Guest Blog by Dave Asprey's Bulletproof staff (https://blog.bulletproof.com/freeze-away-inflammation-with-cryotherapy/)
Cryotherapy has been around in one form or another for ages: exposure to frigid air, cold-water immersion, or just applying ice to sore muscles. The ancient Romans would take plunges in frigidarium baths and the Nords would crack open icy lakes for a winter swim.
Here in modern times, cryotherapy is popular with elite athletes, celebrities, and biohackers alike. Health claims range from increased immunity to shinier hair, and more and more “cryosaunas” are popping up for personal use.
How much is hype and how much is science? Let’s take a look at what cryotherapy is and the evidence for how it works.
What is cryotherapy?
Technically “cryotherapy” could refer to any kind of cold exposure that improves performance. But it’s mostly whole body cryotherapy (WBC) that’s been in the news for claims that it can boost metabolism, increase endurance, and even help reverse depression.
WBC involves short exposure to extreme cold via a cryochamber – a human-sized tank filled with liquid nitrogen-cooled air. Exposure can vary from 2-3 minutes in temperatures that plummet to -130°C (-266°F). Another method is to take an ice bath for up to an hour in water temperatures of about 19°C (66°F).
On the surface, cold therapy works wonders for speeding up healing. When you apply ice to swollen muscles, the cold constricts blood vessels and reduces blood flow to the area, and pain, swelling, and inflammation decrease. The original idea behind WBC was similar: expose the body to cold to reduce inflammation. It turns out WBC does that and a lot more.
Cryotherapy curbs pain and inflammation
Dr. Toshima Yamaguchi started using cryotherapy to help his patients with rheumatoid arthritis (RA) as far back as 1978. News of the therapy spread and quickly became popular with elite athletes in the NFL and NBA. They use it to help lower inflammation and decrease pain, acutely and over time. Cryotherapy triggers anti-inflammatory norepinephrine release that reduces short-term pain from injuries . It also makes intensive physical therapy more tolerable for chronic pain from conditions like fibromyalgia, chronic back pain, and osteoarthritis. 
The cool thing about cryotherapy is that it can decrease inflammation while simultaneously stressing your body enough to keep your cells on their toes. Low doses of physical stress from a cold plunge can elicit an adaptive response and strengthen your immune system by increasing white blood cells and immune cells; your bolstered immune system can then kill viruses and fight off tumor factors. [3,4,5]
Short bursts of cold therapy may also increase the antioxidants glutathione and superoxide dismutase, which help support liver and immune function, optimize cellular function, and protect against oxidative stress. 
Muscle soreness and recovery
Chronic low-grade inflammation is bad, but the inflammatory response you experience after exercise is actually a good sign that your body is in tissue repair mode. As your muscles become engorged with blood and a pro-inflammatory response rushes the area, anti-inflammatory cytokines hit the scene to keep your immune system in check.
This process of inflammation, tissue repair, and anti-inflammatory mediators ensures that you recover optimally and that your muscles heal and grow. Which is why some studies suggest that icing too soon after exercise actually slows your recovery post-exercise. So what about all of those elite athletes who swear by cryotherapy? Turns out the benefits may vary depending on the timing of your cold therapy.
If you interrupt your body’s pro-inflammatory response with cold therapy immediately after exercise, you may actually reduce the benefits from exercise and inhibit performance.  Instead of icing right away, waiting about an hour post-exercise (aka after the peak pro-inflammatory process) may improve performance and recovery.  In fact, WBC performed within 48 hours of an elite race (but not within an hour of the race) increased recovery, speed, and power in athletes by 20%. 
Collagen, the protein behind strong cartilage, joints, skin and hair, also ramps up production after cryotherapy, and collagenase, an enzyme responsible for rapid collagen breakdown, slows down.  While cold therapy is boosting collagen production, it’s also inhibiting the stress hormone cortisol, which works to break down collagen and can disrupt your healthy blood sugar and sleep patterns. 
Increased fat burning
The idea behind cryotherapy and increased fat burning is simple: the body responds to extreme cold by increasing your metabolism to heat up your body, which in turn burns fat through a process called cold thermogenesis. Cryotherapy can increase your metabolic rate by up to 350%. 
Long-term mild cold exposure can also increase brown adipose tissue (BAT), a type of fat that is beneficial to humans.  Unlike other types of fat, brown fat increases metabolism, burning energy and glucose to generate heat.  In one study, BAT was highest in volunteers that slept in mild cold, 19°C or 66°F, which means you can boost your metabolism by cooling your room at night – a practice that may also improve sleep.
Better mood and a better night’s sleep
Cold exposure produces feel-good endorphins and increases production of norepinephrine.  Norepinephrine is a hormone and neurotransmitter involved in your sleep-wake cycle and has profound effects on energy, focus, mood and sleep patterns. This may be because of norepinephrine’s role in neurogenesis – the production of new neurons in the brain – which links to improved mood and memory. 
The rise in norepinephrine along with a decrease in cortisol supports a healthy sleep-wake cycle. [17, 18] It’s also possible that the rush of endorphins and subsequent feeling of relaxation is why so many people claim that cryotherapy is their new sleeping drug of choice.
Cold water immersion at 57°F (14°C) for 1 hour increased norepinephrine 530% and dopamine, another feel-good neurotransmitter, by 250% . You can get similar effects from whole-body cryotherapy sessions at -250°F 2-3 times a week.
You don’t have to join a cryosauna or have a frozen lake nearby to get the benefits of cryotherapy. In many cases, lowering the temperature in your bedroom at night and cold bursts in the shower may help balance neurotransmitters and balance mood, while ice baths 1-hour post-exercise may help speed recovery and increase endurance. If you’re just getting into cryotherapy, you can start slow with this simple protocol. Definitely worth a try!