Risk of non-Hodgkin lymphoma and nitrate and nitrite from the diet in Connecticut women

It has been estimated that 65,980 individuals were diagnosed with non-Hodgkin lymphoma (NHL) and 19,500 died from NHL in the United States in 2009. Although established risk factors such as immunodeficiency and viral infections may be responsible for a portion of the cases, the majority of NHL cases remain unexplained. Dietary nitrate and nitrite intake are exposures of particular interest for NHL risk as they are precursors in the endogenous formation of N-nitroso compounds, which cause lymphomas in animal studies. We investigated NHL risk overall and by histologic type in relation to dietary nitrate and nitrite intake in a population-based case–control study of 1,304 women in Connecticut. Nitrate and nitrite intake were assessed using a 120-item food frequency questionnaire. We found no association between risk of NHL overall and dietary nitrate and a slightly increased risk of NHL with higher dietary nitrite intake (highest vs. lowest intake quartile OR = 1.4; 95% CI: 0.9–2.2). When we evaluated intake by subtype, a significant positive trend was observed for follicular lymphoma and nitrate (p-trend = 0.04) and nitrite (p-trend < 0.01) with an over twofold risk in the highest nitrite intake quartile (OR = 2.3; 95% CI: 1.1–4.9). An increased risk in the highest quartile of nitrite intake was also observed for T-cell lymphoma (OR = 3.4; 95% CI: 1.0–11.9). Animal products containing nitrite were more strongly associated with risk of follicular lymphoma; whereas, both animal and plant sources of nitrite were associated with elevated ORs for T-cell lymphoma. Our results confirm a previous finding for nitrite intake and NHL risk and highlight the importance of evaluating histologic type. We conclude that these results should be replicated in a larger study with data on drinking water as well as dietary sources of nitrate intake.