Flying is a brutal thing to do to a human body. Electromagnetic radiation, dehydration, restricted movement, oxidative stress - oh yes, and emotional stress - are all working hard to wear down the nervous system and suppress immune function.
Air travel is a particularly poor time for immunosuppression, given that you’re trapped in a steel tube with a few hundred people in varying states of health and/or disease.
Even if you manage to arrive at your destination without getting sick in the week that follows, the plane time has unquestionably taken a toll on your nervous system. Your body and (particularly) your brain are going to take some care to get back to their best.
I fly quite a bit and know the consequences better than I’d like to. In the past 3 months, I I’ve been on 20 flights totaling 28400 miles and something like 71 hours of in-the-air time. Several of these have been long international flights, which are obviously the most taxing.
The upside of all this flying is that I’ve had plenty of time to deconstruct the toxic elements of flying and engineer ways to mitigate the damage they do.
Before You Fly
As important as anything you do on the plane, is how you take care of your immune system in the 2-3 days ahead of flying.
The below are some general principles for maintaining a healthy, active immune system. It’s a good idea to follow these with particular diligence in the days preceding your flight.
1. Minimize Alcohol Consumption - Alcohol (beyond a drink or so) is highly immunosuppressive, so avoiding it entirely ahead of a flight is non-negotiable for me. 
2. Sleep Well - Improving sleep quality is the most significant thing we can do to improve immune virility in the short term. 
3. Avoid Stress - The propensity for psychological stress to suppress immune function is well documented. 
4. “Grounding” - Spending time outside to balance the body’s electromagnetic field sounds like new-age woo-woo, but it’s actually reasonably well researched and very effective. 
5. Supplements - Loading your body and brain with antioxidants will do a lot to protect against the stresses of air travel. Astaxanthin, resveratrol and DHA are powerful antioxidants that reliably cross the blood-brain-barrier. I take 10-20mg astaxanthin, 250mg resveratrol and 1000mg DHA about 1 hour before flying.
During Your Flight
Problem 1 - Dry Plane Air = Dehydration - Staying hydrated on a long flight is a serious challenge. The recirculated air on an airplane is bone dry and constantly moving. You can easily lose a pound of water (~16oz) through respiration and perspiration over the course of a 5 hour flight.
What To Do About It - Drinking plenty water before, during and after your flight (obviously). If you plan to sleep on the flight and, thus, won’t be able to hydrate constantly, I recommend hyperhydration.
Problem 2 - Dried Out Mucous Membranes - Your mucous membranes in your nose, sinuses and esophagus (and the beneficial bacteria that inhabit these membranes) are effectively an extension of your immune system and are your first line of defense against airborne viruses and bacteria. Some microbiologists estimate our microbiome comprises somewhere around 80% of our total immune function. Airplane air ravages these membranes, drying them out and cracking them, giving airborne pathogens a clear path into the bloodstream.
What To Do About It - A small saline nasal spray bottle is a permanent part of my travel kit. When I’m in the air, I use this to hydrate my sinus membranes once every hour or two. If I’m planning to sleep on the flight, I’ll wear a lightweight neck gaiter over my nose and mouth to minimize the drying of my membranes. Combining this with a sleeping eye mask and a neck pillow occasionally gets me some strange looks when I wake up, but it’s well worth it when you arrive with intact mucous membranes.
Problem 3 - Breathing Disease-Filled Air - Being trapped in a steel tube recirculating air from a few hundred strangers pretty much guarantees you’ll be exposed to high levels of airborne pathogens.
What to do about it - Don’t suppress your immune system any further than it already is. Cutting out in-flight alcohol is obvious, but the bigger issue is often the things people use to put themselves to sleep in-flight. Alcohol, valium, xanax and other benzodiazepines are widely used to induce sleep on long flights. Of course they’re quite good at this, but they also strongly suppress the immune system in the process. Not worth it, particularly when better tools are available. Which brings me to…
Problem 4 - Sleeping - Sleeping is the single most significant thing we can do to increase immune system activity/vitality and to ensure we arrive feeling sharp, but sleep on airplanes sucks most times.
What to do about it - First make sure the basics are taken care of. Get yourself some good earplugs (I like these), a comfortable eyemask, and a good neck pillow (I’m a fan of this one). If this is enough for you, great. You're one of the lucky ones. Most people need chemical assistance to sleep for a prolonged period, and as mentioned above, a large number of frequent travelers turn to alcohol, xanax or other benzodiazepines to accomplish this. I strongly recommend against this. The immunosuppressive effects of these substances are not to be taken lightly - and even if you do escape illness, there is a meaningful mental “clouding” and loss of stress-resilience for most people, meaning you’re not going to arrive in optimal condition regardless.
So what do I use? The best solution I’ve found for this application, without question, is moderate-to-high dose (10-20mg) oral cannabadiol (CBD) combined with low-dose (1-2mg) oral THC. This combination is highly effective for inducing sleep, does not suppress immune activity, and - best of all - confers a long list of additional benefits for the nervous system and brain. This article goes deeper into the benefits of CBD and contains my (legal) CBD product recommendation. Realistically, accurately-dosed oral THC products are relatively easy to acquire in 2017 in most states in the US, but if you’re unable to acquire one, high-dose (>20mg) CBD alone is still quite effective for inducing sleep.
Problem 5 - Stagnant Lymph - The lymphatic system is the body’s primary toxin elimination system and a critical component of the immune system. It is, however, a passive system and requires that the body be moved and blood flow stimulated to be effective in the removal of toxins. Of course, when you’re in an airplane seat for hours on end, the lymphatic system is largely static and doing little to support the immune system.
What to do about it - When I’m awake on the plane, I try to adjust my position every 15-20 minutes. Sometimes I squat on my seat, or I’ll squat with one leg on my seat and the other on the floor, or I’ll do a light spinal twist or stretch my arms overhead. This is far from enough to move lymphatic fluid as it ideally should, but it’s a huge improvement over sitting static for hours.
Much more impactful, is walking and/or stretching when you get off of the plane. If I have a layover, I make sure I walk around the airport or stretch for a minimum of one hour. If the layover is less than one hour, I essentially do laps around the airport until they’re about to close the door on my second flight.
Problem 6 - Airline Food - In-flight meals seem to have been phased-out in the US, but they’re still the standard elsewhere in the world. Regardless of where in the world they're served, don’t eat this food. It should go without saying that this is low-quality food that is generally carb- and sugar-dominated (read: dehydrating) and contains ingredients that are almost certainly contaminated with mycotoxins, among other things (abysmally low-quality airplane meats is likely the biggest offender).
What to do about it - Bring your own food, of course. My travel kit always includes Ketomanna Nut Butters and Genesis Shake Blend.
Problem 7 - Cosmic Radiation - Sounds ridiculous, but it’s a legit issue on longer flights. With 30-40000 less feet of atmosphere between you and the sun, the plane (and thus you) is getting a meaningful dose of solar radiation.  The amount of radiation you’re exposed to in a 5-hour flight is roughly equivalent to what you get from an abdominal X-ray. This means increased levels of oxidative stress and, thus, inflammation in the body and brain. Independent of oxidative stress, the body’s electromagnetic field is disrupted by radiation, which has it’s own consequences.
What to do about it - A lot of what’s been mentioned above. Hydration and movement (moving lymphatic fluid) helps clear oxidative toxins in the body. Antioxidants that cross the blood-brain-barrier are also helpful here. Every 2-3 hours in-air, I'll take 10-20mg astaxanthin, 250mg resveratrol and 1000mg DHA.
Problem 8 - Jet Lag - What exactly is jet lag? Every day, at about the same time, your pineal gland releases melatonin, which is the first in a chain of hormones that lower your core temperature, reduce alertness, and generally tell your body it's time for zzzzz. Unfortunately, your pineal gland doesn't change it's timing as quickly as your phone does - it usually takes a few days to catch up. Quality sleep is your single most powerful tool for recovering from the stress of travel - so the less you let jet lag screw with your sleep, the better off you'll be.
What to do about it - Take a melatonin supplement. For the first day or two in a new timezone, take 1-2mg of melatonin (ideally sublingual) 30-45 minutes before your bedtime. This will help your pineal gland to 'sync' to the new timezone a day or two quicker.
(If your trip is less than 3 days and you're crossing 3 or fewer timezones, I recommend just staying up to your bedtime in your natural timezone, rather than trying to adapt the rhythm of your sleep hormones).
After you land, two things take priority:
1. Move - Even if you arrive exhausted, it is worth it 100x over to take 10-20 minutes to move and stimulate blood flow and lymphatic fluid. Stretch, go for a quick walk, hop on a treadmill at the hotel - even 10 minutes will do a lot to flush toxins and airborne pathogens from your system.
2. Ground - As soon as I arrive at my destination, I look for the best opportunity to “ground”, or in other words, disperse the electromagnetic pollution (EMF’s) your body has absorbed while in the air. The best possible option here is to jump in a natural body of water - this will return the body to an ideal electromagnetic state faster than anything else. Behind this (in order of efficacy) would be stretching barefoot on grass, jumping in a pool and taking a shower. (more about EMF’s and grounding here). I’ve found taking the time to move and ground post-flight is remarkably effective in not only stimulating immune function, but also dramatically reducing the jet lag and brain fog that so often plague people after flying.
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