Women with subclinical hypothyroidism who are younger than 65 years of age may be at increased risk for hypertension compared with women who are older than 65 years of age according to research

Despite a relatively benign clinical course compared with overt hypothyroidism, subclinical hypothyroidism, an early form of thyroid dysfunction, has been associated with an increased risk of cardiovascular disease. This is attributed to the link between the cardiovascular system and thyroid hormone. However, the connection between subclinical hypothyroidism and hypertension — a key comorbidity in cardiovascular disease risk — has been less apparent.

Subclinical hypothyroidism (SCH), also called mild thyroid failure in this condition body doesn’t produce enough thyroid hormone. It is diagnosed when peripheral thyroid hormone levels are within normal reference laboratory range but serum thyroid-stimulating hormone (TSH) levels are mildly elevated. This condition occurs in 3% to 8% of the general population.

Causes of subclinical hypothyroidism:

Pituitary gland secrets multiple hormones. Thyroid stimulating hormone is one of them  TSH triggers the thyroid, a butterfly-shaped gland at the front of the neck, to make the hormones T3 and T4. Subclinical hypothyroidism occurs when TSH levels are slightly elevated but T3 and T4 are normal.

Subclinical hypothyroidism and full-blown hypothyroidism share the same causes. These include:

1. A family history of autoimmune thyroid disease, such as Hashimoto’s thyroiditis (an autoimmune condition that harms thyroid cells)

2. Injury to the thyroid (for example, having some abnormal thyroid tissue removed during head and neck surgery)

3. The use of radioactive iodine therapy, a treatment for hyperthyroidism (a condition when too much thyroid hormone is produced)

  4. Taking medications that contain lithium or iodine

Symptoms:

Subclinical hypothyroidism most of the times has no symptoms. This is especially true when TSH levels are only mildly elevated. When symptoms do arise, however, they tend to be vague and general and include:

• depression
• constipation
• fatigue
• goitre
• weight gain
• Hair loss

To explore the potential association between the disorders, US researchers examined the rates of incident hypertension in women with subclinical hypothyroidism. The research was based on a meta-analysis of 9 case-control, cohort, and cross-sectional studies that reported hypertension incidences in women both with and without subclinical hypothyroidism.

The pooled population included 21,972 women. The researchers divided the population into a middle-aged cohort of women <65 years of age (mean age, 49.6 years) and an older cohort of women ≥65 years of age (mean age, 71.0 years). Subclinical hypothyroidism was associated with an increased incidence of hypertension in the middle-aged subgroup (OR, 1.64; 95% CI, 1.18-2.27), but there was no similar association in the older subgroup (OR, 0.97; 95% CI, 0.80-1.16).

There were a number of limitations in the study. Among them was the inclusion of only female patients with subclinical hypothyroidism, which may reduce the generalizability of the findings across men with the condition. All of the studies in the meta-analysis were observational in nature, suggesting confounding factors could have affected the analysis.

“However,” the researchers said, “based on our result that showed the positive association between [subclinical hypothyroidism] and [hypertension] in middle-aged women, treating [subclinical hypothyroidism] in this patient population when signs of rising blood pressures are observed, regardless of patients’ [thyroid-stimulating hormone] levels, should be considered.

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