During a 5-year span between 1970 and 1975, 29 states in the United States lowered the legal age for drinking alcohol from 21 to 18, 19, or 20. Advocates for changing the minimum age noted that a person old enough to vote or fight in a war was old enough to drink. Those against it worried about accidents, as car crashes – then as now – were the leading cause of death for teenagers. Then, over the next several years, some states began to raise the minimum drinking age again.
Alex Wagenaar, PhD, now a research professor at the Emory University Rollins School of Public Health in Atlanta, recognized the situation as a natural experiment – something that divides a population into one group exposed to experimental conditions, and one unexposed. “You had 29 examples of experiments, basically each with changing legal ages,” he says. Starting in the late 1970s, while a fledgling graduate student, Wagenaar compared data from those two populations in states that had changed the law, controlling for variables like seat belts and traffic laws, to assess how raising the drinking age affected the rate of alcohol-related car crashes.
He found a decrease in crash-related deaths among teens in states that had raised the drinking age. In 1984, the federal government raised the minimum age to 21, and the rates normalized again.
Wagenaar has spent decades in a field now known as “legal epidemiology,” which uses rigorous scientific methods to investigate how laws impact public health.
Health risk factors are often described and researched in terms of readily identifiable exposure. They may be environmental, like smoking as a risk factor for cancers, or inherited, like mutations in the BRCA gene that increase a person’s risk of breast or ovarian cancer. But a central argument in legal epidemiology is that laws themselves can be risk factors, too.
For most laws, those effects aren’t well understood or studied. “We can think of the law as a treatment, as some kind of pill that we apply to hundreds of millions of people,” says Scott Burris, JD, who leads the Center for Public Health Research at Temple University’s Beasley School of Law.
“But new medical treatments go through all sorts of advanced testing. There’s surveillance after marketing to make sure no unexpected side effects show up.” That’s not the case for many new laws, which are often not evaluated for health risks before they’re passed or surveilled after they’re implemented.
He says it’s no surprise that laws affect health. What is surprising is that so many are proposed and passed without considering those health effects. “It’s crazy that we don’t demand more information about what laws work,” says Burris. “Evidence is important because it’s there if we’re willing to see it. But if you don’t want to see it, you’re not going to see it.”
Finding ways to analyze and use that evidence is central to legal epidemiology. Legal epidemiologists are investigating the health effects of COVID-19 regulations and abortion access laws, but they look at other connections, too, like the one between minimum wage and infant survival, or between housing laws and life expectancy. Researchers in legal epidemiology study the health impact of existing laws and develop new tools to help lawmakers and public health authorities at every level assess or predict the efficacy of a law. Their ongoing goal is to advocate for laws informed by public health evidence and to avoid laws that might lead to adverse public health outcomes.
“Law is one of the most significant determinants of health,” says Matthew Penn, JD, who leads the CDC’s Office of Public Health Law, which was established in 2000. “It also impacts conditions that result in health inequities and negative health outcomes.”
The Science of the Law
Some laws have effects that are easier to recognize than others, says Burris, who has led studies on seat belt laws, how criminalization laws affect people with HIV, and the impact of drug syringe laws on injection drug users.
Some are low-hanging fruit. Seat belts have been required by law in cars since 1968, and the National Highway Traffic Safety Administration estimates that they’ve saved more than 300,000 lives. Compulsory vaccinations for smallpox and polio led to the eradication of those diseases from the U.S. population in the 20th century. During the federal assault weapons ban from 1994 to 2004, homicides due to mass shootings declined, and after the ban was lifted, they rose again.
Other findings are less obvious – and more surprising. A 2016 study in the American Journal of Public Health tied minimum wage increases at the state level to higher birth weight and fewer infant deaths. Previous studies have found that low birth weight is tied to a raft of other problems, from worse health in childhood to lower high school graduation rates, so the 2016 study, which Wagenaar worked on, points to raising minimum wage as a legal action that could improve health across the board.
Housing laws also have some surprising effects. Homeownership is the largest component of personal wealth, and people build wealth by inheriting homes from earlier generations. Myriad studies have linked homeownership to better health and even a longer life expectancy. Overall wealth has the same effect; in July 2022, in a paper published in the Journal of the American Medical Association, researchers from Northwestern University and other institutions analyzed death and financial records of hundreds of thousands of people. They found a gap of more than 15 years between the life expectancies of the wealthiest and poorest individuals studied.
“We know there’s a direct correlation between health outcomes and wealth,” says Georges C. Benjamin, MD, former secretary of the Maryland Department of Health and Mental Hygiene and current executive director of the American Public Health Association, which focuses on public health problems including how laws affect health and access to health care. Racist housing laws offer one example. After his father died 10 years ago, Benjamin was going through paperwork when he found a surprise on the back of the title for his dad’s house – the same one where he’d grown up. “It basically said this home cannot be sold to African Americans,” says Benjamin, who is African American.
Although such racial “covenants” were outlawed in 1968, they still show up in older houses and cause complications for families trying to pass property from generation to generation. “Many of us are now in the process of moving property along, but when you go to pull those titles, you’ll find overt redlining.” Today, studies show, redlining has been linked to higher risk of heart disease, asthma, and other health problems.
A rich subfield of studies has also examined the health effects of criminalization laws. One of the earliest, a 1928 study, reported that mortality rates in children and women declined during the 5 years of the Prohibition era, but rose in men over 35. (The author noted, however, that many causes beyond the law likely contributed to this effect).
More recent investigations look at the connection between criminalization laws and drug overdoses. “It is always important when we use law as an intervention” for a public health crisis like opioid abuse, says Burris. “Overdose is a major killer.” Many states have enacted Good Samaritan laws, which may, for example, protect a person who helps a victim of overdose from prosecution of low-level drug offenses. But “by and large individual studies don’t show very robustly that [these laws] are working,” Burris says. In a paper published earlier this year in the American Journal of Public Health, legal epidemiologists argued that a range of complicating factors, including competing laws, likely blunt the effectiveness.
“It doesn’t mean we shouldn’t try them,” Burris says. “But we have to realize that when we try the law to solve a problem, we’re not finishing the job.” Right now, he says, legal epidemiology studies are woefully underfunded by the National Institutes of Health, but with more financial support researchers could identify – and even predict – which overdose laws could have the biggest impact, both in terms of lives saved and financial investment.
Other recent studies have looked at larger trends to try to identify policies that promote health. A study published in 2020 in The Milbank Quarterly connected state policies including higher tobacco taxes, stricter gun control, and access to abortion to longer life expectancy. If all states were to adopt policies based on gains in life expectancy, the authors estimated that life expectancy in the country would rise by more than 2 years.
Natural Experiments and the Future
Interest in the connection between the law and health effects started to gain momentum around 2000, says Penn, when researchers in public health began to recognize the “centrality of law” in a way they hadn’t before. “Public health law really crystallized between 2000 and 2010,” he says. The term “legal epidemiology” was introduced in 2010 as researchers focused on the idea that a law’s impact on health should be a primary consideration, ideally before it passes but even after it’s put into place.
Wagenaar has spent his entire career in the field. Right now, he says, experts in the field are developing tools that can not only find causal connections between law and health outcomes but also be widely and readily deployed, usable by any public health agency and able to produce results ready for lawmakers’ consideration. He says that unlike medical researchers, legal epidemiologists usually don’t have randomized clinical trials – the current gold standard in evaluating the efficacy of new treatments – to rely on. But that doesn’t mean laws can’t be rigorously scrutinized for how they affect health.
“Randomization is a very good tool, but when it’s impossible to randomize, there are all these other tools that are very helpful,” he says.
He says that many investigations could start by looking at natural experiments unfolding in real time – not unlike the case of lowering the minimum drinking age in the 1970s. At that time, critics of his work claimed that without randomization it revealed only a correlation that could have arisen through other causes, but Wagenaar says he stood by his methods and conclusions. They were rigorously replicated and accurately predicted long-term effects.
“If you’re thoughtful about how you design your study, you can get high levels of causal confidence,” he says.
Now, researchers are working to broaden the reach of legal epidemiology by designing tools that any public health official can use. “Any time you put a new policy in place, health has to be part of the conversation,” says Benjamin.
Legal epidemiology “is applicable to almost anything,” says Wagenaar. And there’s plenty of data – about plenty of policies and laws – to be scrutinized. “Lawmakers are experimenting on us as a society all the time, with everything they pass,” he says.
The COVID-19 pandemic offered a clear case study. In a 2021 perspective published in the New England Journal of Medicine, Wagenaar and others pointed out that decades of scientific research into mRNA vaccines made it possible to quickly develop, manufacture, and distribute enormous quantities of a vaccine. Those decades were built on both basic science research and advances made in the wake of the first SARS virus. But there was no body of research into the health effects of regulations like mask-wearing, stay-at-home orders, travel restrictions, and school closings. The result was a confusing and inconsistent hodgepodge of rules.
He also points to the country’s current tangle of marijuana regulations and sees the current approach to laws and policies as a missed opportunity. The United States has developed strategies, over decades, for using the law as a health intervention to reduce risks associated with drinking and smoking, but he thinks current discussions around new laws for marijuana fail to take that experience into consideration. “We have all that tobacco knowledge and all that alcohol knowledge, and we’re not paying any attention to the lessons we’ve learned,” he says. “That’s an example that’s frustrating.” In other words, decades of practical research has taught us how to regulate substance use to promote public health; putting those lessons into effect is a thorny political matter rather than a medical one.
But in some cases, says Benjamin, legal epidemiology can reveal a simpler solution. In the case of redlining and other racist practices that blunt the accumulation of wealth and impair health, the way forward is obvious, he says. “In some cases, it means going back to the books, and taking those laws off the books.”