Mild hypothyroidism is defined as subclinical hypothyroidism, and it should be treated in certain circumstances. Treatment is recommended for TSH levels of 0.1 to 0.4 mIU per L for: Age 65 and older Postmenopausal women younger than 65 who are asymptomatic and not receiving estrogen or bisphosphonate therapy Younger than 65 years who have heart disease, osteoporosis, or symptoms of hyperthyroidism  Treatment of TSH levels less than 0.1 mIU per L is recommended for: Younger than 65 years