Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
In my last video, I noted how lying at a slight, six-degree head-down tilt for a few hours can boost fat burning. Now obviously, you wouldn’t want to lie tilted back if you had a heart condition, such as congestive heart failure. As many as eight to 12 cups (1.90 to 2.90 L) of blood may be displaced into the torso from the extremities at a tilt like that, so you have to have the cardiovascular fitness to handle it. Acid reflux could also be a problem. In fact, we typically tell heartburn patients to do the reverse—put a few bricks under the posts at the head of their bed to have gravity work in their favor to keep stomach acid down where it belongs. But for those without medical problems, is there a harm in lying tilted back for a few hours? Well, it could give you a “space headache.”
In movies, astronauts are shown practicing underwater. But the gold standard for simulating the physiological effects of the weightlessness of outer space is HDBR, head-down bed rest. On Earth, our blood tends to collect in our legs, so our body is designed to force blood headward. In outer space, our body is still trying to push our blood “up,” so without Earth’s gravity, blood pushes upwards to our head and chest––just like it does when we lie tilted back. This realization came from cosmonauts returning from the space station feeling as though they were slipping towards the foot of the bed, and only feeling “normal” when they were tilted six degrees back.
All of the extra blood pooling in the head is thought to contribute to the headaches reported by up to 70 percent of astronauts during space flights. And a similar percentage of individuals suffer headaches from prolonged head-down bed rest. That’s after days, though. In preparation for a mission to Mars, space agencies put people through head-down bed rest for prolonged periods—eating, bathing, and toileting all while lying in bed tilted back for literally months at a time.
Extended stretches of head-down positioning for weeks may impair lung function, brain function, and immune function, and cause a loss of muscle mass. On the last Apollo mission, the astronauts lost about five pounds (2.30 kg) of fat over the 12-day trip. But they also lost about two pounds (0.90 kg) of lean body mass. Prolonged weightlessness or bedrest, regardless of tilt, can result in muscle and bone loss. But just sleeping on a slant by putting a few bricks under the posts at the foot of your bed could potentially give you a boost in fat metabolism without the long-term adverse effects.
If you want to try it, a note of caution: take it slow when standing back up. After just four hours of a six-degree head-down tilt, most people experience reduced “orthostatic tolerance.” When anyone stands suddenly after sitting or lying for a while, you can get a “head rush,” feel dizzy, faint, or lightheaded as the blood drains from your brain down into your legs before your body can compensate. This can be exacerbated by lying with your head tilted back, so be careful and get up gradually. Drinking two cups (0.50 L) of cold water 30 minutes before rising may also help.
Do not try this at home if you have any heart or lung issues, or problems with your brain (like head trauma) or eyes (even a family history of glaucoma disqualifies you). Ask your physician if they think it’s safe for you to sleep in “mild Trendelenburg.” Friedrich Trendelenburg was a pioneering surgeon who popularized the use of what was formerly referred to as “head-down position” for certain abdominal and pelvic procedures. Angling the operating table back 15 to 30 degrees pulls some abdominal organs out of the way to help declutter the surgical field, resulting in what is now widely known as the Trendelenburg position.
Steep Trendelenburg (at a 25- or 30-degree tilt) has been associated with transient visual problems, thought due to the increase in pressure within the eyeball. Cautions have been issued for those at risk for glaucoma (a disease of increased eye pressure) to avoid “inversion” therapy, where people hang upside down, as well as yoga positions like handstands, which can have a similar effect.
Lying back in mild Trendelenburg, like around six degrees, can cause a fleeting bump in eye pressure that appears to normalize within a few hours. But the pooling of blood in the head may reduce blood flow to the retina sufficient to impair nerve impulses. Similar effects have been noted within the brain. Intracranial pressure also normalizes after a few hours at a six-degree head-down tilt, but the overall blood flow through the brain does drop a bit. This is why you shouldn’t try this if you have eye or brain pathology.
To my surprise, sleeping in mild Trendelenburg was actually put to the test to prevent bone loss in sedentary individuals. Restrict people’s activity to walking less than two miles (3.20 km) a day on average, and within a year they can lose as much as 15 percent of their bone mineral density. What happened to those randomized to the same exercise restriction, but also combined with sleeping at a two-degree head-down tilt that was increased by two degrees about every two months, so they ended up sleeping at a 14-degree slant (or whatever angle they felt comfortable with) by the end of the year? Not only did it completely block the bone loss, they built more bone. Despite the movement restriction, they ended up with about 12 percent greater bone mineral density than when they started. Note that this bone-building effect was only apparent in sedentary individuals. Another group randomized to the same mild Trendelenburg, but assigned to run an average of five or six miles (8 or 9.5 km) a day just maintained their same skeletal integrity.
The study was repeated, and the same remarkable effects were found. There is something about the “periodic fluid redistribution” that comes with sleeping tilted back at night that actively builds both bone density and volume after the day-long stagnant pooling of blood in the legs of sedentary individuals. The research team claims this is just the beginning to the benefits, citing “unpublished studies” asserting a near panacea of perks to sleeping in Trendelenburg. I can’t be too critical of this apparent dodge when I can’t point to a single study supporting my supposition that it will help with weight loss. As far as I can tell, it’s never been tried or even proposed. What I can promise is that any researchers who take on the mantle of putting it to the test will definitely have their study featured in a video on NutritionFacts.org.
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