BACKGROUND
Surgery to promote weight loss (bariatric surgery) is effective in helping obese people lose weight. There are several different types of bariatric surgery, some of which involve decreasing the size of the stomach (so that less food can be eaten at any one time) and others that involve rerouting the path of food through the intestines, which decreases the overall amount of food that can be absorbed by the intestinal tract (called bypass surgery). While bariatric surgery does decrease the number of calories a person can take in or absorb, it similarly decreases a person’s intake or absorption of important vitamins and minerals. For this reason, one possible side effect of bariatric surgery is vitamin and mineral deficiency, in particular, low levels of vitamin D and of calcium. Calcium plays a very important role in normal body function. Normal calcium levels are needed for good bone health and for normal muscle function. People who have low calcium levels may experience numbness/tingling, muscles spasms/ cramps or even seizures, and the effects of low calcium levels may be severe enough to require hospitalization.

Body calcium levels are controlled by four tiny glands, called the parathyroid glands, which are located on the surface of the thyroid gland. All four of these glands make the same hormone, called parathyroid hormone, which helps the body absorb calcium and maintain normal calcium levels. For this reason, thyroid surgeons must be very careful to avoid damaging the parathyroid glands when removing the thyroid gland during thyroid surgery. The authors of this study aimed to determine if people who underwent bariatric surgery and then subsequently undergo thyroid surgery are more likely to have low calcium levels than thyroid surgery patients who have not had weight loss surgery.

THE FULL ARTICLE TITLE
Lorenz FJ et al 2022 Hypocalcemia after thyroidectomy in patients with prior bariatric surgery: A propensity score matched analysis from a national administrative database. Thyroid 32:1382–1391.

SUMMARY OF THE STUDY
The authors of this study looked at a large database that includes information about people who have undergone surgery in the United States. The study identified 29,792 people who had thyroid surgery between 2011 and 2021, of which 446 had undergone bariatric surgery prior to removal of their thyroid glands (total thyroidectomy). The authors found that the risk of low blood calcium levels after total thyroidectomy among people who had previously undergone bariatric surgery was 2-fold higher than for people who had not undergone previous bariatric surgery. This was true within 1 month of thyroid surgery, within 6 months of thyroid surgery and even at 12 months after thyroid surgery. When the authors specifically looked at the risk of low calcium after total thyroidectomy, relative to each type of bariatric surgery, they found that only bypass-type weight loss surgery increased the risk of low calcium levels in these patients.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that the risk of low calcium levels after total thyroidectomy is significantly higher in patients who have previously undergone bypass-type bariatric surgery. This increased risk must be carefully explained to these patients by their thyroid surgeon before choosing to proceed with total thyroidectomy. In addition, the thyroid surgeon should avoid removing the entire thyroid gland (partial thyroidectomy) whenever possible for these patients, as parathyroid glands associated with thyroid tissue that is not removed will not be in danger of being damaged during thyroid surgery. Finally, people who have previously undergone bypass-type bariatric surgery who subsequently need to a total thyroidectomy should be treated with calcium and vitamin D, which helps the body absorb calcium, before and after surgery, to minimize risk of low calcium levels after total thyroidectomy.

— Jason D. Prescott, MD PhD

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