鈥淲hat are nitrates? Cheaper than day rates.鈥� So goes an old joke, appreciation of which requires a bit of chemical knowledge. The nitrate ion is composed of oxygen and nitrogen and occurs naturally in the soil where it serves as a source of nitrogen for plant growth. Nitrogen, potassium and phosphorus are the three minerals all plants require to flourish. Nitrates are an integral part of the nitrogen cycle in our environment and form when microbes in the soil break down decaying plant or animal matter. In addition, bacteria on the roots of legumes can convert nitrogen that is present in air into nitrates. As plants grow, they use up nitrates from the soil which then has to be replenished, most commonly by the addition of a fertilizer such as ammonium nitrate. Nitrates are very water soluble and can present a problem if they leach into ground water in significant amounts. Methemoglobinemia, better known as 鈥渂lue baby syndrome鈥� is a condition that can strike infants usually under six months of age and is linked to excessive amounts of nitrate in drinking water. Bacteria in the stomach of infants convert nitrates to nitrites which in turn react with hemoglobin, the oxygen-carrying molecule in the blood. The result is the formation of methemoglobin which does not carry oxygen effectively and leads to oxygen starvation. With adults this is not a problem because their higher stomach acidity limits the growth of the nitrate reducing bacteria in the stomach. Saliva also contains bacteria that can convert nitrate into nitrite but not in sufficient amounts to interfere with oxygen transport. There has been some concern though that enough nitrite is still produced to react with naturally occurring amines in food to form nitrosamines which are known cancer causing substances. But studies of people exposed to high levels of nitrate have not shown evidence of increased risk of cancer. In fact, nitrates may actually provide protection against heart disease.
Leafy vegetables such as spinach, lettuce and beets are rich in nitrates and their consumption may actually be the secret to the heart-healthy Mediterranean diet. At least so suggests some preliminary research at the Albert Einstein College of Medicine in New York. Dr. David Lefer and colleagues theorized that nitrite in the blood can be a source of nitric oxide, a chemical that dilates blood vessels and improves blood flow. This is just what is needed after a heart attack Nitrites, as we have seen, can be formed from nitrates, so the researchers tested their hypothesis by feeding mice either nitrites or nitrates in their drinking water and then simulating a heart attack by temporarily stopping blood flow to the animals鈥� hearts. The results were impressive. Heart muscle damage was reduced by 48% in the nitrate or nitrite treated mice. It is interesting to note that the Mediterranean diet features a hundred more times more nitrate than the average American diet. Lefer admits that the study does not directly demonstrate the protective effect of nitrates or nitrites in humans but does suggest that a healthy intake of nitrate rich vegetables could spell the difference between a mild heart attack and one that causes lasting heart damage or death. Since nitrite also accumulates in the brain, it could reduce damage from a stroke as well. So Popeye probably had a pretty healthy heart.
