Secondary hyperparathyroidism after obesity surgery - exploring the impact of vitamin D and calcium, and aspects on bone health

Studies have shown a relationship for calcium and vitamin D levels with parathyroid hormone (PTH), and between PTH and bone mineral density (BMD). Secondary hyperparathyroidism (SHPT), with elevated PTH levels, has been investigated less extensively, but associations are found with lower levels of calcium and vitamin D, and lower BMD. SHPT was frequent in our patients after obesity surgery, mainly gastric bypass. It was prevalent even with calcium and vitamin D levels considered to be normal. Uncertainties existed around vitamin D recommendations, and the impact of SHPT on bone health. This thesis is based on four studies. Three focus on vitamin D levels, calcium levels and SHPT after obesity surgery, two cross-sectional and one longitudinal. The 4th investigated BMD at 10 years. We found relationships between vitamin D, calcium and PTH levels. There was a left-shifted calcium distribution, and SHPT may be suppressed further with higher vitamin D levels than are recommended. SHPT was also associated with lower BMD. The thesis reviews central aspects of the vitamin D-calcium-bone homeostasis, and provides an updated understanding in the population having undergone obesity surgery