimated average lifetime THM concentrations in each participant's residential tap water (micrograms/liter; from age 18 to 2 years before the interview) and estimated average lifetime THM ingestion from drinking residential tap water (micrograms/day). RESULTS: We analyzed 2,047 cases and 3,718 controls. Median values (ranges) for average lifetime residential tap water concentrations of total THMs, chloroform, and brominated THMs were 30 (0-174), 17 (0-63), and 9 (0-145) μg/L, respectively. Total THM concentration in residential tap water was not associated with colorectal cancer (OR = 0.92, 95% CI: 0.66, 1.28 for highest vs. lowest quartile), but chloroform concentrations were inversely associated (OR = 0.31, 95% CI: 0.24, 0.41 for highest vs. lowest quartile). Brominated THM concentrations showed a positive association among men in the highest versus the lowest quartile (OR = 1.43, 95% CI: 0.83, 2.46). Patterns of association were similar for estimated average THM ingestion through residential water consumption. CONCLUSIONS: We did not find clear evidence of an association between detailed estimates of lifetime total THM exposure and colorectal cancer in our large case-control study population. Negative associations with chloroform concentrations and ingestion suggest differences among specific THMs, but these findings should be confirmed in other study populations.This work was supported by the Acción Transversal del Cáncer del Consejo de Ministros del 11/10/2007 (M.K. and M.Pollan), from the Instituto de Salud Carlos III-FEDER (M.K.: PI08/1770; C.M.V.: PI08/0533 and PI11/00226) FIS grants and Hiwate EU project (036224), and the Italian Foundation for Research on Cancer (FIRC; C.L.V.)