Weight Loss Not a Certainty With Hypothyroidism Treatment

Nancy A. Melville

October 21, 2013

SAN JUAN, Puerto Rico — Hypothyroidism is commonly associated with weight gain, but contrary to popular belief, treatment of the condition does not result in weight loss in the majority of patients, according to new research presented at the 2013 Annual Meeting of the American Thyroid Association.

"We frequently see patients who are disappointed that they do not have dramatic weight loss following initiation of thyroid hormone therapy, so these results were not entirely surprising," said Elizabeth Pearce, MD, from endocrinology, diabetes, and nutrition section of Boston University School of Medicine, Massachusetts.

"We found that modest weight loss following initiation of levothyroxine treatment for hypothyroidism occurs in only about half of patients," she told Medscape Medical News.

Michael T. McDermott, MD, director of endocrinology and diabetes practice at the University of Colorado School of Medicine, Aurora, who comoderated the session, said the study was limited by the fact that it was a retrospective chart review, but he noted some interesting points nonetheless.

"I would expect weight loss to occur but would expect [it] to be much more significant in people with more severe hypothyroidism and less, if any . . . in those with mild or very mild hypothyroidism, which most of the subjects in the current study had," he told Medscape Medical News. Outcome will depend on the severity of the hypothyroidism, the adequacy of treatment, and the subsequent calorie intake of each person, he observed.

One of Few Studies to Examine Hypothyroid Treatment and Weight

Dr. Pearce explained that surprisingly few studies have examined weight change of hypothyroid patients after levothyroxine (LT4) treatment. For their retrospective study, she and her colleagues evaluated the electronic medical records of 101 patients (mean age, 48; 71% women) who were enrolled at Boston Medical Center with newly diagnosed primary hypothyroidism with an initial thyroid-stimulating hormone (TSH) level of 10 mIU/L or greater between January 2003 and February 2011.

The evaluation also included patients' TSH levels and weight at the point of diagnosis and for up to 24 months following the initiation of treatment with LT4.

Patients were excluded if they had postsurgical hypothyroidism, thyroid cancer, history of radioactive iodine or head/neck radiation, congestive heart failure, anorexia nervosa, end-stage renal disease, cirrhosis, pregnancy, or use of prescription weight-loss medication.

The results showed that while the median TSH levels dropped from 48 mIU/L to 2.3 mIU/L posttreatment, there was only a mean -0.1-kg change in the mean baseline weight of 79.6 kg.

Among the 52% of patients who did lose weight, the mean weight loss was 3.8 kg.

Factors including education, insurance type, age, gender, race, initial TSH, and time to normalization of TSH were not associated with weight change or weight loss.

While only about half of the patients lost weight over the follow-up, the trend might still represent an improvement over what's typically seen in the general population, Dr. Pearce noted.

"Although we did not have a control group for comparison in this study, in general, in adult populations, weight gradually increases over time," she observed.

Prospective Study Required

Dr. Pearce noted that the rate of weight loss in comparison with gain from the onset of hypothyroidism is hard to assess.

"There is no research demonstrating how much weight patients gain with the onset of hypothyroidism; this would be hard to do, as it is usually impossible to determine exactly when hypothyroidism first developed," she explained.

The longest study to date evaluating weight loss after hypothyroidism treatment involved just 18 patients who were followed for 24 months after initiation of thyroid hormone for overt hypothyroidism, she noted. (Am J Med. 1984;76: 963-970). The results showed modest decreases in the first 6 months of thyroid hormone treatment but then an increase back to baseline values by 24 months.

Dr. McDermott said the proper approach to investigate this issue properly would be a prospective study.

He noted that a decrease in the resting metabolic rate occurs in proportion to the degree of hypothyroidism, and appropriate treatment should reverse that, thereby increasing the amount of calories a person burns each day — but overeating can offset that effect.

"If the [increase in resting metabolic rate] is not accompanied by increased food consumption, weight loss will occur," he explained. But "If a person eats more calories when treatment of hypothyroidism is started . . . weight loss will not occur."

"I see this in my practice, and I believe a well-designed prospective study would show this," he concluded.

Dr. Pearce and Dr. McDermott have reported no relevant financial relationships.

2013 Annual Meeting of the American Thyroid Association. Abstract 185, presented October 19, 2013.

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