Friday, June 17, 2005

Apple #81: Tears II


I was going to add on to the previous entry, but I've found enough other interesting facts from the book I purchased that it seemed an additional entry is in order.

Crying: A Natural and Cultural History of Tears
by Tom Lutz

To recap, my question was, why when we feel sad or otherwise extremely emotional, is it our body's response to cry? Why not some other physiological response, such as sneezing, for example, or hiccuping? In reading a book by Tom Lutz called Crying: A Natural and Cultural History of Tears, I came across several interesting facts about tears, but not the answer to my question. But tonight, I found the passage where he addresses my question.
  • Several researchers have suggested that tears help to eliminate toxins or other chemicals that build up in times of stress. One study of emotional tears versus reflex tears found that the emotional tears had 20 to 25 percent more protein than reflex tears.
  • Another study found four times as much potassium in emotional tears than plasma, and 30 times the manganese in blood. This last finding may be significant because high concentrations of manganese have been found, upon autopsy, in the brains of people who had chronic depression.
  • Yet another study found that emotional tears have high concetrations of a particular hormone that is an especially accurate indicator of stress.
  • The upshot of all these studies is that people think that tears are a way to remove toxins from the body, and once a person has finished crying, the tears have eliminated enough toxins to return the body to equilibrium.
  • Lutz points out, however, that there is a problem with this theory in that much of the tears that our eyes produce do not exit the body but rather drain back into it, through the puncta or duct in the corner of the eye. This duct in turn drains into another duct that leads to the nose. So really, compared to other methods such as sweating or urinating by which the body removes toxins, crying isn't that great at expelling something from the body.
  • While Lutz doubts that toxin removal is entirely the reason for crying, he doesn't offer an alternative possibility. So it looks like this theory is the best we have to go on for now, but it's probably not the whole answer.
  • In the meantime, here are a few other interesting facts:
    • The average American adult cries for about five minutes at a time, about three or four times a month. That's an average of men and women together. In general, women cry more often than men; one study found that women averaged 64 crying episodes per year, while men cried only 17 times per year, or 4 times less often.
    • Paradoxically, women suffer more frequently than men from various conditions and diseases which result in dry eye, or inadequate production of basal tears. In the majority of conditions, the lack of tears is caused by not enough of a hormone called androgen, which is a typically "male" hormone. This is why many women suffer from dry eye especially during lactation, because they are producing less androgen.
    • However, men can also suffer from dry eye if their bodies produce too much testosterone. Those hormones. They win either way, whichever sex you are.
    • As we age, the large gland responsible for most of our tears, a.k.a. the lacrimal gland, shrinks. By age 65, the body makes 40 percent fewer tears than it did at age 20, and by age 80, the gland makes 70 percent fewer tears. To compensate for less continual moisture from basal tears, the various glands around the eye produce more reflex tears. This is why older people seem to have watery eyes a lot of the time.
    • At the other end of the spectrum, babies cry a lot. Studies suggest that babies normally cry anywhere from half an hour to two hours each day (can you imagine crying for even half an hour each day?). Anything over two hours a day is generally considered excessive, and attributable most times to colic. Everybody assumes that colic comes from some kind of digestive disorder that's making babies unhappy, but nobody really knows what's the problem. Poor things.
Tom Lutz, Crying: A Natural and Cultural History of Tears, W.W. Norton & Company, 1999

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