Is bigger always better?

It depends. Throughout the human lifespan, body size plays an important role in determining health outcomes and quality of life. It's not just about body mass index, fat distribution, weight, or muscle mass: there also exists a relationship between body size and longevity across multiple species, including humans. On average, larger species seem to live longer and age more slowly—think about the fact that dogs age about seven times faster than do humans, who are both heavier and taller than dogs. But within species, that relationship flips around: larger individuals age more rapidly and live shorter lifespans than do smaller individuals.

As with seemingly everything in aging, the relationship between body size and the rate of aging is complex and the result of an interplay between genetic, environmental, and lifestyle factors, most of which scientists are still investigating. In this episode of Longevity Science, Matt dives into the nuances of body size and aging rate, discussing currently available data about how the two interact, intriguing outliers and exceptions, and potential molecular and evolutionary drivers.

Check out the links below for further information and/or reading about some of the things we discussed in this podcast episode. Note that we do not necessarily endorse or agree with the content of these readings, but present them as supplementary material that may deepen your understanding of the topic after you listen to our podcast. This list is in no way exhaustive, but it’s a good start!

Big mice die young: early life body weight predicts longevity in genetically heterogeneous mice

This study found that mice with a smaller body size outlived those with a larger body size. This association was present in both male and female mice and was stronger for weights taken earlier rather than later in life, suggesting that low body weight at earlier ages is particularly advantageous for mouse longevity. The authors hypothesize that body weight is likely a surrogate measure of biological changes that influence weight as well as later life outcomes.

Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome

There exists a common perception that there are seven dog years to every human year. That relationship is not quite correct—in reality, there are many more dog years to each human year early on in a dog's life, and then dog years more closely track human years later on in the dog's life. This paper presents a useful graphic to clarify the dog-human years relationship, which the researchers investigated using dog and human methylomes.

Is height related to longevity?

Good news for short people: according to this study, rates of diet-related chronic disease are lower in people of shorter height, especially after middle age. Shorter people also tend to live longer. Data from centenarians—people who reach 100 years of age—bear this finding out: the study reported that Japanese centenarians were around 10 centimeters shorter than 75 year-olds, and that Hungarian centenarians had an average height of 154cm (about five feet one inch).

A Single IGF1 Allele Is a Major Determinant of Small Size in Dogs

You've probably observed that there is tremendous diversity in the body size of dogs: a Great Dane can weigh 16 to 17 times more than a chihuahua. The dogs’ life expectancies also differ: the average Great Dane lives for 8-10 years, while the average chihuahua lives for 15-17 years. The paper describes a specific variant in a gene that codes for a hormone called insulin-like growth factor 1 (IGF-1) that influences body size in dogs. Smaller dogs have a variant that lowers IGF-1 levels during development, leading to lower growth.

Growth Hormone Receptor Deficiency is Associated With a Major Reduction in Pro-aging Signaling, Cancer and Diabetes in Humans

Over a 22-year period, researchers studied a population of Ecuadorians with restricted growth caused by growth hormone receptor gene mutations that caused deficiencies in the growth hormone receptor (GHR) and IGF-1 proteins. GHR deficiency was correlated with a very low incidence of age-related diseases such as cancer and diabetes compared to controls. Interestingly, despite a marked decrease in rates of age-related disease, GHR-deficient people did not live longer than controls, with many deaths being caused by accidents, alcohol toxicity, and other incidents unrelated to aging.