The sugar can take many forms, including honey, corn syrup solids, and maple syrup. Adding sugar alleviates the harsh flavor of the salt. It also contributes to the growth of beneficial bacteria like "Lactobacillus" by feeding them. Nitrates and nitrites have been used for hundreds of years to prevent botulism in fish and ensure microbial safety. Nitrates help kill bacteria, produce a characteristic flavor, and give fish a pink or red color. The use of nitrates in food preservation is controversial. This is due to the potential for the formation of nitrosamines when the preserved food is cooked at high temperature. However, the production of carcinogenic nitrosamines can be potently inhibited by the use of the antioxidants Vitamin C and the alpha-tocopherol form of Vitamin E during curing. A 2007 study by Columbia University suggests a link between eating cured meats and chronic obstructive pulmonary disease. Nitrites were posited as a possible cause. The use of either compound is carefully regulated. For example, the FDA Code of Federal Regulations states that sodium nitrite may be safely used: "As a color fixative in smoked cured tunafish products so that the level of sodium nitrite does not exceed 10 parts per million (0.001 percent) in the finished product... As a preservative and color fixative, with or without sodium nitrate, in smoked, cured sablefish, smoked, cured salmon, and smoked, cured shad so that the level of sodium nitrite does not exceed 200 parts per million and the level of sodium nitrate does not exceed 500 parts per million in the finished product." Fish can also be preserved by smoking, which is drying the fish with smoke from burning or smoldering plant materials, usually wood. Smoking helps seal the outer layer of the food being cured, making it more difficult for bacteria to enter. It can be done in combination with other curing methods such as salting. Common smoking styles include hot smoking, smoke roasting and cold smoking. Smoke roasting and hot smoking cook the fish while cold smoking does not. If the fish is cold smoked, it should be dried quickly to limit bacterial growth during the critical period where the fish is not yet dry. This can be achieved by drying thin slices of fish.