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Facts and Theories Why Body Weight is Correlated to Longevity and Mortality
Posted on: November 29, 2002

In the US, obesity has increased by 30% over the last half century. American males are now about 25 kg heavier than during World War I. Increasing body fat has been targeted as the primary cause of this trend and efforts have focused on weight reduction methods through diet and exercise. However, obese people also have much higher amounts of lean body mass (LBM) compared with normal weight people. LBM is subject to increased free radical damage, increased cancer risk and requires more maintenance. Western scientists have viewed larger body size as a desirable byproduct of superior nutrition and a higher standard of living. On the other hand, some Asian countries averaging smaller body size have the greatest longevity in the world despite harmful health practices (smoking, drinking, pollution, congestion, and high salt intake). In spite of many of these negative factors, the smaller mainland Japanese, Okinawan Japanese, Shanghai Chinese and Hong Kong Chinese have excellent longevity, with Okinawa exhibiting the highest proportion of centenarians (34/100,000) in the world. In addition, smaller southern Europeans, such as the long-living Cretans have 1/2 the all-cause and <1/20 coronary heart disease (CHD) mortality of larger northern Europeans. Based on research conducted over the last 25 years, we have concluded that larger body size, not just percent body fat, is a health problem. This proposed risk factor has been ignored in the past because larger body size correlates with higher life expectancy and standard of living, improved public health measures, and advances in medical technology and treatment. Increasing obesity also correlates with these advances but presents a more easily identified cause of poor health in middle and advanced ages. We believe that the following longevity findings raise doubts about the benefits of promoting greater body size. What could be the explanation of possible correlation between bodyweight and longevity? Here it is displayed some facts and statements linked to this theme:

Entropy theory and biological mechanisms

A number of mechanisms can explain the harmful ramifications of increased body size within a species, such as humans. They include the entropy theory, increased cell number, reduced cell duplications due to larger size, and smaller organs in comparison to body weight.

Entropy theory

The entropy theory based on The Second Law of Thermodynamics, states, that there is a high probability that an organized system will spontaneously deteriorate with time. This theory also states, that complexity, large size and the energy content of a system promote disorder. Thus, applying it to humans, larger humans have more cells and more energy intake, and thus, tend to become disorganized more rapidly assuming other factors are the same.

Increased cell number exposed to damage and transmutation

As humans grow in size from conception, the number of body cells increases. Upon completion of growth, a large body may have 40 trillion more cells than a small one. The additional cells are exposed to toxins, cosmic rays, ultra violet light, free radicals, etc. Although most damaged cells arc repaired, more cells are subjected to permanent damage or converted into carcinogenic cells because the total number of cells is greater. In addition, a higher rate of mitosis due to excess cell growth, damage, and over nourishment increases cancer risk. Considerable evidence indicates that taller (bigger) people are at higher risk for cancer.

Fewer cell duplications left in adults of larger body size

Upon conception, the process of human cell doubling begins in order to create the adult human body. However, Hayflick reported that the cell is limited to roughly 50 doublings before dying. Since most of the cell duplication potential is used up in attaining full body size, a larger body uses up more doublings, leaving fewer potential doublings during the rest of its life.

Organs scaled down in size

While the heart and lungs are nearly the same proportion as body mass, many organs (e.g. liver, kidneys, and brain) are relatively smaller in larger individuals. Thus, while these organs may keep up with the demands of the body during youth, cell loss due to aging or injury may cause a greater reduction in functional capability in larger bodies in later life.

Lean body mass

LBM is not completely free of problems. Scientist in the year 1999 reported that systolic blood pressure correlates with LBM, while percent body fat does not have a strong effect on blood pressure. A 20-year study involving 135,006 Swedish construction workers found LBM was positively correlated with prostate cancer. LBM is also a separate risk factor for coronary artery disease. In rats, both LBM and fat mass were correlated with tumors but LBM was more important than percent body fat.

Greater workload on heart

It was suggested that the small body size could favor longevity by increasing the efficiency of the cardiovascular system. A study comparing small to large professional football players found that the largest football players had six times the death rate from heart disease compared with the smallest.
It was reported: "Although obesity has been linked to cardiovascular disease … the NIOSH (National Institute of Occupational Safety and Health) study found that one of the strongest associations to date is between body size and death".
The Framingham Off-Spring Study also found a rapid increase in CVD risk when BM1 rose above 20. Thus, to minimize CVD for a male of average height, the ideal weight should be <63 kg, well below the current weight of 85 kg. Scientists evaluated the blood pressure of 13,810 Danish adolescents with a mean age of 17.1 years. They found that a positive relationship existed between blood pressure and weight for both sexes. Thus, relative weight does not appear to be the major factor in the increase in blood pressure although it can play a role, especially in mature adults. Since high blood pressure is correlated with heart problems, it appears that increasing body weight has a negative impact even for relatively low body weights.

Confounding factors

Studies relating body size to longevity are subject to several cofounders. For example, higher socioeconomic status, larger body size, and beneficial environmental and health benefits tend to be positively correlated. Diet affects body size and susceptibility to infections and chronic diseases. Illness can result in low body weight. Smoking and BMI can also confound results, e.g. studies have found that smaller people tend to be more obese and smokers tend to be lighter. Most epidemiological studies are biased toward tall people because they use BMI to compare shorter, broader people against taller people with more linear builds. To provide a common baseline, epidemiologists should compare short and tall people of the same geometric configurations. The epidemic of chronic disease has been tied to recent western dietary practices, which paradoxically parallels increased life expectancy and larger body size. Yet, rural poor blacks on low calorie and protein diets in South Africa are relatively free of CHD and diet-related cancer. These cofounders may explain why larger corporate executives have lower mortalities than their shorter subordinates and why some large athletes (>86kg) live to 98 years of age (height and weight are positively correlated). It is suggested that the longevity differences between males and females are primarily related to differences in body size and the relatively smaller size of male organs, such as kidneys, the brain and liver. A modest correlation coefficient of -0.203 indicates that weight is only one risk factor that affects an individuals' longevity. Longevity is more strongly affected by other traditional risk factors, such as socioeconomic status, BMI, body type, dietary practices, life style (e.g. smoking, drinking and drugs), exercise, hygiene, genetics, and the quality and availability of medical care (table 1). Therefore, larger bodied people can live a long time when other risk factors are minimized. However, it appears that dietary changes and increased secular growth during the 20th century have had some harmful effects on our longevity potential.

Source: Thomas T. Samaras et al., Longevity, Mortality and Body Weight, Ageing Research Reviews 1 (2002) 673-691;
    Table 1. Confounding factors that may affect results of height vs longevity/mortality studies*

  • Socioeconomic status, lifestyle and educational level affect mortality rates/longevity
  • Use of Quetelet Index vs Ponderal Index/Khosla-Lowe Indexes can affect results
  • Congenital heart disease can cause stunting and premature death
  • Numerous childhood diseases, such as rheumatic fever can cause stunting and premature death in adulthood
  • Energy intake and diet quality during growth and adulthood affects longevity
  • Causes of death should be due to natural causes or illnesses; short stature can affect behavior due to psychosocial factors, which lead to an excess of suicides, substance abuse and violent deaths. AIDS is often higher in lower social classes.
  • Secular growth and shrinkage with age can affect the longevity vs height relation
  • Heavier weight for height of shorter people can provide misleading results
  • Tall, thin people can live longer than short, heavy people
  • Greater smoking among shorter people can reduce longevity significantly
  • Mother's diet and health during pregnancy can affect child's growth and future health
  • Mother's lifetime diet may affect child's growth and health
  • Pre and post natal medical and family care can affect growth and future health
  • Malnutrition or poor nutrition can affect growth and future health
  • Smaller diameter blood vessels in shorter people are more likely to develop atherosclerosis on western diet and cause premature coronary heart disease problems
  • Premature birth or low birth weight appears to have negative health impact in adulthood
  • Heredity can affect longevity significantly, independent of height
  • Cohort differences may affect findings when populations of different birth years are compared
  • Self-reported heights are usually 2.54cm (1 inch) higher than actual heights and may require data adjustment for some studies
  • Psychosocial factors can affect height, health and longevity
  • *Most of these confounders, if not corrected for, will provide mortality or longevity results which will be biased in favor of taller people.
Table:Thomas T. Samaras and Harold Erlick, Weight Body Size and Longevity, Acta Med Okayama 1999; 53 (4):164
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