Endocrine Abstracts

Background: Secondary hyperparathyroidism (SHPT) is common in obesity, and a concern after obesity surgery due to negative impact on bone. Longitudinal data is sparse, and relationships with vitamin D and calcium levels are unclear. We studied the prevalence of SHPT over five years after Roux-en-Y gastric bypass (RYGB) and investigated whether SHPT was associated with serum levels of 25-hydroxyvitamin D (25(OH)D) and ionized calcium (iCa).

Methods: 347 of 568 (61%) patients attending a 5-year follow-up visit after a RYGB at Oslo University Hospital in the years 2004-2008 were eligible for study inclusion. We excluded 14 patients with missing data, four with primary hyperparathyroidism and 10 with elevated serum creatinine. We defined SHPT as PTH >7.0 pmol/l and vitamin D deficiency as 25(OH)D <50 nmol/l. Low iCa refers to serum levels <1.21 mmol/l (lower tertile of reference range or below). Substitution of vitamin D3 (1000 IE/day) and calcium carbonate (1000 mg/day) was recommended.

Results: Among the 319 included patients (230 women) the prevalence of SHPT was 32% before surgery, while the prevalence was 18%, 24%, 28% and 35% after a half, one, two and five years, respectively. Vitamin D deficiency was found in 45% preoperatively, and 18%, 20%, 28% and 33% after a half, one, two and five years. The proportion with serum iCa in the lower range was: 24% preoperatively, and 29%, 35%, 44% and 49% at a half, one, two and five years. Table 1 illustrates the prevalence of SHPT by serum vitamin D and calcium levels (*illustrates P<0.001 between subgroups).

Discussion: The prevalence of SHPT decreased the first half year after RYGB and thereafter increased over time. SHPT was higher in vitamin D deficiency and with iCa levels in the lower range. Improved vitamin D and calcium status may potentially reduce the prevalence of SHPT both preoperatively and after obesity surgery.