Studies on the Biology of Aging

For decades, there have been debates on the topic of lifestyle choices and their effects on the longevity of humans. While there is currently a copious amount of research that exists on this topic, the question of whether one lifestyle exists that extends the lifespan remains unanswered. Due to ethical reasons, researchers have only been allowed to study lifestyle choices such as nutrition and dietary supplements in non-human primates; however, there are plausible and appreciable findings that suggest their influence in modulating the aging process.

Studies show that when humans adopt certain lifestyle practices, they extend their longevity and compress their morbidity; in other words, lifestyle choices do influence in enhancing the quality of life and avoiding premature death (Arking, 2006). Some of these lifestyle choices include low glycemic diet, regular resistance and aerobic exercise, low and steady BMI, avoidance of smoking, moderate alcohol consumption, and certain types of hormone replacement therapy (Arking, 2006). One of the most significant factors contributing to the causes of death in the U.S. population is tobacco. Additionally, poor diet and lack of exercise are factors that contribute to many premature deaths in the United States. Studies show that poor appetite, poor eating habits, difficulty in chewing or swallowing food, hospitalization, and loneliness are all risk factors for malnutrition. Furthermore, aging is associated with body composition changes that include increased body fat, reduced muscle mass and reduced organ mass (Wagner et al., 2016). To delay or minimize the deleterious effects of aging, one must intervene and manipulate his or her diet while being a young or middle-aged adult.

While the U.S. food industry continues to make an effort to promote a healthier diet by introducing low fat and no fat products, people achieve optimum health by consuming a plethora of vegetables and fruit (Arking, 2006). Due to rhesus monkeys having approximately 93% sequence identity with the genomes of humans, they were used as subjects to analyze the effect of caloric restriction (CR) in humans (Mattison et al., 2017). According to Mattison et al., lifestyle choices, such as CR, maximize lifespan in the majority of rodent subjects experimented on in laboratories. Additionally, it delays the onset of age-related disorders and diseases. Furthermore, CR is also correlated to increased longevity in experiments conducted on organisms historically known for shorter lifespans, such as invertebrates and unicellular yeasts (Mattison et al., 2017).

Lifestyle choices are not the only factors that influence longevity; the role of diet regarding CR, exercise, and nutritional supplements also affect longevity. For example, according to Heilbronn and Ravussin, CR reduces metabolic rate and oxidative stress, improves insulin sensitivity, and alters neuroendocrine and sympathetic nervous system function in animals (2003). While some sources show that CR without malnutrition promotes longevity, other sources have provided research that counters this idea (Mattison et al., 2017). According to one study conducted on rhesus monkeys executed by The University of Maryland, there was a positive association of CR with survival. Compared to their counterparts in the control group of animals, their risk of death was more than two-fold lower. In a separate study, rhesus monkeys were used to analyze the impact of CR on gender.

According to the National Institute on Aging, CR did not have a significant impact on survival but almost reached statistical significance regarding its benefits on health (Mattison et al., 2017). On the contrary, the University of Wisconsin Madison reported CR having beneficial effects and improvements in age-related survival as well as in health. In both studies, there is supporting data that concludes that CR is useful in the delay of aging effects in non-human primates; however, there is still a question regarding the age of onset in determining the extent to which beneficial effects of CR might occur. Lower body weight and lower food intake were correlated with improved survival as CR monkeys survived longer than their counterparts in the control group. As a result, research concludes that food intake influences survival. While there is research that concludes this, there is also additional research that suggests the benefits of CR depends on gender, with females reaping more benefits (Mattison et al., 2017). Concerning diet, research shows that the relationship between adiposity and glucoregulatory depends on sex, while the relationship between dietary composition and glucoregulatory impairment is dependent on food intake level. According to one study using rodents, one of the first health benefits of CR recorded was a lower incidence of cancer. An additional study showed a lower incidence of cardiovascular disorders and sustained glucoregulatory function during aging (Mattison et al., 2017). According to Arking, calories are essential, but what is more important is the food we eat in addition to the physical activities we partake in (2006).

Studies performed in the U.S. and British populations suggest that diets lacking vitamins and minerals often lead to a higher rate of mortality and greater risk for degenerative diseases (Arking, 2006). One reason for this is because vitamins contain antioxidant activities found in biological membranes and are considered to protect against lipid peroxidation. For example, vitamin E can assist in countering free-radical promulgation and damage. Studies show that obese individuals have a significantly higher mortality risk than thinner individuals. As humans age each year, VO2max declines. In other words, aerobic capacity decreases; however, with regular and moderate exercise, VO2max values increase, leading to higher respiratory function. Exercise has many benefits for human health. Resistance training increases muscle mass, increases resting metabolic rate, decreases fat body mass, increases caloric intake, increases bone mineral density, and induces significant alterations in plasma hormone concentrations (Arking, 2006). Research shows that caloric restriction, in addition to moderate exercise, is a beneficial and effective intervention. This intervention is beneficial because physical exercise reduces both morbidity and mortality in humans. Researchers believe that antioxidants only occasionally affect the prolonging of life. Even still, people lacking antioxidants are more at risk for developing cardiovascular disease, cancer, and other age-related diseases (Arking, 2006).

Behind each of these lifestyle changes comes a possible biochemical and physiological mechanism as a result; these mechanisms underlying the relation between physical fitness are multifactorial (Silverman and Deuster, 2014). Though weight loss may be insignificant, dieting regimes bring about significant changes in insulin sensitivity. This insignificance is because the timing of the ingestion of calories affects weight loss just as the number of calories does. With CR in animals, there is more excellent protection against exogenous carcinogens. In other words, there are fewer tumors when exposed to carcinogens. This decrease in number is likely due to rapid detoxification, efficient repair processes, and alterations in the activity of DNA repair enzymes. With the immune systems of CR animals, the early effect is a decrease in antibody production of B-cells coupled with enhanced cell-mediated immunity of T-cells. There are several physiological responses to diet restriction in which processes can be manipulated by diet. Some of these processes include lack of exercise, delayed onset of degenerative diseases, total fat intake, accumulation of body fat, and decreased intake of specific toxins. Dietary restriction affects metabolism in a sophisticated manner. CR induces metabolic reorganization including, lowering of core body temperature, change in a motor activity centered around feeding time, and shift away from fat synthesis to glucose synthesis.

All of these result in a lowering of steady-state production. In active enzymes of CR animals, there is 100% control of PK activation or inactivation. However, in old, there is a loss of control of PK, which results in the wasteful synthesis of enzymes of glycolysis and ATP production. Additional metabolic effects in CR animals include CR animals being able to live with lower glucose levels, which leads to decreased glycation and decreased free-radical production. Furthermore, there is a reduced accumulation of advanced glycation end production in RBC and skin collagen. Lastly, there are higher levels of SOD, which lead to lower levels of oxidants, such as superoxide and hydroxide radicals.