Rhonda: Right. I kind of wanted to go back, because you were talking about the effects on how the immune system can be, you know...what did you call it? I mean, it induces sleep.

Matt: Somnogenic.

Rhonda: Somnogenic, yes. How it's somnogenic. So interesting. I had no idea that the cytokines were responsible for that, and it makes perfect sense. So, anyway. But also, so the opposite is true where sleep also affects the immune system, or a lack of sleep also, right?

Matt: It does, yeah.

Rhonda: And that is something, you know...Your immune system is the first line of defense against, even pretty much everything, right: cancer, viruses, bacteria.

Matt: Yeah.

Rhonda: And I think in your book, you were talking about the effects on, some studies, on natural killer T cells. I mean, I was just, like, blown away by some of the numbers.

Matt: This is a frightening study. So it's done by my colleague Mike Erwin. You take a group of individuals, and you're not going to deprive them of sleep for an entire night. You're simply going to limit them, restrict them to four hours of sleep for one single night. And then we're going to measure the amount of reduction in natural killer cell activity.

So just to take a step back, natural killer cells are a critical part of your immune defense arsenal. And today, both you and I and everyone listening to this podcast, we all have cancer cells that have emerged in our bodies. But typically, what prevents those cells from becoming this disease that we call cancer is, in part, these natural killer cells. So what you wish for is a virile set of these sort of immune assassins, these sort of James-Bond-like, you know, that they will annihilate these foreign organisms. You want a virile set of those at all times.

So take a group of healthy people, limit them to four hours of sleep for one night, and what you see is a 70% reduction in natural killer cell activity, seven zero. That is an alarming state of immune-deficiency. And it happens quickly essentially after one bad night of sleep. So you can imagine, you know, the state of your immune system after weeks, if not years, of insufficient sleep. And it's now the reason I think that we probably are finding, at the epidemiological level, significant links between short sleep duration, not getting enough sleep, defined as six hours or less, and your risk for the development of numerous forms of cancer. Currently, that list includes cancer of the bowel, cancer of the prostate, cancer of the breast.

And the link between the lack of sleep and cancer is now so strong that, recently, the World Health Organization decided to classify any form of nighttime shift work as a probable carcinogen. So in other words jobs, that could induce cancer because of a disruption of your sleep-wake rhythms.

So, you know, that's the immune system in cancer. But it doesn't stop there as well. Another great study that was done by Eric Prather [SP], who is over at UCSF, another good colleague of mine, he did this brilliant study that I write about in the book. He basically measured the sleep of a group of healthy people for a week before using these wristwatches that are accurate. And then he quarantined them in a hotel, in a set of hotel rooms. And then he proceeded to stuff up their nose, squirt up their nose, rhinovirus, essentially, a flu virus. And then he quarantined them for a week. And he measured how many of them became infected. And he was measuring all sorts of stuff. He collected every ounce of snot that they blew out of their nose, all of the mucus, everything.

And what he found was that those people who were getting five hours of sleep or less in the week before they came in and were infected relative to those who are getting seven hours of sleep or more, those people who were getting five hours of sleep in the week before they got infected were four times more likely to end up developing the flu than those people who are getting seven hours or more.

The final nail in that sort of immune coffin for me is a study that was done by Eve Van Cauter, who's a wonderful endocrinologist. And I'd love, by the way, to speak about sleeping diabetes and glucose regulation, too. She's doing some great work there. But she did a great study. She looked at the amount of sleep that you were getting in the week before you get your flu shot.

And what she found is that if you're getting sort of less than five or six hours of sleep in the week before you get your flu shot, you only produce half of the normal antibody response, rendering that flu shot largely useless, which stuns me that, you know...And here's where technology could revolutionize healthcare. You know, what if Kaiser, you know, had access to a sleep tracker or had its own sleep tracker. And Kaiser, for those not familiar, is a health care provider here in the United States.

But what if, you know, any healthcare provider or system in any country had access to your sleep in a non-Big-Brother way. And it was tracking your sleep. And through an app, it would say, "Hey, you've had a great week of sleep this weekend in December," or "this week in November. Now is the time to come and get your flu shot. I've listed out three appointments. Just tap on the one that you want."

Or it says, "Look, I know that you scheduled yourself for a flu shot. You haven't quite got the good sleep that you need this past week. Let's try again next week." And if you get the sleep next week, then you give them access to getting the flu shot. Because otherwise, we're wasting money. And the flu, you know, cost the United States, the flu season cost the United States about $10 billion directly in terms of healthcare burden. Even if I could nudge that by just 1% or 2% by understanding people's sleep and helping architect a system that co-opts around sleep time and management, we could save hundreds of millions of dollars to the U.S. economy.