The purpose of this study was to assess whether dietary changes aimed at reducing serum cholesterol can increase the risk of osteoporosis (OP) and fracture. The study group consisted of 311 postmenopausal women with high serum cholesterol levels and following a diet low in dairy products (calcium intake estimated at less than 300 mg/day) for 27.3 +/- 29.1 months. This sample was compared with a case-control group of 622 healthy postmenopausal women paired for age and age at menopause and with a calcium intake estimated at more than 1 g/day. Bone mineral density was measured at the lumbar spine by dual-energy X-ray absorptiometry. Prevalence of OP was significantly higher in women with a low dairy calcium intake (42.1% vs 22.3%; p < 0.0001), as was the number of Colles' fractures occurring after menopause (4.5% vs 1.6%; p = 0.008). Multiple logistic regression analyses demonstrated that a diet low in dairy calcium was a risk factor for OP (OR = 2.52, 95% CI 1.84-3.45) and Colles' fracture (OR = 2.72, 95% CI 1.18-6.26). In the low dairy calcium group, diet duration significantly influenced the risk of OP (OR = 1.13, 95% CI 1.01-1.25 for 1 year of diet). No differences in further risk factors for coronary heart disease were found between the groups, but the proportion of women physically active was lower in the women with high serum cholesterol levels. A diet that severely limits calcium intake from dairy products in an attempt to correct raised serum cholesterol levels is a risk factor for postmenopausal OP and Colles' fracture. Dietary intervention methods to lower serum cholesterol in postmenopausal women should maintain an adequate calcium intake by providing calcium from low-fat dairy products or calcium supplements.