Thyroid Disorders – Impact on Female Reproductive Health

By Georgia Marrion (MNut, BHSci, Adv. Dip Health Sci (Nat).

Broadly, thyroid disorders can be classified as the presence of thyroid gland dysfunctionality and altered hormone synthesis, however the specific types, clinical presentation, pathophysiological processes and biological consequences of different thyroid disorders vary.1 The most common thyroid disorders, overt (OH), subclinical (SCH), autoimmune hypothyroidism (Hashimoto’s thyroiditis [HT]) and postpartum thyroiditis, often occur on a progressive spectrum and are estimated to affect up to 15% of the female population.2-6

SCH, OH and HT are best diagnosed using both clinical and biochemical diagnostic parameters. SCH, a sign of early thyroid failure, can be mild or severe and presents biochemically with elevated thyrotropin and thyroid stimulating hormone and normal thyroxine (T4) and triiodothyronine (T3) levels.2,7-11 OH is characterised by elevated TSH and low T4, in most cases due to inadequate biosynthesis by the thyroid gland.2,5,11,12 SCH and OH are often (in the absence of iodine deficiency, another primary cause) due to HT, identified by the presence of lymphocytic infiltration of thyroid gland and antibodies, specifically thyroid peroxidase (TPOAb) and thyroglobulin (TGAb).4,5,11,13 (See Table 1). In at least 2.5% of individuals, SCH can progress to OH, with women at an increased risk.1,2,14-16

While biochemical parameters are an important part of thyroid disorder diagnosis, they need to be considered in the context of what is normal/abnormal for an individual. It has been demonstrated that changes in TSH levels in euthyroid people occurs within a much narrower range than population-based reference ranges, emphasising the importance of regularly assessing thyroid parameters in conjunction with clinical features in the individual and changes occurring within these diagnostic parameters over time.21

The clinical features of both SCH and overt hypothyroidism reflects the far-reaching biological effects of thyroid hormones in the body. Although many individuals with SCH and hypothyroidism can be asymptomatic, such clinical features can occur in the gastrointestinal (constipation, reduced appetite, difficulty swallowing); integumentary (dry skin, hair loss, loss of outer eyebrow third, puffy face and eyes); neurological (poor attention and memory, anxiety, low mood); musculoskeletal (cramps, stiffness, weakness, fatigue); endocrine (menstrual irregularities, reduced libido, increased serum cortisol); and metabolic (increased oxidative stress, systemic inflammation) systems.2,7,10,14,16,21-25

The significant impact of SCH, OT and HT on female reproductive health can be attributed to the close relationship between the hypothalamic-pituitary-ovarian (HPO) and hypothalamic-pituitary-thyroid axis.6 Also, the widespread expression of TSH and thyroid hormone receptors on human ovarian tissues and follicles highlights the crucial role of the thyroid for normal ovarian function, steroidogenesis, folliculogenesis, ovulation, corpus luteum synthesis, menstruation and fertility.6,22,26-29 Consequently, the presence of thyroid dysfunction, mild or severe, can have a significant adverse impact on menstrual health and fertility in women.

Undiagnosed and un- (or ineffectively) treated thyroid disorders can have a profound impact on the menstrual functionality and fertility in women, however in the majority of cases, these disorders and their consequences are inherently treatable.4-6,11 (See Table 2).

The medical management of suboptimal thyroid function involves levothyroxine therapy when TSH levels are >10 mIU/L.14 However, while it can be effective for normalising TSH (although in 10-15% of individuals treated with levothyroxine, symptoms persist despite normal TSH levels), it can be associated with adverse effects and may not effectively ameliorate the underlying physiological imbalances and processes contributing to the clinical symptoms and progression of suboptimal thyroid function.11,30 Also, treatment of non-pregnant women with SCH is controversial because of a commonly observed absence of benefit associated with treatment.16

Consequently, following accurate diagnosis, effective management of thyroid disorders and associated clinical symptoms such as those outlined in Table 2 is important and also requires a multifaceted therapeutic approach involving appropriate nutritional, lifestyle and environmental strategies. Specific herbs and nutrients can also promote and balance healthy thyroid function to improve the clinical symptomology and comorbidities associated with thyroid disorders.

*References available on request