William Miller, MD
Living Longer and Healthier: Part 1. Life Expectancy.
Updated: Jun 7, 2022
As COVID begins to take more of a backseat to other health concerns, I have received several questions about the future of this weekly column. The feedback that I have received over the past two and a half years has been overwhelmingly positive. Also, I enjoy writing. Thus, I have decided to continue to produce weekly articles covering different health topics. I will try to make my column different from the average health column, most of which promote things like eating well and exercising. Instead, I plan to delve into health and disease related topics like, what is diabetes anyway? Or what is the history of cancer treatment? Why is heart disease more common in some populations than others? I will continue to explore COVID topics if something new develops in that field and I will continue to report on healthcare news relevant to the Coast and Mendocino County.
To start off, I thought we would consider the topic of life span. Last week marked the local kickoff of Blue Zones, which is a community-based program that promotes wellness based on practices that were noted to be consistent in the communities around the world that had the most people living and thriving past age 100. To explore this, I will talk about what average life span means to a population in this first part of a three-part series. In part two, we will look at some of the people who have lived the longest, including the oldest documented person who lived to be over 122. In the third part, we will talk about how community helps us live longer and healthier lives, which will bring us back to the Blue Zones Project.
As discussed below, ”life expectancy” is a statistical term that requires some explanation. It is different than “average life span,” which is simply the average number of years all persons have lived, regardless of when or where they lived. “Longevity,” also known as “maximum life span,” is the term that relates to the longest possible time that any one individual is known to have lived. Life expectancy is more useful because life expectancy changes based on the age of a person as well as the conditions that the person is living under.
A person’s life expectancy is different based on age. For example, life expectancy at birth in the US is 78 years. However, if the person lives past childhood and through all of the challenges of adulthood to the age of 78, then his or her life expectancy is increased to the age of 89. Life expectancy also changes based on the part of the world in which a person lives, since conditions such as access to good nutrition, clean water, sanitation and healthcare vary greatly. Life expectancy at birth in many African countries is around 49 years, as a result of high infant and childhood mortality due, in particular, to poor nutrition and childhood infections. In India it is 69 years, in Mexico it is 75 years, in the US it is 78 years, in Canada it is 82 years and it is highest in Japan at 83 years.
Life expectancy is higher for women than men in all areas around the world by a difference of about 5 years. For males in the US, life expectancy at birth is about 76 years, while for females it is around 81 years. This was not always the case. Prior to the industrial revolution, females at birth had a lower life expectancy than males due to the high risk of death during childbirth. However, if a woman survived her childbearing years, then her life expectancy increased to past that of men, which is what we see today. The difference from then to now is mostly due to taking a sanitary approach to the delivery of infants, which has led to a dramatic reduction in post-partum (following delivery) infections that attributed substantially to maternal death during childbirth.
The explanation for a shorter life expectancy for males at all ages and across all geographics remains unclear. Social risk differences between the sexes are frequently cited. Males have a higher incidence of dying from injuries, especially in early adulthood. Males are more likely to engage in jobs that carry risk of injury. In all cultures, males are more likely to smoke or consume drugs including alcohol. However, research on human aging suggests that there may be a genetic advantage given women through the extra arm of the XX chromosome as compared to the XY chromosome in men. This may help somehow slow down the natural aging process or give a slight advantage to the female immune system.
Life expectancy also changes from year to year depending upon what is happening in the world at the time. During the plagues of the Dark and Middle Ages, life expectancy would drop by as much as ten years, sometimes getting as drastically low as age 15, as was the case for a person born during the Black Death that occurred between 1347 and 1351.
For much of the past 10,000 years, life expectancy at birth has hovered between 25 years and 40 years. However, starting around the turn of the last century, or about 100 years ago, life expectancy at birth has been steadily rising. This has been due to three things. Advancements in public health and specifically in sanitation and clean drinking water, scientific advances in agriculture which have dramatically improved efficiency of food production and staved off starvation for many, and the development of antibiotics which have turned diseases that were often fatal, such as pneumonia, to ones that we routinely expect people to now survive.
A common misconception is that this means that humans are living longer. Instead, it means that more people are living into old age. However, the span of human life has not changed. In other words, during the time of the Roman Empire, people may have lived into their late 80’s and 90’s, if they made it that far. The maximum life span does not appear to have changed.
Next week, we will look at a few of the oldest living people and to what each of them attributed their long lives. Their lifestyle habits may surprise you.