鈥淏oil the nipples!鈥� was the advice given in 1984 by the Food and Drug Administration in the U.S. to parents who were bottle feeding their infants or calming them with pacifiers. The presence of nitrosamines, compounds that had been found to cause cancer in animals, had been recently detected in rubber products and the concern was that they could be transferred to babies. The advice was rescinded within a few months because it turned out that boiling was not an effective way to eliminate nitrosamines and more importantly, the rubber industry had already identified the problem and had taken steps to significantly reduce the formation of these compounds.
The elasticity and strength of rubber is achieved by 鈥渧ulcanization,鈥� a process in which the long polyisoprene molecules in natural rubber are cross-linked by sulfur atoms. Accelerators like thiuram sulphides speed up the process, but also break down to release dimethyl nitrosamine, a potent carcinogen. Once this was discovered, the industry quickly found other safer accelerators. Parents relaxed, as did condom users who had also been concerned about the same issue.
Rubber manufacturers were not the only ones saddled with the nitrosamine problem in the early 1980s. The beer industry was also rattled by the finding of dimethyl nitrosamine in German beer, causing worldwide concern. In this case, the problem was traced to the drying of malt. Beer is made by 鈥渕alting,鈥� a process that begins with steeping barley grains in water to allow for germination, followed by drying of the sprouted grains or 鈥渕alt,鈥� in a kiln to produce the desired flavour and colour. The malt is then mashed, hops are added, and yeast is introduced to ferment the sugars that were produced from starch during germination into alcohol. This time the problem was the drying process.
Traditionally malt was dried with hot air from the combustion of wood, coal or coke. But the heat of combustion allows nitrogen and oxygen, the constituents of air, to combine to form oxides of nitrogen that can then react with hordenine, a protein breakdown product formed during germination, to produce dimethyl nitrosamine. Once this was discovered, the industry switched to 鈥渋ndirect kilning,鈥� in which the combustion products are not passed directly through the malt but pass through a heat exchanger that heats clean, ambient air that is passed through the malt. Presto, problem solved! No worries about nitrosamines in beer or in whiskey, which is also malted, usually from rye, wheat or corn.
But if you are going to have that beer with a sausage, or some other form of processed meat, the curse of nitrosamines rears its ugly head again. Sodium nitrite is one of the most versatile food additives, much loved by the meat industry. It produces the pinkish-red color and unique flavor of cured meats, acts as an antioxidant that prevents fats from reacting with oxygen to produce off-flavours, and most significantly, has an antibacterial effect, preventing the formation of dangerous botulinum toxins.
Unfortunately, nitrites also have a dark cloud hanging over their heads. They can react with amines or amino acids in meat to produce nitrosamines, particularly when heated, as in frying bacon. Sodium erythorbate or sodium ascorbate are usually added to interfere with this process but nevertheless, the International Agency for Research on Cancer (IARC) has listed processed meats in its 鈥淕roup 1,鈥� reserved for substances such as tobacco smoke and asbestos that are known to cause cancer in humans.
To be sure, nitrites are not the only potential carcinogens in processed meats. Heating any meat, particularly when flames and smoke are involved, produces polycyclic aromatics and heterocyclic amines, both of which are carcinogens. That鈥檚 why IARC lists red meat as 鈥減robably carcinogenic to humans.鈥� There is also an issue with the iron that is part of the hemoglobin molecule in meat. Not only can it catalyze the formation of nitroso compounds but can also induce the reaction of fats with oxygen that results in the formation of DNA-damaging free radicals. The carcinogenic potential of processed meat is not only theory. Epidemiological evidence has linked colorectal cancer with the consumption of processed meat, although the risk is not enormous. If a hundred people eat 50 grams of processed meat every day throughout their lives, one will develop cancer as a result. Still, over a large population that is not insignificant especially considering that there is a worrisome increase in colorectal cancer in young people that parallels an increase in the consumption of ultra-processed foods.
Exposure to nitrites is not limited to processed meats. Nitrates occur naturally in vegetables and when mixed with enzymes in saliva are converted to nitrites. These can then react with amines to produce nitrosamines, but the risk is very small because no heat is involved and unlike meat, vegetables do not contain the requisite amines in any significant amount. Also, they contain vitamin C and various polyphenols that interfere with nitrosamine formation. Not only is there no concern about nitrates in vegetables, there is evidence of benefit since nitrates can be converted to nitric oxide in the body. Nitric oxide dilates blood vessels, lowers blood pressure, and enhances the activity of immune cells. Green leafy vegetables are the best source of nitrates with arugula containing by far the most.
Although nitrites are not the only concern in processed meat, the industry is working to reduce their use. This is difficult because there is no alternative that can fulfil all of nitrite鈥檚 functions. Celery extract is rich in nitrates that can be reduced to nitrites by naturally occurring microorganisms in meat and some producers use this ingredient to avoid listing nitrite as an additive on a label. But nitrite is nitrite no matter where it comes from. Another alternative that does not involve nitrites makes use of acids such as acetic, lactic or benzoic coupled with high hydrostatic pressure (HHP). This involves placing the meat and the acid or its salt in a vessel where it is immersed in water to which high pressure is applied. HPP destroys the cell structure of bacteria, so it serves to preserve the processed meat but does not have the other benefits of nitrites. Turkey processed with acetic acid (vinegar) and HHP has become popular because it can claim 鈥渘o nitrite,鈥� but it should also be mentioned that all processed meats are high in salt.
After following the nitrite and nitrate issues for decades, I have cut down on processed meats, but I will still have an occasional hot dog, especially if there is a hockey or baseball game in front of it. I do like the nitrite free turkey, and I don鈥檛 make as much fun of an arugula salad as I used to.
