By Karen Weintraub
It’s common knowledge that we’re in the midst of an autism epidemic, right?
Well, maybe not. Boston University professor Hershel Jick published a paper today in the BMJ suggesting that there was an autism epidemic in the 1990s, but it may be over.
He and his colleagues used what he says is the only database in the world with reliable, consistent data over the last 23 years – from the United Kingdom. And Jick says the trend is clear. Autism increased fivefold between 1990 and 2000, but has held steady since 2004, at least in the U.K.
What might cause such a precipitous rise and then a flat line? “It’s a complete mystery,” says Jick, who has been studying the epidemiology of disease since the mid-1960s and has never seen a similar trend.
“You tell me what there could be out there that increased the risk dramatically for 10 years and then stopped? There has to be something out there,” he says. But what it is? “I haven’t a clue.”
One of the biggest debates in autism in recent years has been genes versus environment. People who develop autism need a genetic vulnerability to the condition, but if it’s truly rising, there must be an environmental trigger, too, because genes can’t change quickly.
Events that affect the child, like vaccines or aging parents are very unlikely to be the cause, Jick says, because that’s not consistent with the data. Nor, he says, is the latest theory du jour: that Tylenol is driving the spike in autism.
The Tylenol study, published in the Journal of Restorative Medicine, also suggests that the other “epidemics” of ADHD and asthma have also been caused by acetaminophen, the drug’s generic name. Again, Jick emphatically says “no way.”
The number of patients on treatment for ADHD increased in the U.K. in the mid-2000s, according to a study he published in 2004, but not in North America, where ADHD treatment has remained high and steady for decades. The timing of acetaminophen’s rise in popularity doesn’t coincide with the trends in ADHD or autism.
Jick and his colleagues examined the General Practice Research Database, which includes data from about 3 million patients from across the UK – roughly 5% of the nation’s population. Looking at 8-year-olds diagnosed with autism, they saw substantial increases in the 1990s, but a plateau between 2004 and 2010, the last year analyzed.
Rates of autism in the UK are also substantially lower than in North America, according to Jick’s research. The US Centers for Disease Control estimates that 1 in 88 8-year-olds has autism, while another federal agency, counting all school-age children, recently put the figure at 1 in 50. The U.K. figures for autism in 8-year-olds are around to 1 in 220, Jick’s study shows.
Jick isn’t the only one saying that we are not in the throes of an autism epidemic. (I wrote about this debate for Nature in 2011.) Useful data sets are hard to come by, so there are lots of different numbers and theories floating around.
One national study, also in the U.K., found that about 1 in 100 adults has autism – suggesting there’s been no substantive increase since those adults were children decades ago.
But data compiled by the advocacy group Autism Speaks suggests autism rates have been climbing steadily since 1975, rising more than 600% over the last two decades. And anecdotally, most doctors of a certain age will say they never saw autistic children when they started out in medicine decades ago.
So, what’s the bottom line?
Unfortunately, it’s a profoundly unsatisfying one. Data is complicated. Autism is complicated. It’s diagnosed by people who are subject to different trends and social pressures. Was there something out there causing autism in British children that’s now gone away?
It’s possible, but “we may never figure it out,” Jick says.
Karen Weintraub, a Cambridge-based Health/Science journalist, is a frequent contributor to CommonHealth. Follow her on Twitter @kweintraub.