Nitrates are chemical compounds which, among other defining characteristics, contain the polyatomic ion nitrate, which is composed of one atom of nitrogen and three atoms of oxygen, together having a single net negative charge. Nitrates are commonly seen in the study of inorganic chemistry as well as organic chemistry. In medicine, nitrates are medications used to treat heart conditions such as angina, and have been in use for over a century.
Many nitrates can be harmful to a person's health, while others can have a more or less neutral effect. Some are actually used to prolong life in emergency medical conditions. If nitrate levels in the blood rise too high, this may in some cases lead to a lack of oxygen absorption by the body. The nitrate ion contains oxygen, and when this part of it bonds with hemoglobin in blood cells, it keeps elemental oxygen from doing so, reducing the ability of the blood as whole to carry oxygen. This condition sometimes presents in newborns and infants younger than six months. Environmental sources of these types of nitrates can include agricultural runoff containing fertilizer and industrial waste water.
A few types of nitrates, such as sodium nitrate, are used in food products as preservatives. Their most common use is in meat products to preserve color and to inhibit the growth of the bacteria which can lead to botulism. It is not known for sure if these chemicals pose any hazard in the levels at which they are normally ingested, and they are generally considered to be safe.
The medical profession has used nitrates at least since 1870 to treat chest pain associated with low oxygen supply to the heart. This condition, known as angina, can be relieved by taking nitrates either orally or by intravenous injection, because it has the effect of widening the blood vessels to allow more blood, and therefore more oxygen, to reach tissues. They may also be prescribed during a heart attack for the same purpose, or in the context of a surgery such as angioplasty.
Glyceryl trinitrate, an alternate name for nitroglycerin, has been one of the longest-used nitrates for the treatment of chest pain. It was discovered in 1847, and it was known around that time that handling the chemical for extended periods of time could cause severe headaches. This indicated that it must have been widening blood vessels somehow, and a few decades later it began to be used in small doses to treat heart conditions. The headaches, it turned out, were the result of overexposure, and did not happen when the chemical was administered medically in proper doses.