For decades, endurance athletes have tried to get an edge by flocking from sea level to higher altitudes, usually 5,000 feet or more above sea level. There they will train in the hopes of boosting performance when they return to competition at or near sea level. 

The adaptations these athletes are seeking typically take 14-21 days of training at altitude for full acclimation without elevation illnesses.1 The adaptations that come with training at altitude are why native high-altitude athletes have historically enjoyed a significant advantage over their low-land competition.

Just be aware that if you live at a lower altitude and want those benefits, then you will be dealing with a lot of environmental changes and additional stress from a higher altitude. Let’s explore how high altitude impacts the body and six research-backed strategies to support acclimation.

How the body is impacted by altitude

Every trip to a higher altitude will be different depending on what you are doing, how long you are there, where you normally live, the temperature, and your current health status. Generally, the higher in altitude you travel, the greater the challenges to normal human physiology. Your body must contend with low air pressure and reduced oxygen content at high altitude, known as “thin air,” until you can adapt or until you come back down. 

Some altitude-visiting individuals will be more sensitive than others, even at moderate elevations (5,000-8,000 feet above sea level). With less oxygenation for the body’s cells, energy pathways must rely on anaerobic metabolism, meaning without oxygen. This biochemical pathway yields far less ATP (cellular energy) than anaerobic metabolism, relies heavily on the availability of carbohydrates, and produces more lactic acid.   

Ventilation rates will increase with exposure to altitude because chemoreceptors (specialized nerve cells) in the carotid artery and aorta will sense the lower oxygen level in the blood. And while hyperventilation adds more oxygen to the blood and helps to exhale carbon dioxide to ward off respiratory acidosis, it can also increase energy expenditure by about 10 percent, even when the body is in a resting state. Exercise, or even everyday activities like climbing stairs or carrying groceries, will feel more difficult at a higher elevation, leaving the average lowland visitor more breathless the higher they go.

The cardiovascular system will see an increase in heart rate and upward of a 5-percent decrease in VO2 max at moderate altitudes.2 At higher altitudes, the release of oxygen in tissue capillaries is enhanced by hemoglobin. The benefit many athletes seek by training at altitude is polycythemia, the increased rate of red blood cell production, which is a rapid response to hypoxia because it increases the carrying capacity of the blood. The hormone erythropoietin (EPO) in the kidneys is stimulated, producing a natural “blood doping” effect. Although changes in red blood cells might be seen within a few days, this is usually due to a loss of plasma volume, potentially resulting in a simultaneous retention of water to offset dehydration. 

Long-term exposure will increase plasma volume and red blood cell mass, increasing total blood volume. Although there are many periodization strategies for athletes (training high and living low, living low and training high, and others), it is well established that adaptations from high-altitude training can have a positive impact on performance at sea level. 

However, these post-altitude benefits come with some short-term drawbacks; many experience the inability to fall asleep, and complain of poor sleep quality or disturbed sleep, which is often a result of the increased respiratory rate disrupting normal sleep cycles. Others report blurry vision and poor memory as the body adapts to the new environment. 

And most known are the effects of acute mountain sicknesses (AMS). AMS symptoms include severe headache, fatigue, irritability, nausea, vomiting, loss of appetite, indigestion, flatulence, constipation, decreased urine output despite normal hydration, and poor sleep. Some individuals experience AMS symptoms as low as 7,800 feet above sea level. There are also serious and sometimes deadly conditions, including high-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE). Given these symptoms, many high mountain climbs are performed in stages to avoid rapid ascent and to aid the body in acclimating.

Although most of the research on nutrition at altitude has been done at very high altitudes, and most of us aren’t scaling Mount Everest, there is still applicable advice for those training or visiting 5,000-12,000 feet above sea level, which are the elevations of the average training camp and destination hike.

Start by checking the elevation of your destination. See if you can add one or two days to the beginning of your trip to arrive, rest, hydrate, and begin the acclimation process. Understanding the mechanisms of the adverse effects of altitude is necessary for knowing how you can prevent or delay the onset. Here are some tips you can adopt before your next trip.

1. Keep up with carbohydrate stores

For decades, the recommendations included a diet consisting of 70 percent carbohydrates to minimize acute mountain sickness symptoms by 30 percent and increase the oxygen level of blood above 8,000 feet.3 More recent reviews, however, are challenging this notion and suggest that exogenous carbohydrate oxidation – or the use of carbs from ones we eat – is suppressed in hypoxic conditions compared to normoxic (sea level) conditions. Research also points to the gut microbiome as a factor in influencing carbohydrate usage at high altitudes.4

What exactly does this mean for you? The research shows elevation, temperature, acclimation period, and exercise intensity all play a role in how many carbs your body will need and whether carbs can help fuel your performance or lessen the risk of mountain sickness.

Regardless, keep in mind that you will be burning more than you normally would if you performed the same exercise at sea level. So, fuel up and top off the tank with a variety of fast and slow carbs to replenish your glycogen stores. 

2. Choose healthy fats

Many athletes need to consume about 45 calories per kilogram of fat-free mass daily to maintain body size and mass.5 At higher altitudes, the body could burn upward of 10 percent more calories; research suggests that athletes who are in an energy deficit at altitude or who have low energy availability might not experience the full hemoglobin increases they are seeking during training camps.6

Maintain energy balance by including healthy, satisfying fat sources, which provide 9 calories per gram versus carbohydrates that provide 4 calories per gram. Some “good fats” to integrate into the diet if you are exercising at high altitude include olive oil, butter or ghee, fatty fish sources of omega-3s, coconut oil, avocado, nuts or nut butter, or some chocolate. 

3. Drink up!

Remember, thin air is very dry. This, combined with hyperventilation and diuresis, will increase acute fluid loss, quickly leaving you dehydrated if you don't stay on top of your fluid needs. Early research suggests hikers at altitude need 3-4 liters for a 7-hour hike to maintain the normal 1.4 liters per day of urine output.7 And depending on the athlete, sport, intensity, and requirements, it is not out of the question to need 7-10 liters of fluids daily.1 Add an electrolyte replacement supplement to your water to help maintain hydration, fuel muscles, and reduce cramps.* 

4. Consider iron status and supplementation

Have your ferritin (a protein that stores iron) level checked 8-10 weeks before arrival at altitude to establish baseline status. The International Olympic Committee suggests cut-offs of <30 ng/mL and <40 ng/mL warrant iron supplementation in females and males, respectively.8

If your ferritin level is below the cut-off, consider iron supplementation and continue throughout the moderate altitude exposure. For help with proper iron intake to support you during this time, consult with a trained professional to assure adequate, but not over-consumption, of iron.

If you have taken Thorne’s Essential Health Panel, then the biomarkers to keep your eye on before, during, and after exposure are collected from a complete blood count (CBC) – including hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), iron, iron saturation, and total iron binding capacity (TIBC). 

Consider an iron supplement that also contains vitamin cofactors, like folate, vitamin B12, and vitamin C, as well as a multi-vitamin supplement to help the body make hemoglobin and maintain adequate intake while in a stressful environment.*1 

5. Support with antioxidants

The body undergoes oxidative stress in a hypoxic environment, which can impair endurance or altitude-based training adaptations. The research indicates that athletes who have very high training loads, who live or train at moderate-to-high altitudes, or who participate in ultra-endurance races have an antioxidant imbalance, and those who train under intermittent hypoxia conditions have lower plasma antioxidant levels. Research suggests athletes training at higher altitudes can benefit from supplemental antioxidants, as well as a varied fruit and vegetable diet.1 Supplements like glutathione, vitamin A, vitamin C and flavonoids, resveratrol, and quercetin will support metabolism and the total antioxidant capacity of plasma and tissue.*1

To maintain ATP production – the energy source of the body – the cell’s mitochondria need a constant supply of fuels and oxygen. At higher altitudes, the thin air compromises cellular function and ATP production.

Thorne’s ResveraCel includes the antioxidant flavonoid quercetin phytosome, the naturally occurring antioxidant polyphenol resveratrol, and nicotinamide riboside to promote the production of NAD+, a coenzyme essential to energy creation.* ResveraCel provides mitochondrial support to individuals before, during, and after high altitude exposure.*

6. Don’t forget about vitamin D

At high altitude, although the UV intensity of the sun increases, you are not always absorbing the rays. Vitamin D supplementation has been shown to protect skeletal muscle against atrophy (wasting) changes seen in high altitude hypoxic conditions.*

In addition, vitamin D is important in skeletal muscle structure and function and can create conditions for more efficient skeletal muscle oxygenation.1 Athletes visiting or training at high altitude will want to consider both dietary intake and vitamin D supplementation to support proper skeletal muscle maintenance and adaptations before arriving, while training at high altitude, and throughout the whole year.* 

References

  1. Michalczyk M, Czuba M, Zydek G, et al. Dietary recommendations for cyclists during altitude training. Nutrients 2016;8(6). doi:10.3390/nu8060377
  2. Guerrero-Pinzón JJ, Alcantara JMA, García-Buendia G, et al. A nutritional intervention for moderate altitude endurance preparation: A case report. J Int Soc Sports Nutr 2022;19(1):650-663.
  3. Edwards JSA, Wayne Askew E, King N, Fulco CS. Nutritional intake and carbohydrate supplementation at high altitude. J Wilderness Med 1994;5(1):20-33.
  4. Pasiakos SM, Karl JP, Margolis LM. Challenging traditional carbohydrate intake recommendations for optimizing performance at high altitude. Curr Opin Clin Nutr Metab Care 2021;24(6):483-489.
  5. Holtzman B, Ackerman KE. Measurement, determinants, and implications of energy intake in athletes. Nutrients 2019;11(3). doi:10.3390/nu11030665
  6. Saunders PU, Garvican-Lewis LA, Chapman RF, Périard JD. Special environments: altitude and heat. Int J Sport Nutr Exerc Metab 2019;29(2):210-219.
  7. Pugh LGCE. Cardiac output in muscular exercise at 5,800 m (19,000 ft). J Appl Physiol 1964;19(3):441-447.
  8. Bergeron MF, Bahr R, Bärtsch P, et al. International Olympic Committee consensus statement on thermoregulatory and altitude challenges for high-level athletes. Br J Sports Med 2012;46(11):770-779.