Environmental exposure to cadmium at a level insufficient to induce renal tubular dysfunction does not affect bone density among female Japanese farmers

Some recent research suggests that environmental exposure to cadmium, even at low levels, may increase the risk of osteoporosis, and that the bone demineralization is not just a secondary effect of renal dysfunction induced by high doses of cadmium as previously reported. To investigate the effect of exposure to cadmium at a level insufficient to induce kidney damage on bone mineral density (BMD) and bone metabolism, we conducted health examinations on 1380 female farmers from five districts in Japan who consumed rice contaminated by low-to-moderate levels of cadmium. We collected peripheral blood and urine samples and medical and nutritional information, and measured forearm BMD. Analysis of the data for subjects grouped by urinary cadmium level and age-related menstrual status suggested that cadmium accelerates both the increase of urinary calcium excretion around the time of menopause and the subsequent decrease in bone density after menopause. However, multivariate analyses showed no significant contribution of cadmium to bone density or urinary calcium excretion, indicating that the results mentioned above were confounded by other factors. These results indicate that environmental exposure to cadmium at levels insufficient to induce renal dysfunction does not increase the risk of osteoporosis, strongly supporting the established explanation for bone injury induced by cadmium as a secondary effect.