**1. Introduction**

Telomeres consist of repetitive DNA sequences, thousands of "TTAGGG" tandem repeats, which are located at the ends of linear chromosomes in most somatic cells [1]. Telomere ends form a cap-like structure to protect the ends of chromosomes from degeneration and fusion. However, telomeres shorten during each cell division, and when they reach a critically short

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length, cell cycle arrest and cellular senescence occur in the cellular level. In the body, telo‐ meres gradually shorten with aging [2]. A number of observations suggest a close connection between telomere length, generally assessed in leukocytes, and mortality or age-related disease, suggesting telomere length as a "mitotic clock," a marker for individual biological aging [3]. In this regard, to date, telomere length in various diseases has been investigated, including cancers, immune insufficiency, and cardiovascular disease. In addition, metabolic diseases, such as obesity and diabetes mellitus (DM), have shown a strong association with telomere shorten‐ ing. Several endocrine disorders, such as polycystic ovary syndrome (PCOS), Cushing's syndrome, and acromegaly, are also reportedly associated with telomere shortening (**Figure 1**).

Furthermore, several recent studies have focused on the pathophysiological role of telomeres for metabolic or endocrine diseases. Telomere shortening is one of the important causes of cellular senescence, and recently, it has emerged that cellular senescence plays a pivotal role in the aging and pathogenesis of age-related disease [4]. Actually, several clinical studies have shown that shortened telomeres at baseline are associated with an increased risk for develop‐ ment of age-related diseases.

Here, we review the association and pathophysiological role of telomere length in metabolic and endocrine diseases. Furthermore, we discuss the mechanistic insight and significance of shortened telomeres and associated cellular senescence. Finally, we discuss a possible thera‐ peutic approach for these diseases in the aspect of telomere shortening.

**Figure 1.** Telomere shortening and human diseases. Shortened telomere length is associated with various disorders, including psychiatric disease, impaired immune function, and atherosclerotic disease as well as metabolic and endo‐ crine diseases.
