Disclosures: The Swedish Research Council, the Swedish Diabetes Foundation, the Swedish Heart-Lung Foundation and the Novo Nordisk Foundation funded this study. One of the study authors reports he has received advisory board fees from Itrim and Johnson & Johnson; another author reports she has received consultant fees from Johnson & Johnson.
July 21, 2021
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High anemia risk persists decades after bariatric surgery

Disclosures: The Swedish Research Council, the Swedish Diabetes Foundation, the Swedish Heart-Lung Foundation and the Novo Nordisk Foundation funded this study. One of the study authors reports he has received advisory board fees from Itrim and Johnson & Johnson; another author reports she has received consultant fees from Johnson & Johnson.
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Adults with obesity who undergo gastric bypass are five times more likely to develop anemia compared with those receiving nonsurgical obesity care, highlighting the importance of long-term adherence to nutritional supplementation.

In an analysis of participants in the long-term Swedish Obese Subjects study, researchers also found that gastric banding and vertical-banded gastroplasty were each associated with a three times increased risk for anemia during 20 years of follow-up, noting that studies of anemia after bariatric surgery with a follow-up period of more than 5 years are rare.

Adults with obesity who underwent gastric bypass, vertical-banded gastroplasty or gastric banding had an increased risk for developing anemia compared with those who did not have surgery. Data were derived from Johansson K, et al. Lancet Diabetes Endocrinol. 2021;doi:10.1016/S2213-8587(21)00141-8.

“Although several studies have reported nutritional deficiencies after bariatric surgery, most were retrospective studies of short duration and the majority did not include a comparison group,” Kari Johansson, PhD, assistant professor in the department of medicine at the Karolinska Institutet in Stockholm, and colleagues wrote in the study background. “Two systematic reviews and meta-analyses, one including 15 studies and the other including 20 studies, found that the prevalence of anemia was increased 1 year after gastric bypass surgery compared with before surgery. As acknowledged by the authors, the meta-analyses were limited by high heterogeneity. Long-term follow-up studies are scarce, with only three reporting on anemia prevalence 10 years after bariatric surgery.”

Comparing surgery with usual care

In a prospective study, Johansson and colleagues analyzed data from 4,047 adults aged 37 to 60 years with a BMI of at least 34 kg/m² for men or at least 38 kg/m² for women, recruited from 480 primary health care centers and 25 surgical departments in Sweden. Within the cohort, 2,007 patients chose bariatric surgery — 266 who underwent gastric bypass, 1,365 who underwent vertical-banded gastroplasty and 376 who underwent gastric banding — and 2,040 matched controls received usual obesity care, ranging from lifestyle advice to no treatment.

Researchers measured hemoglobin concentration at baseline, annually for the first 4 years, and again at years 6, 8, 10, 15 and 20. Anemia was defined as a hemoglobin concentration of less than 120 g/L for women and less than 130 g/L for men. The primary, nonspecified outcome was the incidence of anemia, assessed in the as-treated population. Researchers used HRs to assess associations between treatment type and anemia, adjusted for age, sex, BMI, menopausal status, education, diabetes and hypertension. Follow-up of the cohort is ongoing.

During a maximum of 20 years and a median of 10 years of follow-up, there were 133 anemia events in the gastric bypass group, 359 in the vertical-banded gastroplasty group, 101 in the gastric banding group and 261 in the control group.

Compared with controls (13 cases per 1,000 person-years; 95% CI, 11–14), the incidence of anemia was higher in the gastric bypass group (64 cases per 1,000 person-years; 95% CI, 53-74; HR = 5.05; 95% CI 3.94-6.48), the vertical-banded gastroplasty group (23 cases per 1,000 person-years; 95% CI, 21-26; HR = 2.67; 95% CI, 2.25-3.18) and the gastric banding group (26 per 1,000 person-years; 95% CI, 21-31; HR = 2.76; 95% CI, 2.15-3.52). Associations persisted in the adjusted models.

“Rick of anemia over 20 years of follow-up was increased for all bariatric surgery groups compared with the control group receiving usual care,” the researchers wrote. “The greatest risk was observed in the gastric bypass group, even though the use of nutritional supplements was highest in this group. These findings highlight the importance of long-term compliance to nutritional supplementation and monitoring to enable prevention and early detection of serious nutritional deficiencies after bariatric surgery.”

‘First, do no harm’

In a related editorial, Karl J. Neff, MB, MRCPI, PhD, consultant endocrinologist at the Diabetes Complications Research Centre at University College Dublin, and Carel le Roux, MBChB, FRCP, FRCPath, PhD, professor of experimental pathology at University College Dublin, wrote that the Swedish Obese Subjects study “changes the paradigm,” showing that there is a persistent increased risk for anemia after bariatric surgery that requires ongoing supplementation in the long term. Additionally, more research is needed on postoperative bone health and nerve function, as well as optimal supplementation doses for all micronutrients, they wrote.

“This important contribution from Johansson and colleagues adds to the evidence base, but more needs to be done to optimize strategies for postoperative micronutrient supplementation and, eventually, individualize care,” Neff and le Roux wrote. “Until such time, clinicians should adhere to the dictum, primum non nocere (first, do no harm), even if it means having to rely on guidelines derived from eminence-based medicine instead of evidence-based medicine.”