Do you believe that lack of calcium is the most common cause of osteoporosis? Vitamin D deficiency may be even more important; a study from Amsterdam shows that 64 percent of postmenopausal women with osteoporosis lack vitamin D. A woman's bones are strongest when she is 20; you lose bone continuously over your lifetime until at 90, virtually all women have osteoporosis. Only recently have doctors become aware of this high rate of vitamin D deficiency which weakens bones. Very few people meet their needs for vitamin D from food; the most important source is sunlight. Still, during summer when sunlight is abundant, the prevalence of vitamin D deficiency was 59 percent, and during winter it was 69 percent. Warnings about skin cancers from sunlight exposure may have increased risk for osteoporosis. This study, presented at the 2005 annual meeting of the American Society for Bone and Mineral Research, shows that postmenopausal women should get blood tests for vitamin D, and those with low levels should get more sunlight or take vitamin D supplements.

Findings from the Women's Health Initiative study reported in JAMA (February 8, 2006) suggest that calcium supplements and vitamin D supplements do not prevent osteoporosis, but there was no separation of women with or without deficiencies. Many studies have shown that neither calcium nor vitamin D supplements are effective as treatments for osteoporosis; check with your doctor about the bone-strengthening medications.