As if older men didn't have enough to worry about between hair loss and high cholesterol, according to a recent report in the Archives of General Psychiatry, a journal of the American Medical Association, fathering a child late in life increases the chances of the offspring having bipolar disorder.
The study generated headlines like, "Older Fathers Linked with Bipolar Disorder," and "Bipolar Risk Rises with Father's Age." True enough; the study concluded that "the offspring of men 55 years and older were 1.37 times more likely to be diagnosed as having bipolar disorder than the offspring of men aged 20 to 24 years."
A 37 percent percent increase seems important, but in this study (as in many others rooted in statistics), a few caveats tend to be overlooked.
First, the increase in incidence of bipolar disorder was also tied to the mother's age, though not as much. Researchers believe that the older a man is at fatherhood, the higher the chance that his sperm may be subjected to damaging mutations. Women, on the other hand, are born with a limited number of eggs which are not replicated as they age (and therefore are less vulnerable to mutation).
More importantly, the 37 percent increase in bipolar disorder seems very dramatic until you realize that the incidence of the disorder in the general population is very low to begin with. According to the National Institute of Mental Health, about 2.6 percent of adults in any given year can be diagnosed with bipolar disorder. A 37 percent increase would translate into about a 3.5 percent chance of a father over age 55 having a child with bipolar disorder.
Thus in the general population, 97.40 percent of children will not develop the disorder, and among "old dads" the number drops to 96.43 percent. Does the difference — less than one percent — really justify the headline warnings and caution about fathering a child at an older age?
This is one of those "So What?" studies that are often exaggerated by journalists who fail to put numbers into context and perspective. The research is interesting, but really only relevant to doctors and geneticists.
The increase in incidence of bipolar among the offspring of older fathers may be statistically significant, but it is not socially significant. It is not information that should guide behavior, and scary headlines should not deter fathers from having children later in life if they so choose.
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Benjamin Radford is managing editor of the Skeptical Inquirer science magazine. He wrote about misleading statistics in the media in his book" Media Mythmakers: How Journalists, Activists, and Advertisers Mislead Us." His books, films, and other projects can be found on his website.