Nearly 150,000 Canadian children were examined in a recent study, to examine a possible correlation between increased risk of developing autism and their mothers taking a specific class of popular antidepressants during pregnancy. The study, recently published in JAMA Pediatrics, found that the children of mothers who used SSRI antidepressants during the second and/or third trimester were at an 87 percent higher risk of developing autism than those whose mothers had not.
This study made national headlines and almost certainly frightened many pregnant women. It's only the latest in a series of such findings and reports. A 2014 report in the "Archives of General Psychiatry" found that fathering a child late in life increases the chances of the offspring having bipolar disorder.
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The study generated headlines like "Children of Older Fathers may be at Higher Risk for Mental Illness" and "Older Fathers Linked with Bipolar Disorder." Indeed, 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."
Understanding Risk Medical researchers understand the difference between findings that are statistically significant and those that are practically significant - in other words that have a clear real-world effect. The 37 percent increase in bipolar disorder found among older fathers 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. Therefore in the general population about 97.4 percent of children will not develop the disorder, and among fathers 55 or older the number drops to 96.43 percent-or about a 1 percent increase in the overall risk.
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Many journalists put the risk into perspective. An ABC News article noted that despite the alarming statistics linking autism and antidepressant use, medical experts advised that pregnant woman currently on the medications should absolutely not stop taking them without consulting her doctor.
"The absolute risk is still low and the odds are overwhelmingly in their favor that it's low," Dr. Max Wiznitzer, a pediatric neurologist at University Hospitals Rainbow Babies and Children's Hospital, told ABC News. As a piece on Discovery News correctly noted, autism remains a relatively rare condition and the vast majority of women who took the drugs did not have children with autism.
Unfortunately many people don't read past the scary headlines to the more sober and measured scientific caveats.
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In his book "More Damned Lies and Statistics: How Numbers Confuse Public Issues," Joel Best, professor and chair of sociology and criminal justice at the University of Delaware, explains how a news story can mislead, despite the best of journalistic intentions:
"Suppose that you pick up tomorrow's newspaper and read that a medical journal has published a study indicating that diet cola drinkers are 20% more likely to have a specific medical condition. Such a sentence will confuse some people, who, for example, may now believe that 20% of diet cola drinkers will get this disease. Actually, this statistic means nothing of the sort. Let's assume that, in the general population, 5 people in 10,000 have the disease. If diet cola drinkers have a 20% increased risk, there would be 6 cases of the disease among every 10,000 diet cola drinkers (20% of 5 is 1, so a 20% increased risk would equal 5 + 1, or 6). In other words, what might seem to be an impressive statistic-'20% greater risk!'-actually refers to a very small difference in the real world: 1 additional case per 10,000 people."
One way to look at the situation is that the most significant threats to human health have long been identified. It's unlikely, for example, that a valid new study will find that eating three ounces of pork every day for 20 years doubles your risk of death; if that were the case, researchers would have noticed decades ago that regular pork eaters were dropping dead at rates far higher than average.
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Consumers should be skeptical of claims about anti-cancer "miracle foods" for the same reason: If a regular diet of garlic, spinach, kale or anything else dramatically cut cancer rates, that would have been medically established long ago.
Aside from needlessly alarming the public over a practically insignificant risk, the latest news may lead some mothers of autistic children to blame themselves for their child's condition, when in fact it's more likely than not that the autism would have emerged with or without the antidepressant usage.
Often the real take-home message to medical stories for the savvy news consumer is that while a risk was found in the latest study, it's not really anything most people should worry about - or are likely to do anything about anyway.
People make choices everyday that put them and their families at far greater risk of disease, injury and death-such as smoking, not wearing a seatbelt or texting while driving - than any miniscule (but statistically significant) action like eating a steak, fathering a child later in life or taking antidepressants during pregnancy.