Nitrates, Nitrites and Cancer

There is a commonly held belief that nitrates and nitrites can cause cancer, particularly gastric cancer, which has prompted food manufacturers to introduce all kinds of nitrate-free and nitrate-free products. However, the truth seems to be a bit more complicated than that.

In 2015, a group of scientists from China published an intriguing article on nitrates, nitrates and gastric cancer risk in the peer-reviewed journal Nutrients. The article discussed the results of a meta-analysis, a type of systematic review that gathers all existing studies and crunches them together. In addition to looking at the potential associations between gastric cancer risk and dietary consumption nitrates and nitrates, this review also investigated the potential link between nitrosamine intake and gastric cancer.

Now, before we explore the findings of this meta-analysis, let's try to get a better understanding of what nitrates, nitrates and nitrosamines are and how they get into your body:

• Nitrates. These naturally occurring compounds are abundant in many vegetables, especially leafy greens like spinach and arugula. Nitrates are also used in fertilizers, and occasionally in meat curing processes.
• Nitrites. Nitrites are frequently added to processed meats like bacon, ham and sausages. They function as preservatives, preventing the growth of harmful bacteria, but they are also used to enhance the flavor and appearance of meat products. You can also get some nitrites from nitrate-containing vegetables because the bacteria and enzymes in your body can convert nitrates into nitrites.
• Nitrosamines. These compounds, many of which are thought to be highly carcinogenic, are formed from nitrites in foods and nitrates that have been converted into nitrites in the body (1). Vitamin C has been found to be highly effective at inhibiting the conversion of nitrites into nitrosamines (2).

It is important to make a distinction between these three groups of compounds because, as it turns out, they affect health in very different ways. The meta-analysis conducted by the Chinese researchers found that a high intake of nitrates was associated with a weak but statistically significant reduced the risk of gastric cancer, whereas a high intake of nitrites and the nitrosamine N-Nitrosodimethylamine seemed to increase the risk. Their analysis looked at the findings of 49 studies: 19 studies on nitrates, 19 studies on nitrites, and 11 studies on N-nitrosodimethylamine.

The results of this meta-analysis are in line with other studies which suggest that a high intake of fresh vegetables, even nitrate-rich spinach, appear to provide protection against cancer (3, 4).

Part of the reason why nitrate-rich vegetables do not seem to be harmful is that they are generally also rich in vitamin C which helps block the conversion of nitrates into cancer-causing compounds. Another possible contributing factor is that vegetables like arugula and spinach are loaded with nutrients and phytochemicals with cancer-fighting properties, which may help counteract any negative effects resulting from the ingestion of nitrates.

So, the bottom line is, don't stop eating your green leafy vegetables, even if they contain relatively high levels of nitrates. There doesn't seem to be convincing evidence suggesting that these vegetables would be a problem for healthy adults, and in fact, a growing body of evidence suggests that high-nitrate vegetables like arugula, spinach and beetroot may actually help keep your cardiovascular system healthy.