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(This program is no longer available for online streaming.) A sequel to one of the most popular NOVAs of all time, "Miracle of Life," this Emmy Award-winning program tracks human development from embryo to newborn using the extraordinary microimagery of Swedish photographer Lennart Nilsson.

Trace human development from embryo to newborn through the stunning microimagery of photographer Lennart Nilsson.

Life's Greatest Miracle

US & Territories

Water. Turn on the faucet and it’s always there. Without it we perish. But how safe is our tap water? In this special report narrated by Joe Morton, NOVA investigates what happened in Flint, Michigan, when local officials changed the city’s water source to save money, but overlooked a critical treatment process. As the water pipes corroded, lead leached into the system, exposing the community—including thousands of children—to dangerous levels of poison. NOVA uncovers the science behind this manmade disaster— from the intricacies of water chemistry to the biology of lead poisoning to the misuse of science itself. NOVA follows ordinary citizens and independent scientists who exposed the danger lurking in Flint’s water and confronted those who turned a blind eye. And discover the disturbing truth that reaches far beyond Flint—water systems across the country are similarly vulnerable. How can we protect ourselves from poisoned water? (Premiered May 31, 2017)

What exactly went wrong in Flint—and what does it mean for the rest of the country?

Poisoned Water

Whether they make you fat, fart, or freak out, microbes play a central role in your life. Right beneath your nose—on your face, in your gut, and everywhere in between—trillions of bacteria, viruses, and fungi are so abundant in your body, they outnumber your human cells. But these aren’t just nasty hitch-hikers. Many are crucial to your survival. Evidence suggests that a diverse microbiome can keep you healthy and, conversely, a damaged one could kill you. NOVA Wonders peers into this microscopic world to discover the fascinating, bizarre, and downright surprising secrets of the human microbiome, including the world’s largest stool bank, which transforms raw stool into life-saving poop pills.

Discover how a world of microbes living in and on you can make you sick-and keep you healthy.

What's Living in You?

Koch Foundation

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An elderly woman in a red sweatshirt runs down a path in a park

Image Credit: David Tett via Centre for Ageing Better

How exercise may help prevent Alzheimer's

Your brain loves it when you exercise. Of course, you yourself may not love every sweaty minute of your kickboxing class or Saturday afternoon run—but your brain revels in it. That’s because exercise doesn’t just increase muscle tone. It doesn’t just goose energy levels and enhance mood, fighting <a href="https://www.pbs.org/wgbh/nova/video/depression-memory-alzheimers/">depression</a> and anxiety. It also heightens problem-solving skills and memory. And, research has increasingly shown, it protects against <a href="https://www.pbs.org/wgbh/nova/video/determined-fighting-alzheimers/">Alzheimer’s disease</a>—both delaying onset of the disease and slowing decline in patients who have already been diagnosed.
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As baby boomers age and more Americans live longer, Alzheimer’s is on the rise. In 2020, some 5.8 million people in the U.S. were living with this most common form of dementia, in which inflammation and tangles of misformed proteins in the brain accompany progressive <a href="https://www.pbs.org/wgbh/nova/video/alzheimers-screening-test/">memory loss</a> and inability to perform day-to-day tasks.Despite decades of research, effective treatments for Alzheimer’s have eluded researchers; even a full explanation of what happens inside an Alzheimer’s patient’s brain has remained out of reach. This is in part because the disease is incredibly knotty and multifaceted, says Fang Yu, a researcher at Arizona State University who specializes in applying new dementia science to human trials. Alzheimer’s affects myriad processes in the brain, our most complicated organ, but most treatments developed thus far have only been able to tackle one aspect of the disease at a time, she says. “Even if there is a medication that can help target certain pathways, there are many pathways needed.” That’s why Yu’s Alzheimer’s studies have often focused on the power of moving our bodies. Exercise is unique in that it also affects the body and brain in many ways, she says, making it an important intervention for addressing the complexity of Alzheimer’s. It’s “something quite special,” agrees Christiane Wrann, a neuroscientist at Harvard University and Massachusetts General Hospital. While you’re dancing, bicycling, or running, it may seem like “you’re doing something that doesn’t have anything to do with the brain,” she says. “But you’re actually getting improvement in cognitive function.”
<h3>How does it work?</h3>Perhaps the most straightforward way in which exercise safeguards against Alzheimer’s is by improving cardiovascular health. The effects of a good sweat session don’t stop at our hearts—they help improve the condition of our other organs and blood vessels as well. Those healthier vessels deliver an upgrade in the connections among brain cells called neurons, Wrann says. With reinforced wiring, it’s easier for nourishing oxygen to get in, for waste products to get out, and for the neurons to talk to one another. And improved fitness of the heart and lungs also seems to help the brain take up glucose more efficiently, which helps keep neurons healthy.Plus, <a href="https://www.pbs.org/wgbh/nova/video/cannabis-reverses-brain-aging/">research on mice</a>—a common, if imperfect, source of new Alzheimer’s science, since it’s not possible to ethically conduct some kinds of research on living humans—has shown that exercise is a rare cause of “adult neurogenesis,” or the growth of new neurons in adulthood. Although it’s difficult to prove fully that the same happens in humans, it seems like <a href="https://www.researchgate.net/publication/323624428_The_Role_of_FNDC5Irisin_in_the_Nervous_System_and_as_a_Mediator_for_Beneficial_Effects_of_Exercise_on_the_Brain">one key player is irisin</a>, a hormone manufactured in the muscles in response to exercise, Wrann explains. Irisin is special because it carries a pass to get through the blood-brain barrier, the barricade of tissue and blood vessels that keeps harmful substances from reaching the brain. Once inside, <a href="https://www.researchgate.net/publication/354038429_Exercise_hormone_irisin_is_a_critical_regulator_of_cognitive_function">irisin helps the brain</a> create a neurotransmitter called BDNF, which is important to hippocampus health. The hippocampus is a center of learning and memory in the brain, and Alzheimer’s patients’ hippocampi tend to shrink as their health declines, Yu says. The ability to sprout new cells in the hippocampus, and to prune away connections that aren’t needed anymore—two processes that BDNF supports—is key to stabilizing and protecting it.
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A series of studies at Wrann’s lab in Boston has also shown that, at least in mice, irisin produced during exercise has powerful anti-inflammatory effects in the brain. That could be an important insight because some new research points to <a href="https://www.pbs.org/wgbh/nova/article/brain-inflammation/">inflammation</a>, rather than previously implicated amyloid plaques, as a possible cause of neuron death in Alzheimer’s. Inflammation is caused by the immune response to negative stimuli—not just viruses or bacteria but also, for example, misfolded proteins in the brain. In an Alzheimer’s patient, the immune system may respond to the presence of these plaques by attacking them, Wrann explains, and in its enthusiasm, it may also attack the synapses that connect neurons. “If it gets completely out of control, you have this ‘friendly fire’ that causes damage to the neurons,” she says. But her research indicates irisin may bind to receptors on specialized cells deep within the brain, calming that inflammatory response.And one last piece of the puzzle is <a href="https://www.pbs.org/wgbh/nova/article/healing-sleep/">sleep</a>—not a type of exercise in itself, but caught up in something of a love triangle with exercise and Alzheimer’s disease. When it comes to dementia prevention, sleep and exercise may work together, says neuroscientist Miranda Chappel-Farley, a Ph.D. candidate at University of California, Irvine. Studies have shown that more exercise leads to better quality sleep, which is an important protective factor itself against Alzheimer’s. And people getting better sleep are more likely to feel up to exercising. Together, they create a powerful bulwark against dementia and represent a lifestyle factor ignored at your peril, says Chappel-Farley, who cautions against “targeting exercise but not paying attention to sleep.” 
<h3>What kind of exercise is best?</h3>Aerobic exercise seems to be the champion when it comes to protection against Alzheimer’s and maintaining executive function. Of course, most of the mice participating in Alzheimer’s trials run on their wheels, but that doesn’t mean you have to. Biking, dancing, swimming, or any activity that gets your heart rate up is a good candidate, Yu says. That’s because it has the potential to increase BDNF levels; spur blood flow and shore up blood vessels; and decrease “white matter hyperintensities,” abnormal changes that affect how the brain transmits electrical signals.Newer research also indicates that resistance-based muscle-building exercise may support a broad spectrum of cognitive functions. That effect seems especially promising in patients who have already been diagnosed with Alzheimer’s, where it may help slow their decline, adds Yu, who often works with dementia patients. There, the goal is not improvement but slowing deterioration. “And that’s basically what my research has shown: that exercise can level and stabilize,” she says.Tai chi and other types of movement that incorporate mindfulness also decrease stress and inflammation and improve sleep, she adds. And some research suggests that a mix of many types of exercises may provide stronger improvement than a single activity. In a review of <a href="https://europepmc.org/article/med/34004389">71 studies of exercise and dementia</a>, Yu and her colleagues found the most consistently effective exercise was “mixed component,” a blend of muscle-building and aerobic workouts.Still, “it’s important to highlight that there’s a lot we don’t know yet,” says Chappel-Farley, since exercise comes in so many forms and can be adjusted by duration, intensity, frequency, and timing. “It’s not totally clear which might be best.” Does it take a certain amount of exercise for our brains to reap the benefits? Are there any findings in the extensive mouse research on this topic that can’t be transferred to humans? Wrann says that data is encouraging so far, indicating that the more you exercise the more benefit you’ll experience. And really, what’s the risk? “My big message is that exercise is good for you,” Yu agrees. “Even if in the future we find that it doesn’t prevent Alzheimer’s for everyone, it’s still good for your health and quality of life.”But Wrann also remains mindful of people who can’t exercise because of a disability or physical limitations, or who may develop Alzheimer’s despite getting plenty of exercise; there’s still no silver dementia bullet. While it’s unlikely that researchers could develop a drug that can affect the body in as many ways as exercise can, she’s hopeful about irisin’s potential as a source of new drug therapies. Because it’s a powerful anti-inflammatory that can already wriggle through the blood-brain barrier, she wonders if it might be possible to use irisin to create a drug that goes even beyond the positive effects of exercise. Inflammation in the brain seems to be central to many neurological conditions. That way, she says, “we could reach people with Alzheimer’s disease—or beyond.”
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Exercise could be a powerful defense against Alzheimer’s disease. Three dementia researchers explain how it works.

CRISPR Gene-Editing Reality Check

CRISPR gene-editing technology is advancing quickly. What can it do now—and in the future?

Predicting My MS

A filmmaker with a rare type of multiple sclerosis explores the mysterious causes of MS.

Try Passing this Alzheimer's Screening Test

You have 10 seconds to memorize six shapes.
Two women enrolled in a long-running study of factors that affect Alzheimer&#x27;s take a test in which they have to memorize shapes and draw them.
Try Passing this Alzheimer&#x27;s Screening TestPublished: April 22, 2022DIANE: I’m going to show you a sheet that has six figures on it, and I want you to study the figures so that you can remember as many of them as possible. You’ll have 10 seconds to study the entire display.KIMBERLY: When I take it away, that’s when you start drawing.DIANE: Now draw as many of the figures as you can.SIGRID: Can’t do it.DIANE: All right.Well, that was fine. I’d like to see whether you can remember more, if I give you another chance.KAREN: That’s all I could think of.KIMBERLY: Try not to forget this display, because I may ask you about the figures again later.KAREN: Okay.KIMBERLY: Okay.DIANE: I’ll present the display again for 10 seconds. Try to remember as many of the figures as you can this time, including the ones you remember in your last attempt.Now draw as many of the figures as you can.SIGRID: I was going to really remember that one, but I don’t.DIANE: Okay. That was fine.SIGRID: When you took it, did you feel like you did better two years ago? I mean do you feel…DAVID: Oh, I’m sure I did better.SIGRID: You did. So, you feel like you’re failing a little bit, too?DAVID: Absolutely.SIGRID: Absolutely.I always feel badly about myself, when I do this.DAVID: Yeah.SIGRID: ’Cause I think it’s kind of startling to really have to face your memory gaps and what that means.DAVID: Yeah, it is. It’s hard to take. It’s hard to take.SIGRID: Well, I guess my question to you…DAVID: And I realized, I summed it up…SIGRID: My question to you is this: Did you at any point really feel taken aback or shaken?DAVID: Today?SIGRID: Yes.DAVID: No.SIGRID: No. See? I did, so, there’s a message in that.DAVID: Yeah.SIGRID: Right?DAVID: Yeah. Well I know, I know that you’re worried. I know.

You have 10 seconds to memorize six shapes.

Quinn Brett hikes with her Bomber off-road handcycle on Walter's Wiggles, a steep trail named for its many switchbacks, in Zion National Park. Image Courtesy of Quinn Brett

Adapting national parks for wheelchair hiking

The trails through our public lands weren’t designed for wheelchairs, but new wheelchairs are designed for those trails. National Park Service accessibility specialist Quinn Brett wants parks to catch up with wheelchair technology, increasing access to American wilderness.

Climbers Tell Story of Mt. Washington Climbing Accident

Climbing partners have a harrowing experience on Mount Washington in NH.
Climbers Hugh Herr and Jeff Batzer recount an experience that led to them needing limb amputations.
Climbers Tell Story of Mt. Washington Climbing AccidentPublished: April 5, 2022Jeff Batzer: The first night when we got there was just to get up, to stay overnight on the mountain at Harvard Hut. There was very much of that warning too, the Appalachian Mountain Club folks that were very careful, I think, to warn people like, &quot;Hey, do you know what you&#x27;re doing here? You&#x27;re going to go up into a really rough realm.&quot; And so there would&#x27;ve been a bit of that too. That next morning is where we wanted to choose a route going up through Huntington Ravine, where there are a number of different ice climbs.So we decided... really, I think it was that morning to do Odell&#x27;s Gully. Hugh led it and did a number of pitches on up through, and at one point I had these heavy GORE-TEX mittens and I had slings that were Velcroed on. And so I could let them hang down so I could work on the tools and take screws in and out. And so the one time I did that, the sling came open and looked and the mitten was gone. So that would come in later on, as far as being a major problem with trying to keep my hands from becoming frostbitten. So we&#x27;re at the top of Odell&#x27;s Gully, which is 800 feet from the ground, we decided we would drive on and actually try to get to the summit and just try to knock that all off, maybe about 20, 25 minutes or so. And these little wispy wind gusts and the snow that was coming down turned into just hurricane-force winds.Hugh Herr: Above Huntington&#x27;s, we probably walked five minutes at the most. That was the critical decision that led to the accident.Alison Osius: Among the mistakes that they made was that they didn&#x27;t have a compass. They didn&#x27;t have a map and compass. And they were using the wind and so when they turned around to walk down, they did not realize that the wind had changed, and so they walked in the wrong direction. Instead of going down where they had come from, they went down the wrong side and they went into the Great Gulf which is an immense wilderness.Jeff Batzer: Just some awful events happened that night. There was a river over in that Great Gulf area. Well, let&#x27;s just follow this, which is going downhill at least, maybe that&#x27;ll get to something eventually. And what happened was Hugh fell through the ice and was soaked from the waist down. Maybe within an hour or so it happened again. We were always right next to each other and he would go through the next time he went in up to here.Hugh Herr: It&#x27;s minus 20 degrees Fahrenheit and your feet get wet, it&#x27;s a rapid decay. Given my experience in the mountains, I personally did not believe we would last tonight. What I didn&#x27;t estimate is the power of being with someone else. That&#x27;s critical because if you&#x27;re with another human being, you can hug them and you dramatically reduce the surface area of the dual body, but you double the heat source. So by hugging someone, you can stay alive for a remarkable amount of time in those subarctic conditions. We actually rationalize that the sooner we died, the better. So we actually stopped hugging each other.Alison Osius: It&#x27;s hard to imagine that they could have survived another night. And then by incredible miracle Cam Bradshaw, the 28 year-old hut manager, who was out snowshoeing and she saw these weird tracks and she thought, &quot;Oh, that must be a moose.&quot; Because they were so inconsistent. And so she tracked them for a long time.Jeff Batzer: It was about 2:30, just heard some noises over in the trees, real close to us and could see this girl fighting her way through the trees.Hugh Herr: She came upon us and was standing there. And at first we were silent because we didn&#x27;t trust our minds. And then we shouted and she responded.Alison Osius: And she said, &quot;Are you the guys that are missing?&quot; And they said, &quot;Yeah, that&#x27;s us.&quot; And then everything went into motion really fast.Jeff Batzer: Actually he said to Hugh, I was cheering him on when nobody was around, &quot;Just come on Hugh, hang in there, we need to make it a little bit longer.&quot;Hugh Herr: We felt tremendous elation because we went from being certain of death to, gosh, we might live.Jeff Batzer: Little did we know what our bodies would have to go through in these next days and all that in the hospital and everything.

Climbing partners have a harrowing experience on Mount Washington in NH.

How an Alzheimer’s study reached Black communities

Getting Black individuals involved in a study requires more than just asking them.
Any investigator that doesn&#x27;t understand how communities of color have been unfairly treated when it comes to research is doing themselves a disservice, says Gina Green Harris, director of Milwaukee Outreach.
How an Alzheimer’s study reached Black communitiesPublished: April 5, 2022Gina Green-Harris: I don&#x27;t think it was intentional but there was just a lapse of recruitment of African-Americans in the beginning of the study. Over time it obviously became recognizable that there was the absence of folks of color. So in 2006 they started trying to recruit African-Americans but it was fairly unsuccessful. And I think the original thought was that, oh, we just haven&#x27;t asked. But there was the misunderstanding of how to ask. Often time you have Caucasian investigators coming into black communities and saying, okay, I&#x27;m here in my white coat, I&#x27;m here as the white knight, I&#x27;m coming to save you. And I&#x27;ve got all these ideas and never asking the community for their ideas.Researcher: And notice in our community is a lot of stigma. And a lot of information that has been old information that people have continued to recycle over and over again. Is there any materials that we were able to actually have to be able to talk to these individuals? &#x27;Cause there&#x27;s not a lot of education that&#x27;s going out there.Gina Green-Harris: We still have the issue around Tuskegee. The level of offensiveness that occurred with Tuskegee has also continued to happen over the years. And so that is also in the forefronts of our mind.David Dick (CBS News, Archive): For 40 years the general public in Tuskegee in Macon County, Alabama was unaware the federal government was experimenting with 430 local black men who had contracted syphilis. They were used as human Guinea pigs to determine the effects of the disease. 28 men died as a result of the untreated syphilis. When the program became public knowledge last year, it was halted. But so far a citizen&#x27;s panel has been unable to force AGW to help those who survived.Mayor Johnny Ford (CBS News, Archive): I want to see the citizens of Macon County and Tuskegee who were utilize in this study receive adequate compensationGina Green-Harris: Any investigator that does not understand the impact of how communities of color have been unfairly treated when it comes to research, they&#x27;re doing themselves a de-service. We had to actually convince the community and we had to say what made us different. So what made us different? We didn&#x27;t just go out and say, hey, can you be a part of our research?We actually started by developing our community advisory board to talk about how do we address this thing called Alzheimer&#x27;s and dementia in the black community so that we can build this new research model.

Getting Black individuals involved in a study requires more than just asking them.

Topic: Body & Brain

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