So I recently turned 30 and I decided that I wanna take my health a lot more seriously than I have done in the past.

And I've been trying to figure out what are genuinely the scientific evidence-based habits that I can add to my life that will help me be healthier.

Now in this video, we're gonna be talking about three specific health habits.

We're gonna be talking about should you be getting 10,000 steps a day?

We're gonna talk about how much sun exposure should you get and should you actually be going out in the sun first thing in the morning?

Thirdly, we're gonna talk about how much water should you actually be drinking and should you aim for two and a half liters per day?

I was kind of surprised doing the research for this video because it seems like a lot of the recommendations we get aren't really that evidence-based.

Oh, and by the way, if you're new to the channel, hi, my name is Ali.

I'm a doctor turned entrepreneur and YouTuber and author of the book, Feel Good Productivity, which is about how to be more productive in a way that feels good.

And so in this video, I'm excited to dive into some of the scientific research around these three fairly simple but important health habits.

So let's get into it.

All right, so back in 1964, before the Tokyo Olympic Games, there was a marketing campaign that was used to promote walking 10,000 steps a day.

And this number was chosen because the Japanese character for 10,000 looks like a person walking, apparently.

And during this campaign, they were promoting this device called the manpoukei.

And in Japanese, manpoukei literally means 10,000 steps meter, which counts the number of steps you've taken.

So this number was chosen pretty randomly for the campaign, but it's become mainstream all over the world.

And now it's like the number that everyone talks about when it comes to walking.

But does the science actually support this?

Should we actually be walking 10,000 steps a day?

Now, this is something I've been really keen to find out because 10,000 steps a day is actually quite a lot and left to my own devices,

I only get maybe 4,000 or 5,000 steps a day.

So I've been trying to figure out should I actually be walking more?

Is it genuinely good for my health?

Now, you might not know this, but 10,000 steps is about five miles or eight kilometres with a little bit of variation depending on the individual.

And it roughly takes one hour and 40 minutes to walk 10,000 steps.

Conveniently, this roughly translates to 10 minutes per 1,000 steps.

This was new to me.

I had no idea until we were doing research for this video.

It's like, oh, every 1,000 steps you do, you need to walk for about 10 minutes.

But 10,000 steps is 100 minutes.

And so should we really be spending 100 minutes every single day just walking?

To answer that question, let's look at what some of the data says.

Now, meta-analyses are these big studies that take data from lots of other research papers and bring them together, which is kind of cool.

And this meta-analysis from 2022 looked at 15 different studies to see how daily step count was associated with the risk of dying from any cause.

And in science, this is what we call all-cause mortality.

This graph shows how your risk of death changes with the more steps you take each day.

This is what it looks like for people younger than 60, and this is what it looks like for people older than 60.

So if you're younger than 60 years old, which you probably are if you're watching this channel, the optimal number of steps to take is around 8,000 to 10,000.

And for people older than 60, you actually lower your risk of death by about 50% by only walking about 6,000 steps per day.

Now, because both of these lines are really steep at the start, this tells us that increasing our daily step count is really good if you are currently pretty inactive and you don't move around a lot.

And then over 10,000 steps per day, you can start to see that the graph sort of starts to level out.

But to be honest, this is probably because there's not actually enough studies that specifically look at people who actually do walk over 10,000 steps per day.

So the data in this range is a little bit more unreliable, and we don't actually know quite yet if your risk of dying keeps on decreasing if you just take more and more and more steps.

Now, this graph is for all-cause mortality, but interestingly, we see exactly the same pattern when it comes to your risk of cancer and dementia and heart disease.

In this study, for example, researchers measured the number of steps taken per day by around 80,000 adults in the UK around the age of 61 to see how this changed their risk of getting dementia around seven years later.

And as we can see here, the total number of steps per day that showed the greatest reduction in risk of dementia was just under 10,000, this magic number again.

We can see a similar sort of pattern for cancer, as in this graph.

And again, here you can see around 10,000 is when things start to get interesting.

And we also see pretty much an identical pattern when it comes to heart disease.

And again, if you zoom into the graph, you see that this 10,000 number shows up again and again.

Now, if we look at all-cause mortality again, and we separate it out into people who sit for more than 10 hours a day, i.e. me, and people who sit less than 10 hours a day, if you sit a lot, then actually the benefit of walking those 10,000 steps is greater than people that don't sit a lot.

And so what this data shows is that it looks like walking seems to offset the negative health outcomes associated with sitting at a desk all day.

Okay, so let's talk about the key takeaways from all these studies.

So firstly, any amount of walking is good for you, and you don't necessarily need to hit 10,000 steps to start seeing the benefits from walking.

But in general, the more walking you do, the better.

And also the faster you walk too, the better.

There was a bunch of studies about this, they were too long to include in this video.

But if you walk at a brisk pace, you're more likely to get benefits than if you walk super, super slowly.

Also, if you walk faster, it takes less time to get in your 10,000 steps.

Now, a great target to aim for for most people is around 6,000 to 8,000 steps per day, because beyond that, the benefits do start to diminish.

And if you remember that 1,000 steps is equivalent to about 10 minutes of walking, then this goal actually seems pretty realistic for a lot of us.

This would mean that if you walk, for example, 30 minutes total in your commute to get the train or the bus to work, whatever the thing is, that would be 3,000 steps.

And then you only really need another half an hour walk, which you can take during a lunch break or any other time, to be hitting that target of 6,000.

So what I'm personally taking away from this is that I'm gonna aim to start off my day with a half an hour walk around the local park with a little coffee, and that will be my first 3,000 steps.

And then I'm also gonna try my best to, like, you know, when I have to get to a restaurant that might be half an hour away, aiming to walk there for 3,000 steps rather than getting an Uber or getting the Tube.

Walking also has a bunch of benefits to creativity, which we're not talking about in this video, but, you know, this is why I find whenever I'm kind of feeling blocked on writing or anything I'm working on, actually just going for a walk really helps clear my mind, and it means that I'm more creative, but I also get the steps in, which is always a good thing.

And as of last week, when we did the research for this video,

I've decided to add in my daily walk as part of my ideal week.

If you haven't yet come across my ideal week method for managing your time, there'll be a completely free template linked down in the video description, so you can check that out.

It's one of the time management techniques that has most impacted my life.

But of course, mental health is just as important as physical help, and one way to improve that is with therapy provided by BetterHelp, who are the paid partner of this video.

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Head over to betterhelp.com forward slash Ali Abdaal or enter my name Ali Abdaal during the signup process and enjoy a special discount on your first month.

Anyway, thanks BetterHelp, and let's get back to the video.

All right, now we come to health habit number two, which is sun exposure.

So we're gonna talk about sun exposure in general and also sun exposure specifically in the morning.

Okay, so let's start with sun exposure in general.

Now, back in the day, having darker or tanned skin wasn't very desirable.

And so they used lead in skin whitening makeup to try and make their skin a little bit more fair, fair and beautiful as they say.

The Greeks and Romans did this around 900 BC to 500 AD.

And from the 1500s to the start of the 1900s, this was fashionable across Europe and America as well.

But then everything changed in the 20th century where going to holiday to a hot sunny country and then getting more tanned suddenly became fashionable.

But around the same time, scientists were discovering the links between UV radiation and skin cancer.

So even though people still enjoyed spending time in the sun, we became more conscious of spending too long outside because we were worried about skin cancer.

We're told by doctors and dermatologists and big public health bodies to always wear sun cream, always put on your sunglasses and always wear a big hat to avoid sun exposure.

And apparently this was actually a famous campaign in Australia in the 1980s, Slip Slop Slap.

♪ Slip, slop, slap, slip on a shirt, slop on sunscreen ♪ ♪ And slap on a hat. ♪

And this means slip on a t-shirt, slop on some sun cream and slap on a sun hat apparently.

So in some ways, sunlight has gotten a bad name for itself over the last 100 years because we've been really worried about skin cancer and ageing of skin.

But the truth is that sunlight can be both harmful and also beneficial for us.

So we need to find some sort of balance.

If you get too much exposure to sun and UV light, that can cause skin damage and ageing and contribute to skin cancer.

And if you look at this picture, this is a truck driver where because they've been driving on one side, half of their face has been sun exposed for a very long time and the other half hasn't.

And you can literally see the difference between what sun does to skin and what shade it does to skin.

And there's actually a really clear association between sun exposure and living longer.

So this graph, for example, shows different age groups along the X-axis and then their all cause mortality per 1000 person years along the Y-axis, i.e. how likely are they to die?

This is what the line looks like for people who've been avoiding sun exposure.

This is what the line looks like for moderate sun exposure.

And this is what the line looks like for people who have the most sun exposure.

Now, this doesn't seem like much, but if you zoom in on the graph, you can see that there's actually a pretty reasonable difference in all cause mortality between these different groups.

So essentially, the more sun exposure you get, the lower your chances are of dying in terms of all cause mortality over time.

And researchers in 2011 even came to this conclusion.

The overall health benefit of an improved vitamin D status from sun exposure may be more important than the possibly increased CMM risk, which is a type of skin cancer, resulting from carefully increasing UV exposure.

And there are lots and lots of reasons for this.

So you probably know that UV rays from sunlight help our skin make vitamin D, which means we absorb calcium and phosphorus to strengthen our bones.

In theory, you could take a vitamin D supplement, but actually, even though lots of governments and public health bodies recommend vitamin D supplementation, the actual evidence for it is a little bit mixed.

And what a lot of the studies around this show is that actual sun exposure is generally better for you than just taking a vitamin D supplement.

In fact, this very recent study in 2024 concluded that multiple trials of oral vitamin D supplementation show little benefit.

So basically, the sun does things for our body that taking a vitamin D supplement doesn't really do.

For example, you might not know that UV rays from sunlight actually causes our skin to release nitric oxide into our blood, and this makes our blood vessels relax and therefore reduces our blood pressure.

And that's why, for example, you can see decreases in blood pressure in summer compared to in winter.

So sunlight helps protect against things like heart disease and strokes, and it also decreases our risk of things like obesity, autoimmune conditions like arthritis, and lots of different types of cancer as well, including apparently skin cancer.

So what I'm personally taking away from this is that I should probably spend more time in the sun.

Yes, of course, I'm still gonna use my sun cream, but sun exposure is probably not as bad as we were led to believe.

But the other thing around sun exposure is that if you are a fan of Andrew Huberman, which I am, he talks a lot about getting sun exposure first thing in the morning.

Now, because we are diurnal mammals, we wanna be alert and active during the day, and then we wanna be sleeping, obviously, at night.

And we want all the cells and organs in our body to stay in sync with this day and night cycle, which is called our circadian rhythm or our internal clock.

Now, there is a region in the brain called the suprachiasmatic nucleus in the hypothalamus, which is our master clock.

And this master clock sends signals to the rest of our body about whether to feel sleepy or awake.

Now, the cool thing about the circadian rhythm is that it's actually slightly longer than 24 hours.

And so we need cues from our environment to keep it in sync.

And that is why light is so important.

So our circadian rhythm is most sensitive to sunlight first thing in the morning, and also late at night, which enters through our eyes, hits the retina, and then sends signals to that master clock in our brain.

So first thing in the morning, firstly, sunlight increases our cortisol levels to make us feel alert and focused.

Secondly, sunlight helps our bodies make serotonin, which boosts our mood and makes us feel happier.

Thirdly, sunlight in the morning helps stop our body from making melatonin, which is the hormone that makes you feel sleepy.

And fourthly, getting sunlight first thing in the morning tells our brain to set an internal timer so that 12 to 14 hours later, you'll start to make melatonin again, and you'll therefore feel sleepier.