Nightshade vegetables are potatoes, tomatoes, sweet and hot peppers, eggplant, tomatillos, tamarinos, pepinos, pimentos, paprika, cayenne, and tabasco sauce. The particular groups of substances in these foods are called alkaloids and can impact nerve-muscle function and digestive function in animals and humans, and may also be able to compromise joint function.
Because the amount of alkaloids is very high in nightshade, health problems may only occur in individuals who are especially sensitive to these alkaloid substances. Since cooking only lowers the alkaloid content of nightshade foods by about 40-50%, highly sensitive individuals may want to avoid this category of food altogether.
Nightshades are a diverse group of foods, herbs, shrubs, and trees that have fascinated scientists, doctors, and nutritionists for centuries. "Nightshade" is actually the common name used to describe over 2,800 species of plants, many with very different properties and constituents. All of the plants, however, belong to a scientific order called Polynomials, and to a scientific family called Solanaceae.
Nightshades are actually more famous as drugs than as foods. The best-known nightshades when it comes to pharmacy, include mandrake, tobacco, and belladonna.
What has interested scientists most about nightshades in a pharmacological sense is a group of compounds in them called alkaloids. The alkaloids found in nightshades are not only the basis for consideration of nightshades as drugs but also for understanding adverse reactions to nightshades when they are eaten as food.
Effect of Alkaloids on Health
The steroid alkaloids in nightshades - primarily solanine and chaonine - have been studied for their health effects in two areas. First is their ability to block the activity of an enzyme in nerve cells called cholinesterase. Many of the alkaloids found in nightshades possess this kind of activity, called cholinesterase inhibition. If the action of cholinesterase is too actively blocked, the nervous system control of muscle movement becomes disrupted, and muscle twitching, trembling, paralyzed breathing, or convulsions can result. The steroid alkaloids found in potato have clearly been shown to block cholinesterase activity. They do not usually appear strong enough to produce nerve-muscle disruptions like twitching or trembling.
The second type of problem potentially related to the potato alkaloids involves damage to the joints caused by inflammation and altered mineral status. Whether alkaloids can contribute to joint damage of this kind is not clear from current levels of research. Some researchers have speculated that nightshade alkaloids can contribute to excessive loss of calcium from bone and excessive depositing of calcium in soft tissue. For this reason, these researchers have recommended the elimination of nightshade foods from the meal plans of all individuals with osteoarthritis, rheumatoid arthritis, and joint problems.
If you are an individual with existing joint problems, temporary elimination nightshade foods from your meal plan may be a good step to determine if these foods could be contributing to your joint problems. This same recommendation would apply to individuals with existing nervous system problems, particularly nerve-muscle related problems.