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Iodine deficiency

SOS study: GBP and VBG patients do not have iodine deficiency

Even after the researchers excluded with the few SOS-patients who were taking iodine supplements, the results for 24-UIC and 24-UIE were unaltered

A ten-year sub-analysis from the Swedish Obese Subjects (SOS) Study has reported that patients who received either a gastric by-pass (GBP) or vertical banded gastroplasty (VBG) do not suffer from iodine deficiency, although both patient groups had lower iodine status than the obese non-operated controls (OB-controls). Therefore, researchers Kungälvs Hospital, Kungälv, the University of Gothenburg, Gothenburg and the Mölnlycke Health Care Center, Mölnlycke, Sweden, recommended that dietary supplements after bariatric surgery do not need to include iodine, in iodine sufficient countries.

The paper, ‘Iodine Status After Bariatric Surgery—a Prospective 10-Year Report from the Swedish Obese Subjects (SOS) Study’, published in Obesity Surgery, sought to whether GBP develop iodine deficiency from malabsorption, and if GBP- and VBG- patients develop lower 24-h urinary iodine excretion (24-UIE) than OB-controls due to lower iodine intake.

The authors note that iodine is important for the production of thyroid hormones and in Sweden the main iodine sources are iodised salt, dairy products, fish and seafood. Iodine status is commonly determined by urinary iodine concentration (UIC) in spot urine (range of UIC 100–199μg/L), with 24-UIE the best marker of iodine intake.

Using data from the SOS study, 188 GBP-patients were matched with 188 VBG-patients and 188 OB-controls and with three subgroups from 412 World Health Organization MONItoring of trends and determinants for CArdiovascular disease (WHO MONICA) controls. The primary outcome was 24-UIE and secondary outcomes were iodine intake, iodine supplementation, TSH, FT4 and thyroid morbidity.

Outcomes

In the three groups of SOS-patients, baseline median 24-UIC was similar and within the reference range, i.e., within 100–199 μg/L, but it was higher than in MONICA-controls (p<0.001). 24-UIC decreased from baseline to ten years in GBP- and VBG-groups but was still within the reference range; whereas, it was unchanged in OB-controls. At ten years, 24-UIC was similar in the GBP-patients and MONICA-controls; whereas, it was still higher in the VGB-patients than in MONICA-controls (p=0.002).

Baseline median 24-UIE exceeded 200μg/day in all three SOS-groups, which was higher than the 137μg/day observed in MONICA-group (p<0.001). From baseline to ten years, 24-UIE decreased similarly in both the GBP- (215 to 161μg/day) and VBG-group (201 to 149μg/day) and was similar to MONICA-group (137μg/day) at ten years. However, in OB-controls, 24-UIE was unaltered (203 at baseline and 189μg/day at ten years).

Even after the researchers excluded with the few SOS-patients who were taking iodine supplements, the results for 24-UIC and 24-UIE were unaltered. A sensitivity analysis of those with urine samples on all three occasions compared to the analysis of the whole groups provided similar results. There were too few SOS-patients taking iodine containing supplement for statistical analysis.

The researchers hypothesised that one possible explanation for the lower 24-UIE after surgery in presence of unaltered iodine intake was that both the GBP- and VBG-groups suffered from iodine malabsorption, which was masked by excessive iodine intake. Several factors may influence iodine absorption including:

  • the removal of the part of the gastrointestinal tract where iodine and iodate are converted to absorbable iodide
  • the lack of digestion normally occurring in the stomach
  • the lack of recycling of iodine; and
  • a possible rapid emptying of the stomach

Therefore, they recommend that additional research is required on the physiology of iodine absorption and its alterations after bariatric surgery.

“Bariatric surgery in iodine sufficient countries does not result in iodine deficiency, even though it decreases iodine levels. Hence, the hypothesis of this study was disproved,” the authors write. “We could not explain the decreased iodine levels by our estimates of iodine intake or altered absorption. Dietary supplements recommended after bariatric surgery do not need to include iodine, in iodine sufficient countries.”

To access this paper, please click here

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