A list of common edible nightshades:
One theory on why nightshades may be associated with calcium issues is that the form of vitamin D in nightshades (Vitamin D3) actually prevents proper calcium metabolism, causing the body to deposit calcium in the soft tissue instead of in the bones.
Other research attributes the autoimmune dangers of nightshades to a group of chemical compounds called glycoalkaloids, which are natural pesticides produced by nightshade plants. These include solanine (found in potatoes), nicotine and capsaicin (the chemical that gives peppers their heat). While the plant is alive, these compounds work as a defense against pests and molds. Some believe that these alkaloids may cause gut irritation.
A study published in the Journal of Neurological and Orthopedic Medical Surgery found that diet plays a role in arthritis, and nightshades are an important causative factor in arthritis in sensitive people. Research also found that osteoarthritis appears to be a result of long-term consumption and/or use of solanaceae (i.e. nightshades).
Article courtesy of Woods Eco-cuisine Sdn Bhd