In a recent study, researchers at Bengaluru’s St. John’s Research Institute, the Indian Institute of Science (IISc), and St. John’s Medical College and Hospital, have described how the presence of a particular mineral in the urine can tell a tale about the health of our bones. The findings are published in the journal Scientific Reports, and the study was funded by the Wellcome Trust/DBT India Alliance and the Department of Science and Technology.
Our bones undergo a continuous remodelling process where new ones replace old bone tissues. Osteoclasts, a particular type of bone cells that destroy bone tissues, work in tandem with osteoblasts that synthesise new bone tissues. In a healthy individual, the rate of bone formation and destruction are equal. Any imbalance in this process can result in conditions like osteoporosis leading to weak and brittle bones. Hence, diagnosing such conditions early on can help retain strong bones.
Calcium, a major mineral component of the bone, is considered an indicator of bone health. When calcium is depleted from bones, it gets thrown out in the urine. Thus, the amount of calcium present in the urine correlates with the difference in bone formation and destruction. This difference is known as bone mineral balance. Calcium has six naturally occurring isotopes, or variants, of which 40Ca and 44Ca are the most abundant ones. In the bone remodelling process, the formation of bone favours the lighter isotope (40Ca) leading to a depletion of heavier isotopes (44Ca). The researchers of this study estimated the variability in the ratio of these two isotopes (δ44/40Ca) to evaluate bone health.
Vitamin D3 is a common supplement prescribed to treat osteoporosis. The researchers of this study provided vitamin D3 supplements for three weeks to some patients with a deficiency of vitamin D3. They then analysed the changes in the calcium isotopes in their urine and calculated the bone mineral balance.
In healthy individuals, the δ44/40Ca value in the urine is expected to be positive. The researchers observed that when subjects were treated with vitamin D3 supplements, the δ44/40Ca was positive and the bone mineral balance of these patients was better than those who were not on supplements. This observation indicated the role of vitamin D3 in bone metabolism and health.
Two hormones, calcitonin and parathyroid, play an important role in the regulation of calcium levels in the body. Calcitonin promotes the deposition of calcium in the bones and parathyroid does the opposite. The researchers also observed that vitamin D3 supplements reduced the levels of parathyroid.
The study provides insights into how the urine can tell a tale of our bone health. “Our results indicate that the natural variability in δ44/40Ca of urine and the derived bone mineral balance from it can be used as a novel biomarker for bone health, and could be used for estimation of osteoporotic risks”, conclude the researchers.