Destiny.

We might think of it as that thing that brings two star-crossed lovers together. Or the thing that made us hit the jackpot in Vegas.

Or the thing that made our one true love break up with us because we went on to lose our Vegas winnings. But we don’t often think about our health as being particularly intertwined with destiny. We like to think our health is in our own hands.

And to some extent, it is. We look both ways before we cross the street to avoid being hit by cars. We brush our teeth every night before we go to bed, and we eat vegetables to stay nourished…a pickle counts as a vegetable, right?

And this story of cause-and-effect makes sense to us. Our health doesn’t feel particularly mystical, or like it’s been stitched into the cosmos. But while there are no prophecies or Chosen Ones in the world of public health, there are elements outside of our decisions that actually play a pretty big role in our wellbeing.

From the DNA in our cells to the air quality right outside our homes, there are countless factors that influence our health every day, all the time. But thankfully, public health experts are working behind the scenes to intervene with “fate” and give us all the best possible chance for living a healthy life. Hi, I’m Vanessa Hill, and this is Crash Course Public Health!

INTRO Now, the belief that we are the captains of our health destinies can be appealing, because it suggests our actions are what determine whether we end up sick or, well, dead. Like, in the epic saga of our health destinies, we don’t want to feel like we’re just a character in someone else’s movie script. We want to be, you know, the director.

When public health workers think about the ways that our actions factor into our health, they’re applying a behavioral approach to health. For example, experts taking a behavioral approach might say that when we smoke cigarettes, we’re engaging in a behavior that makes us up to 30 times more likely to get lung cancer than someone who doesn’t smoke. That’s why a big part of many public health workers’ jobs is to encourage people to adopt healthier behaviors, through things like “don’t text and drive” messaging on billboards and anti-drug media ads.

But the behavioral approach isn’t the only way health experts think about our health. For example, public health experts could take a biomedical approach to health, where they approach disease as a condition caused by germs or a problem with our organs, rather than just a problem with our behavior. For instance, public health researchers might examine how smoking tobacco affects our brains.

But one of the most influential and comprehensive approaches to health, the one we’ll be following most closely here at Crash Course, is the social approach. This approach acknowledges that our health choices and behaviors are impacted by the entire world around us, including social, cultural, political, and environmental factors. When addressing smoking, a public health expert taking the social approach might look at how tobacco is portrayed in the media, or what smoke-free policies are in place in businesses.

They may also pay attention to who is most affected by these decisions. In the United States, for instance, advertisers tend to target smoking-based marketing towards urban neighborhoods and neighborhoods with more Black residents. Taking a social approach to health opens the door to the question of health inequity, which is when different groups of people face different health outcomes because of an uneven distribution of resources, or because of structural differences in how they’re treated.

Health inequity is unfair and unjust, and uncovering and addressing it is a big part of many public health experts’ jobs. Now, the social approach doesn’t imply that we totally lack control over our health destinies. What it does tell us, however, is that we’re not the only ones calling the shots.

In fact, in the major motion picture of our health, most of the action takes place “offscreen.” What we’re talking about are the determinants of health. These are the conditions in which we are born, live, and work that all have an influence on our health. They span everything from our education level to our income level, to even our zip code and our genetic code.

While there are many ways to frame the determinants of health, in Crash Course Public Health, we’ll place them into three main buckets. There are the environmental determinants, which consider how environmental factors like our water supply, exposure to pollution, and climate change factor into our health. There are the social determinants of health, which cover the relationship between our health and where and how we live.

These include things like our income, education system, health policies put in place by our governments, and how our access to resources is affected by our race. And then there are the biological determinants of health. These are the particular biological characteristics that can determine our health outcomes– like our genes, sex, and age.

And in public health, rather than looking at just, like, our kidneys, we’re focusing on the biological factors that could affect our kidneys, like a family history of kidney disease. As we’ll see, there are no hard borders between each determinant, and it’s pretty much impossible to talk about one without stumbling into another one. Each determinant is related to the others, and a complete picture of our “health destiny” will always consider all three.

But for now, let’s focus on just biological determinants, looking at age as an example. In a kind of wild statistic, about half of all children will have at least one ear infection before they turn two. And while it’s easy to chalk this up to kids just acting in profoundly germy ways, it turns out these ear infections are at least partially determined by kids’ biologies!

For one, children have shorter and more horizontal eustachian tubes, which are these kind of neat and super necessary tubes that help drain fluid from our ears to the back of our throat. But it turns out the particular shape of these tubes in children means that fluid is more likely to get trapped in the ear, which makes it the perfect destination for bacteria to do some serious growing. So, just being a young kid actually turns out to be a major biological determinant of being prone to ear infections.

Now, while our age isn't really under our control, it still changes over time, which affects the kinds of factors that influence our health, too. A lot of biological determinants are like this– while they can seem permanent, they can actually change due to time, our behavior, or our environment. Let's go to the Thought Bubble for more.

Let’s say there are two identical twin brothers, Gus and Jack, who want to set out and open an organic guacamole business together. The brothers decide to split the business operations into two parts: Gus is in charge of growing avocados in an orchard out in the countryside, while Jack heads to the big city to handle the business negotiations. Now, Jack and Gus are both healthy, but they do have a family history of heart disease and skin cancer.

So in this case, this shared family history is one of Jack and Gus’ biological determinants of health. Anyways, out in the big city, a few years go by and Jack is kind of crushing it in the business world. He’s creating a huge demand for his guacamole by networking with local grocers and promoting his guac all over the city.

Jack spends most of his day tied to his desk, busily tending to phone calls with potential buyers. He doesn’t have much time to exercise because, well, guacamole empires don’t exactly run themselves. After a few years in the city, Jack begins to notice a feeling like there’s a persistent squeezing in his chest.

He goes to the doctor, who diagnoses Jack with coronary artery disease, a condition which puts him at a higher risk of heart attacks. Meanwhile, back at the orchard, all that heavy-duty avocado-tending means that Gus is in the best shape of his life. His heart is healthy, but working on the farm also means he’s spending a lot of time in the sun, which is a serious risk factor for skin cancer.

Sure enough, Gus begins to notice an asymmetrical mole with irregular borders on his neck, which his doctor diagnoses as stage one skin cancer. Thankfully, Gus caught it early and was able to get it removed. But remember kids, always wear sunscreen!

Thanks, Thought Bubble. Now, we can’t know for certain if Jack and Gus were “biologically inclined” to have these particular health outcomes. But what we do know is that despite sharing nearly identical DNA and a family history of skin cancer and heart disease, each brother experienced unique health outcomes that were likely determined by differences in their environments.

To deepen our understanding of the relationship between our biologies and the outside world even further, we can take a peek at a novel area of study: epigenetics. Now, we tend to think of our genetics as an impenetrable stronghold of “me-ness” at the center of our cells. After all, our genes are made up of segments of our DNA, and our DNA is basically a big instruction manual that tells our bodies how to look and act and be, well, our bodies.

But epigenetics says, “not so fast.” Epigenetics is the study of the outside factors that determine how much some genes are expressed in our bodies. According to epigenetics, everything from air quality to stress levels can factor into how our genes are expressed. Now, epigenetics doesn’t mean your DNA sequence is actually changing or mutating.

What’s changing is your body’s interpretation of your DNA. You can imagine epigenetics as a sort of chemical light switch inside your cells, which your environment and behaviors can brighten or dim--or even turn off completely. Let’s travel back to the end of World War II, to the Dutch Hunger Winter, a famine that occurred when the Netherlands was experiencing a bitterly cold winter and a national food shortage.

During this time, pregnant women who were starving were often giving birth to underweight, malnourished babies. Over the following decades, scientists continued to track these babies far into the future, when the famine was a distant memory and all those babies had grown up. What they found was that even decades later, people born during the famine were more likely to develop diseases such as heart disease, schizophrenia, and impaired glucose tolerance, a risk factor for diseases like diabetes.

This suggested that their bodies were able to “remember” the stress experienced in the womb. And wouldn’t you know it, researchers found that individuals born amid the famine had specific epigenetic markers on a gene that played a role in diabetes. This was the first observed instance of early environmental factors, like famine, resulting in epigenetic changes.

With so many external variables at play, it can feel like our health destinies are trapped behind a veil of unknowability. But by continuing to study the determinants of health, we‘ll start to nudge that veil aside and get a peek at the complex factors at play. Next time, we’ll take a closer look into the deep and surprising ways that our environments act on our health.

And – spoiler alert – [whispers] it’s happening to you right now. Thanks for watching this episode of Crash Course Public Health, which was produced by Complexly in partnership with the American Public Health Association. If you want to learn even more about Public Health, head over to APHA’s YouTube channel to watch “That’s Public Health” a series created by APHA and Complexly.

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