On January 3, 2006, the New York Times published a very interesting article by Gina Kolata, an award-winning Science reporter, on the intriguing relationship between education (years spent in school) and longevity. This is an extremely complex subject that we will need to come back to in future postings to try to unravel some of the knotty issues involved.
But for now, I want to focus on one topic in the article that had little to do with education, rather it dealt with the role of social networks. Dr. Lisa Berkman, cited in the article, is a professor of public policy at the Harvard School of Public Health. In the 1970s, she worked at a San Francisco healthcare center that served Chinatown, North Beach (an Italian neighborhood), and the Tenderloin (a district populated with homeless people who lived on the street, mentally ill people, drug addicts, and just plain poor people). She observed that in Chinatown and North Beach, people enjoyed tight and extensive social networks, made up of closely-knit families, friends, and neighbors who cared for each other. In the Tenderloin, people “were sort of dumped”, suffering from almost total isolation.
Thirty years later, after studying another group, Seventh-Day Adventists, well-known for their social cohesiveness as well as prolonged lifespan, she came to the conclusion that social isolation is associated with twofold to fivefold (i.e. 200% to 500%!) increases in mortality rates. This correlation has been corroborated in many other studies and in many other countries. Such a “hazard ratio” (a term used in epidemiological studies, meaning the hazard of dying in the experimental group over the hazard in the general population) is so compelling that even one who insists on biochemical/molecular evidence of causality must sit up and take notice.
And indeed, it reminded me of the Okinawan people who are one of the longest-living society on earth. Their active lifestyle and healthy diet still don’t completely account for their outsized longevity. The distinguishing feature in their culture is the extremely close-knit family, the active role that grandparents and great-grandparents take in the daily chores of the family, and the unusual respect and reverence they are being treated with.
And then, there is the well-known observation that married men live significantly longer than single men. Or the statistic that societies that regard the care of older people as a societal obligation, such as Holland and the Scandinavian countries, also have some of the lowest mortality rates of the industrialized countries.
Is there a biological explanation?
In insect societies, a bee or a wasp separated from her nest will simply curl up and die within a day or two. Solitary wasps, on the other hand, happily live their full lifespan without “feeling” the need for social contact. If you had a chance to observe bees’ behavior in their hive, you’d be struck by the constant touching and stroking of each other with their antennae. Part of it is a form of transmission of information through pheromones, including and “I.D. scent” that says “you belong”.
But is it possible that such pheromones evolved to occupy such a central role in the bee’s physiology as to make life without it impossible? If so, this would be an extreme case of “enforced socialization”, essentially saying “socialize or die”! Another intriguing possibility: The touching and stroking with the antennae could be the equivalent of grooming in primates. Monkeys that don’t get their daily dose of touching, stroking, and grooming become depressed. So do human infants. Could it be that bees require the same tactile sensation?
What could be the biological mechanism that would curtail the lifespan of a bee separated from her hive? I don’t think we know. But there must be one.
What about us humans?
It is known that social isolation is a stressful state, and conversely, social support reduces stress. Put in a biological context, stress is expressed biologically by chronically elevated levels of the stress hormones cortisol and epinephrine (a.k.a. adrenaline). We know that these hormones are pro-inflammatory. The inflammatory response has been associated with coronary heart disease, autoimmune diseases, and cancer. In fact, we now know in precise molecular detail how this happens.
The stress hormones cause the release of peptides from white blood cells that are called interleukins. These peptides allow cells to “talk” to each other and thus coordinate the inflammatory response and the immune response. A certain amount of the stress hormones is actually normal, and it results in the production of normal physiological levels of interleukins. This allows us to have an appropriate level of inflammation and immune function necessary to protect us from foreign invaders and, in some cases, cancer. But when stress hormones are chronically elevated, over months and years, the protective function of the inflammatory and immune responses is turned into a pathological process that causes a variety of diseases and death.
Mind you, this is speculation. All I did here is connect the dots of isolated biological and medical studies, most of them in the test tube or in animals. But what I wanted to demonstrate is that a biological basis for something as “social” as social isolation and longevity most probably does exist.
Should we wait for the ultimate proof?
Absolutely not! Social policy should be based on solid evidence, and the hazard ratios of social isolation are so compelling as to make them an appropriate basis for policy. The cost of social isolation in human and economic terms is very high. We should take it very seriously now, as a huge wave of aging boomers is upon us.