High body fat may protect against hypoparathyroidism after surgery
Patients with higher BMI at lower risk of developing condition, study finds
People with higher body fat — as measured by body mass index, or BMI — have a lower risk of developing hypoparathyroidism following total thyroidectomy, a surgery that completely removes the thyroid glands, a new study reports.
Besides body fat, levels of parathyroid hormone (PTH) before surgery and a patient’s race also were independent predictors of higher PTH following the surgery. Specifically, the scientists noted that individuals of “non-white race have relative protection from postoperative hypoparathyroidism.”
“This study demonstrates a principle known as the obesity paradox — that higher BMI can be associated with a positive health outcome such as in this case, that a higher patient BMI can be protective against postoperative hypoparathyroidism,” the researchers wrote.
These findings may have “important clinical implications,” according to the team. For one, calcium supplements following surgery may be “weaned more aggressively” in patients with higher body fat, they noted.
The study, “The Obesity Paradox in Thyroid Surgery: Is Higher BMI Protective Against Hypoparathyroidism?,” was published in the journal The American Surgeon.
Researchers test hypothesis of lower hypoparathyroidism with high body fat
Hypoparathyroidism is a rare disease characterized by low levels of PTH, a hormone that plays key roles in regulating blood calcium and phosphate levels.
About 75% of hypoparathyroidism cases are caused by removing or damaging the parathyroid glands during neck surgery.
Previous studies have reported a link between increasing PTH levels and higher body fat. Among the reasons for this correlation, scientists have suggested, is lower vitamin D levels — a finding more prevalent among African American and Hispanic patients.
Based on this evidence, a team of U.S. researchers hypothesized that patients with a higher body fat content would have lower rates of hypoparathyroidism after total thyroidectomy.
To test this hypothesis, the researchers analyzed data from adults and children who underwent this surgery between 2015 and 2021. Their main aim was to assess the link between body fat, measured using BMI, a ratio of weight to height, and post-surgical PTH levels.
Of 418 patients who underwent surgery, 352 met the necessary criteria and were included in the analysis. The mean age of these patients was 42.7, and more than three-quarters (77.3%) were women.
Almost half of the patients (46.6%) had Graves’ disease, an autoimmune disorder that makes the thyroid overactive.
Among all patients, almost a third (30.7%) were deemed obese, defined by a BMI between 30 and 39.99. A total of 11.8% were morbidly obese, with a BMI higher than 40.
Overall, the group’s mean PTH levels dropped following surgery, from 60.6 picograms per millilitre (pcg/mL) to 29.1 pcg/mL.
A statistical analysis showed that lower PTH values prior to surgery were associated with a significantly higher risk of hypoparathyroidism after the surgical intervention.
When the researchers compared morbidly obese and underweight patients — those with BMI below 18.5 — they found that increased body fat was significantly linked with higher mean PTH levels after surgery (mean 46 vs. 19.3 pcg/mL).
A positive albeit small correlation was found between higher BMI and higher post-surgery PTH values.
Higher BMI may give patients ‘relative protection’ from hypoparathyroidism
BMI also correlated significantly with patient-reported symptoms of hypocalcemia, or low calcium levels. These symptoms occurred in 50% of those with the lowest BMI scores, and in 8% of patients in the highest group.
Race was significantly linked with pre- and post-surgery PTH levels, and also with hypocalcemia symptoms.
Pre-surgery PTH levels were higher in Caucasian patients (mean 52.7 pcg/mL) and in African American individuals — mean 68.2 pcg/mL — compared with Hispanic individuals (mean 46.6 pcg/mL) and Asian patients, whose levels were a mean of 40.7 pcg/mL. After surgery, the highest PTH levels were seen in Hispanic patients (41.1 pcg/mL) and African American individuals, 33.8 pcg/mL.
Hypocalcemia symptoms were more common among Caucasian people (31.4%) and Asian people (50%).
However, “despite the relationship between both BMI and race with postoperative PTH, there was no significant relationship identified between BMI and race themselves to explain the association with postoperative PTH,” the team noted.
No significant links were seen regarding vitamin D levels and post-surgical PTH levels, nor between the number of parathyroid glands visualized or transplanted during surgery and post-surgical levels of PTH.
Patients with higher BMIs have relative protection from postoperative hypoparathyroidism independent of other factors including surgical indication, number of parathyroid glands visualized during surgery, or vitamin D levels.
A subsequent, more complex analysis showed that higher pre-surgery PTH, higher BMI, and being a non-white person were independent predictive factors of higher PTH after surgery.
The same analysis for hypocalcemia revealed that BMI and the surgeon were linked with patient-reported symptoms.
Overall, “patients with higher BMIs have relative protection from postoperative hypoparathyroidism independent of other factors including surgical indication, number of parathyroid glands visualized during surgery, or vitamin D levels,” the researchers wrote.
“This early investigation into the relationship of BMI and postoperative hypoparathyroidism could serve as a roadmap for additional, prospective studies,” they concluded.