Nightshades are a plant family, botanically known as Solanaceae, that include a number of our most popular vegetable varieties, such as tomatoes, capsicums and eggplants. They are so named because they do their growing in the shade of the night, rather than in the light of the sun.
Nearly all of the plants that belong to this family originated in the Altiplano region of South America near the Andes mountains, and were popularised in the fifteenth century by explorers travelling offshore. While the list of edible nightshades is small, the number of poisonous varieties is quite extensive.
Most nightshades are toxic to humans. The best-known of these is belladonna, or ‘deadly nightshade’, a poison around which the plot of Shakespeare’s Macbeth revolves. It contains tropane alkaloids that cause hallucination and delirium, as well as trouble generating saliva and swallowing. A coma and convulsions usually precede death. Though the root is believed to have the highest concentration of the toxins, the edible-looking berries are usually the cause of accidental poisoning. Ingestion of a single leaf or about 15–20 of its berries can be fatal in adults. Ironically, the name ‘belladonna’ literally translates as beautiful woman in Italian, and it was so named because Venetian women used it to enlarge their pupils, which apparently increased their attractiveness.
Good use of poison?
The powerful poison of the deadly nightshade is now the source of the antispasmodic drug atropine, which is used to treat nerve agent and pesticide poisonings and to decrease saliva production during surgery.
Glycoalkaloids in edible nightshades
As a natural defence mechanism against pests and disease, all nightshades produce glycoalkaloids, which are bitter compounds found throughout the plant. The highest concentration of this compound can be found in the leaves, flowers, roots and unripe fruit. So, they are essentially designed to be toxic, to defend themselves against fungi, viruses and insects. Although typically not fatal to humans, the toxicity can still cause problems, particularly people that have digestive sensitivity or those struggling with an autoimmune disease. If consumed in small doses, symptoms may include vomiting and diarrhoea, whereas at higher doses, much more serious symptoms can occur, such as fever, low blood pressure, confusion and other neurological problems.
Did you know?
Cherries, apples and sugar beets also contain small amounts of glycoalkaloids.
The most toxic?
Potato plants produce the most toxic glycoalkaloids found in the edible nightshade family and it is particularly prevalent in potatoes that are green or sprouting. Potatoes have been known to cause livestock deaths by cows and horses feeding on raw potatoes or the plant’s foliage. Thankfully, our digestive and immune systems are vastly different.
Autoimmunity and vitamin D
We all know that vitamin D is crucial for proper bone formation. There is, however, a potent form of vitamin D3 in nightshade vegetables that actually prevents proper calcium metabolism. The result is the formation of calcium in the soft tissue rather than in the bones, which is where we need it. This links consumption of nightshades to arthritis and joint pain, especially the autoimmune disease rheumatoid arthritis.
Digestive sensitivity
The symptoms of nightshade intolerance are often confused with intolerance to gluten or dairy, and can include digestive distress, such as bloating, heartburn and IBS, as well as headaches, joint pain or stiffness. Intolerance to nightshades is mostly seen in Caucasians and is mostly genetic. Continuing to eat nightshades while you have an intolerance can increase the risk of developing a ‘leaky gut’, which causes undigested food particles and bacteria to ‘leak' through the intestine and flood directly into the bloodstream due to damage of the small intestine.
If you feel you may have sensitivity to nightshades, you can reduce the effects by peeling your potatoes, avoiding unripe fruit and cooking the vegetable rather than eating it raw.