Is Drinking Milk Essential for Building Strong Bones? (Transcript)

Jen Gunter:
We have been told SO MUCH about milk.

SOUND CLIP:
We were told that milk was good for your bones.
I remember my mom always made me drink it.
It was supposed to be very good for my health

Jen Gunter:
Think about ALL the milk messages you’ve heard in your life!

SOUND CLIP:
My dad's mother had just the largest hunch in her back and that was used as a fear tactic...sit up straight, drink your milk. We had people from farms that would visit our elementary school and just basically tell us about the positives of milk.
I remember advertisements when I was a kid that milk is critical for healthy mind and body, strong bones, calcium, things like that. And I think there was a series of TV ads later, with celebrities showing their milk mustache.
Jen Gunter:
You remember those Got Milk ads, right? Everyone from Beyonce to Harrison Ford was in them. They had a message you probably also heard from your school cafeterias, your parents and grandparents, even your doctors … You MUST drink milk to have healthy bones. What’s the logic behind all this?

Here’s the basic explanation that most of us have received...Milk has calcium. Your bones need calcium. So make sure to drink your milk. Otherwise, your bones are gonna be weak and brittle and you won’t end up big, strong, and tall! But it turns out milk isn’t a magic bullet for healthy bones.

I’m Dr. Jen Gunter. From the TED Audio Collective, this is Body Stuff. We’ll dive right in after this…
…
While I was doing some research for my book, The Menopause Manifesto, I realized that the relationship between milk and bone health is actually pretty complex...

I came across a paper with a little tidbit of information that really shocked me. This paper had a graph that showed a surprising trend -- countries where people drank more milk had HIGHER rates of hip fractures.

That’s not what I would have expected -- and probably not what you’d expect either! I mean, if drinking milk leads to strong bones, why would drinking more of it lead to more fractures. Why more bone problems?

It should mean fewer problems! I just want to be clear -- there’s a lot more to this story than the graph shows us. There are many things that affect fractures that weren’t incorporated into it.

But this was one of those record scratch, freeze frame moments for me. Like...WHAT??? What is going on here? Is what I know about milk and bones even true? I knew there had to be more to the bone health-milk story. If milk isn’t the secret to healthy bones, what is? And how did milk and dairy become such a big part of the human diet?

Dr. Joy Wu is an endocrinologist.

Jen Gunter [to Dr. Joy Wu]:
If you could only tell someone one super cool bone fact, what would that be?

Dr. Joy Wu:
Oh, only one? (laughter)

Jen Gunter:
Endocrinologists specialize in the network of chemical messengers called hormones. And guess what? Bone is actually part of that network!

Dr. Joy Wu:
Both because it is involved in the regulation of minerals like calcium and phosphate, but also because it itself secretes hormones.

Jen Gunter [to Dr. Joy Wu]:
So that is super cool because I think when most people think about hormones, they think about the ovaries or the testicles or the thyroid. But we should be thinking about the bones as well?

Dr. Joy Wu:
Yeah. They both respond to hormones and also produce some hormones.

Jen Gunter:
There’s a lot of other stuff you probably don’t know about your bones, so let’s meet your skeleton.

Dr. Joy Wu:
Adult humans have about 206 bones. And the neat thing is every single one is unique in its shape and size and yet they sort of fit together perfectly.

Jen Gunter:
Our bones do a lot for us.

Dr. Joy Wu:
Bones provide mechanical support.

Jen Gunter:
They’re what your muscles are attached to and they help you move!Without your skeleton, you’d be more like a slug or a jellyfish!

Dr. Joy Wu:
They protect our internal organs.

Jen Gunter:
Your skull protects your brain. Your ribs protect your heart and lungs. Your pelvis protects your reproductive organs and bladder!

Dr. Joy Wu:
They store our minerals.

Jen Gunter:
Like calcium and phosphorus...minerals you need for your cells to work right.

Dr. Joy Wu:
And also it’s the site of where your blood cells are made within the bone marrow.

Jen Gunter:
That’s right! Your bone marrow makes your red blood cells, your white blood cells, and your platelets -- constantly making all the blood cells you need!
Now, If I ask you to imagine one of the bones in your amazing skeleton, you probably picture a cartoon bone -- white and smooth, with little knobs at each end. Like you see at Halloween.

You’re picturing what’s called cortical bone. That’s the hard, outer shell.

But there’s actually a lot going on inside that hard shell.

Dr. Joy Wu
If you were then to take a bone and, make a cut through it and look at it under the microscope, there's a second kind of bone often in the middle, that's called trabecular bone. It's a little like, you know, cutting through the kitchen sponge -- you see all those nooks and crannies.

Jen Gunter [to Dr. Joy Wu]:
Ooh, so we might use a sponge analogy like your dish sponge that has like the hard side for scrubbing. And then the spongier side. You could think of cortical bone as the harder part of the sponge and trabecular bone as the spongy part.

Dr. Joy Wu
Exactly.

Jen Gunter:
Your bone marrow, by the way, lives within this spongy maze of bone. Bones are dynamic. Our bodies are constantly replacing old bone with new bone. To build new bone, you need calcium. Imagine building bone as a construction project. Cells called osteoblasts are like the construction workers...”Hey Bob! Hey Jim!”

Dr. Joy Wu:
And what that means is they're secreting mostly type 1 collagen out into the surrounding, we call it matrix, so the material that's near the osteoblast, and the collagen is arranged in fibrils.

Jen Gunter:
Picture a scaffold of collagen, put together by these osteoblast construction workers.

Dr. Joy Wu:
And then the mineral, which is calcium and phosphate, deposits between those collagen fibrils, and that mineralization procedure is what strengthens the bone and lends it the hardness.

Jen Gunter:
So calcium strengthens and hardens these scaffolds of collagen. Bones also store NINETY-NINE percent of your body’s calcium.
Calcium helps your cells communicate and makes sure your nerves can signal properly. If your body doesn’t have enough calcium, it just takes it from your bones...which can make them weak and fragile.

So calcium is absolutely essential for your amazing bones to be healthy!
And though milk IS one source of calcium, it’s not the ONLY source. There’s also calcium in foods like tofu, sardines, kale, broccoli, cabbage, and leafy vegetables.

It’s just that milk has historically had a huge cheer squad in the US, because we have a pretty big dairy industry. But milk consumption has dropped here over the past few decades. And milk has even been pretty demonized lately.

SOUND CLIPS
"We shouldn't be drinking it. It's not good for us."
"We're not supposed to be able to drink it."
"I feel much, much better drinking almond milk instead of whole milk."
"I feel like the rumor I've heard is that you drink milk and now it like actually pulls calcium out of your bones or something."
"I've heard from my father that as you age your body starts not needing it and even rejecting it."
"We don't have a drop of regular milk in the house anymore."

Jen Gunter:
We have this problematic binary thinking about milk -- it’s either amazing or it’s horrible...

Some of my patients have given up milk because they think it caused yeast infections. My friend Tiffany, who’s a music teacher, tells me some of her students won’t drink milk because they’re sure it causes mucus in their throat. And some people even blame milk for their acne!

Dr. Christina Warriner:
Milk is a really fraught food. And the fact is it is a prehistoric food. It's a really ancient food that people have been using for a long time, for a very different purpose, to survive on.

Jen Gunter:
More on that after the break...

…….

Jen Gunter:
Dr. Christina Warriner is an anthropologist who researches how the human diet evolved. She spends a lot of time looking at gut bacteria -- the microbiome. She’s like the microscopic Indiana Jones...

Dr. Christina Warriner:
Exactly. Thank you. I like that.

Jen Gunter:
As part of her research, Dr. Warriner has been digging into a huge puzzle in human evolution...dairy consumption.

In the Middle East, they milk camels. In Mongolia, they milk yak. Some cultures don’t ferment milk. Others ferment it into dozens of different forms, from yogurt to cheese. Genghis Khan’s army traveled across the continent with a lightweight, fermented milk curd that could keep at room temperature for up to TWO YEARS!

Dr. Christina Warriner
This ability to produce an energy dense, lightweight food kind of underlies the success of the expansion of the Mongol empire.

Jen Gunter:
Why did we develop so many ways of consuming dairy? And how...and this is the real mystery...have some of us evolved to digest dairy as adults?

See, milk has a sugar called lactose. To digest it, you need a specific enzyme called lactase.

Lactase is FASCINATING.

Dr. Christina Warriner:
Lactase is made in the small intestine. So once you've consumed milk, the lactose enters into your small intestine and it's digested.

If there’s no lactase in your small intestine, you can’t digest milk. So instead it heads on down to your colon...

Dr. Christina Warriner:
Where you have trillions of bacteria that will digest it for you, but as byproducts produce hydrogen gas, methane and carbon dioxide, which contribute to the symptoms of lactose intolerance.

Jen Gunter:
Symptoms like bloating, gas, and stomach cramps. Things that leave you rolling on the floor, grabbing your stomach and farting! When we’re babies, our bodies produce lactase so we can digest breast milk. But as we get older, we stop producing it and we lose our ability to digest dairy.

Dr. Christina Warriner:
And that's just part of the normal weaning process for mammals in general. The fact that some populations around the world continue to produce lactase into adulthood, is actually a mutation. And there was some incredible work showing that these mutations that allow this, this continued production of lactase, has evolved at least five times independently in different human populations predominantly in populations in Europe, also in East Africa and in the Arabian peninsula. And then the same variant that's found in Europe is also found throughout the Caucuses, Northern South Asia, and Iran.

Jen Gunter:
This genetic mutation seemed like the answer to the dairy puzzle! The mutation came first, then people started producing and consuming dairy products. Mystery solved!

But then...there was a twist.

Something called DNA sequencing was invented. Suddenly researchers could examine the genes of ANCIENT humans.

Dr. Christina Warriner:
And they tested all these Neolithic farmers and none of them have these genetic mutations. And in fact, we now know that the mutations don't arise until 4,000 years after people start dairying. This kind of left this open question of what's happening during these 4,000 years that we have strong evidence that people are milking animals producing dairy products, but how are they digesting them?

Jen Gunter:
Dr. Warriner, our microscopic Indiana Jones, has been searching for answers in the steppes and plains of Mongolia...

Dr. Christina Warriner:
They milk more species of animals than any other country on earth. Cattle, sheep, goats, yak, camel, horses, and reindeer. And, they make a really wide variety of dairy products. And yet the people in Mongolia today do not have the ability to produce lactase as adults.

Jen Gunter:
They are not producing the enzyme that digests lactose! But...dairy is a huge part of their diets...

Dr. Christina Warriner:
Even today in the countryside, 30% of their calories are coming from milk and milk products. Some men consume up to 250 grams of lactose per day in horse milk, which are they also then ferment to make a kind of, um, alcohol

Jen Gunter [to Dr. Christina Warriner]:
Wait, wait, wait, wait, wait. There's horse milk. Alcohol?

Dr. Christina Warriner:
Yeah. So this is something that isn't, that well-known outside of central Asia and inner Asia, but yes, it's very fizzy and very fresh, but yeah, it's an alcoholic horse milk, and they also, distill cow and yak yogurt to make a kind of milk vodka.

Jen Gunter [to Dr. Christina Warriner]:
It amazes me how people are able to ferment whatever they have to create alcohol. I'm continually impressed by the innovation.

Dr. Christina Warriner:
Me too, me too!

Jen Gunter:
OK so Mongolians are consuming all this dairy, even alcohol made from dairy! But like lots of other people in the world, they do not have the genetic mutation that allows them to digest lactose.

Shouldn’t they be groaning in pain from bloating and gas after all that horse milk alcohol and yak yogurt? HOW are they digesting dairy?

Dr. Warriner thinks the answer might be in the microbiome, that diverse ecosystem of bacteria in our guts.

Dr. Christina Warriner:
There was a study a few years ago that, was the first gut microbiome study shown for Mongolia. And it showed that they had a quite unusual gut microbiome profile. And one of their unusual features is they have very high amounts of a group of bacteria called bifidobacterium and bifidobacterium are a milk adapted bacteria. They're extremely high in infants. And so we're starting to wonder if there's a different adaptation mechanism happening in Asia, where people are able to maintain an infant-like state of the gut microbiome to also aid in lactose digestion.

Jen Gunter:
So some adults can digest milk because they have the genetic mutation from thousands of years ago, some might have this unique microbiome, and some people have neither and cannot digest milk.

We still have SO MUCH to learn about this ONE mystery in human evolution.

What amazes me is that humans seem to have a limitless capacity to evolve with our food! And that’s probably one of the biggest takeaways from the story of the human diet.

Dr. Christina Warriner:
There is no one perfect human diet. There's many different,
successful and healthy diets for us. And I think that's really characteristic of our species. And I think that's also what allowed us to survive the last ice age, when so many other megafauna, we’re megafauna too, went extinct. It's our ability to be flexible and our ability to handle many different diets.

Jen Gunter:
There was never just one diet among ancient humans. This is why diet fads like the meat-focused “Paleo diet” are nonsense.

Throughout history, people ate what they had! Some people ate meat, some people ate fish, some people ate lots of fruits and vegetables, and some people ate dairy. Groups of humans have even adapted differently to the same environment. Like in medieval Greenland…
Dr. Christina Warriner:
The major limitation with Greenland is just plants. You can't grow crops there. It's too cold. And that means they have a limitation on the amount of glucose in their diet, right? And so we see that the Vikings colonize Greeland, and the Greenland Norse, set up very intensive dairy farms. So they were able to then get glucose from milk. Also living on Greenland at the same time were the Intuit. The Inuit had a completely different strategy. So rather than focusing on sources of glucose, they consumed large amounts of fat and blubber, which allows their bodies to produce glucose through a process called gluconeogenesis. So in this really extreme environment, you have two different groups who in completely different ways develop cultural and biological adaptations to surviving. And I find that absolutely fascinating.

Jen Gunter:
We’ve developed many ways to get the nutrients we need. And getting calcium is no exception. There are many ways to do it. Milk might work for some people. Other sources of calcium might work for other people.

But you don’t NEED milk.
I spend a lot of time thinking about how to get enough calcium in my diet. That’s because my mom actually died from complications of the bone disease, osteoporosis. When you have osteoporosis, you have low bone density. That means your bones are thin, fragile...and susceptible to fractures. Spine and hip fractures are two of the most dangerous complications of osteoporosis. And one risk factor for osteoporosis is not getting enough calcium.

Remember, calcium hardens and strengthens your bones. And, if your body doesn’t get the calcium it needs, it pulls calcium from your bones -- making them weak and brittle. But there’s a reason osteoporosis happens to people when they’re aging and not when they’re young adults. Bones change over our lifetimes. Here’s Dr. Wu, the endocrinologist.

Dr. Joy Wu:
As children and young adolescents are growing, of course, bones are getting bigger and also getting stronger over time and increasing in what we call bone mass. So peak bone mass in adults happens in the late twenties, early thirties. After that there's a very gradual decline slowly year by year in the amount of bone that people have.

Jen Gunter:
This is because the balance between making new bone and breaking down old bone changes.

Dr. Joy Wu:
With age the rate of bone breakdown tends to outpace the rate of bone formation. In women, there's a period of more dramatic decrease in bone density and bone mass in the years right around menopause.

Jen Gunter:
Hormonal changes around menopause are a big reason why there is a higher rate of osteoporosis among women, although men can get osteoporosis too.

Jen Gunter [to Dr. Joy Wu]:
So, um, you're talking to somebody who's maybe in their forties or fifties or a young whipper snapper like me at 54. What would be some of the preventative measures that we could take to protect our bones and protect us from osteoporosis?

Dr. Joy Wu:
I think the most important would really be exercise for all sorts of reasons, but one of them being that it is great for bone health. So, regular exercise averaging about 30 minutes a day, but particularly with an emphasis on weight training or resistance training, maybe two to three times a week. At any age exercise should sort of approach a limit where it stretches you, right? Where it challenges you.

Jen Gunter:
Exercise is absolutely critical for keeping your bones healthy.

Putting physical stress on your bones -- by lifting weights or biking or running -- stimulates osteoblasts. Remember, those are the construction worker cells that build new bone. So exercise is a bit like the start of shift bell at a factory saying “hey boys, time to get to working, gotta build some bone!”

Exercise also increases blood flow.

Dr. Joy Wu:
And so you can deliver more oxygen to the tissues, including muscle and bone. Blood flow in bones is an important part of, bringing nutrients to bone and also, helping the cells that are making new bone.

Jen Gunter:
For some people, Calcium and Vitamin D supplements may be another strategy to prevent osteoporosis. Vitamin D’s main job is to help your body absorb calcium. But it’s important to know that taking EXTRA calcium and Vitamin D, beyond what you need, isn’t going to protect your bones.

Dr. Joy Wu:
More is not always better. I mean, I think for both calcium and vitamin D there has been sort of waves of enthusiasm where people have tended to maybe go a bit overboard.

Jen Gunter:
The amount of calcium you need a day depends on your age. Until you’re 50, it’s a thousand milligrams. For women over 50 and men over 70, it goes up to 1200 milligrams. And this includes your diet and any supplements you’re taking.

Dr. Joy Wu:
There are a couple of things that have a high concentration of calcium in the diet. Dairy containing products are a great example. On average, a serving of dairy products, which is a cup of milk, a cup of yogurt and ounce of cheese, is about 300 milligrams. So I tell people if you're going to do dairy products, two to three servings a day would be most likely adequate. Cause we also get calcium in, for example, green leafy vegetables and other dietary sources*.*

Jen Gunter [to Dr. Joy Wu]:
So what's your favorite calcium rich food?

Dr. Joy Wu:
I really love all forms of cheese.

Jen Gunter [to Dr. Joy Wu]:
Hm. Yeah. We should do a bone health tour in France where we're required to sample all the cheese.

Dr. Joy Wu:
Oh, we did this, biking tour in the Loire Valley. It was amazing because everywhere you went, there was cheese. So I think my bones were very happy on that trip.

Jen Gunter:
So Dr. Wu and I both love cheese. And milk and dairy are good sources of calcium! They’re just not the ONLY source. I try to get calcium from chia seeds and leafy vegetables and sardines! (It’s so good on toast!)

And that’s one of the amazing things about how humans have evolved -- we can get nutrients from many, many sources.

Dr. Christina Warriner:
We are dietary generalists, but more than anything, we are flexible.

Jen Gunter:
We’re creative, brilliant, flexible omnivores! We’ve managed to survive an Ice Age, make alcohol out of horse milk, and develop not one but two completely different ways to survive in Greenland’s harsh climate. We are constantly adapting to survive.

Jen Gunter [to Dr. Christina Warriner]:
Is there one thing that you hear people talk about on social media, your friends, or, you know, in the news about the human diet, that just makes you roll your eyes or drives you crazy?

Dr. Christina Warriner:
Yes! There aren't super foods. There's just foods. Um, I, you know, there's no, there's no magic bullet. There's no one quick fix. Um, I often say that the, the, the, the advice I give is, you know, eat more root vegetables, eat vegetables in general. That's incredibly healthy for you, but no one seems to like that answer!

Jen Gunter:
There are no miracle diets! There are no single superfoods! And looking at human evolution is a great way to bust sticky food and diet myths, because evolution shows us there is no one right answer…. No one magic dietary bullet for healthy bones.

Just make sure you’re getting enough calcium and Vitamin D. And of course, exercise! Your bones will thank you.

Next week on Body Stuff...when the pandemic started did you look for zinc, Vitamin C, Vitamin D, or other things to “boost” your immune system?

Then you’ve probably heard one of the most powerful, pervasive myths out there...

SOUND CLIP:
It's everywhere. It's absolutely, it's everywhere! And it was sorta everywhere before we were in the middle of a pandemic. Of course, post-pandemic, the idea’s just exploded. And it’s actually become I think more complicated.

Jen Gunter:
We’ll ditch the disinformation and explore the REAL science of your immune system.

Body Stuff is a member of the TED Audio Collective. It’s hosted by me, Dr. Jen Gunter, and brought to you by TED and Transmitter Media. This episode was produced by Camille Petersen and edited by Sara Nics and Lacy Roberts. The rest of the team includes Alice Wilder, Gretta Cone, Michelle Quint, Banban Cheng, and Roxanne Hai Lash. Alex Overington is our sound designer and mix engineer. Krystian Aparta and Neeraja Aravindan are our fact checkers.

Special thanks to the people around the world who make such a diverse array of creative foods from dairy. I’m looking forward to meeting all the cheeses I’ve never heard of before.

We’re back next week with more Body Stuff. Make sure you follow Body Stuff in your favorite podcast app so you get every episode delivered straight to your device. And leave us a review! We love hearing from our listeners. And leave us a review! We love hearing from our listeners.

See you next week!