*2.3.4 Metabolic factors affecting aging and lifespan*

Metabolic factors play an important role in the aging process and lifespan (**Figure 7**) [10, 11, 21, 33, 34, 39, 41, 44].

The decrease in autophagic activity observed with aging contributes to accumulation of damaged macromolecules and organelles. It can aggravate age-associated diseases and, therefore, shorten lifespan [21].

Mitochondria play a key role in several theories of aging. The reduction in mitochondrial activity with aging can impact lifespan [10, 11, 39, 44].

The inflammatory state associated with aging is responsible for insulin resistance. Insulin resistance is a risk factor for the development of several chronic disorders (e.g., obesity, type 2 diabetes, and ischemic heart disease) that are influencing aging and lifespan [10, 14, 42].

The amount of body fat influences health and lifespan. Both insufficient or excess body fat as observed in subjects with underweight or overweight/obesity have been reported to be associated with increased mortality and reduced lifespan [33, 34, 41].

#### **Figure 7.**

*Metabolic factors impact aging and lifespan (Picture downloaded from the internet "Google Images").*

### *2.3.5 Endocrine factors affecting aging and lifespan*

Hormones influence the aging process and lifespan (**Figure 8**) [9, 10, 12, 13, 31, 35–41, 45–49, 52–54]. Several endocrine-signaling changes occur during normal

#### *The Centenarians: An Emerging Population DOI: http://dx.doi.org/10.5772/intechopen.96327*

aging. Some hormonal changes may be beneficial while others can be harmful. The role of GH in aging and lifespan has been reported in several studies [37, 38, 52]. Reduced GH may lead to delay aging and increased lifespan while excess GH can have the opposite effects. GH secretion rate in offspring of long-lived families is lower than controls. Thyroid hormones play an important role in aging and lifespan. There is a negative correlation between thyroid hormone levels and lifespan [39]. The timing of menopause, a physiological condition occurring in women around the age of 50 years and associated with important decrease in E levels, may affect lifespan [48]. Indeed, E replacement therapy can reduce mortality (increase of lifespan) in post-menopausal women younger than 60 years [13]. In men, low T levels are associated with increased mortality [40]. Treatment with DHEA decreases insulin resistance and inflammatory adipokines and may positively impact lifespan [53]. The elevated levels of pro-inflammatory adipokines (e.g., interleukin 6 and tumor necrosis factor alpha) can negatively impact aging and lifespan. Elevated levels of adiponectin (anti-inflammatory adipokine) may be beneficial and associated with increased lifespan [41, 54].

#### **Figure 8.** *Endocrine factors influence aging and lifespan (Picture downloaded from the internet "Google Images").*

## *2.3.6 Disease occurrence with aging*

The "successful aging" is aging without any disabilities and severe diseases (extension of healthspan) [42, 43]. It is more important to promote healthier aging than better treat age-related diseases.

Several geriatric syndromes (e.g., frailty) and diseases (e.g., cardiovascular disease) occur with aging and affect quality of life and longevity [19, 42]. The incidence of adult diseases increases with age. In subjects older than 60 years, the most common age-related and life-threatening diseases and disabilities are ischemic heart disease, stroke, chronic obstructive pulmonary disease, cancer, respiratory infection, type 2 diabetes, osteoporosis, and dementia (non-exhaustive list) [14, 42]. The majority of older people may have more than one disorder. The incidence of multimorbidity (e.g., three or more diseases) increases exponentially with aging (**Figure 9**) [15]. For several of these conditions, the burden is greater in low-income and middle-income countries [42]. Some diseases (e.g., thyroid diseases) may have subtle symptoms that can be attributed to normal aging [55].

#### *2.3.7 Life expectancy*

At the beginning of the 20th century, life expectancy in most developed countries was between 45 and 50 years. Over the last several decades, there has been a gradual increase in life expectancy in most countries [27, 56]. The study of mortality and life expectancy in 195 countries and territories showed that globally, between 1950 and 2017, life expectancy increased from 48.1 years to 70.5 years for men and from 52.9 years to 75.6 years for women [56].

In less developed countries, the increase in life expectancy is mainly the result of reduced mortality at younger ages. In high-income countries, the increase in life expectancy is mainly due to rising life expectancy in subjects who are 60 years or older.

The increase in life expectancy together with the decrease in fertility rates are leading to the rapid aging of populations around the world. This has important demographic and socio-economic consequences worldwide.

#### **3. Centenarians**

Centenarians are subjects living 100 years or older. They represent a model of successful aging [3, 5, 6]. Semi-supercentenarians are those who reach an age of 105–109 years. A very small fraction of centenarians (up to 0.5%) will live 110 years or older (supercentenarians) [5, 30].

#### **3.1 Prevalence**

The total world population is currently around 7.8 billion and is projected to reach 9.9 billion by 2050. In several countries, the increase in life expectancy has led the very old to become the fastest growing segment of the population [1–4]. Some forecasts suggest that most babies born in developed countries since 2000 will become centenarians.

Estimates of the centenarian population can be difficult since some centenarians do not have birth records to confirm their age. According to United Nations estimates, in 2020, the number of centenarians in the world was approximately 573,000. This number was approximately 34,000 in 1950 and could reach approximately 3,676,000 by 2050.

#### *3.1.1 Prevalence by gender*

The majority of centenarians are females. The female to male ratio is currently around 3.6/1 and is expected to be approximately 2.9/1 by 2050 (**Figure 10**).

#### **Figure 10.**

*Centenarians are mainly females but the female to male ratio is gradually decreasing (Picture downloaded from the internet "Google Images").*
