00:02The news is full of headlines of officials drawing bold lines between two things happening at once.
00:09Americans are eating more ultra-processed foods while the number of people with obesity and chronic diseases are rising.
00:16More children are being vaccinated while autism and ADHD diagnoses climb.
00:22More people are spending time on social media as mental health declines.
00:26The implication is often the same. If two things rise together, then one must be causing the other.
00:32Often these notions are based on data that show timely correlations between two events.
00:37A correlation can be misleading. For example, data from the Department of Agriculture and the Centers for Disease Control and
00:45Prevention
00:45show a strong correlation between national margarine consumption and the divorce rate in Maine.
00:50As margarine consumption steeply declined from 2000 to 2005, divorce rates fell.
00:57From 2005 to 2008, people across the country started to eat more margarine, and lo and behold, more people in
01:04Maine got divorced.
01:05As convincing as that graph might be, margarine isn't spreading divorce. That graph is simply showing a correlation.
01:12Two other things that move together, ice cream sales and shark attacks, both increase seasonally in the summer, peaking around
01:19August.
01:19They just, they both happen in the summer, you know, when people are sort of, it's aught and people are
01:24swimming more.
01:25Um, so the distinction there is like, again, correlation is sort of just things that kind of move together in
01:31a sense.
01:32Causation is really this concept or idea that something leads to something else.
01:38While some relationships reflect true biological links, others, like ice cream sales and drownings or margarine consumption and divorce rates
01:46are mere coincidences.
01:47Confusing correlation and causation is easy to do.
01:51Researchers report different, sometimes conflicting findings.
01:55But major health and science decisions, such as the approval of a new drug or the reversal of long-standing
02:01health guidelines,
02:02require that scientists and politicians follow careful procedures to sort out correlation from causation.
02:08In the early 1970s, doctors blamed stomach ulcers on stress.
02:14But then, in the 1980s, Dr. Barry Marshall and Dr. Robin Warren noticed a certain bacteria, called H. pylori,
02:22consistently colonized the stomach lining of stomach ulcer patients.
02:26H. pylori is now known to spread through contaminated food or water or through direct contact with a contaminated person's
02:32feces.
02:33The doctor's observation was a correlation.
02:36Then, in 1984, Marshall, who later won the Nobel Prize, famously drank a culture of H. pylori bacteria.
02:44A few weeks later, he developed gastritis, an inflammation of the stomach lining that can cause a burning pain or
02:49ache in the upper belly,
02:51vomiting, or a loss of appetite.
02:53This proved causation, albeit in a not-so-ethical or controlled way.
02:57Marshall then cured himself with antibiotics.
02:59So, the best-case scenario, and this is sort of very common in the medical and, like, food and drug
03:07association world,
03:08is a randomized trial where we might have some exposure of interest, some, again, maybe a new program, a new
03:15medication,
03:16and we literally enroll people in a study and randomly assign them to get it or not get it.
03:22In many situations, scientists cannot perform the types of controlled experiments needed to prove causation.
03:28There's a number of approaches that people can use, you know.
03:31So, basically, a lot of the time, in the absence of randomization, people try to sort of at least find
03:36a comparison group,
03:38like a group of people who didn't get, say, the new medication, but who look as similar as possible to
03:44those who did.
03:46And so, the idea is to, again, sort of, in some sense, try to have data that looks like it
03:51could have been randomized.
03:53It wasn't, and we have to acknowledge that.
03:55But where we at least say, well, you know, maybe we want to compare what is the effect of eating
04:01ultra-processed foods.
04:02Scientists know that people who eat a lot of ultra-processed foods are quite different from those who do not.
04:08They live in different environments.
04:09They might have different exercise strategies.
04:11They might have other pre-existing health conditions.
04:14What an epidemiologist might do is look at their data and find a group of people who are similar to
04:18the ones who eat a lot of ultra-processed foods,
04:21but who didn't consume them.
04:22Perhaps because they lived somewhere where they had better access to a grocery store or fresh foods.
04:27Statisticians might try to group people based on similar health conditions, age, or other socio-demographic factors.
04:33Whether it's ultra-processed foods or autism risk, new studies are constantly published around the world.
04:39Some studies agree. Some conflict.
04:42At what point do scientists and policymakers determine that we know enough to form a conclusion?
04:47There's sort of a spectrum here, and certainly for, say, a new drug approval by the Food and Drug Administration,
04:54there's a very formal process and they require randomized trials and sort of a very thorough process to sort of
05:01establish that causal link
05:03and, in some sense, like statistical proof that some new medication or treatment really does improve outcomes.
05:11In other scenarios where, yeah, it's maybe more recommendations like the ultra-processed foods.
05:17And honestly, also, those are often murkier.
05:20There's just sort of, there's so many factors that relate to health broadly.
05:26I think that's where it really is about a body of evidence.
05:29In the early 2000s, nutritional epidemiologist Carlos Augusto Montiero noticed a shift in Brazil.
05:36As traditional diets of rice and beans were replaced by soda and cookies, obesity rates surged.
05:42While he hypothesized that eating ultra-processed foods might cause the rise of obesity and chronic disease,
05:48so far all he had was a correlation.
05:51Since then, studies have found links between consumption of ultra-processed foods and a range of diseases,
05:56from obesity, diabetes, and high blood pressure, to depression, anxiety, inflammatory bowel disease, autoimmune disorders, and even cancer.
06:06Nutrition science is challenging because health is shaped by intertwining factors such as genetics, income, environment, and lifelong eating habits.
06:15That makes controlled experiments difficult.
06:17This has become especially important in recent months,
06:20when science is cited in public debates to support political claims,
06:24like what has happened recently with Tylenol and autism.
06:28In late 2025, US researchers reviewed 46 studies examining links between acetaminophen use in pregnancy and autism or ADHD.
06:38Of those, 27 studies reported an increased risk.
06:42Nine found no association.
06:44And four suggested a possible protective effect.
06:47Several studies also observed a dose-response relationship, where higher use was tied to higher risk.
06:54Late last year, President Donald Trump said pregnant women who take acetaminophen, commonly known as Tylenol in the U.S.,
07:01may increase their child's risk of developing autism.
07:04I want to say it like it is, don't take Tylenol. Don't take it. If you just can't, I mean,
07:11it's a fight like hell not to take it.
07:14There may be a point where you have to and that you'll, you have to work out with yourself, so
07:19don't take Tylenol.
07:21Numerous health organizations pushed back.
07:23Earlier this year, European researchers published a separate comprehensive review.
07:28They found statistically insignificant increases in the odds of autism and intellectual disability, about 3 and 11 percent higher odds,
07:37respectively.
07:38The researchers also found a decrease of 3 percent in the odds of developing ADHD.
07:42The researchers also examined sibling comparison studies.
07:46These helped control for factors such as shared genetics and family environment.
07:51And those analyses found no increased risk of autism, ADHD, or intellectual disability associated with acetaminophen use during pregnancy.
08:00All of the studies included here were observational studies.
08:04They described a correlation. None of them established causation.
08:08Thinking back to the correlation between shark attacks and ice cream sales, there was a third factor at play.
08:14It offered an explanation, and that was temperatures.
08:17In the summer, as temperatures rise, more Americans go on beach vacations and swim in the water.
08:22They also eat more ice cream.
08:24Similarly, other factors might explain sporadic correlations between Tylenol use and autism.
08:30Fever during pregnancy, especially during the first trimester, is linked to an increased risk of autism.
08:36Because pregnant women might be taking Tylenol to treat the fever,
08:40the increased risk of autism and ADHD could be from the fever and not from the medicine.
08:45While the correlation between Tylenol and autism has been well researched,
08:50there has yet to be a single study that proves how acetaminophen causes a range of neurodevelopmental disorders.
08:56But this might be difficult, if not impossible,
08:59because it would be unethical to experiment on pregnant women and their fetuses.
09:03For Straight Hour News, I'm Jess Craig.
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