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Calcium supplement formulations similarly ineffective for normalizing parathyroid hormone following bariatric surgery

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August 31, 2018

In adults with slightly elevated parathyroid hormone following Roux-en-Y gastric bypass surgery, supplementation with either calcium carbonate or calcium citrate did not restore normal PTH level, according to findings published in Clinical Endocrinology.

Lene Ring Madsen

“Despite clinical recommendations of lifelong vitamin D and calcium supplementation, elevated levels of PTH, which is potentially harmful to bone health, are frequent following RYGB,” Lene Ring Madsen, MD, a doctoral student in the department of endocrinology and internal medicine at Aarhus University Hospital, Denmark, and colleagues wrote in the study background. “Besides vitamin D and calcium malabsorption, an altered diet including less dairy products may also influence the calcium intake after [Roux-en-Y gastric bypass surgery].”

In a 12-week randomized double-blind, controlled trial, researchers enrolled 39 adults (mean age, 49 years; 13 women) who had undergone Roux-en-Y gastric bypass surgery a mean of 6.2 years before study entry. Participants had elevated PTH levels after adhering for at least the previous 12 months to daily multivitamin supplement use (including 400-500 mg elementary calcium plus 400-800 IU of vitamin D3) plus use of a calcium carbonate (800 mg elementary calcium) and vitamin D3 (1,520 IU) supplement. The multivitamin was continued through the study period, whereas the other calcium carbonate and D3 supplement was discontinued at the start of the trial. Participants had PTH greater than 6.9 pmol (normal range, 1.6-6.9 pmol/L), 25-hydroxyvitamin D level greater than 20 ng/ml and normal levels of plasma ionized calcium (1.18-1.32 mmol/L).

Participants were randomly assigned at baseline to received either 1,200 mg elementary calcium daily in combination with 2,280 IU vitamin D3 (3,000 mg calcium carbonate daily as one tablet and one calcium-free placebo tablet 3 times daily with meals) or 1,200 mg elementary calcium in combination with 2,400 IU vitamin D3 (5,712 mg tricalcium citrate daily as 2 two tablets 3 times per day with meals). The primary outcome was the change in PTH from baseline to week 12.

Based on tablet count, both groups showed a high level of adherence to their regimens, according to researchers. Overall, the two calcium regimens were well-tolerated, although the calcium citrate group reported more symptoms of constipation vs. the calcium carbonate group (37% vs.10%; P = .047). At baseline, the calcium carbonate group self-reported lower daily intake of dietary calcium (791 g vs. 996; P = .042) whereas the calcium citrate group had somewhat higher levels of the bone-turnover markers CTX, osteocalcin and bone-specific alkaline phosphatase.

At 12 weeks, the researchers found no difference between the groups in changes to mean PTH levels or number of participants with PTH greater than 6.9 pmol/L. During the intervention, the calcium citrate-treated group showed more significant decreases in the bone turnover markers P1NP (-16.6% vs. -3.2%; P = .021), osteocalcin (-17.2% vs. -4.3%; P = .007) and bone-specific alkaline phosphatase (-4.0% vs. 3.7%; P = .027), and these differences remained significant after adjusting for daily intake of dietary calcium, the use of loop diuretics and thiazide. No difference in urinary calcium excretion was observed between the groups.

No significant changes in mean PTH levels were seen among the entire cohort during the intervention. However, in a subgroup of 12 participants with PTH greater than pmol/L at baseline, the added calcium supplementation did lower mean PTH levels by 1.25 pmol/L; P = .005) regardless of the type of supplement used.

A study with longer follow-up will be valuable in further investigating this topic, Larsen told Endocrine Today.

“The take-home message of this study is that based on current evidence, we cannot recommend calcium citrate over calcium carbonate as vitamin supplementation after Roux-en-Y gastric bypass. This is opposite to existing recommendations,” she said. “In Denmark, calcium citrate is not only more expensive, but requires more pills every day to get the amount of calcium recommended. We can now tell our patients that they can stick to calcium carbonate.” – by Jennifer Byrne

Disclosures: The study was funded by the Research Council of Central Denmark Region, the Health Research Fund of Central Denmark Region, the Novo Nordisk Foundation, the AP Møller Foundation and the Danish Diabetes Academy founded by the Novo Nordisk Foundation. The researchers report no relevant disclosures.

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