Will drinking milk help me live longer?

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1:07All right, I'm at the Neighbourhood Dairy. This is right smack in the middle of a residential, lower income neighbourhood, very close to where I live. I've passed this place at least 100 times and obviously never stopped here. You're listening to CrowdScience from the BBC World Service. I've always been astounded that there is a place like this where cows are just tethered by the side of a pretty busy road and there's manure and hay just strewn all along the sidewalk. CrowdScience is the show that ruminates over your science questions and then goes to great lengths to answer them. Oh God, it really smells bad.

1:59Oh no, I just stepped into a cow plot. Okay, let me find out about milking. Brother, it's not time for their milk. I'm Chavi Sajtev. I'm in India, in Prabhadevi, Mumbai. And I'm on a quest to find a cow to milk.

2:20These cows belong to Arun, whose family has basically had a dairy here. For 100 years, way before, there were big apartment buildings in this neighborhood. So he's got 12 cows. There are six that are being milked this afternoon. Raju, who's worked here for three years, is now milking a black cow with a little white star on her forehead. I wasn't allowed to milk a cow myself for safety reasons, but I was allowed to get up close and personal while Raju got on with the job, although I was slightly too close for comfort.

3:01She's flicking at me with her tail and passes by and laughing.

3:11I'm being told to step to the side. she's going to keep whacking me with her tail, which is not clean. This is the first time I've seen a cow being milked up close. And, you know, it looks bizarre. It's intrusive. It's so weird, the things we do to get milk to drink. Like 70 % of the world's population, I'm lactose intolerant. In fact, 90 % of Asians can't break down the lactose in milk to some degree. Cheesy pizzas, gulab jamun and lattes make us feel rather unwell. Which is why I found it odd that people go to such great lengths to drink milk at all. And I'm not alone. Crowdscience listener JJ in Singapore is so dairy curious that he wrote to us about it.

4:03I want to live a long, healthy life. And for my reading, I think cow's milk is not healthy. So my question to crowd science is, is milk healthy for us? Should I drink milk for a long life? So in India, I grew up here in India. And as a child, I was forced to drink not one, but two mugs of milk every day. Not tiny glasses, mugs of milk. And we were told it's good for our bones. It's going to make us taller. It's going to make us smarter. longevity didn't quite come up so tell me what you've heard what is the general consensus about milk where you are yes i think from my side i have been asked to drink a lot of milk too and exactly as what you said to improve our calcium to improve the intake of protein so that we can grow tall and strong however i have read that cow's milk can lead to cancer cardiovascular risk.

5:05So then I decided to find out more about milk drinking. Do you still drink milk? I don't. But I have a weakness. I like to bake. I like to cook. So, you know, it's difficult to bake without milk. If I'm on a holiday, I have a weakness. I say, okay, it's a holiday. I will drink cups of latte, cappuccino and all that. But it's on a holiday. But what about things like cheese or yogurt? because it's gone through a different process. So do you think we could continue with that? Yes, I think that's possible. I do believe that taking fermented products like kefir, yogurt, they are good, and cheeses. Right.

5:53So I make my own kefir and I really, really enjoy it. Ah, good. High five. High five. Yes, I do that too. Oh, that's awesome. So it sounds like you've got your mind made up about milk. What do you want us to find out, Fereem? I want you to see whether the sign supports what I believe.

6:16JJ wants to know about cow's milk and whether it's contributing to longevity or not. Cows produce milk to nourish their calves, and human babies start life drinking our mother's milk. But all mammals produce milk, which makes me think it's pretty important. But what even is it? Breastfeeding, as we call it in humans, or lactation more generally in mammals, has evolved over many million years, probably dating back to around 350 million years ago. And that was a long time before mammals emerged, which was probably more like 150 million years ago. So it was before mammals actually were in existence and our ancestors were walking on four legs and laying eggs.

7:02This is Mary Futrell. She's a professor of paediatric nutrition at University College London, which means she's an expert on the role and composition of breast milk. So the hypothesis is that lactation evolved as an adaptation of probably a sweat gland in these animals, so that they would produce fluids which would prevent their eggs from drying out, and also immune components to stop them from becoming infected. What is breast milk made of? So the main sort of nutritional components, so the protein, fats and carbohydrate, micronutrients, vitamins, but then, as I say, all of these different bioactive factors, which also change over the course of lactation.

7:46So different hormones, stem cells, the milk has its own microbiome. So it's a very complex fluid. And is this a two-way thing? Like, does the babies need drive what's happening? That's a really interesting question, actually something we're doing quite a lot of research on. I used to see breastfeeding almost as a one-way process where you'd assume that the mother is basically giving the baby whatever it needs to grow and develop. But actually, I think it's far more complicated. It's a sort of two-way signalling process. So, of course, the mother has some influence over when she feeds the baby, how long she allows the baby to feed, etc.

8:29But then the infant of whatever species actually can influence the process by crying and how vigorously they suck. So it's sort of almost like a complex signaling system where the mother can be providing information to the infant about the environment, but also about her past experiences. And that may also influence how the baby behaves and grows and develops. So it's a lot more than just transferring these nutrients which allow the baby to grow. So calcium, protein and fat and growth hormones and things, are those different from species to species? is? Definitely. I mean, protein, for example, tends to be related to how fast the young mammal needs to grow.

9:12So for a rapidly growing mammal, such as a calf, the milk will have much higher protein than, for example, a human who grows relatively more slowly. But most of the nutrients in mammalian milk are adapted for that species. So for example, when we make an infant formula, which is typically based on cow's milk, then we have to make quite a lot of adaptations to it. You can't just feed a human infant, a newborn infant, with unaltered cow's milk. It can become very ill and even die. A cow's milk is so tailored to their own young that if a human baby drinks it, it can be fatal. Which, again, makes me think how crazy it is that we drink the milk of another animal.

9:58And there's loads of evidence pointing out how important mother's milk is. So, I mean, there have probably been thousands of studies, and I think probably the best of those meta-analyses would suggest the most convincing effect is protecting against infection. So, you know, gastrointestinal infections, respiratory infections, ear infections. And that makes complete sense if you go back to what I said earlier about how lactation evolved with immune components to prevent infection before it took on a nutritional role. And then, of course, you mustn't forget there are also some benefits for the mother in terms of reducing the risk of breast cancer, possibly ovarian cancer as well.

10:39I think having mother's milk as either a human infant or any mammalian infant is basically what's intended biologically. So there's no question that milk is hugely important in early life, setting up our early immune systems, and even transmitting information on our mother's environment. But as Mary said, each mammal's milk is highly personalized to their own needs and how fast they grow. So when did cow's milk enter the equation? That's what we'll be investigating next. Pop quiz. What's in your kid's lunchbox? At Whole Foods Market, they've already done the studying. Over 300 food ingredients are banned from their shelves.

11:25No hydronated fats in the peanut butter and no high fructose corn syrup in the cookies. And for sandwiches, there are no synthetic nitrates or nitrites in any of their deli meat. So you can pack lunch boxes with peace of mind. Get back to school ready at Whole Foods Market.

11:45The summer savings event is here at Apple vacations it's the perfect time to bring everyone together for the getaway you've been dreaming about book between july 24th and august 27th and enjoy up to 55 percent instant savings from relaxing beach days to unforgettable moments with the people who matter most your next vacation starts here travel through july 31st 2027 start your vacation today at apple vacations.com or through your travel advisor you're listening to CrowdScience from the BBC World Service, the show that hears your questions and tries to find the answers. I'm Chavi Satchdev and we're investigating whether cow's milk is actually good for us, thanks to a question from listener JJ in Singapore.

12:33We are the only animal to systematically seek out and drink the milk of another animal as part of our diet. Here in India, we consume buffalo milk, cow milk and goat milk. Dairy is a huge part of our culture. I mean, we've got arguably the best desserts in the world and the majority are made of dairy. And don't even get me started on our tea. I popped out to my local tea stall or Chaiwala where I was told they use 30 to 40 litres of milk a day.

13:15So across from a college right by a construction site, Mahinder is running his tea stall and is doing roaring business and on basically a makeshift platform of wood, he's got a gas stove running with three aluminium cook pots on the flame. One of them is just milk that's boiling. Another one is a giant pot. I'm thinking it's at least a 10 litre container which has slow simmering tea continually going from morning to evening. Mahinder is not unusual there is someone like him at pretty much every corner. In my neighborhood every road has at least one chai valla with people standing around it at any given time of day.

14:11But I'm not a customer. As I mentioned before, I'm lactose intolerant. But 30 % of you out there, including our listener JJ, are able to digest cow's milk. How come that ability got given to some, but passed others like me over? To find out, we have to go back in time to when the habit of dairying began in the first place. To the best of our knowledge, that begins at least 9 ,000 years ago, but it's probably earlier. One of the problems we have is that one of the ways we can detect milk in the archaeological record is by identifying milk fats in pottery. And it's very clear that milking predates the invention of pottery.

14:54So we're really hopeful that with some new techniques, we might be able to push that date even further back into the past. This is Christina Warner, a professor of anthropology and evolutionary biology at Harvard University in the United States. A few years ago, her research team came up with a new way to detect historical traces of milk in our diet that doesn't involve ancient pottery. If you analyze the tooth tartar on the surface of teeth, which is a kind of calcified form of dental plaque that you make during life, when you consume milk, that tooth tartar preserves some of the dietary proteins that you consume during life really well, especially milk proteins.

15:35So these people who were eating dairy, they were able to digest it, right? So this is one of the kind of really big surprises that's come out of recent ancient DNA work in particular. So we know that milking is very, very old and dates to the Neolithic period. And so people expected to find evidence of lactase persistence or these genetic mutations that some people have that allow them to produce basically infant levels of lactase for their whole lives. So break that down for me. When you say lactase persistence and infants, so yes, babies can obviously digest their mom's milk. Are you saying that it caps out at a certain time?

16:20Yeah, and this is true for all mammals. So basically, when we're first born and when we're very young, we produce large amounts of the enzyme lactase in our small intestine. And this specifically breaks down the milk sugar lactose. However, mammals in general are kind of genetically programmed to decrease the amount of lactase expression as that offspring ages. It's part of the natural weaning process. It never drops fully to zero, but it becomes really, really low in most adult mammals. What's unusual about humans is at least five times independently in the past in different human populations, genetic mutations arose within the region of the genome that controls this process, such that people who have these mutations continue to produce their lactase as if they were an infant for their entire lives.

17:15And this makes it much easier for them to digest milk and dairy products. So to digest the milk sugar lactose, we need an enzyme called lactase, which breaks all that lactose down into smaller sugars that are easier for our body to deal with. We're born with it in order to digest our mother's milk, but levels drop off after infancy. That's what happened to me. So when I have milk, the lactose isn't broken down properly, and it can lead to some seriously awful digestive distress. But some populations evolved to keep producing lactase into adulthood. When did this genetic change take place? So we know that dairying begins at least 9 ,000 years ago, but we don't see the first evidence for genetic adaptations to lactose digestion until 4 ,000 years later.

18:07So there's a 4 ,000-year gap between the earliest dairying and the first genetic mutations that allow for lactose digestion. So people were drinking milk even though they couldn't digest it? Yes, and isn't that really interesting? But this was a big surprise to the medical community because it was largely assumed that if you lacked this enzyme, you would have the symptoms of lactose intolerance. But if you take a closer look at ethnographic studies, you quickly see that this relationship breaks down. So, for example, in Mongolia, they have a very long history of a dairy-based diet. We've been able to trace it back more than 5 ,000 years.

18:47And yet the genetic ability to produce lactase is extraordinarily low. It's less than 5 % of the population. How people manage to eat dairy without the biological ability to digest it is still a bit of a mystery. But Christina has some theories. Bacteria can also produce lactase. And basically, they just break down the lactose. And so if you consume a dairy product that has live cultures of these bacteria, they're actively reducing the lactose content. And what's amazing is this enzyme is so stable that even if they die, even if you digest the bacteria in your intestines, the enzymes that are released when their cells burst continue to break down the lactose.

19:29So there's a number of different bacteria out there that can also produce lactase to break down milk. In essence, they're doing the digesting for us, as long as they're present in whatever dairy you're eating. Even once the bacteria dies, say after you heat the milk, its lactase enzyme stays active, still working away at all that milk lactose in our gut. But why did these populations start consuming dairy when they weren't lactose tolerant? What benefits could there have been? Well, it's a fascinating question, and it has a lot to do with history. In the past, people would have been much more reliant on what is immediately available to them.

20:09And so there are certain parts of the world that are really productive, and there's many things that people can eat. But there's also a lot of places in the world that are quite difficult for humans to survive in. And where dairy products have arisen over and over again are in areas like grasslands and semi-desert or arid environments, because these are places where there may be abundant grass or shrubs that animals like ruminants can digest, but that we as people cannot. And what's really great is these ruminants can take these inedible foods and convert them into something that we can eat, which is dairy products.

20:45You know, our listener wanted to know if consuming milk, and we're not talking about fermented milk now, but just milk products, is bad for health. So what are the ways that dairy can affect health that you've seen? Well, milk is a fundamentally nutritious food. As with any part of your diet, it can be a really great source of your nutrition, but you have to balance out the whole diet. Today, we face the challenge of overnutrition because we have a lot of nutritious foods in our diet. And sometimes people make the argument that milk is necessary for calcium, for example. And it's true. Milk is a great source of calcium.

21:27But actually, a better source of calcium is kale. It's just that a lot of people don't like eating kale. So I think you just need to be thoughtful about the choices you make. I love kale, but not that much. You'd need a bushel of kale, okay, six cups of kale, to get the same calcium as a glass of milk, which may be one reason milk is so popular today. Milk has been considered a good source of nutrition for a long time. But in today's connected world, not just in those areas where dairy animals could thrive, modern-day marketing may have had something to do with it too. I remember the Got Milk campaign on billboards all over the US and even on the radio when I was in college in the 90s.

22:12Got Milk. And here in India, one of our most recognizable icons is the Amul Girl, a cartoon mascot for the dairy brand.

22:24But what happens when you do got milk? JJ specifically wanted to know if it's hindering longevity. We have all heard that drinking milk will provide you with stronger bones, but it's very difficult to see that in the science world. This is Karl Michelson. He's a professor of medical epidemiology at Uppsala University in Sweden. Over the years, Karl has worked on a massive study of over 100 ,000 people, And in 2014, he found that women that drink a lot of milk are at higher risk for some medical conditions. We noticed that in women, there was a higher risk of fractures and also early death with an intake of non-fermented milk higher than two glasses of milk per day after the age of 50 and onwards.

23:18And what about men? We didn't see the same associations in men. We have repeated this study but changed the outcome to ischemic heart disease and myocardial infarction some years ago. And we again see the same pattern, an association with high consumption in women but not in men. That is so interesting. Did you go further in your research and did you find out why? Lactose is composed of two components, glucose and galactose. And galactose is a sugar that if you provide that in high doses, corresponding to two glasses of milk per day, research animals get oxidative stress. You provide galactose to research animals to have them age early.

24:13Let me break that down. Oxidative stress is when the DNA in our cells gets damaged by a buildup of unstable molecules called free radicals. And this damage, in turn, can cause our cells to age faster. With milk, our enzymes break lactose down into galactose, which has been seen to cause oxidative stress and aging in animals. So Carl's theory is that the same thing is happening in humans. And the underlying cell stress is causing cells to age faster, along with other health impacts like fractures and heart attacks. But why are these adverse effects only being seen in women? Galactose is degraded in our bodies to glucose, and these enzymes seem to be less active in women and female animals than in men.

25:07And if you don't degrade galactose to the same extent, you can increase the concentration of galactose in your blood. And that could lead to higher oxidative stress in the end. Research has found that women aren't able to break down galactose as much as men are, which means that if they drink the same amount of cow's milk, there's more galactose left over in women's bodies than men's. JJ is also concerned about links to cancer in regular cow's milk. Is there any evidence for that? There seems to be weak evidence for that. There have been some reports several decades ago about high risk of prostate cancer with high meal consumption.

25:49But the present evidence is that he shouldn't be concerned about that. So that's the evidence on non-fermented cow's milk, at least for women. But what about fermented forms of dairy, like kefir or cheese? It seems that fermented milk products will not lead to the same negative health impact as non-fermented milk products. There is galactose also in fermented milk products, but to a somewhat lower degree. What is your take on the status of milk research? Yeah, it's a very complicated but interesting field of research. because it's quite complex to perform these studies. And we have not the possibility to perform long-term randomized controlled trials in this field.

26:42But we're moving forward and increase our knowledge year by year. But we don't have the final answer yet. Yeah, I'm not signing up for a randomized trial to see what dairy does to me anytime soon. JJ, you wanted to know whether cow's milk is healthy for us. But we've discovered it's a bit more complicated than just a yes or no answer. If you're a baby, then human milk is basically like our own personalized medicine. We need it for proper growth and development. If you were an adult 9 ,000 years ago, then dairy may have been your best choice of nutrition in areas where it was impossible to grow crops all year round.

27:25But if you're an adult in today's world, there's a lot more factors at play. So many things can impact our health that it's hard to disentangle the root causes. If you're a woman over 50, though, there is evidence that drinking a lot of cow's milk can increase your risk of bone fractures, heart disease and early death. If that description fits you, maybe it's best to enjoy your dairy in moderation. If it doesn't fit you, then feel free to carry on enjoying your milky coffees, kulfis and cheeses. Finally, if you're lactose intolerant like me, probably best that I keep away from all things milk.