The butterfly-shaped thyroid gland lying at the base of the neck is a complex organ, serving as a master control for many processes in the body, including metabolism, bone growth and regulation of body temperature. Diseases of the thyroid are intricately associated with reproductive issues in many stages of a woman's life and are among the most common medical conditions in women, increasing with age.
In girls and young women, thyroid dysfunction can produce delayed or irregular menstrual periods. McConnell noted that as recently as the 1970s, when he was in medical school, "teenage girls who had delayed menarche (onset of menstruation) were often given thyroid hormone just to stimulate the period. It was just done empirically," he said.
The bodies of young women with eating disorders frequently don't produce the sex hormones necessary for monthly menstrual periods or ovulation; at the same time, their bodies sense starvation and turn down or turn off the thyroid gland to conserve energy, slowing the heart rate, digestion and lowering body temperature. These issues are particularly relevant in the modeling business, where young women may reduce their calories to dangerously low levels in the pursuit of highly prized thinness.
Women may become aware of thyroid issues when they're trying to become pregnant. "Thyroid conditions can cause infertility," said Dr. Loren W. Greene, an endocrinologist at NYU Langone Medical Center. "One of the oldest treatments for infertility…before doctors could measure thyroid function…was to empirically give people thyroid pills and see if it helped. Sometimes it seemed to work."
Thyroid problems in women who do become pregnant can increase the risks of miscarriage or premature birth and may be associated with Down syndrome in the child.
Not only can thyroid problems produce early menopause in young women, but they sometimes are mistaken for menopause among women in their 40s. Greene said she's particularly concerned about "the woman who stops having periods in her 40s and goes undiagnosed for thyroid conditions which could probably correct her period."
Premature menopause, also called premature ovarian failure, occurs rarely among women in their mid-20s, but is not unheard of, McConnell said. It can be due to an autoimmune disorder that attacks the ovaries and prevents the patient from becoming pregnant. The autoimmune attack can be associated with low thyroid function or with an inflammation of the thyroid gland called chronic thyroiditis or Hashimoto's disease.
Greene cautioned that within the population of models who may be excessively dieting, "it's much more likely if you're not having periods and you're that skinny that the association has to do with...not having enough body fat to put out sex hormones to have normal periods."
A woman who develops menstrual irregularities or experiences weight changes that cannot be explained should consider having her thyroid checked. That's easily done with blood tests that measure the level of thyroid-stimulating hormone (TSH), which is "usually the first sign of an underactive or overactive thyroid," Greene said.
Patients with low thyroid levels can take daily thyroid supplement pills. Those with excessive levels may be given prescription medications that interfere with formation of thyroid hormone. Some diagnosed with hyperthyroid conditions like Graves' disease may be treated with radioactive iodine that is absorbed by the thyroid gland and kills it. Afterward, the patient must take daily thyroid supplements to restore normal levels of thyroid hormone.