I love the name “nightshade”, and apparently these plants are so called because they are grown in the shade of night. I imagine that the one most people will be most familiar with is the poisonous plant deadly nightshade, or belladonna. But did you know a lot of the relatives of this plant are common in our diets?
Nightshades (Latin name Solanaceae) are an extremely diverse family of flowering plants, which include some of our favourite and most common vegetables, i.e. potatoes, peppers, tomatoes and aubergines. Although these are important agricultural crops and usually feature strongly in the diets of vegetarians and vegans, a lot of them are toxic. Nightshade is a generic name which describes over 2,800 species! Throughout history they have actually been more famous and widely-used as drugs and poisons rather than food, especially mandrake and belladonna (deadly nightshade).
The family includes Jimson weed (datura), mandrake (mandragora), deadly nightshade (atropa belladonna), wolfberry, tomatillo, Cape gooseberry flower, chilli pepper and bell peppers (Capsicum), potatoes, tomatoes and aubergines/eggplants (Solanum), petunia, and tobacco (Nicotiana). Most parts of the plants, especially the green parts and unripe fruits, are poisonous to humans (although not necessarily to other animals), but some of the species bear edible parts, such as tubers and fruit, and several are cultivated and are of global importance, e.g. potatoes, tomatoes and aubergines. Potatoes and tomatoes contain small amounts of nicotine, not surprising since they are related to the tobacco plant.
A certain group of substances in these foods called alkaloids can have an adverse effect on digestive and nerve muscle function in both humans and animals, and they may also impact on joint function, as they have inflammatory properties. The plants produce these toxic alkaloids to protect themselves against attack by insects, but they can also adversely affect humans (some people, it appears, have a certain sensitivity to them). Anyone suffering from arthritis or other inflammatory diseases should consider excluding these vegetables from their diet, and research suggests that the rest of us would do well to eat them in moderation. The alkaloid content in the food plants, however, is very low compared to that in other nightshade plants, which can be highly toxic and dangerous. Cooking the vegetables lowers the alkaloid content by about 40-50%, so bear this in mind when eating them. If you find green and/or sprouted spots on potatoes, this usually indicates a high alkaloid content, so remove these spots before eating, or do not use the potatoes.
It is not just the vegetables you have to be careful of, but certain condiments and seasonings as well. The seasoning paprika is also derived from Capsicum annum, the common red pepper, and the seasoning cayenne comes from another nightshade, Capsicum frutenscens. Hot sauces that contain hot peppers should also be considered as a nightshade food, a prime example of this being tabasco sauce. It may be helpful to note here that black pepper, which belongs to the Piperaceae family, is not a member of this group. However the nightshade influence can even be found in some popular drinks, and other household products: chilli pepper and paprika are found in cola drinks (hence the name Dr Pepper), and a lot of pesticides are based on nicotine.
So although certain members of this plant family are highly nutritious, delicious and a food staple, they can also have certain potentially harmful effects which it is wise to be aware of.