According to a study done at the Department of Family and Preventive Medicine at University of California at San Diego, a lifetime equivalent of two cups of coffee per day is associated with decreased bone density at both the hip and the spine in older women if they don't also drink milk (JAMA, 1994; 27: 280-3). (Moderate daily milk consumption, about one glass of milk per day, seems to counterbalance somewhat the calcium wasting effect of caffeine.)
The concept that the nightshade vegetables affect calcium balance has been put forth for over 20 years by Dr Norman Childers, a professor of botany at the University of Florida at Gainesville and formerly of horticulture at Rutgers University. The nightshades comprise a family named Solanaceae, which includes potato, tomato, aubergine, red, green, chili and other hot peppers, paprika, and tobacco. Professor Childers has shown that nightshade consumption contributes to osteoarthritis because these plants contain substances called alkaloids, which disturb the calcium metabolism and tend to remove calcium from the bones, causing aches, pains, even deformations.
It has been my speculation since the early 1980s that people eat so many nightshades simply to counterbalance their consumption of milk products, which have more calcium than human beings need. Theoretically, then, dairy products and nightshades are opposite and complementary: if you eat one, you need the other. Conversely, if you stop eating one (say, dairy), you might do well abandoning the other, or else there may be repercussions in the body's calcium balance. Many of my students and acquaintances have found that if they keep eating nightshades in a low fat, dairy free diet, their joints begin to ache.
I haven't found any studies that directly link osteoporosis and nightshades. Nevertheless, it may be sensible to pay attention to them because of their ability to affect calcium balance. For those at risk for osteoporosis, an occasional potato or tomato may not cause any trouble; however, it may be a good idea to refrain from relying heavily on these vegetables in the diet. In all cases in which I enquired, women with osteoporosis and a history of bone fractures relied on heavy daily use of potatoes as a major source of starch, and tomatoes as both a flavouring and a raw vegetable.
Annemarie Colbin's latest book, Food and Our Bones (Dutton-Plume, 1998), published in America, is available to WDDTY readers through her internet website at www.foodandhealing.com or by writing to Natural Gourmet, 48 W 21st St, New York, NY 10010 USA. Tel: 212-645-5170). $13.95 plus postage and handling.