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Sometimes it can seem like it's impossible to do all the things it takes to be as happy and healthy as you want. I mean, who can sleep enough, exercise enough, drink enough water, and spend enough time with their friends? And that's not even mentioning how many conflicting sources there are about these things. Thankfully, lots of scientists have explored how the way we live our lives can help or hurt, and their studies have revealed that there are plenty of little things you can do if you want to make some changes this year.

First things first: for many people, everything starts with a good night's sleep. After all, if you can't sleep well, that can make it hard to tackle everything else you have lined up in a day. All kinds of things can affect your sleep, from medication to stress, but sometimes you can't sleep well because you just can't get comfortable. If you tend to spend nights tossing and turning, trying to find the right position, well, maybe you can take advantage of the fact that scientists have too, and they've found some solutions.  Here's Olivia with more on the best position for sleeping.

OLIVIA: Every night, when you turn out your light and pull up the covers, there's a good chance you settle into the same sleeping position. If you're like most people, you sleep on your side with your knees tucked up in the fetal position. But, lots of people also sleep on their back, sprawled out on their stomach, or twisted around three pillows and a stuffed animal.

But is one of those positions better than the others? Well, there's a lot of pseudoscience out there. But the real answer is: it depends.

If you're dozing off without a problem, and not waking up with weird aches and pains, your setup is probably okay. But if you have some complaints, the way you sleep could be the issue.

For example, sleeping on your right side seems to aggravate heartburn. None of the sample sizes were huge, but a handful of studies have shown that people lying on their right side after eating high-fat meals had higher levels of acid in their esophagus.

We don't really know why that is. But some scientists think sleeping on that side relaxes the valve connecting your stomach and esophagus. The valve that normally keeps stomach acid where it belongs.

So if you struggle with heartburn, it might be worth rolling over. As a bonus, sleeping on your left side might also improve circulation, although focused studies haven't really looked into it.

Your body returns bloods to your heart from your right side so sleeping on the left means those vessels aren't being compressed by your body weight. Left side sleeping is also recommended for people who are pregnant, better blood flow means more blood and nutrients to the placenta. It also keeps the growing uterus from compressing the liver, which is on the right. 

Sleeping on your side might also be good for your brain, at least if we're anything like mice. Using MRI scans a 2015 study in the Journal of Neuroscience found that 8 rats sleeping on their right side cleared waste from their brains more efficiently than 7 rats on their stomachs or 9 on their back. Side sleeping is most common in mice just like it is with humans and the authors speculated that animals may have evolved to sleep like this because it's the best way to clear brain waste.

But until this study is replicated in people it's probably not worth shaking up your routine.

Now side sleeping has its pros and cons but if there's any position that's the worst it's probably sleeping on your stomach. This puts pressure on your entire body and doesn't let the spine sit naturally and if you turn your face sideways to breathe that also awkwardly contorts your neck. So if you wake up feeling sore and you sleep on your stomach, it might be something to think about. If this is really your jam though a flatter pillow can at least help reduce neck strain. 

On the flip side, literally, sleeping on your back puts your spine in a neutral position, so it can be good for back pain. It also keeps your head elevated on a pillow where gravity can keep stomach acid out of your esophagus and cut down on heartburn. But sleeping on your back with your head on a pillow also makes your neck flex forward which tightens your airway and makes it harder for air to pass through. That can make snoring and sleep apnea, a condition that causes breathing to stop and start during sleep, more severe. 

Ultimately though the best sleeping position seems to depend on the person. If you're pregnant or a snorer some might be more beneficial than others.  

But in general if you're comfortable whatever send you of to dreamland best is probably perfectly fine.

MICHAEL: 
Somtimes sleep just doesn't happen though, and whether you're catching up on a restless night or just napping on a cozy Sunday napping can be an awesome way to get some shut eye. Except it might not be for everyone. Here's what research says about that.

Study after study has shown that napping is awesome, even for young healthy adults who get enough sleep at night. On average people feel better after catching a few Z's and their brains work better too. Which might make you wonder; should everyone be napping?

Well, not necessarily, the answer is more complicated than you might think. Lots of people swear by naps, in the US for example, about half of adults nap in a given week. And there's a ton of research about napping which suggests the benefits are impressive. 

Post-nap, people do better on tests that measure math skills, logic, reaction time, memory, mood...all kind of things, really. And on some tests, a nap is even better than caffeine. But such results area bit biased. Because a lot of this work has been done in people who are either sleep-deprived or habitual nappers. And the studies suggest the gains for people who nap regularly are so great that even if a study includes non-nappers, the nappers' benefits can skew the results of the whole group.

Now, it makes sense that researchers have relied so heavily on nappers and people who are downright exhausted. It's not exactly easy to fall asleep in the middle of the day in a weird lab bedroom with wires attached to you. But, it also means we're only now starting to figure out who benefits from napping and why.

And while naps are great on average, not everyone benefits equally. When researchers have taken paints to look at a more representative sample, they've been able to tease out some differences between people who nap regularly and those who don't. Non-nappers typically don't get a cognitive boost from napping. Lots of times, they just wake up feeling groggy. And it may be because there are differences in what happens in their brains when they nap.

Non-nappers spend more time in deeper sleep, which could make it harder for them to wake up. They also have fewer brain-wave signatures of memory consolidation, when new information moves into long-term storage--which could explain why they don't perform better on memory tests post-nap.

But what if non-nappers just need more practice napping? Researchers looked into that question for a study published in 2018. They put non-habitual nappers on a training regimen to try to build their napping skills. Basically, participants took a 20-minute nap, 3 times a week. And, after 4 weeks, it made zero difference. They still had the same patterns of brainwaves during a nap, they woke up feeling just as groggy, and they did no better on cognitive tests.

That could be because nap aversion is hardwired. There's some evidence that it may come down to the gene variations that you're born with and your childhood napping habits. Non-nappers could just be people who have learned through experience that napping doesn't work for them. Or, it could be that the participants simply didn't train long or hard enough. But even if everyone could learn to nap like the pros, there are a few other caveats to consider before we say the should.

For shift workers and people with sleep disorders, or atypical sleep schedules, things get even more complicated. And even though older adults are more likely to take naps than younger folks, napping in seniors is associated with higher rates of some pretty nasty health outcomes. There's no direct evidence that napping is causing these problems, but we need more information about this connection before we can say napping is great for this group.

Still, if you are a younger, healthy adult who enjoys a good siesta, you'll probably get a lot out of napping regularly. And there's plenty of science that can help you optimize your routine. Research says that the sweet spot for nap length is somewhere around 10-30 minutes. Anything shorter is not restful; much longer than that and you'll wake up groggy. And the best time of day to nap seems to be sometimes in the 2 to 5 PM window. This could be because circadian rhythms naturally dip in the afternoon, hence that mid-afternoon lull. And that may make it easier to fall asleep which is definitely an important factor in napping success.

But there's also evidence that late day naps interfere with nighttime sleep, so it may just be that 2 to 5 is early enough to avoid that. So even if you usually avoid naps, you could try following these best practices and see if napping does anything for you. But if it doesn't work out, you don't need to feel bad. Your brain might just work a little differently.

So naps aren't a magical solution for everyone, but hey, maybe knowing that can help you out.

Now, whether or not you manage to sleep well through the night, there's a good chance you start your days fresh by popping in the shower after you wake up. But how often do you really need to shower? Especially if you're not sweating much, do you actually need a scrub every day? Here's Stephen with the sudsy details.

Stephen: Nothing really beats a steamy shower to relax after a hard workout. And good hygiene is how we protect ourselves from infections and the social stigma of being smelly. But do you really need a daily shower to stay clean? Or is it doing more harm than good? Turns out there aren't any definite rules, but some scientists have recommendations based on what we know about the biology of our skin and what might be living on top of it. 

Your skin is a giant organ that physically blocks harmful stuff from getting inside your body. It's covered in a bustling community of bacteria, fungi, viruses, and even teeny-tiny arthropods. They make up what's know as your skin micro-biome. For the most part, researchers think these microbes you carry with you are pretty harmless. But as you interact with the world you can pick up other microbes that could make you sick. And when you, like, rub your eyes or put food in your mouth, your hands can help those germs slip past your skin and get into your body. Which is why washing your hands with soap is so important--especially if you work in medicine or food service. The soap is a surfactant, which means it's made of molecules that can bind to water and things like dirt, oils, or bacteria. This lets you rinse all that junk away, and fewer germs means a lower chance of infection. But what about washing the rest of your body?

Well, your skin has glands that are always producing sweat and oils which cools you down and keeps your skin moisturized and healthy. But there is a fine balance. Certain bacteria break down sweat, and release smelly molecules like thioalcohols. And if you skin has too much dirt, dead skin cells, or oils, your pores can get clogged, leading to problems like acne. So showering with soap can help get rid of some sweat and oil to manage your looks and smell. And in some cases, like the night before a surgery, a doctor might tell you to shower with an antimicrobial soap, which has extra chemicals to kill microbes.

If a surgeon is making cuts in your skin, they don't want any potentially dangerous stuff sneaking in.

On the other hand, showering too often might not be great for you either. For one, it can mess with the microbes that naturally live on your skin. And since soap and water wash away oils, your skin might get too dry. So the outer layer cracks, making it easier for disease-causing microbes to slip into your body. So dermatologists seem to say that daily showers where you scrub everywhere with soap is probably overkill, unless you sweat a lot, like people who work out every day. Otherwise, showering every couple of days should be just fine, to keep your skin micro-biome healthy and happy. 

Michael:
Speaking of things you probably don't need every day, at some point you may have heard some reason to take vitamin supplements. And there are so many of them, the vitamin aisle at the health stores can look like a candy shop for adults. The unfortunate thing is, most of them don't actually do much for you. There are a few supplements that might actually help you though, and Hank's got more on that.

Hank:
Supplements are super popular. One recent survey estimates that more than half of Americans use them and we spend billions of dollars on them each year. The truth is though, most people don't need any supplements, unless they're deficient in a vitamin or mineral. And even if they are, they should probably switch up their diet instead of buying pills or powders. That's because when these chemicals are eaten in food, your body can absorb and use them much more easily. Plus, it's much harder to overdose. 

A surprising number of supplements have actually been shown to hurt us. In fact, every year, about 23,000 Americans head to ERs because of adverse reactions. That being said, there are a few supplements in the right situations that might be worth it. Before you take anything though, you should definitely talk to a doctor who will look at your personal situation and help you make an informed decision. We are just internet people--not your doctor.

So that being said, here are 6 supplements that scientific research seems to have given a green light to, at least in some cases.

One of the clear winners in the supplement world is one that might actually look kind of sketchy since it's all over body-building powders and energy bars. But creatine is the real deal.

deal. It's a molecule that you naturally make in your liver and kidney and mostly store in your muscles. And, besides workout supplements, you can get it from foods like beef and fish.

Not everyone responds to extra creatine, but studies have shown that many people see improvements in sports that require short bursts of power, like sprinting. People can run faster, lift heavier weights, and build more muscle. Creatine can also help with muscle recovery from intense workouts, but it doesn't seem to help with endurance sports like long-distance running or swimming.

Scientists think that the extra creatine gets modified by your body and helps make the main molecule that cells use for energy, ATP. That extra available energy lets muscles work harder than they normally would, especially in bursts.

Outside of weight-lifting competitions, creatine can also help people with muscular dystrophy, a genetic disease that causes progressive muscle loss and weakness. These patients tend to have lower levels of natural creatine, and, in certain forms of the disease, supplemental increase muscle strength and let patients go about their daily lives more easily.

Didn't think we'd mention a trendy juice, did you? But beet, or beetroot, juice seems to actually do something. It's made from beets. I don't know why we even mentioned that. And, in multiple studies, researchers have found that it can improve athletic performance, specifically for aerobic sports like running or swimming.

While the juice has lots of potentially good stuff in it, scientists think that the part that's most beneficial for exercise is the nitrate. Beets are chock full of it. Our bodies will turn it into nitric oxide, which triggers blood vessels to get wider. This allows more blood to flow, so more oxygen gets to your muscles. Your muscles use oxygen to break down food to create energy to contract, so, with more oxygen around, you don't tire as quickly.

At least that's the working theory. For those same reasons, beet juice might also help lower blood pressure. If you drink a lot of it, though, just be prepared for some red or pink pee. Happens.

Now, like we said, you typically don't need supplements unless you have a deficiency, so there's no real good reason to take multivitamins, and non-food antioxidants

generally don't help either. But there is one exception for people with age-related macular degeneration, or AMD. People with this condition are usually over the age of 50. They slowly lose their vision because of damage to the macula, which is the central part of the retina, the light-sensitive cells at the back of your eye.

The basic idea is that, because cells in the retina absorb light, which can excite electrons and create reactive molecules called free radicals, they could get damaged. So antioxidants, which sop up free radicals, might help, and some of the most familiar vitamins, including vitamin C and E, are antioxidants. 

There has been a lot of scientific debate and lots of clinical trials to pin down which vitamins and antioxidants are actually helpful, and the general consensus is that certain combinations do work well enough to slow the progression of AMD. They don't prevent eye damage, but slowing it down is still good.

And you've probably heard about this one, but it's worth mentioning, because it's one of the few cases where we have pretty indisputable evidence that a supplement does some good. Folic acid, or folate, is a B vitamin. B9, to be exact. Vitamins are compounds that your body needs to work and grow that you can't make on your own, so you have to get them from somewhere else like your food.

Specifically, folic acid is important for making red blood cells, and thymine and cytosine, 2 of the 4 bases that make up DNA. If that sounds kind of important, let me assure to you it is. You can't make new cells without it.

So while everyone needs folic acid, pregnant people really need it, because they're rapidly growing a whole new human inside of them. That's a lot of cell creation. That means that the usual folic acid that we eat, either naturally in leafy vegetables and other foods or in fortified things like breakfast cereals, may not be enough.

So doctors advise people to take folic acid both before and during the pregnancy. Without enough folic acid, they can develop anemia, too few healthy red blood cells, and that can mean their tissues don't get enough oxygen, making them tired. And deficiencies can affect the baby's growth too, since they're getting the vitamin from their parent.

Not enough folic acid can cause a neural tube defect early in development, which can be serious. In one defect, known as spina bifida, the baby's spinal column doesn't close all the way, which can damage nerves and leaves some kids paralyzed. In another, called anencephaly, the baby doesn't develop its full brain or skull. Most of these babies die before or just after birth.

Melatonin is marketed as a cure-all for sleep-related problems. Its track record is a little spotty, but studies have found small benefits in certain cases. It may be most useful for people who have abnormal or disrupted circadian rhythms, like people with jet lag, night shifts, or a condition called delayed sleep phase syndrome, which is when your biological clock is perpetually several hours behind.

And that's because melatonin is a hormone that helps control our cycling in and out of sleep. As it gets later and dark outside, the pineal gland in your brain starts to release the hormone, and it binds to receptors deep in the brain to help usher you into dreamland. So when your body isn't naturally making melatonin, like if you've changed time zones, taking some could help reset your internal clock and let you get more rest than you otherwise would.

And some studies support this idea, while others find barely any improvement. Also, melatonin might help people with insomnia fall asleep faster and increase the total amount of time they sleep. It's typically only about 10 extra minutes though, and, in some experiments, those gains aren't there.

Last year, the American Academy of Sleep Medicine even revised its guidelines to say that they don't recommend melatonin for insomnia. Although, they admit that that is also based on relatively weak evidence. So the scientific community isn't positive about this one.

Part of the problem is that, even though melatonin is relatively well-studied, researchers have tested it at different dosages, at different times, and for different things, so we can't be too confident about what it can do.

The other big thing worth mentioning is that, even though people may use melatonin like a drug, basically to treat or prevent a condition, the FDA doesn't classify it as one. So it's regulated in the US like a supplement, which basically means

it's not very well-regulated. A study published in 2017 found that 70% of melatonin supplements have less than 10% more or less melatonin in them than their labels say, with some falling in an enormously wide range.

The supplements could also have other things that aren't listed on the label, like the neurotransmitter serotonin, and that could get dangerous. Like, too much serotonin can lead to overactive nerves and a bunch of potentially severe symptoms like seizures.

Last, but not least, is one of the oldest supplements in the world, St. John's wort. The saintly name comes from the fact that the plant's yellow flowers bloom around the birthday and feast day of John the Baptist. It's been used for lots of maladies at least to the ancient Greeks, but it's most famous for its effects on mood.

Modern scientists think this is because of the chemical hyperforin. Hyperforin prevents neurons from taking up certain neurotransmitters like serotonin, norepinephrin, and dopamine, which leaves more of them in synapses between cells.

Scientists aren't sure why this helps, but having more of these neurotransmitters around may let neurons communicate better and strengthen the circuits in the brain responsible for controlling mood. Many standard antidepressants do the same basic thing, even if their mechanisms are slightly different. 

Now, St. John's wort has been tested in multiple placebo-controlled trials. These are clinical trials in which some people get the substance being tested, and others get a placebo, like a sugar pill. That way, researchers can tell if a drug or supplement does anything. And those experiments showed that it helped people with mild to moderate depression.

The best case for St. John's wort is a 2008 meta-analysis that included 29 different studies. It concluded that the supplement does better than a placebo and is just as effective as standard antidepressants, but with fewer side effects.

But that meta-analysis also included a lot of studies from Germany, where St. John's wort is popular and tends to do well in trials. And other studies, especially those outside Germany, have sometimes failed to see St. John's wort doing much more than a placebo. Regular antidepressants sometimes fail in those same

tests too, though, so really it goes to show how strong the placebo effect can be.

A huge downside of St. John's wort is that it interacts with a lot of other drugs and makes them less effective, like HIV antiretrovirals, birth control, and organ transplant rejection drugs, and we're not even close to listing all of them. Researchers think that hyperforin triggers the liver to make more of an enzyme that breaks down certain medicines, so you go through them more quickly.

And you most definitely should not combine St. John's wort with other antidepressants, because those drugs can also increase serotonin levels, which can lead to a serotonin overdose. Because of other mechanisms, St. John's wort can also make you more sensitive to the sun, and it can lead to miscarriages, so pregnant people should avoid it. Not to mention, some people are just straight up allergic to it.

So even the best of the best supplements come with some pretty huge caveats or are very specific to certain people, and that's the biggest lesson here. In recent years, study after study has debunked any benefit from a lot of supplements that we assumed were good. So, unless you work out a specific plan with a medical expert, resist the urge to pop vitamins and botanicals to get healthier. Usually, you're better off without them.

So some supplements might be helpful, but there's no magic combination of vitamins that will make you healthy. You're probably better off just trying to work those vitamins into your diet, if you can.

But, even then, it can be hard to figure out how to get all the vitamins you need and eat the right number of calories, especially because people's bodies are so different. How are you supposed to know? Well, a lot of people have that same question, including scientists. Here's what we know.

How many calories should I have in a day? You're probably asking because you want to know how many is too many. After all, you know that if you take in more energy than you need, your body will store that excess energy as fat. But, before we can talk about how many calories you need, let's start with what a calorie is.

The calories that you find on food labels aren't the same as what scientists call calories. In chemistry, a calorie is the amount of energy it takes to raise the temperature of one gram of water

by one degree Celsius. But the calories listed on your can of soda are actually kilocalories, each one equal to 1000 of the small calories that chemists use to measure energy.

So, when your soda pop says that is has 150 food calories, you'll notice that it's written with a capital C. That's the same as 150,000 small calories with a little c. So that's enough energy to raise the temperature of a whole liter of water by 150 degrees. Kind of puts things in perspective.

But how many calories you need depends on who you are and how you live your life. First, there's your age to consider. Despite the stereotype of the ravenous teenager, your calorie demands actually peak when you're in your mid-20s. That's when your metabolism is higher than at any other point in your life, and, because you keep growing in your early 20s, once you're done you have more lean muscle mass, which requires more energy to maintain. So, depending on your lifestyle and other factors, when you're in your 20s, you may need from 2200 to 3000 calories a day.

You sex is a factor, too. Men tend to have more total body mass and more muscle mass than women on average, so their caloric requirements can be slightly higher. According to the US Institute of Medicine, the average calorie range for the adult woman is 1800 to 2400 calories a day. For men, it could be anywhere from 2000 to 3000. 

But that's obviously a pretty broad range, and, as delicious as it sounds, most of us don't need to be eating 3000 calories a day. And that's because the most important factor, by far, that affects your calorie needs is your activity level. For example, if you're a woman in your 30s or 40s, and you live a rather sedentary lifestyle, meaning you don't set aside time for exercise, then you probably don't need any more than 1800 calories on average.

But, if you regularly take a nice, brisk walk, say between 2.5 and 5 kilometers a day, then your caloric needs go up about 10% to 2000 calories. And, if you regularly walk more than 5 kilometers or burn the equivalent amount of energy doing some other exercise like running, then you're looking at another bump up to 2200 calories.

So, when it comes to calorie intake, medical professionals will tell you that the real goal is to focus on your energy balance. That's the balance of calories you take in compared to the calories you burn through physical activity. So, naturally, if you burn more calories than you take in, you're going to have

going to have to use more of the energy that you have stored up as fat. And, on the other hand, if you consume more than you use, you'll just keep building up those "energy reserves" around your midsection.

Since no one burns the same exact number of calories as they eat every day, the key is to maintain energy balance over the long term. So, if you consistently ingest more energy than you use, you'll be out of balance, just as you would be if you keep burning more energy than you supply for your body. But, if you ask me, you look fantastic.

So, for a lot of these questions, there's no easy answer. No one can tell you exactly how to eat, how to sleep, or what it will take to make you healthy, and many of those conversations are important to have with a medical professional. But hey, let's end on a high note, because there is one simple thing you can do that won't make you healthier but just might make you happier. Here's Hank to tell you why you might want to invest in some house plants.

Houseplants Might Make You Happier
HANK: Instagram is full of seemingly happy plant owners cultivating succulents and philodendrons. You might have even seen local plant stores advertise their wares as stress-reducing roommates. And the truth is there is some evidence that houseplants are good for your mental health. It's just not really clear why.

We've been studying how houseplants make us feel for decades in a range of different indoor situations, but some of the most robust evidence that houseplants can improve mental health comes from hospitals. For example, a study from 2009 looked at how the presence of plants and flowers affected the recovery of 90 patients in the hospital for hemorrhoidectomies. And that is what it sounds like. It's a time in your life when it's probably not bad to have a plant friend around.

They found that patients in rooms with plants did fare better. Their blood pressure was lower, and they reported less pain, anxiety, and fatigue. The patients also said that the plants helped them to relax and feel less anxious and made them feel more positively about the hospital staff caring for them. And the researchers who led this study have found similar results with plants in the rooms of appendectomy and thyroidectomy patients, as well. The thing is these hospital studies don't tell us

a whole lot about why this effect occurs, just that it seems to.

Researchers have tried to drill deeper into mechanisms by looking at plants in other indoor environments like offices, and these studies seem to back up the idea that plants can positively affect our moods, but the data start to get a little murkier. One of the big questions is whether plants affect specific cognitive processes, and therefore make us feel better by lifting our mental load, or are just generally de-stressing.

Some psychologists think that indoor plants and other living things have a restorative effect, based on the idea of attention restoration theory. According to this theory, voluntary attention, the attention needed for things that aren't inherently fascinating but must be focused on nonetheless, is finite. But if you can just stop focusing so hard on things, you can give your mind time to replenish its attention reserves, and the plants may help you do that because they are inherently interesting, so you don't have to force yourself to pay attention to them.

One research team found that having plants in a room did help the 34 student participants to increase their attention capacity after a proofreading task, but they felt that that might have been because the plants made the room feel more pleasant and reduced the participants' stress levels in general, rather than having a real restorative effect. And there are good reasons to suspect that the presence of plants is just kind of relaxing. Like in a 2013 study, 18 tested participants reported being more comfortable in an office environment with plants than a space without them.

Even if a relaxing effect is real and directly induced by the plants themselves, it still doesn't tell us what about plants what about plants makes us feel less stressed. Researchers in that 2013 study asked the participants to say what they preferred in terms of color, odor, and plant size, and found that the group favored small, green, lightly-scented plants. So it may be that those sensory experiences--seeing small bits of green or smelling living things--somehow triggers relaxation.

But unfortunately, studies that have tried to tease out whether it's the color, three-dimensional shape, scent, or some other aspect of a plant that really matters haven't shed a ton of light on things. In part, that's because many of the studies use surveys to ask the participants about their emotional and psychological responses to the plants. While these results are relatively consistent across studies, they're subjective measures prone to all kinds of biases, and linking mental states to more objective measures like physiological changes is tricky at best.

Many studies look at changes to blood oxygenation in parts of the brain, for example. Participants in these studies wear a special sensor that uses spectroscopy ot measure near-infrared light absorption. You see, red blood cells absorb light differently when they're carrying a lot of oxygen, and since oxygenation and blood flow in the brain have been linked to neural activity, this measure might give the researchers a peek at how the brain is responding to different conditions.

But studies often get confusing results. Like, in a 2016 study, researchers had 24 men in their 20s look at either live plants or an empty flower box for three minutes. After that, the scientists detected a decrease in blood oxygenation in the right prefrontal cortex in the plant viewing group. That went hand-in-hand with reports of feeling more comfortable and relaxed by viewing the plants, so you might think less prefrontal cortex oxygenation equals a more relaxed state of mind.

But another study from 2015 found significant increases in blood oxygenation in both the left and the right prefrontal cortex when 18 participants viewed a real plant as opposed to a projected image of it. This lack of consistency shows just how difficult it can be to untangle the correlations between physiological and psychological responses.

And some researchers have been critical of the methodology of studies looking at indoor plant effects on mood in general. A 2009 review of 21 studies took issue with a number of methods in the field, including the fact that studies often used small

sample sizes. You wouldn't expect the effects of indoor plants to be, like, huge, and if they have small effects, from a statistical perspective, you'd need a large number of participants to pick them up. Similarly, they criticized the variation in how the plants were presented in different studies. The type, size, and placement of plants, as well as the duration of exposure all differ greatly, and that makes results difficult to compare. 

But the reviewers did feel that the question of whether or not indoor plants can affect our mental health is worth studying, so they made some recommendations for future experiments. These recommendations included implementing more systematic approaches to plant exposure and making sure that studies looking at "restorative" effects of plants actually had the participants do something taxing enough to require restoration.

So, even though we been studying this for decades, we still don't seem to understand why we see positive effects from plants in places like hospitals, or if the results mean houseplants boost your brain power or improve your mental health in general. But look, here's the situation. Those plants on your desk and by your couch are almost definitely not harmful to you, as long as you're not allergic to them or something, so if you feel like your world is better when your desk or living room looks a little bit more like a jungle, you do you.

So, if you could use a little boost, you might want to spruce up your home with a little green. Thanks for watching, and a special thank you to our patrons on Patreon for making all these episodes possible. It takes a lot of people to make a SciShow video, and we couldn't keep creating them without your support. If you'd like to learn more about how you can support SciShow, head over to patreon.com/scishow.

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