Why Are Humans Always So Sick?

Super-hygiene, sedentary lifestyles, and a lack of worms in our stomachs may all contribute to modern ills, scientists theorize. Image (Image credit: Dreamstime)

The swine flu outbreak this spring is just the latest in the mountain of ailments that seem to beset humanity, from the incurable common cold to each potentially deadly cancer diagnosed at the rate of every 30 seconds in the United States.

So is our species sicker than it has ever been? Or is our current lot far better than it used to be?

It turns out the answer to both questions might be yes. While humans as a whole do live longer than ever before, we now suffer certain illnesses to a degree never seen in the past — including skyrocketing rates of diabetes and obesity and, surprisingly, ailments such as hay fever.

Among the possible causes for our modern ills: super-hygiene, sedentary lifestyles, and a lack of worms in our stomachs.

Life expectancy shot up dramatically on average across the world during the 20th century, increasing from just age 30 or so in 1900 to roughly age 67 now. (It’s not that many people didn’t live to ripe old ages back then. Rather, the shift was due in large part to vast reductions in the number of infant deaths, which brought the average way down.) In 1900, there was just one country worldwide where under one in ten children died before their first birthday, while now out of the 187 nations for which there is data, this holds true for 168. These striking changes are due in large part to improvements in nutrition, sanitation and medicine.

"As a world population, on average we are far healthier than before," said historian of medicine Naomi Rogers at Yale University.

Modern ailments

Infectious diseases once were the main cause of death worldwide, "but around 1950 or so, there was a moment called the epidemiological transition, a long term that just means that in most Western nations, chronic diseases became the major causes of disability and death instead," Rogers explained.

Although infectious diseases seemed to Westerners to only be a "back then" or Third World problem for decades, ever since HIV in the 1980s and 1990s, "I think that element of hubris is gone," Rogers added. "But the infrastructure of public health facilities that responded to infectious disease and epidemics that disappeared in the United States has only slowly been rebuilt, and there's now that shock that comes with new epidemics."

The modern era has brought a unique host of problems. The number of American children with chronic illnesses has roughly quadrupled in the past 50 years, including an almost fourfold increase in childhood obesity in the past three decades and twice the asthma rates since the 1980s.

"It's a combination of environment and lifestyle," Rogers said. People are more sedentary and less physically active than before, and fast food is more available.

"A powerful way of thinking of metabolic problems such as obesity and diabetes regards toxic environments," she explained. "One study showed that pregnant women living in areas that had large numbers of fast food places gained very unhealthy levels of weight during pregnancy compared with pregnant women who maybe lived a mile further away. That's a toxic environment. So the society we live in has its own dangers."

Body fights itself

Unusually, the number of ailments involving malfunctions of the immune system has gone up as well.

Multiple sclerosis, a disease where the fatty insulation around the nervous system comes under attack, appears to be on the rise, and type I diabetes, "a childhood form of diabetes almost unheard of at the turn of the 20th century, is up from one in 5,000 or 10,000 to one in 250 in some regions," said Joel Weinstock, chief of gastroenterology at Tufts University Medical Center in Massachusetts.

Even hay fever, which plagues roughly 1 out of 4 people in the United States, is something that may have largely emerged only in the 20th century, Weinstock said "What if I told you that there are some countries that don't even know what hay fever is?" he asked.

The rise of these disorders might be due to the very improvements in hygiene that have helped reduce infections in much of the world. The body's immune system is regularly exposed to antigens, molecules that it recognizes and reacts to, such as compounds from viruses or bacteria.

"But the immune system needs to be controlled, needs to not act up when exposed to things that aren't truly injuring you," Weinstock explained. "What we think is happening is the regulation mechanisms are becoming less effective. As to why that is, is it possible that it's due to lack of exposure to antigens? Do you need to be exposed regularly to antigens for it to work properly?"

You need worms

For instance, many fewer people are infected with worms than before.

"If you look back at the human race in the 20th century, every child and adult had worms in their gastrointestinal tracts," Weinstock said. "They were part of the ecosystem of the gut. As it turns out, worms are very potent at controlling immune reactions, in order to live happily ever after in the gut. Our theory is that when we started deworming the population, that is one factor that led to the rise in immunological diseases."

As part of this "hygiene hypothesis," Weinstock also notes that dirt roads, horses and cattle used to be far more prevalent in life than they are now.

"Our theory is that when we moved to this super-hygiene environment, which only occurred in the last 50 to 100 years, this led to immune disregulation," he said. "We're not saying that sanitation is not a good thing — we don't want people to jog up to river banks and get indiscriminately contaminated. But we might want to better understand what factors in hygiene are healthy and what are probably detrimental, to establish a new balance and hopefully have the best of both worlds."

Charles Q. Choi
Live Science Contributor
Charles Q. Choi is a contributing writer for Live Science and Space.com. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica.