TH and Alzheimer disease: The alternative view is that the development of AD causes changes in thyroid hormone levels, meaning that thyroid dysfunction may be a result of the disease, support for this hypothesis can be explained by secondary deficits in AD neurodegenerative features, such as a worsening of the pituitary gland, which can lead to a reduction in TRH and TSH production, the resulting low TH levels [15] are explained by a lack of response to normal physiological stimuli, including melatonin from the pineal gland, TRH, and melatonin from T4 [16, 17], based on hypophyseal degeneration.